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Discussion Starter · #1 ·
Ok so I thought I had a pretty good handle on the items above.

I have noticed some pretty severe wear on the inside and outside edges of my front tires and generally wasn't sure what the exact problem was. I think I know now.

After I did my steering box adjustment and centerlink, I needed an alignment. On the alignment rack I learned that the front passenger side had -1.0° camber. Incidentally, that's the side that has the worst wear, and it's on the inside edge of the tire. The other side showed -0.7° with correspondingly less inside treadwear. Ok, this makes sense. So to answer the question, -0.7 and especially -1.0° is too much negative camber as far as tire wear is concerned.

But what I wasn't as sure about was the outside treadwear. While I was on the alignment machine, I also learned that my caster was about 4.9° on the right and 4.7° on the left (or thereabouts). I know I was on a caster kick a while back, but now I'm not as sure. I am 99% sure I need new lower ball joints (they were part of a PST front end rebuild 100k ago but the grease boots failed) so this is probably a factor. But what else is a factor is the caster.

I turned the wheel to left and right lock and got out of the car to look at the camber of each wheel/tire. Not only does the camber curve get fubared during suspension travel but it also gets messed up at high steering angles, especially when a lot of caster is dialed in. The inside tire had so much positive camber that I could stick a finger under the tread. The outside tire wasn't nearly as bad, being nearly flat, but still appearing to have some degree of positive camber. This is obviously not good when a 2+ ton barge is trying to make the best use of its (expensive) RE-750 contact patches. I think we can all agree on that. So I believe the positive camber when cornering (plus the worn LBJs) is responsible for the worn outside part of my tires.

The next thing I did was try to figure out if there was a more ideal caster/camber setting to avoid this problem. I looked at the axis of the upper control arm and noticed that it's actually not parallel to the centerline of the car. If you were setting in the car looking outward and drew lines from where the upper control arms bolt to the frame, the axis of those lines appeared to converge at some point in front of the car. Now we know caster is added by adding shims to the rear shim packs, which moves the upper ball joint back, but also in an arc, which means the arm is also going to move in or out (which effects camber) depending on where in the arc the UCA is. The convergence of these axis lines tells me that adding more caster actually pushes the upper ball joints outward, which is where the effect of positive camber at high steering angles comes from.

What is the fix? Seems to me that if I back down the caster, as well as the negative camber (and replace the LBJs) that I should be able to fix my odd tire wear problem, and should even improve handling at higher steering angles. The reduction of camber should offset the reduction in straightline stability from the decreased caster, because more negative camber will cause wide tires to tramline more. The funny thing, at least to me, is this puts the alignment specs closer toward what GM originally wanted, as well as the "modified" specs. Guess I wasn't as smart as I thought I was and I'm still not 100% positive about this.

The moral of the story is, more isn't always better.

As usual, I ask those who know to either confirm or deny what I am claiming to be true.
 
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Discussion Starter · #2 ·
Just a guess, but....

what was/is your toe?

Gut feeling, but it might have more to do with that tire wear than you think ;)

Also keep in mind that looking at a car and how it looks when turning on the rack like that is neglecting what happens as the car turns in real life under any kinda load....namely, suspension movement (i.e. compression). And like most cars, our barges have pretty noticable dynamic camber changes as the suspension compresses (or unloads).

IF you stay conservative on toe (i.e. static toe-in, so that under load and speed it ends up at zero toe) you'd be surprised how much camber you can get away with without affecting tire life much. But let it toe out at all under load, and it'll chew up the tire insides...quick.
 
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Discussion Starter · #3 ·
Ed, I am not sure what my toe was before the centerlink. I suspected it could be off but I couldn't tell for sure. I will say that I replaced the idler arm a few months ago and didn't get an alignment because everything seemed exactly the same. The steering wheel was still centered even. But that doesn't mean toe didn't change.
I'll say I know my tires didn't wear this much in a few months, maybe got worse, but they were still wearing in this way before the idler arm.

