S2K steering rack?

[jimrankin]

What steering rack was used as the "stock" build for an S2K? My rack is metric and does not line up exactly with the stock frame mounts. It also has four mounting points. Looking at another S2K I noticed it used a different rack.

I know that the Mustang II / Pinto rack seems to be the standard for most hot rod/kit builds.

Thanks for any information on what you are using and if yours is metric or SAE.

[rss]

jim,

i'm pretty sure it's usually the mgb rack from flaming river. that's what's on my car.

[jimrankin]

I have the MGB unit also. evidently it wasn't used on all or some were modified by the builder, probably to save weight and cost as you can get the lighter aluminum Mustang II / Pinto rack cheaper. I've also noticed different front wheel hub carriers than on mine.

When I ordered the Teflon heims to match some previous owners swap outs I didn't realize my front steering linkage was metric. Either the other racks were SAE or they have modified the tubes to take the standard heims.

Same with my carriers. It's been stated that there are no 5/8" heims on the front suspension but mine were. Guess I'll stay with the rack I have but if the Pinto unit fits they are on sale right now for only $129.00, cant beat that. The two Teflon heims and suspension tubes I'm not able to use with the current rack cost almost that much and I'm going to have to find some Metric units to replace them. Also, the frame mounts on my car were welded on a bit "off" as the rack did not line up (1/8"+out) and the only way to get it on was to taper the ends of the bolts and have them stress the mounts as they threaded in.

I wish I had done an "exact" center to center on the mounts while I had the rack out so I could see if the Pinto one would fit. Might still be able to get something in there to measure with.

[JohnK]

I just sold the rack and all related bits from my "kit" to a guy who's restoring an MG-B (and is putting in a V-8 that's known to fit ! ). To confirm, he brought the bent rack from his MG in for comparison and it was clearly a match (though the steering input shaft was real long on his).

.........So what are you doing that you have your R&P out? I (in my usual gonzo developer approach) did my steering from scratch and found a company that makes really really fine racks if you want to engineer out all bump steer and speed up your steering (but they're a bit more than $129)- it's out there written up on this site.

[jimrankin]

...without taking the steering rack out. Both ends of the rack had to be moved away from the frame mounts for the forward lower suspension arms to get the existing bolts out so I could replace the heims and install new shoulder bolts. Cars back in the trailer and stored right now so I can't check but I seem to remember that the MGB rack is 3 turns lock to lock. How much faster did you make your steering? I'm going to have to start looking at other 7's as I get the chance because things like the turning C/L of the hub to steering knuckle actually change the ratio quite a bit. Still same number of turns "lock to lock" but you can gain several degrees of turn by shorter distance to knuckle.

I find the MGB ratio to be just a little heavy when driving slowly but it could be a bit faster at speed, especially if the car is set up to oversteer a bit.

[JohnK]

Oh boy - did I open a can of worms, now that I think about it.

I had no other choice but to move my rack since the way the car showed up, the tie rods would have run in to the front link of the lower a-arm had I tried to drive around a corner ... Along with that, when I cut out the front end and made it like a standard S2K (if there is such a thing) I found that, no matter what I did, I recorded bad enough ride steer that I started exploring other solutions.

 

The general specs on the Flaming River Cobra/MGB manual Rack & Pinion: 3 turns lock to lock; 6.25" travel; 3/4" 48 spline interface (Sweet carries such fittings).

 

First of all, I would very highly recommend going to http://www.woodwardsteering.com/ and finding the section "Basic Rack and Pinion Tech" and reading "Configuring a rack for your race car." There are many many pieces on the site that give the best info on steering issues I've ever found - and that includes the works of Carroll Smith. One, "Steering ratios for oval track racing:", gives a superb explanation of the importance of quick steering. While all of this info concerns dirt/oval track race cars, the principles are perfectly applicable to sports cars.

 

...Steering systems are one one of those things that give new meaning to "everything is connected to everything else". The number of turns lock to lock depends on the pinion ratio of the rack (degrees of steering wheel movement to inches of rack travel), the steering ratio at the hub (the distance from the end of the tie rod connection to the hub to the kingpin line - or steering arm length), and where your steering stops are positioned, which determine your turning radius. There's a little trigonometry involved with the how much out of parallel the rack is with front axle line which shortens the effective rack travel, and this non-parallelness also influences how much Ackermann there is (my experience with this is that you want a lot of it). The rack travel has to be long enough to move your wheels to their steering stops. If the rack travel is longer than you need, your lock-to-lock value decreases. Generally, if both or youroutside front wheels turn to 20 degrees or so when at full lock and you've got less than three turns lock to lock, you've got pretty fast steering.

Quick steering is usually very desirable (certainly in a Se7en-type car) but getting that is a lot more expensive than just buying a rack with a high pinion ratio and/or fitting a really short steering arm - the faster (and hence the more fun) the steering is, the more effort it takes to turn the wheel, 'cause you're moving all the pieces faster and generating greater turning force faster. Having to use more force makes you less accurate/precise in piloting your car - finesse and brute strength usually don't occur together. As you reduce your caster toward zero, you make it lots easier to turn the wheel (witness any of the videos of people tossing Caterhams about on wet roads) - but the caster has to be dialed in really really precisely and both sides have to be very close to the same, and this is a LOT of work - 'specially when changing caster will change your camber, and correcting the camber change will change your caster. You also lose directional stability and the car can become very twitchy feeling with low caster. A very effective solution is to fit power steering which takes the work away and makes low caster unnecessary. I chose hydraulic, but there are electric solutions too. Porsche likes electric, Ferrari likes hydraulic...) All of this gives you a great response to the guy who says "What kind of fool would put power steering on such a light car?"

 

I wound up with 1 1/4 turns lock-to-lock, which is the same as the McLaren MP4-12C.

Very surprisingly, and I've explored this on a bunch of different roads, I never got the feeling that it was too quick - after I threw away the tires that came with the car and which were dead by that time anyway.

 

For those not easily bored I wrote up my little adventure in this area at

http://usa7s.com/vb/showthread.php?t=7989&highlight=note+steering

 

Anyway, carried away as usual, I hope that some of this was useful.