Ithaca Lemonade

[JohnK]

“When you set sail for Ithaca, wish for the road to be long, full of adventures, full of knowledge. ...” *

And if your Ithaca is a Seven kit, the journey just may allow you to learn

how to make some pretty interesting lemonade

from that lemon you got stuck with.

 

Out of my journey came:

A completely new brake system

from the pedals in the footwell to the calipers on the uprights;

a completely new steering system

from the steering wheel to the steering arms on the uprights;

much of a new suspension system

from shocks and roll bars to links and uprights;

and dozens of ergonomic, mechanical design and good practice issues,

the solutions of which brought me to a new appreciation of the difference between

something slapped together from a grab-bag of parts and

a car that might have put a smile on the face of the good Mr. Chapman.

 

Now that I've finally arrived at Ithaca,

Laissez les bons temps rouler , as they say in N'orleans.

 

 

===========================================================================

============ Serious update, 3 years after first getting it on the road =====================

==========================================================================

. . . . . . So, now that it's a couple of years later, and after getting the car on the road and driving it

for a season, I found some changes were justified. Here's a LINK

http://www.usa7s.net/vb/showthread.php?7421-Ithaca-Lemonade&p=97613#post97613

that describes what I decided to change, how I made the changes, and the results of the work.

==========================================================================

 

 

*http://en.wikipedia.org/wiki/Cavafy His famous poem, Ithaca, is echoed

by the Caterham motto, “When the journey is as important as the destination.”

 

 

Many thanks to:

 

Steve Sheddy for opening the door many years ago to my learning from the homeland

what Sevens were all about at se7ens.net. And of course all the good folk at

usa@se7ens.net , http:// http://www.usa7s.com and Ultralite_USA@yahoogroups.com

for sharing their knowledge, experience and helpful suggestions.

 

Also,

-The late Carroll Smith for laying out so clearly much of what one needs to understand and

do in order to make a sports car that works. And Allan Staniforth for doing the same in

matters of suspension.

-Wm. C. Mitchel and his friend Warren Rowley whose softwares allowed me to see

how the chassis / suspension would behave as the car was driven and

how to determine spring rates and design effective roll bars,

all to make a car handle like the gods that rule such things intended.

-Speedway Engineering for providing all one could need in the area of anti-roll bars.

-Koni Racing Tech for identifying the right model of shock to fit my needs and building a set to fit

my specs perfectly; superb suspension control, priceless advisory service.

-Woodward Precision Power Steering for an extraordinary R&P along with a superb explanation

of how to make such a thing deliver steering that gives new meaning to the word 'precise'.

-And Miller Welding for creating their Dynasty DX 200 power supply for TIG and Stick welding;

an amazing piece of technology without which I could not have fabricated all the pieces that

make my 'lemonade' work.

 

Pictures below are 800x600 as per site directions.

 

More pics at higher resolution can be gotten through an annotated index at

 

https://www.dropbox.com/s/1h5vxfz5bvp6zes/Annotated_IndexEd01.doc?dl=0

 

This will allow you to download the file, (Word format),

and you can get back to DropbBox by clicking on the hyperlinks.

(Dropbox changed its rules so this is completely redone internally.)

.

.

.

Edited December 23, 2016 by JohnK
DropBox mandated changes -- in progress.

[S1Steve]

Really Nice..... Great things take time.....

[Croc]

Wow! After all this effort and time you have reached Sevens nerdvana. Congratulations! Your linked photoblog is fascinating to read to see how you sweated the finest of details to make sure the car was as close to perfect as possible. Now that Spring is here I hope you find the time to enjoy the car. :hurray:

[Kitcat]

I saw this car abt 2 years ago when John was still rethinking and re-engineering things. His attention to detail borders on the obsessive (in a good way:)). For instance-notice the center mounted tach and speedometer. Not many sevens of this ilk have that. Nice job with the upper bracing of the driver's seat as well. For everything he built he first mastered the science and technology behind it, then applied it.

 

It sure looks good John. Love the color. Who did the paint job? I will bop over some sunny weekend day and take a close-up look.

 

Mike M.

Edited March 16, 2012 by Kitcat

[Mondo]

Nice to see it come to fruition. Kind of reminds of how they say dogs resemble their owners... no two 7s are alike.

Look forward to hearing how much you enjoy it this summer.

[JohnK]

Thx guys. I'm still amazed that it's operational. Putting together the collection of pictures, and then annotating them helped me walk through several of the more challenging fixes - and why it took so bleeping long.

