"Shimming" the front axle

[JohnL]

Completed rebuilding and locking the rear axle, now am doing the same up front, as well as center arm & tie rod end replacements. I have OME stiff rate springs, Toy powersteering and 32's. HFS 2.5" longer than stock shackles going on now too.

Steering was always a bit "skittish" which I attributed to the short wheelbase compared to my 60. When i got the axle off, I didn't notice any "shims," which I have heard referred to when discussing lifts and correct steering geometry. My questions are;
1. Am I /how would I know if I am a candidate for shims
2. Can I get a pic of some installed

Thanks!

john

 

[Deep South Cruisers]

My fj40 has a 4" TPI lift and 6 degree shims came with the kit, shims install fat end forward and mine were backwards on the first go around...which made for some scaaaaaaaaaaaaaary steering geometry.

 

[JasonH]

Do a search on SOR's catalog for caster shims. They have a good rule of thumb for when you need shims and how much you need.
With your longer shackles, you will probably need shims. I would recommend it. To really know how much you need, go to an alignment shop and have them measure your front caster. Factory spec is +1 deg. Figure what shims you need to get there - or maybe to +2 or 3. More positive is more stable, up to a point where it gets hard to steer.

 

[theo]

The front axle should be rotated back relative to the road to provide some caster. That means with the whole shebang assembled, the front differential output shaft is pointing downwards slightly.

You can use a $10 angle finder to measure with. The caster should be at least 1 degree. Many go a little more (2-3 degrees), especially with bigger tires.

Use shims between the spring packs and perches to bring it into spec.


Holy smokes! In the time it took me to reply you guys already had him covered!

 

[JohnL]

Thanks for the responses...
Its all apart now, so I can't bring it over to the shop. Sounds like I'll need to disassemble the ubolts and the axle from the spring pack at least, so I should go ahead and order the u-bolts and some shims now?

Will check our SOR

thanks!

 

[theo]

The shims only require an extra 1/4" of u-bolt or so, so whatever u-bolts you plan to use should be fine.

You should reassemble the whole thing and measure the caster, then decide how thick you want your shims to be. It's easy then to just support the truck, loosen the u-bolts one side at a time, and put the shims in.

You may end up wanting taller heads on your spring pins, though. I pulled mine out and cobbled them longer with the welder, then turned them on the lathe. That way the shims can't shift around. That's assuming you are SUA with stock perches, etc.

 

[JohnL]

Yes, I'm SUA.

I remember hearing it was a good idea to replace u-bolts when rebuilding the axle, which is what I'm doing. In any event, they are VERY rusty and corroded...not sure I won't have to cut them off. I was asking about replacement for reliability and practical reasons rather than reach though that is important also!

john