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I took my '81 in to have a 4-wheel alignment but they were not able to get the rear wheels to come into spec. They couldn't tell me exactly what was wrong but when I look at the car from the back the camber is easily visible, the tires lean in significantly at the top. I've ordered the strut rod bushings although I cannot tell for sure that they are bad. I had the car jacked up yesterday and tried to find some slop in the rear suspension but did not find anything excessive. I know there is a busing at the front of the rear trailing arm, is it likely that this bushing is bad as well? Is it replaceable? What else will cause this camber issue with the rear wheels?
Short answer: If they don't understand enough about how these cars work to tell you what is wrong, they have no business working on your car. Find a Corvette shop, or a mechanic who works on old cars.
Long answer: You can absolutely do this yourself! There are many informative threads on how to do this. The trailing arm bushing will affect rear toe, but even if it is all the way out, making the car undriveable, the camber shouldn't be visually affected. Your strut rods are too long, or your half-shafts are too short. The only adjustment on a stock car is on the inboard strut rod bolts. Barring any bent components (which would likely add positive camber, top angled out), I'm hard pressed to imagine why they can't adjust the camber within spec. Even if your strut rod bushings are worn out, the slop would fall within range. Perhaps your differential is shot, and your yokes are buried inside the case? Can you post some pics?
If you do replace components, heim-jointed strut rods will make this adjustment much easier in the future.
EDIT: Please post pictures! If your rear end is jacked way up, and your half-shafts droop way down, you could run into this, too.
Last edited by Bikespace; Jan 24, 2019 at 11:15 AM.
either the bushings are worn in the strut rods or the yokes are coming out of the differential, either one should be easy to see/check. Jack either side of the car up towards the rear of the frame, support it with a jack stand, and grab the bottom of the tire and try moving it in and out. If you have play watch whether the yoke is moving in and out of the differential.
By all means check the simplest things first, the strut rod bushings. More often than not this is what results in too much negative camber.
As MelWff said, the differential side yokes can contribute to this, but usually not enough as to be visible from the rear of the car.
You haven't mentioned how many miles are on the car and the overall condition of the suspension. As others have mentioned pictures do tell a story, so add some if and when you can.
The car has 90k miles and looks to be all original and in very good shape. I had the car jacked up by the frame yesterday and I pushed and prodded on everything I could find/see/get to with no significant movement. I was not able to twist the tire in and out of alignment. The tire did move just a bit but it was almost insignificant. Not enough I would think to cause the camber issues I am seeing. I will post some pics as soon as I can. Thanks for all of the responses already.
My thought was that the rear suspension only has two real components that keep the tire in line, the trailing arm with it's front bushing and the strut rod and it all pivots around the half shaft? The strut rod only applies force to the bottom of the rear spindle/hub/trailing arm so it must be up to the trailing arm bushing to keep the top side of the trailing arm from moving in/out and affecting camber. If the front bushing is shot the trailing arm would be free to twist in place around the strut rod pivot point. It would seem to me that the strut rod is more of a fine tuning component so if the trailing arm front bushing is shot and all of the other components are in good shape, would the camber still go out of alignment?
I have the strut rod bushings on order and will replace those for sure. The more I think about it the more I think I should just go ahead and do the trailing arm bushings too and be done with it.
The forward trailing arm pick-up, by virtue of it's rubber bushing does allow a degree of twisting of the trailing arm regardless of the condition of the strut rod bushings. However, what maintains control of camber is is the strut rods and the half shafts. The half shafts (when fully functional) remain fixed so adjustment of the camber, under normal circumstances is controlled by the strut rods. Focus on that first and if you still want or need to replace the control arm bushings do it then.
With 90,000 miles on the car the rear wheel bearing may well be due for servicing (if they've never been serviced before) and that would be a good time to change out the control arm bushings.
A COMPETENT alignment shop would be able to tell you what the problem is if they couldn't align it.
Go to another shop.
If you post your location, you might get a recommendation.
The OP has Negative camber, top of the wheel is in, bottom is out. A few pictures will save a lot of speculation. I don't see how worn bushings could cause anything but excess positive camber.
From: At my Bar drinking and wrenching in Lafayette Colorado
Originally Posted by motogotro
My thought was that the rear suspension only has two real components that keep the tire in line, the trailing arm with it's front bushing and the strut rod and it all pivots around the half shaft? .
The half shaft is what provides the third link to stabilize and establish the camber. A common problem on the Vette rear ends is that the half shaft yokes wear against the spider gear pin inside the differential, until they wear right through the thrust surface and into the snap ring groove. This wear will make the yoke (and the halfshaft) move inward when the suspension is loaded, thus tilting the top of the tire inwards. It can be severe enough that the strut rods cannot compensate for the wear. Someone unfamiliar with this problem would not be able to identify why the camber cannot be adjusted. When the car is jacked up, the yokes will move outwards, allowing the top of the tire to tilt out.
