SOA & 35"+ tires - What's your Caster? (1 Viewer)

[pjohnson]

I am SOA with 37" MTRs. Springs are stock FJ40 and flat keeping the height reasonable. Everything in the front end has been rebuilt and is tight. Tires seem balanced as there are no other vibration issues at any speed.

My caster is +3* (tilted up in front is positive, correct?)

I am having intermittent death wobble issues when I hit bumps in the road at above 30 mph. I'm considering increasing my caster, but I'm not sure how much.

A related question, how much of an increase in caster degrees would come from increasing the shackle length by 1 inch?


Phil

 

[MtnTrucker]

You didn't say whether your front axle has been cut & turned as part of the SOA conversion? I have a 1974 FJ40 SOA with Alcan springs and no C&T on the front axle, so whatever stock caster is, is what I had. Running 35's I had no issue with death wobble. I norder to try and take some of the angle off of my front U joint, I put 2 degree caster shims in to tilt the pinion up a little more towards the TC. That seemed to make it even more stable than before and still no wobble. I added power steering so I also didnt see any difference in how hard it was to steer.

Have you checked your toe-in? With the wobble problem and those big tires I would make sure you had at least 1/4" of toe-in. You might have to trade off a little tire life to get rid of the wobble.

 

[pjohnson]

Yes, cut and turned. Toe in is 1/4".

Phil

 

[John Smith]

Yes, cut and turned. Toe in is 1/4".

Phil

1/4" is way too much. I am running 1/8" toe in and 5 deg caster here with 36" Iroks and rides great. Start by changing your toe in and see what happens.

 

[pygpen]

I'm at 7* on both a 55 and a 40. Toe in is set to 1/8". Both rigs run straight at highway speeds with no wobble.
PMK

 

[Isotel]

mini is like 4.5 Degrees

1/4" Measured where??

I think its different for every rig, Play with it a bit till it works good.. an easy redneck way is to Take the Tires off and Clamp a nice piece of tube or Angle iron to the Rotors.


Tires make a HUGE difference My 35" MTR's track perfect.. My Pit Bulls Have never tracked nice, and i dont think they ever will.

 

[pjohnson]

I measured for toe in at a point on the front inside edge and rear inside edge of the tire, the same distance from the ground halfway up the tire. Compare the two points and set the front distance to be 1/4 smaller than the rear distance.

I don't think toe in is a problem as it tracks straight and steers good. Tires are in excellent condition with even wear.

I am thinking of adding 1" to my front shackle to add a bit more positive caster (I am at 3* now). Any idea how much caster that might add?

Phil