 

Local guy, who I've since lost touch with and who I was lucky enough to find named Geoff Moore did the paint. I wanted a high-visibility color and 1970 Dodge Charger "sublime" is what we both found acceptable, but Geoff twisted my arm to add just a touch of pearlescent dust and a couple coats of clear. His experience was that that treatment makes irregularities in the bodywork disappear. I showed him pictures of several different Se7ens with different paint jobs and let him exercise his judgement re the graphics which are in dead-flat black, like the Charger. The traditional nose circle stayed, but he chose to split the trad center stripe, de-emphasizing the hump. In sunlight it really looks like a show-car.

 

Mike, you're on the test-drive list along with S1 Steve. Will be nice to see you again and hear of your recent adventures. Steve, come on down!

 

While I'm pleased that people like the way it looks, the goal here was to see how well I could get it to WORK. In all of 62 miles it seems like the steering handsomely justifies all that work and adding anti-roll-bars feels similarly worth the effort. Instant turn-in with what seems to be zero roll, precise pointing, fine directional stability but instant response to input. It/I may like softer coils. It's gonna take me years to get to know this thing well.

Edited March 18, 2012 by JohnK

[MHKflyer52]

JohnK nice WCM Ultralite you have created. Have fun and be safe.

[jimrankin]

Are the wheels 5X100? If so, what brand, size and off set? Really clean look.

[JohnK]

Jim,

Thx, but you have to give Brian credit for the good looks- I had asked for something else (light weight) and got them instead. Best I can do on the brand is MSR, which is what's on the axle cover. Using that as a search I found someone selling them a while back when I was looking for the mfg's specs but never got a source that was their origination. The wheels are all identical, 17x7.5 with a 1 11/16" (45 mm) offset and are 5x100 bolt pattern. This is the bolt pattern of the Subaru WRX axles but the front hubs are Wilwood Pinto, drilled for 5x100. The hubs I got were junk (way off center and hacked machining, came with an assortment of 1/2"-20 and 12-0.5mm studs) and I threw the hubs away and started over with a new pair. I expect that they were a good deal at the time and the mktplace has moved on. I seem to remember Chad saying that the bolt pattern and offset are the same as one of the popular Audi models, so that should open up sources a bit. Anyway, glad you like them and I hope this helps if you'd like to source a set for yourself.

[JohnK]

 

. . . . . . So, now that it's a couple of years later, and after getting the car on the road and driving it for a season, I found some changes were justified. Here's a LINK . . . that describes what I decided to change, how I made the changes, and the results of the work.

 

 

Sections covering work not described in the first write-up or after getting the car on the road:

 

On Steering: http://www.usa7s.net/vb/showthread.php?7421-Ithaca-Lemonade&p=97614&posted=1#post97614

On Brakes and what it takes to make them deliver what they're supposed to:

http://www.usa7s.net/vb/showthread.php?7421-Ithaca-Lemonade&p=97616#post97616

On Handling (fixing an evil oversteer problem): http://www.usa7s.net/vb/showthread.php?7421-Ithaca-Lemonade&p=97617#post97617

On the last component in the powertrain: http://www.usa7s.net/vb/showthread.php?7421-Ithaca-Lemonade&p=97618#post97618

 

 

Preamble (read this to see why I went to all this bleeping trouble).

 

I put this thread together to pass on my experiences and share what I think I've learned as I turned my 'kit' into a car, a car that's not only sound and fun to drive, but actually deserves to be called a 'Se7en'.

 

I hope readers will appreciate that:

- this is one person's take on what Se7ens are about,

- my view is based on what one builder delivered,

and claimed it qualified as a Se7en kit,

- a Se7en can be any number of things, depending on the driver's expectations,

which can change as the driver/builder/tinkerer gains experience.

 

. What THIS driver happens to be focused on is what a Se7en DOES when you drive it. A Se7en should be an invisible link between you and the road. If the car has to be wrestled through the twistiest parts of the road, then it is not a 'good' car and it doesn't deserve to be called a 'Se7en'.

 

. A Se7en really is a thinly disguised race car that can be legally driven on the street (if you're careful). Happily, we have examples of what a 'good' race car is in the reports of what 'good' race cars do in competition, and to those with mechanics' chops, what's involved in actually making race cars that folk think of as 'good'. The best description I've found of what a good race car IS, is in an article by Robert Cumberford on the OSCA MT4 appearing in the August 2011 issue of Automobile.

http://www.automobilemag.com/features/news/1108_giant_killer_osca_mt4/

I still get chills up my spine when I read Cumberford on Bugatti, OSCA and Lotus, and feel very fortunate that I'm able to take part in this kind of experience with something I've been able to build and develop myself, and that aspires to delivering the kind of behavior I read about. As far as actually MAKING a 'good' Se7en, Carroll Smith runs down the 'from-the-trunk-of-the-tree' fundamentals in his “Prepare/Tune/Engineer to Win” series of books. Every time I re-read a section in one of his books I get a better understanding of how the different systems in a race car are supposed to work and, for a person building such things themselves, how to do it right.

