Wheels-Tires Extreme Tire Wear/Rear Misalignment

[Haas99]

I bought a 2001 Mustang GT about 6 months ago and soon after replaced the rear tires. I put about 7,000 miles on them and had to replace them again because they were worn so badly, the insides more than the outsides. I had an alignment done at the same time and this is the specs I got. My understanding is the likely cause for the tire wear is the extreme toe on the rear wheels. Since this isn’t adjustable, what might have caused it and how do I fix it?

 

[tsemmett]

Because they're not adjustable, the total toe on a solid rear should be at or really close to 0º; if one side is .5º in one direction, the other side should be .5º in the other. The only thing I can think of that would change this is damage to the rear end (something is bent), which seems to be the consensus I can find on toe issues with an SRA in general. Has this car ever been hit/wrecked?

 

[Haas99]

I just bought it six months ago but I don’t know if it was wrecked previously. I can’t find any indication that it was in a bad wreck by looking at it but I think the carfax report might have said it had been. Is there anything I can do to fix it?

 

[tsemmett]

Well, the most likely cause of this seems to be a bent axle tube; if the axle itself were bent, the wheel would wobble, which shouldn't yield consistent results on alignment like you have, and would cause some serious vibration. The axle tubes are welded to the center housing (some really big spot welds). Repair would require having the housing straightened, or replacing it. Definitely verify that is the issue though, I'm no expert, just an enthusiast whose done a fair bit of research (my rear end need other repairs/updates).

 

[Haas99]

So the negative toe means the front of the tires are farther apart than the rear of the tires which would indicate axle tubes have been bent toward the rear right?

 

[tsemmett]

Yeah, they're toe out, so basically pointed out from the car up front, so the rear would be closer together than the front.

 

[Deathtrap02]

check the upper and lower torque boxes for stress or cracks. split metal or anything. where the rear suspension attaches to the body forward of the axle. might need reinforcements installed. very common on the unibody mustangs

 

[Haas99]

I plan on checking it out in depth this Saturday. I’ll let y’all know what I find.

 

[kiddiccarus]

Can I Chime In. I manage an auto shop and can say that the above advice is sound.

Well, the most likely cause of this seems to be a bent axle tube; if the axle itself were bent, the wheel would wobble, which shouldn't yield consistent results on alignment like you have, and would cause some serious vibration.(my rear end need other repairs/updates).

With the SRA itself please let me know if there is any sound coming from that corner of the car. If you are hearing a roaring of any kind, the bearing in that side may be an issue which can play into the overall result. If this is an issue, look into the "Axle Saver Bearing" which I recommend for every SRA. Saying this, I quoted tsemmett because a bad bearing would most likely have the vibration mentioned. ALSO, get that wheel off the ground so it is free spinning, put one hand on the coil spring and spin the wheel with the other hand. If you feel grinding in the spring, that bearing will need to be replaced. Regardless if this is solves the tire wear, its a good thing to check since you have a concern that an accident may have occurred.

check the upper and lower torque boxes for stress or cracks. split metal or anything. where the rear suspension attaches to the body forward of the axle. might need reinforcements installed. very common on the unibody mustangs

Here is also a very good thing to look at. I am in the process of researching Torque Box solutions to bullet proof my build. So it would benefit you to get the car up on the lift and remove the rear wheel to check this part out with a flashlight.

 

[tsemmett]

Torque box and bearings are certainly worth a look. A degree and a half is a pretty decent amount though. Hopefully for your sake it's something simpler like this.

Correct me if I'm wrong, but wouldn't a torque box issue affect the entire rear axle (for instance if the left side is being pulled forward the right side should angle back)? Seems like it wouldn't create a toe issue like this one, though again I agree it's worth looking at; not hard to bend/break things in that area.

 

[Haas99]

Thanks for all the suggestions! I got the car on the lift and did some measuring and used a laser to check the straightness of the rear axle tubes. Turns out one side was bent back over 1/4” and the other side was bent back about 1/8”. This resulted in a total toe out of over 1/2”. After a few hours of careful pushing and pulling with chains and hydraulic rams I got the rear axle straight and got the toe to zero. I am sure this was the cause for the tire wear and I can feel a huge difference in the back end when driving. It’s no longer fishtails when the roads are slightly wet. Thanks for the help and I am glad the problem was easily resolved.

 

[01Stang65]

I'm just getting done going through this as well on my car. Most bizzar thing ever...

Bought my car with 47k mi on it from private seller. Had new tires on it. Put 7k miles on it and the rears were showing wire on the inside. Same thing with the new set. I'm 20k miles in and on my 3rd set.

I got my rear end out from under my car and found that one axle slid out really easy, while the other axle had to be hammered out, which proved to me that the housing was bent, since the axles were fine.

I found a rear axle near me with relatively new 373s for $50. I stripped it (to have it repainted and bearings gone through) and noticed that one was bent as well. So I took those 373s, bought another rear axle from a local mechanic, and out the 373s in that rear end, with all new bearings.

Needless to say, I'm ready to be over this mess. My mechanic should be getting my rear axle to me soon and I should be able to drop and replace my current rear end over a weekend. Other odds and ends are connecting the dots for me: the previous owner abused the heck out of my car in it's 47k mile lifespan.

Also, I don't know how your going to check the straightness of the rear end. I think it's nearly impossible as there is so many places a bend could be. It's literally the only thing that could cause the uneven tire wear on these cars. I would just recommend finding a used 8.8 rear on Facebook or Craigslist, they are all over cheap. For the most part if 8ts coming out of a decently low mileaged car, you wouldn't have to worry about stripping it unless your anal like me. Good luck!