Here is a rear end with just moderate wear on the ends of the yokes. Here the yoke is all the way "out" and up against the snap ring:
When the suspension is loaded, the yoke will move inwards until it hits the spider gear pin. Here the yoke have moved almost 1/4" inward, which will dramatically tilt the top of the tire inwards:
Here is what the worn-out end of the yoke looks like - it has been ground off through the case hardened surface, and will keep getting worse:
There should only be very slight movement of the yoke in the differential case (.010").
So no slip joint in the half shafts like you find in a regular driveshaft? That makes things clearer. I will check to see if the yokes on the inboard end of the half shafts move in and out significantly.
From: At my Bar drinking and wrenching in Lafayette Colorado
Originally Posted by motogotro
So no slip joint in the half shafts like you find in a regular driveshaft?
You can't have a slip joint since the half shaft takes the full load as the 3rd member in the triangle geometry. The driveshaft cannot shift or move inward or outward. If it does, the entire wheel will tilt in and out incontrollably. It's really clear in the photo posted by Gusto14 above: You can see that the halfshaft is the "upper a-arm." The strut rod is the "lower a-arm." The control arm then forms the 3rd link going forward, controlling the toe-in.
The half shaft is what provides the third link to stabilize and establish the camber. A common problem on the Vette rear ends is that the half shaft yokes wear against the spider gear pin inside the differential, until they wear right through the thrust surface and into the snap ring groove. This wear will make the yoke (and the halfshaft) move inward when the suspension is loaded, thus tilting the top of the tire inwards. It can be severe enough that the strut rods cannot compensate for the wear. Someone unfamiliar with this problem would not be able to identify why the camber cannot be adjusted. When the car is jacked up, the yokes will move outwards, allowing the top of the tire to tilt out.
Here is a rear end with just moderate wear on the ends of the yokes. Here the yoke is all the way "out" and up against the snap ring:
When the suspension is loaded, the yoke will move inwards until it hits the spider gear pin. Here the yoke have moved almost 1/4" inward, which will dramatically tilt the top of the tire inwards:
Here is what the worn-out end of the yoke looks like - it has been ground off through the case hardened surface, and will keep getting worse:
There should only be very slight movement of the yoke in the differential case (.010").
if this turns out to be my problem, does the differential have to come out to replace the half-shaft yokes?
Unfortunately, yes you will. Removing the rear cover (which has the integrated batwing support), would be more work than pulling the differential out of the car, and with the diff out, you can do more things to restore your differential.
If that is the problem. Did you get the car back up on a lift, and do you have photos from when it was?
From: At my Bar drinking and wrenching in Lafayette Colorado
Originally Posted by Bikespace
Unfortunately, yes you will.
You have to drop the rear crossmember out of the car with the differential case attached to it. It's not as bad as it sounds...
To get a good and accurate indication of the condition of your yokes, disconnect your halfshafts from the yokes once you have the car raised. This will allow you to freely move the yokes in-and-out without fighting the rear suspension, which will not allow you to move the yokes to check the endplay.
Unfortunately, yes you will. Removing the rear cover (which has the integrated batwing support), would be more work than pulling the differential out of the car, and with the diff out, you can do more things to restore your differential.
If that is the problem. Did you get the car back up on a lift, and do you have photos from when it was?
I do not have access to a lift and I have not had a chance to see if I can determine if this is my problem yet; however, from what I am hearing there are not too many things that will cause this condition with strut rods being the other likely candidate. My strut rods are already adjusted as far as they can go and I still have significant camber. My strut rod bushings are showing some signs if bushing deterioration but they are not completely shot and I was told that even if they were I should be able to pull the wheel back into alignment so I don't think they are the root problem. So I'm hoping for the best and preparing for the worst. I hope to have a chance to get back under the car this weekend and see if I can confirm one way or the other.
This is a really common problem with Corvettes and I can't believe it took 10 posts before someone figured it out. The procedure for replacing the yokes isn't really all that bad. The bigger problem is likely to be finding quality replacements.
This is a really common problem with Corvettes and I can't believe it took 10 posts before someone figured it out. The procedure for replacing the yokes isn't really all that bad. The bigger problem is likely to be finding quality replacements.
I found some new reproduction yokes on ebay for $220 that fit my car. It looks like they are different for automatic vs manual cars....not sure why but the ones on ebay fit the '81 manual which is what I have.
Rear Camber