 

. My first/introductory post (http://usa7s.com/vb/showthread.php?t=7421) includes some threads that describe the work involved in first getting the car on the road. From here on are threads describing work done after I put 'release 1.0' on the road and saw what else had to be done to make it 'right'. What I've found interesting is that doing all of this has taken place on so many different levels. Some of it involves mathematics, some insight, some purely matters of mechanics, techniques and procedures . . . You can read, learn and study all about, say, suspension - but at some point you have to figure out how to select the materials and then develop the skills to fabricate and assemble things into parts that perform the task you've intend that they should do – and also find some way to verify that the things you've made are actually delivering what you intended. And when you integrate the collection of systems you've created into a car that actually delivers what you want, it's quite a trip.

 

To get some perspective on what other people have brought to bear on the problem of creating a 'Se7en', you might refer to my post

http://www.usa7s.net/vb/showthread.php?3533-Another-thing-to-consider-when-choosing-a-Seven

or just go to the post that my post references:

 

https://www.dropbox.com/s/edccxybb5nq2pgr/oconnell.pdf?dl=0

 

The take home here is that a current Caterham is the product of a lot of development done by skilled and talented folk that's taken place project by project over many years starting with the original Lotus 7. Such things just don't happen by accident, and there's no rule-book to follow that tells you what to do.

 

Return to home page: http://usa7s.com/vb/showthread.php?t=7421

Edited December 24, 2016 by JohnK
Fixing chages due to DropBox changes.

[JohnK]

I found one compelling reason to analyze and eventually redesign the steering on the 'kit' I got and wound up with something that works better than I could have imagined.

http://www.usa7s.net/vb/showthread.php?7989-A-note-on-steering

Also, here's a collection of pictures showing how to mock up a steering system in order to, first of all, place the rack accurately in the chassis so you can then determine where it actually needs to be in order for it to work right, and along the way determine the dimensions of all the parts that comprise a rack.

https://www.dropbox.com/sh/8qlli08y8zfftua/AABtEyYGIUK0EmclUVFOwMNha?dl=0

 

Also, there were some comments on fitting electric assisted steering.

See http://www.usa7s.net/vb/showthread.php?7421-Ithaca-Lemonade&p=97615#post97615

for some notes on this.

Edited January 28, 2017 by JohnK
Changes mandated by DropBox

[JohnK]

I remember reading about people fitting electric power steering to their cars. I've also read reviews saying that electric assisted steering delivers poor feedback. I know that Honda's been criticized for delivering Civics and Fits with numb feeling steering allegedly caused by their electric power steering lately, and statements that electric power steering in general provides poor feedback compared to either manual (no question) or hydraulic (requires a setup designed for racing, rather than production/street parts adapted for re-use in a sports car). Making it more confusing still, currently Porsche uses an electric steering assist system while Ferrari uses hydraulic, but I'll bet the Porsche system would run you more than the hundred bucks I've heard mentioned and wouldn't even be willing to guess what Ferrari does with its hydraulics – anyone have experience with Moog's electrically controlled hydraulic valves and the computer programs necessary to manage how it behaves? Also regarding Honda's choice of electric over hydraulic here, the energy savings of the former are huge in comparison to the latter, so this may figure significantly in their decision making. It's worth noting that not only is the rack I used designed from the ground up for racing applications, the 3 HP pump that delivers the oil to drive the rack is also designed specifically for racing applications. These are very specialized pieces of equipment, and it shows in the way the steering effort disappears when you're driving fast and very quick and ultra precise control becomes effortless.

Also read http://www.usa7s.net/vb/showthread.php?9243-Handeling-Thread&p=80842#post80842

[JohnK]

. I seem to have found a brake problem that's common to Se7ens and is due to their light weight. All the after-market brake systems I know about require new pads to be “bedded in”. If this isn't done, the brakes will be weak due to what's known as 'green fade', and this fade shows up as a lack of instant 'bite' when the brakes are applied as well as overall poor stopping ability but can improve dramatically once the brakes get hot.

 

Bedding in is accomplished by getting the pads hot enough to drive off chemicals created in the manufacturing process that keep the brakes from working like they should until they're hot. This is very hard to do if the car is light.

 

. The following post describes this phenomenon and the process. (The link below is to the thread's post #6, which is the result of my rewriting the first post to make it more understandable and spell out what's happening more concisely.)