I was thinking about all the stuff I said above about caster and I think it might be wrong. If you adjust caster by pulling the UCA back, which makes it follow that arc, giving more positive camber, that would effect both straight ahead camber and lock camber. All one would have to do is change the shims in pairs on each side and that could be accounted for. So I am back to not understanding.

Does caster effect camber differently at lock than it does straight ahead or am I chasing nothing here?

I had the guy dial in something a little less than 0.2° total toe, which should amount to nothing under deflection.
 
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Discussion Starter · #4 ·
After thinking about it some more, I don't think caster is necessarily to blame for my tire wear issues. I think it might be more a worn lower ball joint thing (for the outside part of the tread). I am still going to back off on the negative camber, maybe down to a 1/4 degree.
 
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Discussion Starter · #6 ·
Well i remember someone saying that our factory alignment is concidered to be off anyhow...so what is supposed to be the REAL numbers?
 
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Discussion Starter · #7 ·
That sounds like a problem I had. Check the lower ball joints. I was getting odd tire wear and it was the lower ball joint. Or, check and make sure that the nut on the lower ball joint isnt creeping up its shaft.
 
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Discussion Starter · #8 ·
Kevin, to alter caster without significantly affecting camber, add a shim to one UCA mounting point
& remove an equal amount from the other point.
 
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Discussion Starter · #9 ·
One thing , well a couple to throw into the works.

Steering axis inclination ( angle difference between ball joint center line and spindle) adds positive camber as the wheel turns in OR out.
Caster adds positive on the inside wheel and negative on the outer.
This is why high caster cars look "broken" with the wheels hard over. The outside wheels balance the KPA off the negative camber gain some. The result is not a huge neg gain, but the inside adds them resulting in a greater change.
In it self not so bad as they both counter act body roll.

One place that large increases above normal caster limits can cause unseen issues is the unchecked toe change ( bump steer).
As the caster goes higher you are also raising the outer tie rod ends.
This can result in toe change as the susp rises and falls.
When you get your alignment checked ask them to recheck the toe with the nose raised a bit and pulled down a bit.
Gerry
 
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Discussion Starter · #10 ·
Kevin:

I run -.50 negative camber and 5.0 degrees of caster with zero toe-in. Using stock wheels and tire size, I ususally get 20,000 to 22,000 miles on a set of street tires. Ed's correct about the toe out. Helps a bit on the track but just kills the tires if you drive any distance.

Allen
 
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Discussion Starter · #11 ·
I need to figure out how many miles I have on these RE-750s. The middle of the tread still looks like 40% to me. I believe I got them in August of 2003. I bet I have like 30k on them. I'm hoping the funny outer wear is from the worn lower ball joints allowing the wheel to have positive camber during high cornering loads. I'm definitely going to back the camber down to -0.5° or more positive, but I guess I'll leave the caster until further notice. I'll also leave the toe since I believe that helps braking stability (something these cars need every bit of help in).
 
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Discussion Starter · #12 ·
Kevin,

I may not be understanding your predicament here, but I will add something anyway.

When shimming is necessary to correct the front end alignment, I have seen the alignment machine computer tell the tech to not only remove a shim (or two) from the rear position but also add a shim (or two) to the forward position to kep the upper BJ from being moved in or out (thus adjusting Castor and leaving Camber as is). Likewise...removing shims from the forward position and adding to the rear position. Adding/subtracting shims equally (forward and rearward) will adjust Camber only.

Pages 3A-3 and 3A-4 of my '94 FSM do a pretty good job of describing what the shimming does, and how to shim to correct for different misalignments. But, you are probably more into the alignment stuff than what may be cocvered in the FSM.

FWIW,

Gary Meier
 
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Discussion Starter · #13 ·
All the tech did was bring the -1.0° of camber down (up?) to -0.7°. And he adjusted toe to about 0.15-0.2° total. All for $73. Ouch.

The predicament is worn outer and inner edges. At first I thought it was from too much caster (the outer edges) but now I think it's just worn LBJs allowing the tire to tip under heavy loads and scrub the outside needlessly, despite a lot of static (unloaded) negative camber (which, combined with possible toe-out, caused the inside wear).

