Trouble with front end camber at neg. 2 degrees

T

tomcolitt

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This is the second Coupe where I've had these numbers out of specifications, even though everything looks straight and all the related arms, ties and bushings are new or fresh. (I'm getting pretty heavy wear on the innermost edge of one of my 205/55/16s. Is the negative two degrees camber enough to cause such unusual wear?). I don't think the spindles on the struts can bend easily?

Does anybody know of a good way to diagnose where the problem might be? My alignment guy suggested taking it to a frame shop for diagnosing, but I can't really see how they could make any good measurements because usually those guys don't have the right adapter or the right tools or data for these cars. I also don't usually like some "trained technician" working on my classic car.
 
On BMWs X3s the rear tires wear prematurely on the rear as your coupe does on the front, due to negative camber. I just replace tires often because the all do that. Come to think of it so does the M3.

May want to run narrower tires up front. Are you running decamber plates and CN springs?
 
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If both sides were the same I might have to accept that, but since only one wheel has the high wear, I know that there must be some solution. I do have CN springs but it doesn't seem like lowering the front should affect camber more than by a few minutes of a degree, at most... In the rear, I have welded in Paul Cain's adjustable plates and no problems there.
 
Bent strut maybe?
You could also run a string line down the middle of the engine bay from the base of the wind screen to the front point of the car, then measure from this string line to the strut tops to give a estimation within a mm or so if both sides are the same, the trick is finding the centre of the car accurately. You would expect to see a smaller measurement on the side that is getting the tyre wear.
 
When I replaced the control arms on my e9, I noticed that one of the bolts holding the lower control arm to the subframe had worked its way lose, allowing the control arm to move away from the frame under load on one side. (The bolt was actually bent and was a b!tch to get out).

The seller had put new tires on the car before I bought it, so the new tires obscured exactly what this was doing, but it could cause camber to change on one side and not the other.
 
Left arm is 31121104387, right is 31121104388, 381mm, do you still have part number? The 74s used a 402mm arm with a longer tension strut but only one part number shown now for both applications. Check length of both arms. And e12 ends in 388/389 for L/R, don't know length.
 
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I think the "under load" may be the issue. I would start with the simple stuff, the strut rod bushing would be my first guess. Agree that the (-)camber would wear them on both sides if that were the problem.
Check the wheel bearings also- you know, the normal suspects. Please let us know!

Thanks
 
Thanks for all the quick responses. As I said above, the parts have been replaced so I hoped that Chris' answer was the key, but unfortunately I found that I had replaced both of those lower control arms at the same time with OCAP parts (Italian-made) that had the ...387 and ...388 part numbers. As best I could measure with these parts installed the original and the replacement parts measured about 40cm from pin to center of the rubber bushing, just like the originals which I had saved (not 381mm, but we may be measuring differently)...
Also, it's hard to see how minor wear in the rubber strut rod bushing could effect a full 2 degrees too much negative camber, since the strut rod locates the control arm mostly in the fore/ aft direction and the control arm itself is mostly responsible for movement in and outward (affecting camber). That's why I was hoping that I had the wrong version control arm (20mm longer) in there, but it looks like the correct replacement control arms are still available for the pre-74 Coupes (mine). I can't how the strut could bend out of shape other than at the axle, outside of any obvious collisions or impact. Any more good ideas?....

I just had one, but it also seems like a long shot. Isn't it possible to install the upper spring plate rotated the wrong way? Wouldn't that move the shock absorber off center and thereby tilt the strut in a way in which it wasn't intended?...
 
Tire rod front subframe, damper?

Based upon no real knowledge other than taking mine apart and reading the manual,here are my ideas.
When I took mine apart I found different length dampers in the two front struts, worth a look?
Springs the same?
Unless you have modified it, top mounts only go in one place, took me a while to work that out. Alloy spacer above spring, approx 18 mm, fitted to one side only?
The tire rod that goes from the front by the tow point to the control arm, are the beveled washers all fitted the correct way around? Is this rod correct and equal to the other?
Is the front subframe out of line, ie where it bolts onto the car? Or even bent?

How about the driver, like throwing it around certain corners and not others, I am guilty of this.
Slow puncture so it runs flatter and wears differently?

Perhaps, just rotate tyres frequently and enjoy it as it is!
C
 
Hi Tom, I'm thinking "simple", but if the car is on the alignment rack, toe is set correctly, camber is close to equal and caster, which is not really adjustable, is equal and you're wearing on one side, there is some kind of "load" problem; also, please check that tire's balance- I recently helped one of the office ladies with a flat tire, the threads were showing on the outside of one tire only, I said "what did you hit", well she hadn't hit anything, she lost a weight on the wheel and the balance was off and the tires were cheap (China) and I had her check the alignment when she got the new tire and it wasn't off really, so the "cupping" caused that. I wish I took a picture, never seen anything like it.

Keep us informed- thanks
 
20mm is quite a difference, I would think measurement is from center of each bushing. RealOEM shows only size 402 available, Penske shows both sizes available, strange.
 
