Front End Alignment Specs on a '40 LTD ?

[FLYER15015]

Hi Guys,

I want to ask the "big" car guys what they use as  alignment specs when you put the car on a modern alignment machine.

My book says on page 174,  Caster = 7/8 Rev plus or minus 3/8. Camber = 1/4 Rev to 1 Pos. Toe In 0- 1/16"

 

I don't understand Caster @ 7/8 Rev. Does this mean 7/8 of a degree, or 7/8" and if so measured where ?

 

Same is true for Camber. This has to be 1/4 degree Rev to 1 degree Pos.

 

However on page 169 it says that Camber is not adjustable on the series 90 cars unless you order "eccentric pivot pin" for the upper control arm.

It is listed as part number 231760.

 

Does anyone know of a source for these ?

 

Reason I ask is that with the summer season upon us I'm doing a bit more driving and the 2 inner bands up front are showing a bit of wear .

 

Thanks,

Mike in Colorado

[Daves1940Buick56S]

-7/8 of a degree on the caster. My 1940 Super is -3/8 deg plus or minus 3/8 deg. My camber is not adjustable, in fact the book says if it is off, get new front end parts!

 

Cheers, Dave

[FLYER15015]

Boy, I would sure like to see a sample of that GM part # 231760 eccentric upper, that lets you tune in the camber.

I'll bet my machine shop in Denver could crank them out for a very reasonable cost, and we could make them in 4140 NiCrMo steel.

I just replaced my uppers with NOS parts from Bob's. Really came in a very old box which added to the high cost, so now we can replicate these, but the eccentric version would really be nice.

Anybody have one I could buy or borrow to copy ?

 

Hey Big Dog, you out there ?

 

Mike in Colorado

[Matt Harwood]

I don't think more camber is the answer, it doesn't really do anything except change the angle of the tread to the pavement--negative camber will tilt the top of the wheel in at the top. I used to dial in a lot of negative camber when I was racing so that when going around corners, the tire contact patch would flatten out better as the sidewalls flexed, but on the street at modest speeds with these tall, skinny tires, it does nothing but accelerate tire wear on the inside edge. If you have zero camber or just a little negative, it's all good. I bet those adjustable camber bushings were designed to compensate for worn parts, not improve handling, especially not on a limousine.

 

A good baseline, in the absence of actual factory alignment specs, would be 1/16" total toe in (1/32" each side), which enhances stability and tracking, and as much positive caster as you can dial in using the stock specs (I'd guess not much), which will help the steering "self return." Too much toe in and it gets twitchy and wears out the tires, but a little toe in pulls the wheels almost straight as you drive, helping keep it tracking straight. Zero toe or toe out will make it a little darty (think of how it steers when you're backing up, that's toe out). I don't think these cars need very specialized settings, just enough to keep them rolling straight and minimize tire wear. A little toe in will make it much easier to hold a straight path and won't have much effect on tire life. You can play with toe settings to compensate for things like the crown on the road, which plays havoc with my '41 90 Series--it drifts towards the curb on roads with a heavy crown--but the suspensions are so primitive that I wouldn't really bother trying to get it that precise. Just not worth it.

 

Hope this helps!

[Daves1940Buick56S]

Also I was wrong in my comment to Mike above. My caster on the Super is +3/8 degree +/- 3/8 degree. I stated it was negative which is incorrect. Also, I think the Reverse indication in Mike's book means top of the kingpin to the rear, which would be positive caster as well.

 

Cheers, Dave

Edited June 30, 2016 by Daves1940Buick56S (see edit history)