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Discussion Starter · #1 ·
I'm new here so I thought I'd just say hi first. I have an 87 YJ with a 350 sbc and th 350 automatic tranny that me and the wife use for a daily driver and for pulling our tent trailer here in Alberta. That is until I installed the 2 1/2" lift on it. Now it shimmys and shakes like all get out when its pulling the trailer. I've lowered the tranny and shimmed up the pinion so I know the angle is good. Just replaced the rear U joints and had the shaft rebalanced. While I was at that I installed all new tie rods and front axle U joints which leads to my next problem.The front axle seals leak like crazy now. I`ve never changed these seals so I'm hoping someone can kind of give me the low down before I start. Sorry for the long post but I figured if I threw out both problems at once then someone might have some of the answers.
Remi
 

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Welcome to the site.
The t-case drop should have eliminated your drive shaft vibration problem.
Do you have a slip yoke eliminator or does the shaft slide in and out of the tail shaft of the transmission?
This is important info to help figure it out.
If you do not have a slip yoke eliminator, remove the shims from the diff. The angle of the rear pinion shaft does not change for a tail shaft yoke.
If you DO have a slip yoke eliminator, what angle did you set the pinion at?
More than likely your problem is coming from the drive shaft. Take some pics of the angle if you can, and the back of the t-case where the drive shaft connects to it.
The front d30 axle seals are not hard to replace. It's just time consuming. Do both sides leak or just the passenger side?
 

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Discussion Starter · #3 ·
Hi, thanks for the response. The tranny / transfer case drop consisted of 3 pieces of pipe of different lengths which provided a total drop of 1 1/2". These were installed between the skid plate and the frame. I don't have the slip yoke eliminator just the regular yoke and shaft. The reason the rear diff needed shimmed was because after the lift was installed there was to much angle between the transfer case output shaft and the rear diff. The drive shaft hung 1" higher than the diff when everything was at rest. Now I have almost equal play both up and down.. As for the front axle seals they both leak. About time really, they are the originals. I will have damaged them when I pulled the axles to install the new U joints. I was just looking for advice or a procedure for changing them. I have a Haynes book but it don't show squat about the seals just info on how to pull the axle.


 

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Take the shims out. You do not change the pinion angle unless you have a double cardan drive shaft and an SYE.
MW is correct. Your pinion angle is too steep. It needs to be horizontal for the setup you have.
Imagine how it works: As the rear diff moves up and the pinion angle is flat, the yoke will freely slide in and out of the tail shaft.
If you had an SYE you would point the pinion directly at the t-case tail cone, and then bring it down two to four degrees. The slip yoke is in the center of the drive shaft on a DC drive shaft, so it compresses there.
But you have the stock setup. Remove the shims and make the pinion angle flat. That should solve the vibes.
I have the same lift you do but I have a Furd 8.8 rear end and an SYE with the double cardan DS.
I eliminated the t-case drop by installing Brown Dog one inch motor mounts which lifted the front of the drive train. Then later I went to the SYE setup when I swapped out the Dana turdy five for an 8.8 Furd.
 

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Discussion Starter · #6 ·
I have the jeep in the shop right now so I will remove the shims and set the pinion back down. The reason for the shims was the U joints were binding. Now I just can't remember if that was before or after I did the transfer case drop. No matter I will set it horizontal like you suggest. I need to change the front axle seals before I will be able to test it but I will let you know how it turns out. Thanks for the advice. I was stumped and just couldn't figure it out. Later and thanks./
Remi
 

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Keep us posted. Happy to try to help.
 

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Discussion Starter · #8 ·
OK here's a bit of an update. LH axle seal installed, no problem. RH axle seal went in crooked and got screwed up. New seal will be in tomorrow. Fabbed up a proper tool that fits inside the axle tube to remove any play in the rod Im using to pull in the seal with. Also made a seal driver from 2" muffler pipe, a 7/16 washer, a 1/2 washer, and a 1/2" bushing that also takes any play out once it is connected to the rod. Should work now I hope.
Next is the Pinion Angle. I removed the shims and laid the diff back down to the original position. This would work great if I didn't have the lift kit installed. As it is, the driveshaft hangs about 1 1/2 inches above where it's supposed to hook up to the drive shaft even with the 1 1/2" transfer case drop. The 350 had 1" spacers under the motor-mounts so the exhaust would clear the front driveshaft U joints before the lift was installed. I removed these and gained some ground. The transfer case drop was 1 1/2". Now that the motor is dropped I still needed to lower the transfer case some more so the drive shaft could have enough play up and down so it didn't bind. The skid plate now sits about 2" lower than the frame at the front and about 3 1/2" at the rear. ( I know pics would help but the camera is dead and my blackberry is at work) I was just going to cut some 3/16 plate with the plasma and weld in a box to fill the gap for the skid plate to bolt to. The gap seems like alot but the diff now is parallel and has the same angle as the transfer case shaft less 2*. If this isn't right please let me know. If it is let me know anyways and I can start cutting and welding in the skid plate spacer... Looks like camping might be pretty close... Thanks.
Remi
 

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It sounds like you are close. The sliding spline needs to be into the back of the t-case output cone at least half way if not a little more.
And yes, pics would help. But it sounds like you are on the right track. I'll see if I can find the pic of how your pinion/t-case angles work geometrically and I'll post it here.
Worst case scenario, you may have an SYE and DC drive shaft in your future. A Cherokee front drive shaft can be cut to use for the DC drive shaft. That is what I did.
Try to get some pics of the side view of your t-case drop and your pinion posted. That will help.
 

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Discussion Starter · #11 ·
By God I think I got it. Between the help offered on here and the driveline phasing site I have everything aligned and bolted back together. I\ve been using it for work with no problems since my last post. Last weekend I picked the tent trailer up of the farm and hooked it to the jeep and went for a drive............with no noticeable vibrations. In fact at 65 mph it has never ran smoother. So thanks to you all for your help. Problem is solved it looks like.
 
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