 

Start of the "weak brakes" thread: http://www.usa7s.net/vb/showthread.php?10484-Weak-brakes

(This is a long thread with lots of discussion. If you want to skip to the conclusion of

the "weak brakes" thread go to http://www.usa7s.net/vb/showthread.php?7421-Ithaca-Lemonade&p=101568#post101568 and you can ignore the rest of this paragraph. The following stuff is interesting if you can find information useful to you in a similar situation.)

 

 

(Note that this hasn't been completely resolved yet - it's turning out harder than I thought to get the brakes over 300 degrees F, even when pulling down several times from 120 MPH. Stay tuned.)

 

January 2016: Over the winter of 2015-16, and prompted by something Wilwood suggested, I'm working on making covers for the front calipers to keep them from shedding heat which the do really well, hanging out in the air stream like a formula car and all. Time spent at the dragstrip doing runs to warm up the brakes and then pulling down from 120 MPH several times and then letting the car rest showed less than 150 degrees F. when measured directly at the caliper with a thermocouple bolted to a caliper and connected to an electronic thermometer. Along with covers for the calipers I'm planning on plugging the entrance to the cores of the rotors so the vents won't flow air. That along with the covers, 'specially over the slot at the top of the caliper where you can see the rotor and its vanes, should get me some heat staying in the caliper. Who was it said that this was supposed to be easy?

N.B. that, when the brakes were warmed up, they worked extremely well - very modest pressure on the pedal put you in the area where wheel lock-up was not far away and the feel was excellent - coming down from 120 MPH I could keep the front tires at the point of chittering (?) all the way down to low speed gassing myself on rubber fumes in the process.

. To remind me of the goal here, the brakes should do this when they're cold, just like the brakes in my Civic do. That's what bedding in is supposed to achieve.

Edited November 22, 2016 by JohnK
adding final link.

[JohnK]

. How I approached and fixed my very evil oversteer problem. My posts in this thread are in sequence, but are embedded in a thread dedicated to a general discussion of handling.

This thread (Handeling (sic) Thread) starts at

http://www.usa7s.net/vb/showthread.php?9243-Handeling-Thread&

 

My collection of posts starts at

http://www.usa7s.net/vb/showthread.php?9243-Handeling-Thread&p=80768#post80768

and ends in the Handeling-Thread at

http://www.usa7s.net/vb/showthread.php?9243-Handeling-Thread&p=94723#post94723

[JohnK]

My particular car was delivered with a perfectly fine limited slip differential built into a 5-link rear suspension, but it had an absolutely terrible ratio and was mounted in the chassis in a really awful way.

This explains how I dealt with these problems.

Due to length, this is explained in the following two posts.

 

The starting point and the design: http://www.usa7s.net/vb/showthread.php?7421-Ithaca-Lemonade&p=97620#post97620

 

The implementation of the fix made to the front of the differential mount: http://www.usa7s.net/vb/showthread.php?7421-Ithaca-Lemonade&p=97621#post97621

Edited November 28, 2015 by JohnK

[JohnK]

. With respect to the Subaru differential that was included and delivered mounted in my 'kit's chassis, I've assumed a couple of things. First is that Honda knows how to engineer powertrains (engine+transmission+differential) that provide the driver with optimal performance, and that this involves optimizing the engine's torque curve via the gear ratios of the transmission and differential. Second, Subaru engineers have a good handle on mounting their drive train components in their chassis, including those in their over-the-top rally cars such as the Impreza WRX (not the STI) which is what the differential I got was engineered to work in.

 

- First, the differential itself. The Honda S2000 engine is, in absolutely stock tune, a very high performance engine, so saddling it with a sky-high 3.54 differential (which is what my 'kit' showed up with), when Honda determined that a 4.10 ratio is what matches the output characteristics of it and it's transmission, is stupid and unless one wanted to waste such an extraordinary engine-transmission by lugging the crap out of it all its life, it needed to be changed.

. I found out that, with one exception, there is no junk yard that will deliver what you ask for when it comes to Subaru differentials (the one exception actually admitted that it could find no sourcing yard that actually had this item in the spec requested, and apologized – the other yards just tried to pawn off whatever they could get their hands on in the hopes that the buyer wouldn't know what they were getting). Subaru does indeed supply such a thing and after doing the homework and providing Subaru with the spec (Subaru Impreza WRX manuals), provided me with one and it came in exactly as ordered. They were pretty pleasant to deal with too, in contrast to all the rest of the yards. (I'll ignore feeling bad about how much it cost me to throw away what came in the kit I paid for.)

 

- Second, mounting the differential in the chassis.

