GT6 Mk1 GT6 Alignment

[dklawson]

A bit of history on our GT6. It was raced by my father-in-law during the early 1970s. He lowered the car and I'm sure the camber, castor, and toe were changed. Years ago I put new bushings in the suspension when I restored the car. BUT, I only drove the car locally and since I didn't notice any driveability problems I never set the alignment.

The car has a brand new set of tires and my wife wants to drive it more frequently and on the highway. After her first trip she reported the car was smooth as glass up until 60 MPH and developed a shake in the steering wheel above that. I seem to remember similar behavior on the old tires the few times I had the car up to highway speed.

I've searched here and I've read my factory manual on the settings. However, since the car has been lowered I doubt I'll ever see the factory specs again. Therefore, I have the following questions.

The factory spec for an empty car is 1/16" to 1/8" of toe-in. The camber was something close to 2 degrees positive (out at the top). The castor was also specified but I can't figure out how I'd measure it. Are there any easy ways to measure castor?

I'm OK with checking and setting the toe. However, is the camber REALLY supposed to be POSITIVE? That's counter-intuitive to me I'm also very confident (without measuring yet) that the car currently has negative camber. However, if the car is supposed to have positive camber and if I remove enough shims to move it back into positive territory, what should I aim for? With the short front springs I doubt it will ever go to 2 degrees positive. If I ended up at something close to zero degrees would that be “good” or “bad”?

Should I just focus on the toe and leave the camber alone? The steering effort is a bit heavy but not too bad. It DOES make ugly tire squealing sounds when making low speed turns at near full steering lock.

Again, how exactly are you supposed to check castor? How critical to driveability and tire wear is castor? I understand that this is adjusted by removing and installing shims to "pivot" the lower A-arm forward or backward but I can't imagine how you measure this. Should I leave a sleeping dog alone?

Lastly, so I don't go around in circles, is there a logical order to make these adjustments so they don't "fight" each other?

Thanks in advance for the advice.

 

[DrEntropy]

Castor angle is something you MAY be able to determine with a plumb-bob and protractor viewing the upright compared to the string. It really only affects the way the steering behaves to put the thing back to straight ahead when rolling. It "should" be a bit forward at the lower part of the pin for street driving. This, of course, with the suspension "loaded".

Positive camber would seem to me to be a bit goofy for a highway car, AND it can cause "hop" at speed with toe-in over 1/16" (IMO). A short contractor's level (the bubble kind) with a pair of screws of equal length tapped into it at wheel rim bead diameter can get you a guesstimate as to positive/negative/neutral of the set-up. "Degreeing" it can be done with a protractor and some patience.

I almost hate to suggest this, but: can you gain access to a laser alignment rig to see where it is at the moment? At least then you have a "base" to judge from.

And I'll assume you have ruled out a balance issue already.

 

[tomshobby]

Not sure what might be wrong with your car but I had one when it was new. It seemed to drive better over 100mph than it did at 55mph and it was great at 55.

Might be worth the money to take it to a good alignment shop.

 

[vagt6]

Doug, the rear wheels on a GT6 are supposed to have a degree or two of negative camber.

Go to the Yahoo Groups NASS board or the "GT6 Enthusiast" board and ask, very experienced folks there.

Also the Kas Kastner board is a big help. Mostly racer stuff, but they are very knowledgeable.

 

[dklawson]

Thanks to everyone for your suggestions.

Mark, I already searched the NASS Yahoo group archives and over the past 2-3 years the only topics that come up about alignment don't focus on my issue. I had already posted the same questions there and the first response I received suggested that I focus on what the toe is if the car is otherwise driveable and the steering isn't too heavy. BTW, I'm concerned about the camber on the front wheels, not the rear.

Tom, I think the big issue is that the car was converted away from "stock" years ago and short of restoring all its suspension components back to stock I have to find a way to make it drive better with what I've got.

Dr., the tires/rims were just worked on. These are wire wheels with new Khumos installed by Hendrix Wire Wheel. Their practice is to true the wheels when possible, then shave the tires true, followed by balancing. Then they identify the best wheels and tag them for installation on the front. I have confidence in their work and as I mentioned, I think the 60+ MPH shake was there before the new tires.

I have no access to high-tech tools for alignment. I could always break down and take it to a shop. Even if I took the car to get the toe set, I'd want to have the camber sorted out in advance. There's no chance local shops would have the shims necessary for a 42 year old Triumph.

I also thought the positive camber sounded strange... but there it was in my manual. I'm 100% certain the setup at the moment has negative camber and frankly I like the idea as long as it's not causing the shake. I know that this is likely to accelerate the tire wear on the inner edge of the tread. However, I anticipate the tires "aging out" long before wearing out at the rate we drive the car.