Off Roading Forums banner
1 - 12 of 12 Posts

·
Registered
Joined
·
792 Posts
Discussion Starter · #1 ·
I have a 79 CJ 5 with a rancho 2.5" lift and 1 3/8 shackle lift. After I put on the shackle lift I have noticed some fairly extreme drive line vibrations. I posted a question this question a few weeks ago and I was told I need to re position the spring perches so the ring and pinion will line up they way they did when stock. Does this Sound right? I was also told to do the math to find out how much to move them, but I can't find anything that says how to do this, could anyone figure this for me? Those are the only modifacations to the suspension, rancho lift and shackles, nothing to the driveline or transfer case.
If someone could figure out how many degrees they need to be rotated on the axles? Or how much length around the axle tube they need to move? Also if someone could explain the "Math" to me, I wont have to ask next time.

thanks very much, you guys are helping keep this project moving.
Tony

79 CJ 5, 258, dana 30, model 20, T18 tranny, dana 20 transfer case, 2.5" rancho suspesion lift
 

·
Registered
Joined
·
1,271 Posts
Tony,

It sounds like somebody either gave you a bum steer or you've mis-remembered something.

1) YOU DO NOT HAVE TO MOVE THE PERCHES!!! If you were doing an SOA, or had to put new ones on anyways, you could do this, but just lifting a couple inches is not necessary. They make wedges that go between your spring and the perch which set the pinion angle. I've seen everything from a .5 degree shim to a 5 degree shim, typically in .5 degree increments.

2) Shims are cheap, get 2 or 3 sets when you go so you can try them out for the best fit/ride.

3) The other option: the easy way out is to lower your crossmember using spacer pucks. Typically 2.5 lifts don't really require this, but it is something you could try, it's a HECK of a lot easier than re-shimming, if you don't mind losing the clearance.

4) "Doing the math": it's pretty simple really, the reason you are getting vibrations is because your driveshaft is at a bad angle. If the angle is too extreme you may want to consider going with a CV shaft which alters the equation some.

4a) If you are using a straight drive shaft, the pinion angle should be set such that the input yoke on the axle points directly at the output of the transfer case. If the angle between them is too steep and the shaft is binding, then you have to go with a CV shaft.

4b) if you are running a CV shaft the input yoke on the axle should be pointed 2 degrees BELOW the output of the transfer case.

Make sense better?

'83 CJ-7 nothing original but the tub and axle tubes
 

·
Registered
Joined
·
792 Posts
Discussion Starter · #3 ·
About what degree shim do you think I need, just so I am in the ballpark. I will probably buy a few sets and try which works best.

If I was to lower the cross member, how much should I lower it? and what should I use. Could I do a combo of both cross member lowering and shims?

Thanks
tony

79 CJ 5, 258, dana 30, model 20, T18 tranny, dana 20 transfer case, 2.5" rancho suspesion lift
 

·
Registered
Joined
·
1,271 Posts
I would start out with something around a 2-2.5 degree shim (just guessing without seeing the angle).

If you lower the crossmember, you would go anywhere from a half inch to two inches depending on the angle.

You COULD do both, but typically the issue is resolved by doing one or the other, rather than trying to juggle two variables. Besides, I'm willing to bet your angle is not bad enough that you'll NEED to do both.

'83 CJ-7 nothing original but the tub and axle tubes
 

·
Registered
Joined
·
1,286 Posts
-snip-4) "Doing the math": it's pretty simple really, the reason you are getting vibrations is because your driveshaft is at a bad angle. If the angle is too extreme you may want to consider going with a CV shaft which alters the equation some.-snip-

I have to disagree,
On a standard driveshaft, It's not that the driveshaft is at a bad angle(up to about 15 degrees), It's because the two Ujoint angles are not the same as each other. The downward angle of the t-case output needs to be the same as the upward angle diff pinion . If your using soft springs, set the diff pinion angle 1 or 2 degrees lower then the t-case output angle to compensate for spring wrap(axle wrap).

-snip-4a) If you are using a straight drive shaft, the pinion angle should be set such that the input yoke on the axle points directly at the output of the transfer case. If the angle between them is too steep and the shaft is binding, then you have to go with a CV shaft.-snip-

This is not correct, read what I said above, You need to buy an angle finder to set the diff pinion angle correctly, I'd cut and reweld the perches but If you want slims, make sure to buy steel ones, not aluminum. And be sure you want to use those shackles, if you change your mind later and remove them , the angle will be off again.

Dropping the t-case is the absolute last resort, you don't need to with a 3" lift anyway.

LEVE posted some good drawnings a while ago on U joint angles, I think the were from Tom Wood's site, go there and check it out.

BTW, did you lengthen the shaft? if not not, it may also be loose in the slip yoke.

Wayne @ Big Island RockCrawlers
"PYRO" The Rock Crawler
Web Site: http://www.members.tripod.com/surfmac/Index.html
 

·
Registered
Joined
·
792 Posts
Discussion Starter · #6 ·
where can I get the Spring perches, and about how much will they cost?

Also did you guys that have CJ5s and about 4" of lift have to buy a new driveline, mine is stock.

79 CJ 5, 258, dana 30, model 20, T18 tranny, dana 20 transfer case, 2.5" rancho suspesion lift
 

·
Registered
Joined
·
1,286 Posts
A&A manufacturing is a good source for brackets of all types.
http://aa-mfg.com
Part # AA-106-A $7.59 each

With a 4" lift, you need to lengthen the shaft. But if i'm reading right, your's is a hair over 3" (2.5 springs, 1 3/8" shackles which is only 11/16" lift).
Are the splines showing on the slip yoke(when sitting flat)? I've put on 2.5 lifts with stock shafts and they worked OK, not the best but OK.

Wayne @ Big Island RockCrawlers
"PYRO" The Rock Crawler
Web Site: http://www.members.tripod.com/surfmac/Index.html
 

·
Registered
Joined
·
792 Posts
Discussion Starter · #8 ·
If the splines are showing does that mean I need a new shaft, I have not yet checked will in AM.

Also can I get the shims from a local autoparts store (Kragen, Napa, CarQuest?)

thanks



79 CJ 5, 258, dana 30, model 20, T18, dana 20, 2.5" rancho lift, 1" shackles
 

·
Registered
Joined
·
792 Posts
Discussion Starter · #10 ·
I live in a medium sized town and I dont think we have any specialized "Drive shaft shops", can a machine shop do this? Or can I send in my shaft to these places?

thanks very much for the help so far?
tony

79 CJ 5, 258, dana 30, model 20, T18, dana 20, 2.5" rancho lift, 1" shackles
 

·
Registered
Joined
·
292 Posts
Tony,
I have a 4" kit on mine, and I had a CV driveshaft made. It cost aound $250. I had to get some shims as well and was able to get them from a truck parts distributing company locally. With only a 2.5" lift you should be able to get your angles back in line and be good to go...

Lugnut 77 cj5
 
1 - 12 of 12 Posts
Top