Subaru engineered all of this :

https://www.dropbox.com/s/adhzhj0mzh1iro9/Subaru_Diff_mount.JPG?dl=0

to connect the rear of its Impreza WRX drive train to its chassis.

The builder of my WCM S2K 'kit' cut this up in order to fit these parts into this chassis. At the front of the shell (item (1)), the nose along with its wings was cut off and a boss was welded to the top front of the shell behind its hacked-off nose and tapped for a 1/2”-20 bolt. A rubber donut was put over the boss and a mounting plate on the chassis went over and around the donut and a 1/2”-20 bolt connected the two together. So this attached the front of the differential mount to the chassis instead of the wings. This turned out to be not strong enough (what a surprise!) and was found to twist apart in use, breaking the boss-to-shell weld and allowing the front of the differential to crash about in the driveshaft tunnel making awful noise and beating anything within its reach to death.

https://www.dropbox.com/s/ghlp8tzcozw4xa2/Diff_Mount_Fwd_Pullout.JPG?dl=0

I wasn't about to trust this lame fabrication attempt with my brand new differential, or the driveshaft that I had to have fixed on my own to replace the junk u-joint in the driveshaft that showed up in my kit, not to mention the future well-being of my right hip and leg.

 

To fix this I made three changes:

. I fabricated a structure that duplicated, in smaller extent, the wings and nose of the shell originally designed by Subaru to support the input end of the differential;

. I created a support (a 'nose') around the front of the differential-supporting-enclosing shell to strengthen and stiffen the shell to deal with rotation, and vertical and horizontal forces the differential generated, and attached this fabrication (at upper and lower points) to the chassis with a pair of very stout industrial bonded bushes (i. e. I created shortened wings and positioned them vertically instead of horizontally);

. I also bought the stock Subaru lower shell supports to tie the shell to the differential at the shell's open part on the bottom (item (6) in the drawing). These supports makes the shell a lot more rigid and ties the differential rigidly to the shell. Details follow.

 

I don't know how serious a thrashing my fabrication is strong enough to take, but it's gotta be vastly better than what showed up in my driveway on my birthday in 2006. Also, because the differential's entire support system is attached to the chassis both fore and aft via heavy bonded bushes, shocks from the drivetrain to the chassis are damped so the car is a lot quieter and fatigue failures must be reduced. I'm trusting that, since the load-bearing advantages of the stock Subaru design can't be implemented because of the lack of space, this weakness may be offset by the much lighter weight of the entire car, and this configuration imposes lower loads on the drivetrain. (At least that's what this fool hopes.)

 

Rubber bushes bonded to steel are used in many support structures in industry. I found the following family of mounts at:

http://www.hutchinsonai.com/products/product.cfm?cid=1&fid=5

and details of their sizes and ratings at:

https://www.dropbox.com/s/vjd3xugl6uj0a3x/Barry%20Bond%20Series.pdf?dl=0

Scroll down to see the drawing that shows how this type is installed (basically it's installed as what looks like a mushroom, and then compresses when bolted together into dumbbell shape. The end result is that the two pieces -the chassis and the differential- have a heavy layer of isolating rubber trapped in compression between them where they connect to each other).

And scroll down to see the dimensions and load ratings for BC-1122-4 which is what I fitted. (Subaru uses a similar construction at the rear.) The two different ratings for maximum load in each size range are due to differences in the durometer of the rubber used in each part.

Edited December 28, 2016 by JohnK

[JohnK]

With respect to the Subaru differential that was included and delivered mounted in my 'kit's chassis, I've assumed a couple of things. First is that Honda knows how to engineer powertrains (engine+transmission+differential) that provide the driver with optimal performance, and that this involves optimizing the engine's torque curve via the gear ratios of the transmission and differential. Second, Subaru engineers have a good handle on mounting their drive train components in their chassis, including those in their over-the-top rally cars such as the Impreza WRX (not the STI) which is what the differential I got was engineered to work in.

 

- First, the differential itself. The Honda S2000 engine is, in absolutely stock tune, a very high performance engine, so saddling it with a sky-high 3.54 differential (which is what my 'kit' showed up with), when Honda determined that a 4.10 ratio is what matches the output characteristics of it and it's transmission, is stupid and unless one wanted to waste such an extraordinary engine-transmission by lugging the crap out of it all its life, it needed to be changed.

