The Stovebolt Site Forums The Parking Lot Big Bolts 49 GMC COE wheel alignment specs?

Tough keeping the truck in my lane. (Truck shop rebuilt steering box and new kingpins and bushings.) I did a rough alignment with straitedges and reset (was out an inch) the toe in to straight ahead and no difference in the steering. New ball joints coming fron a vendor but the old ones seem fine. So what am I doing wrong? Is there a factory to in spec for this truck?
Thankyou, John Drabik

The specs are in the shop manual and it is online at "Old Chevy mnanuals". You probably can't get a good idea with a straight edge. You need to put a mark on both tires and measure between them in front and behind the wheel. What I do is spin the tire and draw a chalk line while it is spinning. It is more accurate to use one mark. I assume that the suspension hasn't been lowered and the caster shims are installed under the springs?

If there were caster shims they were removed afore I bought the truck. Did my truck have them from the factory?
In the meantime, I`m studying the Old Chevy manual online for anything else I can find.
Feel free to offer up anything else that may help.
Thanks, John Drabik

Hi John, They all didnt have them from the factory. they only added them if they needed to.
Sagging or dislocated springs, or a bent axle will also effect caster. Negative caster will cause wandering or not comming out of a turn normally.
Did you check the toe in and toe out? The easiest way is to center the wheels so they are pointing straight.
Drive the truck back & forth in a straight line a couple of times
This will allow the wheels to center themselves

Then with a tape measure,measure the distance from the left tire to the right tire.
Measure from the center of the tread to the center of the tread at the very front of the tire facing the front of the truck. Then on the same wheels measure the tread facing the back of the truck, center to center
Both measurements should be the same.

JeffL,

You ended your message above by saying "both measurements should be the same". I believe this is incorrect, there needs to be some Toe-In so as the truck rolls forward the truck will track straight.

My 1957 Shop Manual calls for 1/4" Toe-In, which means the front measurement will be shorter than the rear measurement.

Mike B

I`m making arrangements for new springs as mine are visually sagging, and the new tire rod ends should be here by mid month. So in the meantime I will have to sit tight and hope the new stuff eliminates or sheds fresh light on the problem.

The good news is this is the last big issue to be adressed to make the truck comfortably driveable as its truck show season soon.
Thanks, John Drabik

Mike you are correct, I should have mentioned there may or may not need a slight toe in, not all trucks require this. The straight on measurement will at least get you in the ball park.
I usually start there and make further adjustments as needed.
Thanks for pointing that out.

After a perusal of the old chevy manual in the 1950 front suspension section shows the mounting shackle at the spring front mount. My truck has the shackle at the rear. This would certainly affect the geometry.

So what is correct for my 49 GMC 2 ton FF 353 coe truck?

I know I`m not the first owner to have the front end apart and maybe the previous owner had accidently it mounted backwards?

Found the answer in the Old Chevy manual. COE and Cab Forward models had shackles mounted to the rear mounts and vice versa for the others.
So I`m back toother aspects of my steering issues.

I am pretty sure that all the trucks came with caster shims. Caster values are specified for each type of truck.

I'd suggest a toe-in adjustment of 3/16" or so, measured after the truck has been rolled forward a few feet on a flat, hard surface. Do you have any way to check caster and camber? Unless there is significant wear to king pins and/or bushings, the camber should be close to correct if the axle isn't bent. Camber problems usually create a pull to one side or another, not a problem with wandering back and forth.

You're most likely encountering a situation where there's too little caster, the angle the kingpin makes with vertical looking at it from the side. An example of caster is the front fork angle of a bicycle- - - -tilted slightly forward at the bottom. This makes the steering try to return to center after making a turn. If the kingpin is too close to vertical, the wheels will wander around aimlessly, rather than trying to return to a straight-ahead condition after a turn or a minor steering correction. A tapered shim can be inserted between the axle and the spring on both sides to increase the tilt of the kingpin and assist the return to center after a turn. Too much caster makes for hard steering, so it's definitely possible to have too much of a good thing!
Jerry