[68ragtop]

Can anyone tell me why the wheel alignment specs changed for 1971-1972?

The specs for my 68 are:

0.25 degrees camber
-1.50 degrees caster
0.06 in total toe

1971 -1972 are:

0.00 Camber
-1.50 caster
0.13" total toe

Only thing I can think of is maybe 1971 was the beginning of radial tires. Not sure, just a guess. I am running the goodyear bias ply repops

I am going to see if I can increase the caster some & still keep the camber in spec.
maybe cut back some of that ditch searching negative caster always has.

Any thoughts? Probably should have made this post a week ago, I just didn't realize there was a change when all the parts invloved are pretty much the same.
pretty much in the middle of it right now

[68ragtop]

Well, finished up & spent a good part of the day getting it setup.

I was pleasantly surprised at how much positive caster I was able to get out of it. 2.4 degrees. Was not expecting that. Not bad for stock control arms.
I went with a neutral 0.00 on the camber & was a little light on the toe & bumped that to .008 total after this pict.

All set for the first shake down ride in the next couple of weeks or so.

[dataway]

Since you seem to know what you are talking about ... what numbers should I shoot for on my stock 68 with 225/70 R14 TA's ?

[68ragtop]

I know a little, but there is plenty more for me to learn. I bought a Hunter P611 alignment machine about 10 years ago from a local GM dealer the was upgrading to new equipment & got a great deal on it. Was just a timing thing or I would not own it. So I have it & know how to use it, but am a long way from being an expert.

That being said, the one thing I have figured out is I really like the feel of having more positive caster. It helps the car want to go straight down the road. It would seem when the wheels are turned, the contact point moves towards the edge of the tires & ever so slightly "lifts" the vehicle upwards which takes more effort to to make corners, but this geometry makes the wheels want to go back to the straight ahead position. In some sport cars, the caster is closer to 6 degrees positive & beyond. You turn a corner & the steering wheel returns to straight by just releasing your grip. Power steering is a must with positive caster though. Pulling into a tight spot at low speeds would be a heck of a workout with a manual gearbox. Might be why the original specs are negative caster? Easy to turn with manual steering is my guess & maybe better tire wear? IMO nothing beat the feel of positive caster going town a road, the car just wants to go straight instead of searching for the ditch

I have read that guys are setting the caster slightly less on the drivers side to compensate with road crown. Some roads are worse than others & I have no real experience in an A-body to say one way or the other. I guess I'll find out in the near future, but most of the roads around me do not have much of a crown. Just enough for water runoff, but nothing exaggerated that I can notice.

As far as Camber goes, I am a novice, I know that has to do with keeping the contact of the tire on the ground when turning. Combats tire roll and grip loss, but can tear up your tires too. In general a slightly negative camber improves cornering, but too much can cost you tires. On toe, it would seem the idea is to have it slightly positive, so that it becomes close to neutral when going town the road. Thats my belief anyway. Would really like to know why GM doubled the toe spec in 71. for now until I know better I will assume this is for radial tires. Because I am running the GR70 bias ply I went just over the 68 spec of .008" total toe. Not sure if that's best, it was just a guess so I could finish up.

There also seems to be a relationship between camber & toe. That's what actually sparked me making this post yesterday. In 1971 Pontiac got rid of the .25 positive camber (not much) & increased the toe (pointing them slightly more inward) I am really not sure why this is. Again I am assuming its from a tire change. So maybe with radials you want a little more more positive toe & a slight negative camber?

Hopefully some others with jump in here & share what they know. Would enjoy learning more on why the change in 71 & what others are running for alignment specs and why.

I can tell you that you car needs to be suspension settled when you do your alignment. Its one of the reasons I waiting so long to do mine. The camber changes dramatically with ride height. Might even want to throw weight on the drivers side of the car to simulate a driver

[Scarebird]

Originally Posted by 68ragtop

...Might be why the original specs are negative caster? Easy to turn with manual steering is my guess & maybe better tire wear?

There was an article in one of the magazine in the late 80's that covered this caster issue and manual steering was the OEM reason given for negative caster.

[68pongto]

I know on the C2 Corvettes, everybody always uses the mid-70's alignment specs because they tweaked them a little bit for radial tires. I would suspect it is the same for A-bodies.

[dataway]

When the time comes I'll basically just be giving some guy that does the alignment whatever figures you guys give me and hope for the best

[68ragtop]

I had done a little reading since starting this thread & I found some talk that Bias ply tires do not like positive caster as it wears them premature.
Radials, no problem. If I ever drive my car, I will give you some feedback.

Lots of mixed opinions out there.

[Shiny]

Where did you both end up on this?

I need to find a shop that will align my car (70 LeMans) and would like to know what to tell them.

The 2.4 degree caster sounds high but I appreciate the reason behind it. We have a car that randomly tracks on the highway and it drives me nuts.

What specs did you end up with and how is it working?

Thanks,

Mike

[north]

I think the change in 71 (less camber, more toe) was related to the new fiberglass belted tires that became standard in 70 along with the growing popularity of wider tread and lower profile ratio tires. Radials were only somewhat popular in 73 and not dominant until 75 or so.

I agree that more caster (1 to 2 degrees positive) really improves the feel of a car but it makes manual steering more difficult. Also agree that the likely reason for factory alignment specs was that they wanted one size fits all so it was a compromise between power and manual steering, belted vs ply vs radial and vehicle weight etc.

A proviso about positive caster is that two much positive creates shimmy sensations at highway speeds and any even minor looseness anywhere in the front end will be amplified. Also radials can easily handle about 2 degrees but if you are running repro non radial tires I'd stay at 1 degree maximum.