The Stovebolt Site Forums The Shop Area General Truck Talk caster angle off?

I have a front IFS from a 72 c-10 on my 53 3100. The problem is the steering wheel will not return to straight after making a turn. Is this a caster angle issue? Could someone please possibly explain caster? I put new ball joints ,tie rods, control arm bushings, idler arm but cant seem to get it all working properly. Thanks

fasteddie1017,

If you were to draw an imaginary line through the top and bottom ball joints it would represent caster. If the line tilted back at the top, it would be positive caster, if the line tilted forward at the top it would be negative caster.

A chopper with extended front wheel demonstrates massive positive caster which tries to straighten the wheel forces it to track straight...it's hard to turn it left or right.

I think this is accurate although I'm not a front end man. Why your rig won't self center, I don't know! Is something binding?

A trip to a front end shop would be a necessity in my book, in for no other reason, than to get the caster, camber and toe-in set professionally...and perfectly.

Stuart

I guess I need to find an "old school" alignment shop that can align it pretty much by the seat of their pants. I took it to one shop and they were completly mystified by the sight of a 72 front suspension on a 53 pickup. Thanks for your input

You need to find an alignment shop that uses the "Hunter" 4 wheel computer alignment system. It will have the specs for the '72 Chevy truck front end. Use those specs for your alignment.

Caster is responsible for the steering to naturally go from turned to straight (if you let go of the steering wheel).

You do want positive caster for this to happen. I run as much as I can get on my track car, hopefully about 5 degrees.

Positive caster is like a the front wheel on a grocery cart. The front wheels want to naturally go straight. (Stuart, I think your example of a long-forked chopper is actually negative caster.)

R-Bo,

I think the grocery cart phenomenon is called 'trail' and has zero caster. I think the chopper thing is actually positive caster, but as I mentioned, I have been all wet before.

Stuart

I think the grocery cart phenomenon is called "pull towards the ice cream".
At least all the grocery carts i grab anyway...................

Choppers are positive caster. They track straight.

Bicycle forks are positive caster like the Choppers. Did you narrow the crossmember when you put it on. If not you may have some steering geometry problems.

I can get you the specs for a '72, my spec book is in my toolbox at the shop. Sounds like the caster definetly needs to be laid back a bit, should run at 3.5 degrees positive, give or take .5 degree.

Caster can be used to compensate for road crown by setting the drivers side 1/2 degree less positive than the passenger's side. For instance, if the pass. side is 4 degrees +, the driver's side should set 3.5 degrees +. When the IFS system was installed, was any attention paid to setting it up to the original steering geometry? It sounds like the crossmember is tilted too far forward, causing the caster to be zero, or possibly a negative angle. If it's bolted to the frame, it might be possible to install shims at the rear of the X-member to tilt the whole assembly back a bit, then tweak the adjustment with the individual sides to make it track correctly. If it's welded, you'll need to do all the correction with the upper control arm shaft shims if possible.
Jerry

Good point about the road crown settings. In fact, that's almost exactly the settings the late model GM trucks use for that (specs on them is 3.5 L, 4.5 R).
I looked it up today, here's the specs for a '72 Chevy 1/2 ton- Camber; .25, tolerance .50, Caster; 1.5 @ 3.50" ride hight measuerment, tolerance .50, total toe; .38, tolerance .12.
The caster spec is dependant on the ride hight measurement, which is taken from the jounce cushion on the A-arm to the rame horn. The lower the hight, the deper the caster spec is. 3.5" is the middle of the spec range.