. I found out that, with one exception, there is no junk yard that will deliver what you ask for when it comes to Subaru differentials (the one exception actually admitted that it could find no sourcing yard that actually had this item in the spec requested, and apologized – the other yards just tried to pawn off whatever they could get their hands on in the hopes that the buyer wouldn't know what they were getting). Subaru does indeed supply such a thing and after doing the homework and providing Subaru with the spec (Subaru Impreza WRX manuals:

http://www.wrxinfo.com/service_manuals/

), provided me with one and it came in exactly as ordered. They were pretty pleasant to deal with too, in contrast to all the rest of the yards. (I'll ignore feeling bad about how much it cost me to throw away what came in the kit I paid for.)

 

- Second, mounting the differential in the chassis.

Subaru engineered all of this :

https://www.dropbox.com/s/adhzhj0mzh1iro9/Subaru_Diff_mount.JPG?dl=0

to connect the rear of its Impreza WRX drive train to its chassis.

The builder of my WCM S2K 'kit' cut this up in order to fit these parts into this chassis. At the front of the shell (item (1)), the nose along with its wings was cut off and a boss was welded to the top front of the shell behind its hacked-off nose and tapped for a 1/2”-20 bolt. A rubber donut was put over the boss and a mounting plate on the chassis went over and around the donut and a 1/2”-20 bolt connected the two together. So this attached the front of the differential mount to the chassis instead of the wings. This turned out to be not strong enough (what a surprise!) and was found to twist apart in use, breaking the boss-to-shell weld and allowing the front of the differential to crash about in the driveshaft tunnel making awful noise and beating anything within its reach to death.

https://www.dropbox.com/s/ghlp8tzcozw4xa2/Diff_Mount_Fwd_Pullout.JPG?dl=0

 

I wasn't about to trust this lame fabrication attempt with my brand new differential, or the driveshaft that I had to have fixed on my own to replace the junk u-joint in the driveshaft that showed up in my kit, not to mention the future well-being of my right hip and leg.

 

To fix this I made three changes:

. I fabricated a structure that duplicated, in smaller extent, the wings and nose of the shell originally designed by Subaru to support the input end of the differential;

. I created a support (a 'nose') around the front of the differential-supporting-enclosing shell to strengthen and stiffen the shell to deal with rotation, and vertical and horizontal forces the differential generated, and attached this fabrication (at upper and lower points) to the chassis with a pair of very stout industrial bonded bushes (i. e. I created shortened wings and positioned them vertically instead of horizontally);

. I also bought the stock Subaru lower shell supports to tie the shell to the differential at the shell's open part on the bottom (item (6) in the drawing). These supports makes the shell a lot more rigid and ties the differential rigidly to the shell. Details follow.

 

I don't know how serious a thrashing my fabrication is strong enough to take, but it's gotta be vastly better than what showed up in my driveway on my birthday in 2006. Also, because the differential's entire support system is attached to the chassis both fore and aft via heavy bonded bushes, shocks from the drivetrain to the chassis are damped so the car is a lot quieter and fatigue failures must be reduced. I'm trusting that, since the load-bearing advantages of the stock Subaru design can't be implemented because of the lack of space, this weakness may be offset by the much lighter weight of the entire car, and this configuration imposes lower loads on the drivetrain. (At least that's what this fool hopes.)

 

Rubber bushes bonded to steel are used in many support structures in industry. I found the following family of mounts at:

http://www.hutchinsonai.com/products/product.cfm?cid=1&fid=5

and details of their sizes and ratings at:

 

https://www.dropbox.com/s/vjd3xugl6uj0a3x/Barry%20Bond%20Series.pdf?dl=0

 

Scroll down to see the drawing that shows how this type is installed (basically it's installed as what looks like a mushroom, and then compresses when bolted together into dumbbell shape. The end result is that the two pieces -the chassis and the differential- have a heavy layer of isolating rubber trapped in compression between them where they connect to each other).

And scroll down to see the dimensions and load ratings for BC-1122-4 which is what I fitted. (Subaru uses a similar construction at the rear.) The two different ratings for maximum load in each size range are due to differences in the durometer of the rubber used in each part.

 

 

Part Two: the implementation: http://www.usa7s.net/vb/showthread.php?7421-Ithaca-Lemonade&p=97621#post97621

Edited December 26, 2016 by JohnK
Changes mandated by DropBox

[JohnK]

Modifications: ----------------------------------------

 

This is the front mount structure installed.

 

View of the cockpit from the left side of the car:

https://www.dropbox.com/s/4lkfmqm7v1qgrmi/Diff_front_fix_overview.JPG?dl=0

. The yellow zinc plated bolts identify the connections which tie front of the differential-enclosing shell (the nose of the shell) to the chassis.

