Hey Guys, I have been a long time reader but have just became a member. I bought my white 91 sport about 6 months ago. i have replaced alot of parts. motor mounts, tranny mount, steering components, interior pieces. Installed a 3" rough country lift. bought a set of procomp tires for 200 bucks. Well my question is my vac diso lines were melted by my exhaust so i took all the associated vac lines out and put in a homemade cable pull for the front axle. when i engage the front axle but DO NOT engage the t-case i get a vibration from the front driveshaft above 40mph. i have pulled on the driveshaft and it all feels tight. I havent taken it out yet. Do you guys think the ujoint need to be replaced or the entire shaft. Thanks in advance

 

Usually if a U-joint needs to be replaced, you can see the play in it, although you will want to take it all the way off to look for it - that way, there are no forces on the joint other than what you put on it. Secondly, is there no vibration issue when the T-case IS engaged? No vibration when nothing is engaged as well? If there is no issue in either of those scenarios, then just don't drive it with the disco engaged and no tcase. There should be no reason I can think of to engage the front axle if you are not also engaging the T-case.
Also, make sure to take it out and see if there are vibes in any scenario when the front shaft is removed, so you can be sure it is the shaft and no other components.

 

Thank you for the ideas. I have thought about taking the shaft out and trying it. The only reason i wanted to be able to engage the front axle and leave it was for the wife. she doesnt know how to engage it. she is a push a button type girl. I have also scouted out a front high pinion non disco 30 at the J/Y and wanted to know if i do put that type of axle in then wouldnt my front driveshaft be turning all the time anyways?

 

There are two things on the front driveshaft that will cause vibrations...either a worn out slip-joint in which case the whole shaft needs to be replaced or bad u-joints. If the slip joint is bad you'll be able to tell by it having a more than a little play if you push/pull on it with the DS in the Jeep. If the slip joint is ok then your u-joints are shot. replace them and you should be fine.

and yes if you install an non-disco front axel from the JY your driveshaft will be spinning all the time.

 

a friend told me that it could be the joint that is in between the two u-joints. i think it is a ball joint. what do you guys think?

 

which two u-joints? there are three u-joints on a front DS, there's the single one on the pinion and then the two that are back to back at the transfer case end. there's no ball joint. there is a slip joint in the middle of the driveshaft that will cause vibes if it goes bad

 

this is the joint i am talking about. in the pic there is a centering ball seat assembly. I dont know if there is a rebuild kit for this joint.

 

What makes you think that went bad? I've never heard of those causing driveline vibrations

 

The cv ball kit is available. It comes with a little spring, seal and the centering ball. The Precision part # is 617. At least that's what it was for my 2001. I just did all three u joints and this cv centering kit last night. I was getting a lot of squeaking from mine which is all gone now...

 

lack of lubrication, the greaser on it is the concave type and you need the small grease gun with the needle nozzle for it.

 

Just to be a little more precise: It is not a constant velocity (CV) joint, it's a double cardan joint. The CV joint was available on the early 84-86 models.

 

On my way back from the UP in dec. the cardan joint in my 95 xj failed. could not drive above 60 mph. when I took it apart the ujoints seemed fine, the socket for the ball on the cardan joint was all wore out. new driveshaft from egay, and back in business.

 

grease the ds and check the ujoints first.

your thinking of the centering ball. it has two seals, an outer rubber seal and an inner seal. i just had to rebuild mine with a new centering ball. Rockford driveline sells a rebuild kit for about $40- part number R2-21-1355. spicer part number is i think 211355X, $65 from NAPA. i saved about $15 on mine by buying a double cardain assembly from someone and just taking it apart to get to the centering ball. inspect everything if you do this because i ended up smashing two of the inner seals due to the rubber seal being bent, which was caused by the cup being bent inwards on either side.

stu olson's tech writeup on his site is very useful for this issue.