Jeep Enthusiast Forums banner

1987 rear vibration

2K views 47 replies 12 participants last post by  Thumbs27 
#1 ·
Hi i am new to this site. I have a 1987 jeep wrangler yj tht has been converted to the 4.0l with a 42re automatic. The rear end has had the leaf spring perches rewelded on. The pinion angle seem to high, an whn u take off it shakes. But goes away aftwr a few seconds. This only happens on take of
 
#5 ·
So i knw it cant be the clutch because it is an automatic. It has ubolt stay straps on it. As i add different degree shimes to it it makes it better. The people tht started building this jeep cut the original trans crossmember apart an rewelded it back together so im wondering if tht is part of the problem.
 
#8 ·
You mean you dont see the problem there? First your driveshaft is like 2 inches than resting angles are wrong any suspension travel at all takes you beyond what the u-joints can compensate for. There is everything wrong there. I dont know if an SYE would get you enough driveshaft but you definitly need one. I am also assuming that almost non existant driveshaft isnt balanced as I cant believe an driveshaft shoop would even entertain the idea of making a driveshaft that small.

I am starting to question if this is a troll post
 
#10 ·
Doesnt change the face that everything is wrong, Literally.
The driveshaft is waaaaay to short and I am sure unbalanced. The pinion angle is set up like its got an SYE and double cardon drive shaft. If the pinion was set right the u-joint angles would be way to severe. You at a minimum need an SYE and new driveshaft and probably a stretch too to get enough length on the driveshaft. I see of no way you can make that set up work as is
 
#22 ·
:rofl: How did I miss this post? I was nearly on the floor when I saw that picture. :rofl: :rofl:

...
The driveshaft is waaaaay to short and I am sure unbalanced....
At this point, does it even matter if it's balanced? I mean, there's so little rotating mass there...... :rofl:

Per this thread, it's pretty unlikely it's actually a 42RE because he'd need to do a computer swap to make it work to begin with.............. and who in their right mind would do all THAT work and then put a 4" driveshaft in?!

EDIT: This wasn't posted on April 1st, was it?
 
#13 ·
The drive shaft is 6 1/2 inches long there is still 2 inches of in travel on the slip yok. As i add degree shimes to it turning the pinion down the shake has gotten better. An no this is not a troll post. This jeep was someones project. It has a 42rh automaticin it tht is why the drive shaft is so short
 
#14 ·
good god. could almost hard mount that rear to the trans lol......hard to be worse then this and think its close? Fc me.

yea a CD joint would take up about the space he has now and room for a spline joint. Might want to call someone like TW and ask whats the shortest shaft they could build, then move the rear so you have at least that much. You can gain some with a short SYE, not all that much though.
 
#36 ·
Without disregarding anyone else's posts: It can get expensive to buy shims. What degree have you added so far? I'm going to say that YES, shimming the diff down is good (just not all you actually need). Looks like you could add anywhere from 6 - 10 degrees or so?

As mentioned, the problem on take-off is likely caused by the diff rolling up under initial torque. You can compensate for that with downward shimming. BUT you can easily get into a problem in the other direction...THEREFORE:

I would suggest getting several shims. Install a mild degree, say 2 degrees. Drive it. DO MORE THAN your driveway. Drive over a few bumps and potholes. IF you don't get any additional issues when the axle drops for road issues, you could go back and try another 2 degrees or so. Repeat. Eventually you will find the sweet spot for eliminating as much of the initial shudder as your setup will allow and not cause other issues on drop.

Now you'll need to decide about suggested changes as money allows depending on your success. And, yep, I would send off that pic to the TW shop and just ask what they might recommend.
 
#17 ·
if you're unwilling to stretch that rear axle and get a longer drive shaft to help with the shake there's nothing we can really help you with. if lowering the angle helps for now that may be your best option. it will wear out your bushings and joints much quicker since it's not correct however. the reason you're having these drive shaft length issues is because of the 42RE transmission. it's much longer than the TF999 that came in it stock. longer transmission leads to shorter drive shaft unless the rear axle is stretched farther back
 
#18 ·
Plain and simple if you get rid of the vibs by setting the angle right(SHould be parallel to the transfercase output yoke) Then your gonna start eating u-joints and its a matter of time before you spin the pinion bearings are tcase output shaft bearings. There isnt a way to make that work in any way resembling acceptable. You need more driveshaft period.
 
#23 ·
Ya the shock has since been fixed. An the drive shaft is 6 1/2 inches long. An it has the 42rh automatic in it. Tht was a type error. I also need to find an install a factory dana 35 with 3.07 gears. Cuz the current axle thtis under it was motified in all the wrong ways.
 
#24 ·
OH alot more than that axle was modified in all the wrong ways. Before you spend another cent on this thing I think you should send that picture to Tom Woods Driveshaft and ask them if you have any options.

The way I see it you have 2. Put a shorter transmission in or stretch the wheelbase(Move the rear axle back) atleast 8 inches in which case it would no longer be street legal. A Turdy5(Dana35) isnt going to help you here and what is the sense in a ****ty axle if you cant even spin it.

Short version is how much money are you willing to spend in this rig to make it reasonably driveable because as it stands right now I would like to know what brand u-joints your going to use so I can buy as much of thier stock options as possible. I may buy stock in the bearing and bushing manufacurer of your choice as well.

If this really isnt a troll post I am gonna say the PO of your jeep might be worst than the PO of mine. TO give you an example I am 10 grand into straightening mine out and thats doing the work myself. If you have to pay someone to do the work triple that.

So seriously how much coin are you willing to drop to fix this thing.
 
#27 ·
Dude, if you're serious, then you're much better off unloading this pile and getting a different Jeep. It doesn't sound like you know enough about vehicles to fix what's wrong with this one.
 
  • Like
Reactions: Siva283
#28 ·
I have another jeep tht i have been building also so i knw enough to work on thm. So thnx for u insight but i will continue working on this jeep just like i will continue getting all the parts for the 4.0l an ax15 swap on my other jeep tht people said im dum for doing
 
#29 ·
Here's what I'd do.....

* Get a super short SYE
* Get a new set of spring perches for the axle (with multiple pin holes) that will allow the axle to move back an inch.
* Properly set the pinion angle and measure for a new CV shaft
* Install new shaft and be done.

There's enough room there to do this.
 
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top