 

Note the front of the driveshaft tube's absence of paint. The car was run for a couple thousand miles with the 'as delivered' front mounting of the differential, and the paint was rubbed off of the front of the driveshaft tube as the differential moved around in the driveshaft tunnel (rubbing against the driveshaft loop and/or my handbrake fittings). Seeing this when I took things apart in order to replace the differential with one that had the correct ratio convinced me that I'd better undertake this fix if I valued the well-being of my right thigh, not to mention expecting the drive train to stay in place as I drove the car.

 

Preparatory to this I had the driveshaft redone by a local commercial driveshaft place. The rear universal was bad (in all of the THREE successive units which I received from the “kit's” builder), and the driveshaft had not been balanced (the driveshaft place showed me the evidence). “Spicer” (see later shot) makes equipment specialized for balancing driveshafts which the shop used. I disassembled, cleaned, re-lubricated with CV joint grease, and reassembled the CV joint connected to the transmission's tail myself – the innards were filthy (water+grease), but the surfaces turned out to be OK (rust had not yet set in, nor had grit been ingested). If Honda had put a u-joint here as well as at the far end you'd feel a pulsing with each driveshaft rotation as the car cruised at a steady speed when there was any angularity in the driveshaft. The effect may be subtle but contributes to the overall feeling of soundness/quietness of the car. All front-wheel drive cars have these expensive-to-manufacture joints on both ends of each of their half driveshafts – which usually run at considerable angle to their transmissions. Otherwise the sound/vibration/pulsing would be really annoying, not to mention being hard on the mechanicals.

 

Back to this picture:

 

Above and below the driveshaft are the bonded bushes fitted with 1/2-20 Grade 8 bolts (Thanks be to W. W. Grainger for stocking these in packages of fewer than 100) and which connect the chassis and the front of the differential shell through the vibration-absorbing bushes.

- The base which receives the lower mount's bonded bush is tied to the chassis tubes beneath it through vertical 1/8” plates welded to these chassis tubes, which are tied to the mount base with allen head cap screws (what you see in this picture is one of these plates welded vertically to the chassis – the mount base is trapped inside this/these plates). The top part of this lower mount is tied to the shell by vertical nut-plates which receive allen head cap screws through the shell. So the upper part of the lower mount encloses and thus stiffens the bottom and sides of the front of the shell (the 'nose') as well as tying the shell to the chassis via the bonded mounts (see following links/shots for details).

- The top bonded bush is bolted to a boss welded to the top front of the shell. This boss is reinforced as shown in later links/shots. (Yes, the front part of this mount is indeed sawed through on one side. I got the whole thing done and then realized that that's where the handbrake assembly goes!)

- Toward the rear, a single bolt head can be seen at the lower edge of the shell. This is one of the four bolts used in the two brackets which tie the differential to the shell, greatly stiffening the shell around the differential and tying the two together rigidly. See following pictures.

 

Overall this treatment is designed to both make the shell much stiffer (more like an egg shell) and to feed the loads that occur at the front of the differential into the chassis while handling shock in a way that an engineer would approve of (and which wouldn't contribute to this sub-system's early death). The bonded bushes are very strong and absorb shock to the chassis as torque goes through the drivetrain to the wheels.

 

This was hard. The bonded bushes are pulled into place as they are bolted in (they go from mushroom to dumbbell shape as their central bolt is tightened) meaning everything has to be lined up exactly – since the top mount is going into a threaded boss, the danger of cross-threading (and ruining the whole shell assembly) is high. Many careful preliminary attempts and tests here avoided disaster, or at least having to buy a new shell and having to do all the work over again.

 

Following shots show the components.

 

Differential lower front mount.

 

. Complete assembly supporting the open end of the front of the shell and providing the attachment to the chassis at the bottom of the shell: https://www.dropbox.com/s/kuvov9xi35n3rgy/Diff_front_lower_mount_assy.JPG?dl=0

. Detail.

https://www.dropbox.com/s/eerrritev6hbz03/Diff_front_lower_mount_assy_detail.JPG?dl=0

. Installed in chassis.

https://www.dropbox.com/s/094yf05mee7iwdi/Diff_front_lower_mount_install.JPG?dl=0

 

. Modification of front of differential-supporting shell, upper mounting. A and B shots:

https://www.dropbox.com/s/64bv94pwlvs8yxm/Diff_front_upper_mod00.JPG?dl=0

https://www.dropbox.com/s/xp120rd1ybnxl84/Diff_front_upper_mod01.JPG?dl=0

 

. Installation of Subaru brackets (above, item (6) and the T4 attaching bolts) which bridge the open/lower part of differential-supporting shell to the differential. This along with item (2) turns the shell into a rigid enclosing structure around the differential. A and B shots:

https://www.dropbox.com/s/5ozsgf7ekt1xpaq/Diff_ShellMod_shell-to-diff_bracket_01.JPG?dl=0

https://www.dropbox.com/s/rw3ax6orkna1gt9/Diff_ShellMod_shell-to-dif_bracket_02.JPG?dl=0

(that bit of wood in this last shot is the cane I was using to get around when I was doing this work while I was waiting my turn to have a hip replaced.)