In other words, the next step is some nice PPM lower ball joints and a slightly more conservative alignment (-0.5° camber maybe, same caster, same toe).
 
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Discussion Starter · #14 ·
Can I tell if its my alignment thats causing the odd steering feel?

I've replaced all the front end steering and new ball joints and bushings (ppm extreme kit) and had to buy new tires. The tire shop did an alignment on it but the guy said that the upper control arm shims were spot on and needed no adjustment. I really didn't believe him because I only stuck a equal amount of shims in each of the four studs just to drive it straight to the tire shop.
The car has a very anoying steering feel. The steering response is almost too quick but yet feels like there is slop in it at the same time. It doesn't pull, but yet I'm constantly herding it down the road. I'm very ticked off at it because a lot of time, money and pain was put into having a car that wouldn't drive like it was worn out.
I've since gotten a set of 95 SS springs (it has the (B4U towing springs in it now) and if I'm able to change them out this week, I'm going to try and find another shop that knows what there doing on the alignment. Just wanted to know if any of you had some ideas of what might be wrong?

The set of tires came with free life time alignments (2 per year) and I thought this would be great since I might be switching from SS alloys to steel rims between summer and winter, but if this shop doesn't know how to align a conventional front end then the free alignments are a waste.

Thanks for any advice,
 
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Discussion Starter · #15 ·
Kevin,if all the tech dod was back the camber to-0.7 and set the toe you need to find a different alignment tech.In 2000 the GM TSB was issued for a revamp of the B and D body camber specs due to excessive inner tire edge wear.
The UPDATED specs show the camber at -0.5 as the MOST negative allowed.Here is a proven set of specs that I have used for appx 5+years
CAMBER -0.2 LF and RF
Caster 3.4LF 3.9RF--higher if possible,keep spread at 0.5 with the RF being the higher of the 2 to counteract road crown.
TOE-IN 0.03per side with steering wheel centered.
MAKE SURE the shop/tech does a THRUST ANGLE alignment so the angles of the non adjustable REAR END are taken into account.
I have done this work-Alignments,brakes,professionally since 84 and am a recertified GM and ASE undercar specialist and a line tech at a Chevrolet/Cadillac dealer in Louisville KY.I use these specs on my own car as well and have had good results.
 
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Discussion Starter · #16 ·
Kevin,if all the tech did was back the camber to-0.7 and set the toe you need to find a different alignment tech.
From what I can tell he only adjusted the tie rods and nothing else. He didn't even get the steering wheel centered good.

I stressed the point several times that the car was a frame off and every part on the front end has been replaced or moved.

This shop lets me stay out there with the car and talk to them while they work and I can look around under the car and see if anything needs attention. Thats the main reason I use this place.

The first thing he did after getting the (don't know what there called) put on all four wheels and entering the model year info I gave him, was to start on the tie rods. I watched him for a while and knowing that it was going to be a long while, I walked back into the waiting room to talk to one of the other employees. I could still watch the guy doing the alignment through the glass door and I notice him lowering the car down and drivers it off the lift around to the front door. When he comes in I question him about not making any adjustments to the upper control arm inner shafts and he tells me they were already in the correct position.

I didn't believe him but not one to argue and knowing that if I drive it and its not right they will do it over and any tire damage I'll make them replace. Well, like I said before the steering is weird.

I asked a friend of mine to drive it and tell me what he thought and after he did, he told me that it drove exactly like his car (not a GM) did when it unknowningly put the upper ball joints in swapped left and right. He didn't know there was a left and right and thought they were the same like our cars. He said that with the ball joints wrong in his car, it put the top part of the spindle a little forward. (sorry, I don't know about caster and camber terms so I'm not describing this very well)
He said that my car drove the exact same way.
I doubled checked to make sure that our cars don't have a left and right part and looks like there the same part.

I've thought about taking a small shim out of the front position on both upper inner shafts and adding it to the rear position making the top of the spindle move back slightly and test drive and see if this improves or makes worse.

I'm just going to try and swap out to the SS springs this week and then take it to one of there other locations and complain about the alingment.