Having been a heavy collision man for too many years I can tell you that a ¼” of movement in or out at the top of the strut (or the bottom) is needed to get 1 degree of camber change. I highly doubt you can get ½” movement from worn bushings so I too am also thinking you’ve got a bent strut or knuckle (spindle).
Assuming you have the same size rims & tires on the front of your coupe (you’d be surprised how many people don’t), well then you should have the same distance between the tire’s inner sidewall and the strut tube, otherwise figure something is bent. ~ John Buchtenkirch
 
John Buchtenkirch said:
Having been a heavy collision man for too many years I can tell you that a ¼” of movement in or out at the top of the strut (or the bottom) is needed to get 1 degree of camber change. I highly doubt you can get ½” movement from worn bushings so I too am also thinking you’ve got a bent strut or knuckle (spindle).
Assuming you have the same size rims & tires on the front of your coupe (you’d be surprised how many people don’t), well then you should have the same distance between the tire’s inner sidewall and the strut tube, otherwise figure something is bent. ~ John Buchtenkirch
Click to expand...

Actually I stand corrected….. I suffered a senior brain fart and used the radius instead of the diameter of the circle when I figured out what a degree of strut top movement is equal to.
So if the pivot points / length of the strut at ride height measures 29” (a number I took from a E28 parts car I’m breaking) that is only the radius, the diameter would be 58”.
So now we are talking 3.14 x 58” = 182.12”
182.12” divided by 360 = .506 which is slightly larger than ½”. So we are talking a full inch of movement to get 2 degrees of camber change, certainly more than worn bushings could cause. So my assessment of the problem likely being a bent strut still stands (even stronger) but the ¼” measurement equaling a degree of camber change is incorrect, it takes a ½”. Sorry, I will try to be more accurate in the future. ~ John Buchtenkirch
 
Overall, I'm at a loss about this whole thing. This is the most rust free Coupe on the planet, so there should be little weakening of the uni-body that could throw things off. Everything has been replaced and appears to be symmetrical. The control arms that came out of the car are the same length as the new ones that went in and yet the camber is two degrees different. (The control arm pin and the rubber bushing don't run quite parallel, so it is not easy to get a good measurement, but it's definitely around 400mm. I wish I could see a car with the 381mm parts to confirm. I only see the versions ...387 and 388 in the parts book, but it doesn't mention their length).

Thanks for the numbers John. Intuitively, I also thought that 2 degrees is a lot, but I will take a look at the distance between the strut and the rim on each side, which seems like it is at least measurable with some degree of accuracy. I still can't picture the strut tube being bent without an obvious severe impact and without visual cues. The same goes for the axle, but I guess it's somewhat more likely.
 
tomcolitt said:
Overall, I'm at a loss about this whole thing. This is the most rust free Coupe on the planet, so there should be little weakening of the uni-body that could throw things off. Everything has been replaced and appears to be symmetrical. The control arms that came out of the car are the same length as the new ones that went in and yet the camber is two degrees different. (The control arm pin and the rubber bushing don't run quite parallel, so it is not easy to get a good measurement, but it's definitely around 400mm. I wish I could see a car with the 381mm parts to confirm. I only see the versions ...387 and 388 in the parts book, but it doesn't mention their length).

Thanks for the numbers John. Intuitively, I also thought that 2 degrees is a lot, but I will take a look at the distance between the strut and the rim on each side, which seems like it is at least measurable with some degree of accuracy. I still can't picture the strut tube being bent without an obvious severe impact and without visual cues. The same goes for the axle, but I guess it's somewhat more likely.
Click to expand...

Struts can easily be bent by an impact with a former tire & wheel which may have already been replaced. First thing I’d do is cut the steering all the way to the left, then look at the distance between the top of the left tires inner sidewall and the strut tube. Then cut the wheels to the right and check the same clearance on the right side. That clearance should be much tighter on the side with negative camber, if it isn’t you’ve got some other problem. Again, this check is based on the 2 front rims and tires being exactly the same and having minimal run-out, a bent rim could throw everything off on this otherwise quick & easy check. ~ John Buchtenkirch

P.S. What axle, there's no axle in the front end ?
 
I meant the axle stub on the end of the strut. I guess that is the part you probably meant by a bent strut?

I checked the numbers and the measurements on both sides between the strut and the wheel and even the frame member and the wheel are fairly close. So that tells me that the axles aren't bent. The strut itself could still be mounted wrong at the upper end, but the distances to the frame members don't seem to suggest that. I can't think of an easy way to measure the upper bearing mounting points since all sheet metal structures like fenders, etc. could have there own variances that are greater than the frame geometry.

My idea about the upper spring plate being rotated was nonsense, of course, because the spring plate isn't bolted to the upper bearing. The strut is and so it can't be out of alignment.

So now I basically have distance measurements at two points on the strut that are about the same (the lower control arm and the distance to the wheel).

News flash! I just took off the dust caps at the upper strut mounts and the strut is visibly off-center in the round opening in the wheel well, on the bad side. I got the upper strut rubber mount moved another 2mm towards the center of the car using the play that is available in the three mounting studs, but it seems that the rubber mount itself is deformed by about 5mm. That is odd because I don't think it is very old. The difference at the top is about 7mm total, so I guess that could be the answer. I'll report back once I've swapped out upper strut bushings.
 
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