C1 Caster

[Dan D.]

Back in the day, I drove my 1954 Corvette for 9 years. I always liked he way it handled and steered. The front end was obviously tight; it did not wander, steer hard, and was fun to drive. Fast forward to today, my 57 wanders, shimmies, steers hard, and is not as much fun to drive. The 17" steering wheel is definitely 'different', but with no power assist I don't think it would be good to go to anything smaller. Right now all you have to do is think about changing lanes and you are on your way.

The front end is worn and is being rebuilt. The kingpins are a little loose, the the left side outer upper control arm bushing is quite loose, and the 3rd arm is really loose. Fixing this should cure a host of ills.

But in general, the drive-ability of these old cars is middle ages compared to new cars with their modern suspension systems, power assist everywhere, smaller steering wheels, quicker steering lock to lock, etc. Its just in the old days there was nothing to compare them to, and they were great!

My question is this: In 1957 Arkus Duntov did not like the way the car handled so he added an extra degree of caster to the front end by adding tapered shims between the front cross-member and the bottom of the frame. This increased the caster from 1* to 2*. The change was effective at about VIN# 4000. My car is 4122 (mid-May build) and it has the shims.

But seeing how the front end is out of the car being re-built, I have been toying with not putting the shims back in, in hopes that it will steer easier and more reflect how my 54 seemed to be back in the day. Perhaps I am just too used to modern cars now and can't relate to how they were back in the 60s, I don't know.

Anyhow, I have been advised that if I don't put the shims back in I will regret it. My question is for those of you with 54, 5, 6, and early 57s, did you add shims when your cars were rebuilt-restored, even when they were not there originally? Are they stable and return to center okay after turning?

More in general, what would be the consequences of not having the shims? They could always be put back in with a few hours of work. My car is a nice driver and will never be judged.

Dannnn

[Dan L.]

Re: C1 Caster

I added the shims to my ‘54. It improved the alignment which improved the handling.

[Robert L.]

Re: C1 Caster

My early '57 was rebuilt with the shims. The car was fun to drive, stayed where you pointed it and was solid on the road. My brothers '54 was not quite as nice (but I did not drive it very often).

This last summer I went to a car show with the '57 and found it really difficult to park. I am not as strong as I was 40 years ago, and my belly is now far closer to the steering wheel.

IMG_8945.jpg

MCMLVII

[Jim L.]

Re: C1 Caster

Dan,

My un-restored '54 (#3300) does not have the shims. The steering is light and precise. It goes where you point it, it has good return-to-center, and doesn't wander. I think your memory of your '54 is probably accurate.

Jim

[David B.]

Re: C1 Caster

Fix the front end first then PUT IT IN ! All '57's and a majority of 56's had it installed at assembly. Reference Chev. Tech Bulletin October 10, 1956 DR #267 for all specs. Copy in 56-57 JM Page 299. Shim installation was a result of high speed testing at Phoenix in 1955.

[Joseph L.]

Re: C1 Caster

The issue of handling in the early cars is well documented. There is a Chevrolet Inter-Organizational Letter dated March 29th, 1954 by Zora Arkus-Duntov addressing Maurice Olley's concerns about the Corvette's ride and handling peculiarities. The Corvette test car #856 mentioned in Zora's letter was the second car built under the Project Open Work Order #19000 which was in between the two 1953 Corvettes that were specifically built for the GM Motorama. In the letter, Zora lists handling and ride peculiarities of this Corvette, proposed changes, the changes he made, and the results. At least two of these items made their way into 1956-57 cars.

The Tech Service Bulletin DR 267 dated 10/10/1956 states that after VIN 4156, ALL '56 Corvettes had the new suspension with shim plates above the front crossmember. The Bulletin says they are there to address "an unstable condition exist above 60 MPH on 1956 Corvettes." The JM says to check for shim plates from approximately 1956 VIN# 4000 through the end of 1957 production. The JM also identifies the rear spring front hanger bracket has a higher bolt hole location. This was something that was also identified by Zora in 1954 to improve handling.

My 1957 front suspension was completely rebuilt a few years ago. I make my own alignment measurements and could not get the car to be within alignment specifications and there may be frame issues. I added a second caster shim and the results were impressive. Alignment is not just within specification but is at nominal settings. 2 degree caster, 1/2 degree camber

If one makes careful measurements on the shim plates, they add 1 degree of caster, not 2 as some believe.
With bias ply tires, the car handles well on the freeway and backroads.