When a GRAIL buddy took his wagon to be aligned after the front end rebuild the guy spent I think he said over 4 hours working on the front end.
I think this guy spent 20 minutes on mine. :mad:

Wish Louisville was a little closer and I'd see if you could do the alignment. I think its about 5 hours drive from me, not sure, never been there. I'm in Illinois, but only about 10 minutes from Paducah, KY.
Thanks for the alingment specs, I've printed them out and I'll take them with me next time.
 
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Discussion Starter · #17 ·
You need to find a good alignment shop. No-one can reset a poorly aligned suspension in 20 mins. 2-3 hours is more realistic, depending on the adjustments needed. 20 mins is enough to do a toe-in.
 
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Discussion Starter · #18 ·
Definately right there!!
Anyone that can set caster/camber and toe-in in 20 min is a GOD!!! :eek:
I'm not that quick and have been doing it since 1984!!
It took me appx 65-70 min to do my car and I had just put in a centerlink and idler arm.
The shims are a little tough to get to if you still have the fendrwell splash shields in place.
 
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Discussion Starter · #19 ·
Went back to the alignment shop Friday afternoon. I had already decided to remove the splash sheilds before it went in for an alignment anyway, ever since I watched a guy reach in and just rip the shields out of his way on my parents 79 boxy I drove back in high school.

The guy that did the first alignment was out sick and one of there best guys worked on it for 3 hours. It feels a whole lot better, but its still not right. I could tell that the guy was up set because it took him several tries just to get a first reading from the machine. I decide not to ask about the updated specs and just let them get it were I wouldn't have tire wear. Next spring I'll try to take it to an actual proformance type shop were there use to guys swaping out springs and such and not argue with me because it isn't stock. It actually is stock for 95 SS, just not stock for its Vin code. The guys at this shop know the whole story about the frame off rebuild and I've mentioned several times that the steering and suspension setup of this vehicle is the same as 95 SS, but when he begins to set up the machine, what does he do but opens the drivers door and starts to read the sticker. I had to remind him again that the only thing the Vin matches is the sheet metal and the glass.
 
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Discussion Starter · #20 ·
Originally posted by R96IMP:
Kevin,if all the tech dod was back the camber to-0.7 and set the toe you need to find a different alignment tech.
I absolutely agree. I took a chance because this was a Town Fair Tire (I've had good luck at two different locations, but never used this one) and because it was extremely close to where I replaced my centerlink. The guy was "good" but unwilling to align to what I wanted, nor spend the time to get the shims just right. Typical, but disappointing nonetheless.

Originally posted by R96IMP:
The UPDATED specs show the camber at -0.5 as the MOST negative allowed.
Yeah I'd like to make sure mine is there, or even lower, like -0.4°. I replaced my ball joints recently and I wonder where caster, camber and toe are. Steering wheel is perfectly centered still.

Originally posted by R96IMP:
Here is a proven set of specs that I have used for appx 5+years
CAMBER -0.2 LF and RF
I think I'd like a little more, but close enough.

Originally posted by R96IMP:
Caster 3.4LF 3.9RF--higher if possible,keep spread at 0.5 with the RF being the higher of the 2 to counteract road crown.
Mine is up well into the 4° range, where it was set on my last performance alignment. I'm not sure I believe in a spread (caster OR camber) for road crown, as the passing lane has no crown, or even a crown to the left. I believe factory stock is 3.5° nominal, so I think 3.4 isn't enough. I'll probably try to keep mine in the 4.2° to 4.8° range when I find a shop that'll work with me again.

Originally posted by R96IMP:
TOE-IN 0.03per side with steering wheel centered.
That doesn't seem like enough to compensate for bushing or part slop, especially under heavy braking. Any thoughts on whether 0.10° to 0.20° total toe (or 0.05° to 0.10° per side) would be better for tracking or braking stability? I don't think 1/5th of a degree would be too aggressive for tire wear. I think I read in a suspension book years ago that about 1/8" toe-in at the tread is about right. I'd have to calculate what that works out do in degrees for our tire diameters. I bet a dollar it's a lot more than 0.20°.
 
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