DeDion

[slngsht]

Does anyone here have good detailed drawings / pictures of their DeDion setup?

[slomove]

Wait.....you are not planning another car mod!

[slngsht]

for next winter. I'm very happy with EVERY mod made this year. I still did not get to modding my front suspension (when I made my current set of Aarms before the Dragon, I did not take into account the inside of the wheel interfering with them when the wheel is turned all the way - still have to do that.

 

The other thing, is the poor ride quality on bumpy surfaces due to the rear... so I'm thinking about it. No more mods this driving season though, unless something breaks. Enjoying the car WAY too much right now.

 

Independent rear is out of the question for me given my frame layout, but DeDion is a possibility.

[yellowss7]

Mazda, I can take a few pictures tomorrow if you can wait. Tom

[slngsht]

  yellowss7 said:

Mazda, I can take a few pictures tomorrow if you can wait. Tom

I've not picked up the sawzall just yet

[slomove]

Well, maybe I am spouting BS here but my feeling is the DeDion principle is a bit over-rated. I mean it was never very successful in production cars and died out in the 80s (although I read a version of the new Smart car has it, as well as the 4WD Dodge Caravan). After all isn't it a glorified life axle? Same mechanical constraints with a few pounds less of unsprung differential mass and a whole bunch of added complexity and total weight.

 

I don't know....I have driven both DeDion and life axle Sevens and did not feel a discernible difference. But maybe that is just my lack of driver's "butt feel" sensitivity.

 

From my perspective a good choice of springs/shocks makes much more of a a difference.

 

Gert

[slngsht]

Gert, I've been playing with my shocks a bit, but not spring rates yet. I'm curious - do you know how much your axle - including rotors, calipers, etc..., minus wheels - weighs?

 

My problem may be that my axle is heavy (but then again, so is the car) at 215 pounds.

 

Anyway, I'm casually thinking about a jag IRS rear with inboard brakes, adapted for deDion use... That would minimize my unsprung weight.

[Birkin42]

A Birkin live axle weighs 150 lbs plus the calipers and rotors, so about another 25 lbs.

 

Besides reducing unsprung weight, a DeDion also does not have the live axle problem of transfering weight side to side due to drive shaft torque. In a high powered light car with sticky tires, this can be significant.

[DeanD3W]

Slngsht - Regarding a Jag rear end assy being made part of DeDion rear suspension... I think the rear axles act as upper control links in the Jag, so neither end of the axle includes any plunge (similar to earlier Corvette rear suspensions). I think this means that it won't work as a DeDion unless mods are made to allow the axles to change in length with suspension travel.

 

Maybe a Thunderbird, or if you want an aluminum housing a Lincoln MK VIII, would be a good choice for your LS1 powered car?

[MHKflyer52]

The live axle in my car with drum brakes installed weighs 178lbs.

I found that a good set of shocks with bounce and rebound adjustments are worth their price (one of the most expensive parts on my car). It took me a number of drives down the same bumpy section of road to get them dialed in so the ride was not a back and kidney killer but with the twist of a knob and a couple of clicks of the adjusters the car can become as stiff as a board if wanted or just the opposite. It is very evident when any of the adjusters have been moved and can be quite interesting when you do not know that someone has messed with them so I have mine marked so that I can check them especially after the car has sat somewhere where people are looking at it and being curious and I am not around.

As a side note do to the lightness of our cars wheel balance is critical so you might want to have that checked also.

[slngsht]

  DeanD3W said:

Slngsht - Regarding a Jag rear end assy being made part of DeDion rear suspension... I think the rear axles act as upper control links in the Jag, so neither end of the axle includes any plunge (similar to earlier Corvette rear suspensions). I think this means that it won't work as a DeDion unless mods are made to allow the axles to change in length with suspension travel.

 

Maybe a Thunderbird, or if you want an aluminum housing a Lincoln MK VIII, would be a good choice for your LS1 powered car?

 

Yeah, I was kinda wondering about the axle situation with the Jag rear. hmmm...

[scannon]

Mazda,

 

Here's some differential info from Flyin Miata who are now installing LSx engines into Miatas. They have several choices depending on how much HP and torque you are planning on blessing the car with.