If one studies the affects of positive caster, the front end of the car is raised when one makes a turn. That is not the case with 0 degree caster. It takes effort to move the car that small amount and you are the one inputting the effort. That effort to turn the car is also the reason the car tends to self center and have better straight line stability with additional caster.

[Dan D.]

Re: C1 Caster

I received 5 reply's from this thread. Thank You very much Dan, Robert, Jim, David, and Joseph.

General consensus is to add the shims, but it was not unanimous.

Last fall I had a front end shop measure my front end. I might add that this shop is very good. They have a new $50-60k drive-on laser controlled 4 wheel machine (needed for newer cars), and they are very experienced, very friendly, very knowledgeable, and good to work with. The attached print-out is the results - with my badly worn front end. The machine's database has specs for just about every car made, but it lists Corvettes from 54-57 as the same; it does not pick up the caster change. It measured my caster at 2.0 and 1.9*, so it is right on, as specified. Based on that, one would think that without the shims it would be just about 1*.

So this is what I have decided to do. I am going to put it back together without the shims, see how it handles, and have the shop re-measure the front end with the left side camber eccentric at both ends of its 3/32 range, and then adjust it to meet spec. Interesting enough, there is no means to adjust right side camber????

If handling is not good, then I will add the shims. Not that big of a job with the learning curve now behind me, all new hardware, and I don't have to takes everything apart just to insert the shims. I will then compare how it handles, repeat the alignment routine and have documented data on the effect of the shims. That should be beneficial to all C1 owners.

I will advise on this thread when I get the front end back and the weather returns to 'mild', wherever that will be in upstate NY, probably not anytime soon.

Thanks again to the 5 people that took the time to respond. It is much appreciated. If anyone else would like to relate their experience with the shims, please be my guest; the more input I get, the more accurate and valuable this experiment will be.




Dannnn

[Gary C.]

Re: C1 Caster

Dan,

Attached are '58 Frame Specs. Don't have '53-57 Frame Specs.

Gary
....

[David B.]

Re: C1 Caster

If not reinstalling shims (Chev. Engineers wrong?) be sure to remove the 2 idler arm spacers #3733479 which are a very important part of 56-57 installation procedure. This idler arm bracket was redesigned for all 58-62s so spacers not required.

[Kenneth F.]

Re: C1 Caster

The Technical Bulletin letter says "toe-in both sides 1/8." Where would I take these measurements? If I measure from tire to tire this seems to be different from "both sides 1/8."
Would this specification be for bias ply tires only?
Ken

[Dan D.]

Re: C1 Caster

The Technical Bulletin letter says "toe-in both sides 1/8." Where would I take these measurements? If I measure from tire to tire this seems to be different from "both sides 1/8."
Would this specification be for bias ply tires only?
Ken

Ken,

I just had my newly rebuilt front end (1957) aligned on June 21. The alignment shop has a new $50k laser controlled Hunter machine. The spec in their software specifies each wheel as 0 to 1/8. On mine they set one wheel to .05 and the other one to .08 for a total toe of .13. (I wouldn't think you would want them both at 0).

This is a very good shop. Very knowledgeable, very high quality, and easy to work with.

It is hard to measure toe from tire to tire as you can't measure half way up in the rear. It should not matter what tires you have.

My advice - spend a couple of bucks and take it to a good shop, where castor and camber can be measured and set as well as toe. Castor is pretty much not adjustable, although the camber adjustment does have some effect on castor.

A good modern day machine will also do rear end alignment. While there are no specs on these rear ends, their measurement will tell you if anything is bent or out of wack back there. Mine looked real good in the rear.

Dannnn

[Rod K.]

Re: C1 Caster

David, where are the 3733479 spacers installed? I do not find them in the AIM drawings unless not under front suspension. Thanks.

[David B.]

Re: C1 Caster

The 2 spacers 3733479 referred to in Tech Bulletin DR267 are round 1" diameter (visualize a small piece of pipe) as described and installed between idler arm bracket (back side) and center of front end cross member. They must be installed along with aluminum shims to get proper alignment. If you cannot find them this might explain some of your front end problems. NOTE: As mentioned idler arm bracket was redesigned in "58 and are no longer required.

[Rod K.]

Re: C1 Caster

I see what looks like about 7/32 thk X 1"+ dia washers at the rear two idler bracket mounting positions between the bracket and the cross member. Assume this is what you're referring to. Thanks for the info. Appreciate the help.

[Robert I.]

Re: C1 Caster

Do the shims only come in one thickness?