Setting caster angle

say you've got zero caster (you're hands are straight up and down) then someone comes over and lifts one side of your desk for some unknown reason (while you're keeping your hands square to the desk). your hands are no longer straight up and down in relation to the ground... so your caster has changed.

where the square interface was the axle tube and perch
the guy lifting you desk was the shim
and the floor was the spring

as long as you didn't change shackles at the same time the ground is still on the same plane as it was to begin with (completely horizontal) so the tilt of the tire changed a little bit.

 

Sorry, but nope the ball socket on your axle is still what sets your caster. I have had them apart and the ball socket (knuckle) is welded on your axle at the same angle as your outer knuckle sits. Your outer knuckle pivots on the bearings on the ball that is welded on your axle tube, this is still the way your caster is set from the factory, you could machine the caps and hole in your knuckles to any angle you want it won't affect the caster cause if the the caps aren't machined on center and true with each other your simply not gonna reassemble it.
The same principles apply to the dana 27 as the dana 30.

 

Well, looks like I caused a bunch of confusion. My Jeep has a shackle reversal on it with pretty tall shackles so it's got a TON of negative caster. Wayyyyyy too much. It steers nice and straight, but it eats the sides of the tires off when I turn. I suppose I could just start shimming it back and do it by trial and error.

Oh, maybe to clear up some confusion - The shims being talked about here are actually little wedge shaped blocks that bolt in between the leaf spring and the axle perch. The wedge shape is what rotates the entire axle assembly thus setting the caster.

 

sounds to me like either low tire pressure, someone is cornering too fast ( my normal problem) or camber.

 

None of the above...Well cornering too fast sometimes maybe, but my tire press is good and the camber is not adjustable.

I KNOW my caster is off since my front pinion points at the ground, not at the T-case. You want to see some funky angles...

THE CASTER IS ADJUSTABLE ON ANY STRAIGHT SOLID FRONT AXLE (Dana 25, 27, 30, 44, 60 etc etc etc)
This is accomplished by putting a wedge shaped block between the spring perch on the axle and the spring itself.

Now, Does anybody know how to actually measure the angle??? Do I just measure the angle through the kingpin centers relative to verticle?

 

They make a tool for angles at most tool shops. It is an angle meter. I have one I use for installing angle on spring perched for spring overs and such.Maybe use it and a strait edge

 

Have the front end aligned and they will tell you your caster and camber settings. Get STEEL shims to install based on their readings and you should be alright. This same thread is on the intermediate forum, because I have the same problems on my '78. Look at page 3. Good info there, too.

 

Makes no difference Billy, for practical purpose they are the same axle.

 

The caster angle is built into the front axle when it is assembled....

It can be changed by cutting the welds, realigning the outer knuckle, or ball on D25/27, and rewelding... this is really the right way as driveshaft angle to the tcase is inaffected, assuming it is right....

You can also install the shims, this generally makes the caster better but the driveshaft angle worse....

Longer shackles with front shackles will reduce caster but reduce driveshaft angle, ie point it more straight at the tcase.

Longer rear shackles would increase caster, and point the driveshaft down away from tcase...

Seems I have read somewhere about offset bushings available for ball joint style front ends that allow for some caster adjustment... I guess a guy could machine new offset kingping bearing races, they might have to have a bigger outside diameter, and machine the holes in the ball to fit them, seems like a lot of work, just cut the ball loose and reweld. I say just like it would be easy....not

I have also heard of tapered shims that go behind the spindle to adjust camber, seems like it would put the axle shaft ujoint in a bind....