 

Diffs for V8s

[Ian7]

  Birkin42 said:

Besides reducing unsprung weight, a DeDion also does not have the live axle problem of transfering weight side to side due to drive shaft torque.

 

excuse me? not entirely correct... engine torque must be reacted by something touching the ground, and that's the front and rear wheels, (with reactive force distribution F/R determined by many factors).

What the dedion doesnt do relative to a live axle is "climb the ring gear" which causes the axle to want to rotate around its axis and bind up the suspension.

 

having said that, I also dont sense a huge dedion benefit relative to my live axle in a street use situation.

[slngsht]

Ian, I think what you refer to as "climb the gear" is exactly what he was talking about.

 

also, the definition of huge depends on whether there is an actual problem with the current setup. I have one right now, so, in my case it's huge. I'm playing around with shocks and springs to see if I can find a happy medium, but if my unsprung weight in the back was 40 pounds instead over 200 (not counting wheels), I think ride quality would just be better.

[Ian7]

  slngsht said:

Ian, I think what you refer to as "climb the gear" is exactly what he was talking about.

 

yeah, sorry to seem like I'm throwing rocks, not my intent, but live axle wind-up and lateral load transfer under engine torque produce vastly different (although combined) effects, even though they result from the same drive torque.

 

ever see "Bullitt" ? remember the chase scene where he overshoots the corner, and reverses back at max throttle? now THAT was axle tramp !!

[slngsht]

k, I have played with my shocks a little bit. I used to have the shocks at 7/4 (compression/rebound), then lowered to 4/2, the switched and made rebound stiffer than compression @ 2/4 - that seems to give much better ride, but more squat, and I'm still not happy with wheel control over bumpy surfaces.

 

On another note, I think a Jag style IRS may actually fit. The main reason I have no room for traditional dual Aarm IRS is that the frame is boxed in near the rear wheels. As Dean mentioned, the Jag setup is similar to C2-C4 corvettes in that the half shaft also doubles as one of the links... so there is a lower link and the half shaft. I have asked one of the Jag vendors for dimensions.

 

http://upload.wikimedia.org/wikipedia/commons/8/87/Jaguar_IRS_coloured_diagram.png

[MHKflyer52]

Hi Mazda,

 

First I have to say the model you posted is very good, is it a 3D model like SolidWorks.

Second I can give you dim on the jag rear end as I have one in the shop to an XKE that is being restored at the moment.

Here is a photo I just happened to take this morning for some unknown reason at the time but is now clear to me.

[slngsht]

Hi Martin. There was a higher purpose in your picture taking

 

The main dimensions I need are...

1. from the back of the pumpkin to the mounting surface of the driveshaft

2. from the back of the pumpkin to the center line of the half shafts

3. from the bottom of the uprights to the center line of hub

4. a couple of pics of the pumpkin mounting points if you have it out of the cage.

 

I'm pretty sure I can find one of the jag rears that's already the right width to match my axle. I would not be reusing the jag links or cage, and would go to single shocks on each side...

 

BTW, if you're rebuilding that rear, this site is worth a read... seems very thorough:

 

http://home.bresnan.net/~dazed/JaguarIRS1.html

[yellowss7]

Sorry for the delay Mazda. Here's a shot of the dedeion tube and the diff. Let me know if you need a different perspective. Tom

[ottocycle]

Mazda,

I have a Jaguar C type replica that you can take a look at. It has a Jag IRS. Strong, reliable and able to handle a lot of HP but it is a heavy setup. The old XJ6 and 12 rears are wider and cheaper than the E type. I am looking at ways to change it for lighter bits. There must be a modern car with an IRS that is lighter.

Following on the monster Miata link I was thinking of looking into what those guys are doing. I believe they have a 2,600+ lb. car with as much and more horsepower as you. Another one I am considering the recent Ford Mustang. I may have a line on one that came out of a supercharged car. A lot of drag race guys change them out for live axles. If I get to see it you are welcome to come and check it out. How about the pre transaxle Corvette. The model before yours. That design came out of GM's post Lotus ownership pillage and was a good handling car.

We should pool our knowledge on this as I would be interested in doing something in the future.

Cheers-

 

Dermot.