I have nearly destroyed a set of rear tires in about 1000 miles, due to excessive toe-in. Alignment settings are as follows:

Ride height is 193mm both sides. Slightly out of the FSM spec range of 173mm +/-10mm, but I wouldn’t guess this to be the cause of the problem.

Camber is within spec at about -0.8° both sides.

Left toe is 0.08° out.
Right toe is 1.21° in.
Factory spec is about 0.17° in, per side.

Both toe adjusters are completely maxed out toward the outside. So, it looks like the left side can be brought into spec, but the right side cannot. The car shows no evidence of any collision damage to the chassis or suspension components. Also, none of the bushings appear to be damaged or collapsed.

Has anybody else encountered this problem before? Any specific ideas about the probable cause?

 

I was once told that as the bushings wear out in our complex rear suspension, it gets more difficult to properly align it.

I'm curious to hear, if others here think the bushings might be at fault in your case.

 

I was having rear toe problems until I replaced a rear arm that you couldn't tell was bent.

 

Lets assume good things - your chassis isn't bent and all the suspension components aren't bent either.

Have a good look at the subframe mounting points - Is there a shadow where it used to be? I don't think this is the most likely problem but you never know.

One assumes that the Toe aduster on the right side was maxed out to give maximum toe out (even tho' that ended up as 1.21" in) on the right.

It seems like a lot of toe in but it could be either corrosion of the adjuster nubs on the bushing housing that has effectively reduced the range of adjustment (try putting a screwdriver blade between the steel eccentric and aluminium nub on the housing to gain some more adjustment) or the bushing has collapsed ( talk to Mark A at 928 intl about getting a good used control arm)

 

It's usually the rear camber that cannot be adjsuted because of the bushing. The camber will not usually cause the tires to wear out prematurely unlike a mis-adjusted toe. So I usually try to get the camber to be even on both sides.

The rear toe adjusters often times get buggered up and will not fully adjust or will "cam lock" preventing you from getting them fully adjusted. If the adjuster does work, and you cannot get it into spec, it's either a bent suspension arm or a tweaked frame.

 

My bet is on this too. Those rear arms get bent when a car is tied down on the flatbed, with hooks over those too-easy-to-bend flat blades on the lower control arms. It takes just a tweak to do the damage, and the best way to test is to buy another ubbent arm and bolt it in. Sometimes the bend is enough to see with a straightedge, other times the eye can easily pick out the 1/2" or more of bend from tie-down damage.

 

Thanks so much for all the responses. When I discovered the problem, the toe adjusters were not quite maxed out yet. With the suspension loaded, I lubed the toe adjusters and was able to spin each one all the way around. Each one seems to have full range. I even used a pry-bar to apply outward pressure as I was turning the eccentrics, in order to get each eccentric bolt as far outward in the slot as possible.

I also thought about the slots on the subframe that allow fore/aft adjustment. I'll look more closely to see if there is any evidence of movement. It doesn't seem like that could effect the toe settings as much as I'm seeing, but if anybody has seen otherwise, speak up!

Any idea how it got bent? Bent control arms would certainly be a good explanation, but it seem like it would take quite an impact to bend these things. The PO of my car parked it with brand new tires, and then passed away sometime thereafter, so I'm guessing this problem was known to him, but no one knew how to fix it. I can't find any body damage on this thing. Insides of the fenders are untouched. Underside of unibody has no visible creases or bends, and undercoating is completely intact. Also, all four matching wheels are without even a scratch. Then again, the wheels could have been replaced, and I would have no way of knowing.

The flat blade portion of each lower control arm is bent, but no more than a half-inch or so. Nearly every 928 I have looked at has the control arms bent this way, from pulling it onto a flatbed, or what have you. I was assuming that this type of damage would actually move the toe outward, as you are effectively shortening the control arm. Maybe I'm wrong here. Has anybody verified what typically happens to the toe when the arms are bent this way?

I'm looking at the following as a solution: I'm going to measure the distance between the toe eccentric bolt heads on this car, and then take the same measurement on another car with known good alignment. If the properly aligned car has a bolt spacing less than or equal to my car, then I'll know that the problem is not a tweaked unibody. At that point, I'll probably swap out the entire rear suspension, subframe and all, with suspension off of a car with good alignment.

 

On the other hand... I just remembered my parts car is an '80, which means I'd have to change out not just the suspension, but the transmission and torque tube also. Maybe changing out one of the lower control arms would be worth a try.