These two shots really make it obvious how asymmetric the drivetrain is – and why the axle half-shafts are different lengths – and why an owner of an S2K has to spend lots of time ensuring that all four wheels are exactly at all of the four corners where they're supposed to be when doing the alignment, along with ensuring that the axle bearings aren't binding as the axles move through their range of bump/droop (easy to get bind through compression here, or have the axles pull out of the differential when things move – the latter is embarrassing, the former is expensive).

 

If you spend a little time thinking about all these connecting pieces, it becomes clear that the builder seemed to think that all the power that the engine produced was going to magically go right to the rear wheels without having to worry about how the wheels were going to connect that power to the chassis.

 

Return to home: http://www.usa7s.net/vb/showthread.php?7421

Edited December 26, 2016 by JohnK
Changes mandated by DropBox, additions - seller

[JohnK]

Way back in http://www.usa7s.net/vb/showthread.php?7421-Ithaca-Lemonade&p=97616#post97616

. I seem to have found a brake problem that's common to Se7ens and is due to their light weight. . . .

I went through theory and practice of what, on the face of it, is a straightforward matter of rolling one's own brake system. While the physics are just a matter of applying the relevant physics, the barrier to success finally came down to understanding the properties of brake pads that have not been "cured" as production pads are. The combination of a light car and race-car brakes makes it very difficult to get the brakes hot enough to bed them in - to drive off the compounds present in un-bedded or un-cured pads that keep the pads from developing the friction they're designed to deliver. What the manufacturers do to the production pads you buy at NAPA is cure them in commercial temperature and time controlled ovens, applying a schedule that their engineers/chemists have determined does the job. What you're supposed to do when you can only get un-bedded pads is generate that heat by doing a schedule of progressively harder stops - IF you have car that's heavy enough, which you can determine via the physics involved in the design of the brake system. If you have a very light car, you have a problem.

. So, plan B was to get the pads hot by other means and I decided to use a hot-plate rather than an oven. I found a commercial-grade hot plate for a reasonable price* and set to work. With a bit of experimentation and some patience, this approach proved itself productive and revealed that the schedule of heating was not simple. Still I came up with vastly improved behavior in the brakes.

First trial showed me that the fumes that come off the pads when they're being heated will not only make you sick, they'll damage the skin in you respiratory system. I had an awful cough for weeks.

I had a good electronic thermometer that allowed me to see what temperature I was working with. With the pad face down, the temp at the highest setting and the pad lifted 0.020 off the heating plate with a piece of wire, I could see 450-500 F on the steel backing plate. I made a wind shield to go around the heating plate with a cylinder of roofing flashing. At the highest temperature, roughly 750 F on the plate, 2 hours heating improved the grippyness , a second 2 hours made a bit more, .. and I decided, Hell, the specs for the pads show that they still make friction a 800 F so I of the flipped the pads over so the backing plate was on the heating plate and let it heat for 6 hours. The color of the pads was much lighter, like Carroll Smith says they're supposed to be - and when I picked up a pad I found that this heating treatment had killed the cement that holds the pad to its steel backing plate and the two fell apart. So with a new set of pads I went back to pad face down supported by 0.020" wire, wind shield/chimney around setup, and heat at full tilt for 2 hours, 2 iterations.

. When first installed after heating, the brakes were initially weak but became progressively stronger as they were used hard, and they stayed that way - probably an initial conforming thing between the pads and rotors. After this initial period the behavior stayed the same. Now the brakes show a progressive increase in strength as they get warm but the initial strength is, given firm pressure on the pedal, acceptable - but I don't expect to be able to lock up the wheels when they're cold. Modest use when enjoying the twisties makes them grippier. If you're driving fast and doing a lot of braking, the brakes become very strong and are very controllable with only light pedal pressure. I may get another set of pads and try a longer heating schedule, but as is they're greatly improved from the hazard they were when first fitted.

 

Overall, one has to keep in mind that, without vacuum assist, even wonderful brakes don't give you initial grip like you get in a daily driver - as a demonstration pinch off the vacuum connection to that big tank (brake booster) that fits on the end of your master cylinder and see what it feels like.

 

* http://www.burkett.com/Waring-WEB300-Electric-Hot-Plate-p/war-web300.htm