Lifts / Shims / Caster

I searched the forum a bit and found a whole bunch of threads about this, but not specific enough to my setup (at least that I read)

I'm installing a 2.5" lift kit, +1/2" Shackles, and plan to sit on 33x12.50's with 15x8's. I'll be replacing the body mounts, but will use stock height.

The lift kit came with 2 degree aluminum shims for the rear axle to correct caster angle.
Is 2 degrees enough? Needed at all? Is aluminum a good choice of material for shims?


Thanks

 

The rear has pinion angle concerns, not caster. The front has caster angle and pinion angle. You’re going to want to have something around 7degrees. Use an angle finder you can buy at any big box or hardware store to see what it is. Stick it to a flat spot under your knuckle. Have correct shims made or cut off your spring perches and weld on new ones at the correct angle. It will most likely make your pinion angle point down slightly. If it’s not too much, go with it, I did. If you don’t like it, you’re going to need to cut your outer “c”s or knuckle off and re weld. Mcruff makes very nice caster shims.

 

X2 on mcgruff.

 

Mmm. Regarding pointing the front pinion down, you need the Jeep to be driveable first, then worry about the pinion angle. The pinion angle on the front axle does not matter so much because you typically only employ 4WD at low speed. I'd suggest you set the caster and not worry about the pinion angle.

An alternative to the angle finder is to have your local tire shop do an alignment after you assemble eerything. The shop can only set the toe and center the steering without a significant upcharge, but you want the printout from the machine. Then order shims from Mike to bring the caster to 5 to 7 degrees.

For the rear axle, split the driveshaft angle between the two u-joints by tilting the transfer case down and pinion up (with shims). Geometry of this is shown on the Tom Woods site - Tom Wood's Custom Drive Shafts - Tom Woods Custom Drive Shafts Custom Driveshafts Specialist - go to tech info and "Geometry 101".

 

Looks like more than I had thought about... which... happens...

Thanks for the replies, once again

 

You really want to have caster angle approaching 7 degrees. It really make your jeep a lot safer and easier to drive. My experience was that at 0~1 degree caster, it was kind of unstable. When I went to 7 degrees, m jeep became much easier and forgiving to drive. The easiest thing to do is have the shims made. Its an easy job to do especially since your going to have your springs and axles separate anyway.

 

Yes - tilting the back of the transfer case down will worsen the front driveshaft angle when the front pinion is tilted down. I would expect you are more likely to get away with that than a higher angle on the rear shaft because front driveshaft is so much longer than the rear on a CJ. The alternative might be a CV drive shaft on the rear axle - that is also shown on the Tom Woods site in that article. I can't link it directly because of the frames on the Tom Woods site, but you can see the article by going to the site linked above and navigating to tech then the article name.

 

I'll back up what James said above, exactly. In PA, front caster shims are, or at least were, NOT legal in terms of state safety inspection. I never used any and my JEEP still drives all right. Never had an alignment done so I have no idea what my numbers are. I just set the toe in and called it good and it seemed to drive okay and still steers well in all respects. I do have degree shims at the rear to help with the pinion angle. FWIW, I am also running a 2.5" lift with .5" lift shackles and 33 x 9.50 x 15s on my '71 cj5. I suppose the Dana 30 may react differently than my old Dana 27 so, your results may be different.

 

Thanks all for the replies.

My inclination is to go with shims in the rear... procomp supplied 2* aluminum worthlessnesses, and my thought is that I'll start with that numeric angle.
As for the front, I'm going to go without to build, get it aligned for $$, and see how I feel.

So... a gripe about the procomp supplied shims... they state in the supplied instructions that you need shims, and they supply a pair, but they're aluminum (okay, $avings, right) and the holes in them are wider than the centering pin. Also, if installed on the pin between the perch and the spring, there is no pin left to fill the perch's hole... which makes me uncomfortable with the install, due to worry about travel. I PM'd McRuff, as I'd rather use steel... but am going to install the aluminum jobbers for the time being.

Thoughts encouraged!

 

Wait for the steel. u bolts stretch some and shouldn’t really be reused.

 

The U bolts are new, and the likelihood is that they will see zero miles with the aluminum shims due to the amount of work remaining on the balance of the Jeep.

 

The shims I got from Mike (McRuff) had a flat surrounding the hole, and I secured them with a new center bolt through the spring pack and shim. Very solid. With the shims on hand, it seemed obvious. And the center bolt head protrudes nearly as much as it did when holding the spring pack originally. I used the Rancho spring center bolts, which are long enough to draw the spring pack together.

 

Yes, based on pics I've seen of Rubicon Express steel shims with the hole smaller than the center bolt's head, that seems like the smart way to design it. Unfortunately the garbage I got with the kit isn't built like this. The center bolts that came with the kit look like they'll have enough extra thread to accommodate the extra thickness of a shim, so at least there's that...

 

They may not be long enough to draw the pack together once it's apart. When released, the leaves likely will no longer nest perfectly.

 

It really is simple to remove the spring perches, set the proper caster and reweld. Like stated above, shims or any blocks are illegal on a steer axle in many states

 

I used some C-clamps to hold my springs together when I recently did this with mcruff's shims - hint, put the c-clamps on before you take the center bolt out. I was able to use the provided the center bolt from BDS even with the shims - it was plenty long enough with the spring pack held together by the c-clamps.[/QUOTE]

Yes, this is what I did yesterday when I was mocking it all up. The existing pin will do.

 

I trust my welding skills to spot weld some sheet metal, but welding a perch would be a brave new world that I'm not sure I'm ready to set foot into. Also, my welder is itty-bitty.

 

With manual steering I'd suggest a tiny bit less caster, maybe 5 degrees would be good. In theory anyways more caster=harder to steer and 5 is still a good number. If you get hassled on inspection about running shims I know I've seen them in the service manual somewhere (maybe it was for my 79), they're a legitimate way of adjusting caster. I got my shims from 4crawler.