Just whats a vibration

Just finished my bastard pack QT HD packs placed under my old main late yesterday. Sits at 2.25 inches hub to flair. Took it out last night to test and experienced nothing that sounded or felt like vibrations from the DL. This morning I took it out and there was a very low pitched somewhat rumbling sound and slight vibes through a range of only about 40 to 42 mph. The sound was not grinding or metallic. Drove several different roads and noticed the same thing. Now had I not just installed the lift I doubt if I would have noticed anything out of the ordinary, especially the vibes which are more subtle than the low tone. I have a 96 XJ with the 242 TC and the C8.25 axle. I wish I'd gone for a drive to listen for baseline sounds/vibrations before the installation.

My question is what exactly constitutes vibrations arising in a newly lift XJ? Are they really conspicuous, or can they be as subtle as I've described?

i have a 96 242, d35 with the same vib/growl... I did the rear first then the front end... drove the assend high for a few days as soon as I did the front the grumbling started. I'd jsut replace all your u-joints and go from there

J-Roc said:

i have a 96 242, d35 with the same vib/growl... I did the rear first then the front end... drove the assend high for a few days as soon as I did the front the grumbling started. I'd jsut replace all your u-joints and go from there

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If its just u-joints I'll be happy. I've not yet done the front.

I'm in the same boat. I recently did a 2" BB and get very slight vibes from 30-40mph. Hardly noticeable when accelerating slowly, but you can feel it when getting on the gas hard, like going up highway onramps. For now I think I'll live with it since it's very minimal, but a tc drop would probably fix it.

XJ5 said:

I'm in the same boat. I recently did a 2" BB and get very slight vibes from 30-40mph. Hardly noticeable when accelerating slowly, but you can feel it when getting on the gas hard, like going up highway onramps. For now I think I'll live with it since it's very minimal, but a tc drop would probably fix it.

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I notice mine only on acceleration, not at all slowing down. I wonder if a 2 degree shim would be a better idea than a TC drop. Again, I have to wonder if I would have noticed anything had I not just done the modification, hence my original question.

Yeah, it's only during acceleration from 30-40, and I definitely noticed it after the install, because it was smooth before. I thought about the 2* shim also, but I don't know if it's the angle at the pinion, or at the slip yoke that causes the vibes.

XJ5 said:

Yeah, it's only during acceleration from 30-40, and I definitely noticed it after the install, because it was smooth before. I thought about the 2* shim also, but I don't know if it's the angle at the pinion, or at the slip yoke that causes the vibes.

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Now that you mention it, I also get this effect at around 35 mph, but moreso at 40 mph like I indicated above. Since we are noticing the same thing, I tend to think there is something to it besides my own imagination. Just what if anything should be done about it, I dunno.......

Rod Knee said:

Now that you mention it, I also get this effect at around 35 mph, but moreso at 40 mph like I indicated above. Since we are noticing the same thing, I tend to think there is something to it besides my own imagination. Just what if anything should be done about it, I dunno.......

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Transfercase drop will fix it.

Vibes on acceleration, your pinion is to high. Deceleration pinion is to low.

So in our case a 2* shim may help, huh? But we'd have to install it with the thick side forward to point the pinion down, right? Would like to avoid the tc drop if possible.

I just replaced my stock rears that had an AAL with RE 3.5 leafs. I have that rumble between 30 and 40 mph.

I'm putting 2 degree shims in in the morning. I'll let you all know what affect it has on my 2001.

A jeep buddy I turn to for advice told me once..."what did you change? Start from there to figure things out." Your lift changed the angle of your rear DS in relation to your rear diff. You have some vibes happening now as a direct response to your change in angle. And now you want to shim your rear by putting the fat end forward? If you do that you will be increasing your angle of change which will increase your vibrations. That shim would be put to better use if it were fat end toward the rear which would slightly tilt your pinion upward and reduce that angle change you made with your lift. If you do that and consider a 1 inch TC drop, your vibes will be non existent...probably. It would also help to look up and at available diagrams of how your Ujoints work. They have a maximum eliptical comfort zone and if pushed beyond this point, are nasty vibration machines that will break down sooner rather than later. Also on my 96, my 3 inch lift pulled the boot off the TC/yoke until I shimmed and dropped and things relaxed. Lastly, check your track bar up front for alignment. Although some say it doesn't effect the ride having your front end off a half inch in relation to your chassis, I found that it was one additional adjustment easily made along with front tire alignment. Good luck.

M21 said:

I just replaced my stock rears that had an AAL with RE 3.5 leafs. I have that rumble between 30 and 40 mph.

I'm putting 2 degree shims in in the morning. I'll let you all know what affect it has on my 2001.

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That would be much appreciated, and let us know which side the fat part of the shim goes, if you would. Like my friend, I do not want to go to a TC drop, from what I've read they just transfer the problem to other parts of the vehicle.

Also, if you know where to get a steel rather than aluminum 2* shim I'd like to know that too!

BTW, in my opening post I meant that I am 2.25 inches hub to flair LONGER THAN STOCK, in case that wasn't obvious.

Thanks for all your help Hudson Bend.

Hudson Bend said:

A jeep buddy I turn to for advice told me once..."what did you change? Start from there to figure things out." Your lift changed the angle of your rear DS in relation to your rear diff. You have some vibes happening now as a direct response to your change in angle. And now you want to shim your rear by putting the fat end forward? If you do that you will be increasing your angle of change which will increase your vibrations. That shim would be put to better use if it were fat end toward the rear which would slightly tilt your pinion upward and reduce that angle change you made with your lift. If you do that and consider a 1 inch TC drop, your vibes will be non existent...probably. It would also help to look up and at available diagrams of how your Ujoints work. They have a maximum eliptical comfort zone and if pushed beyond this point, are nasty vibration machines that will break down sooner rather than later. Also on my 96, my 3 inch lift pulled the boot off the TC/yoke until I shimmed and dropped and things relaxed. Lastly, check your track bar up front for alignment. Although some say it doesn't effect the ride having your front end off a half inch in relation to your chassis, I found that it was one additional adjustment easily made along with front tire alignment. Good luck.

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You argue convincingly. I'd go a step further in saying that by pointing the pinion up by putting the thick side of the shim rearward, you would seemingly shorten the distance between pinion and TC output shaft, which would address the issue of the DS being too short after lift.

Elsewhere I've read that with the single cardon you keep the output shaft and pinion parallel, which is what Dirk at DPG told me in a phone conversation. The individual in the links below seems to have gotten satisfactory results putting the thick side of the shim forward.

http://www.4x4wire.com/jeep/tech/susp/xj_ome_tflx/sideeffects/lktsshims.jpg
http://www.4x4wire.com/jeep/tech/susp/xj_ome_tflx/sideeffects/

Rod Knee said:

That would be much appreciated, and let us know which side the fat part of the shim goes, if you would. Like my friend, I do not want to go to a TC drop, from what I've read they just transfer the problem to other parts of the vehicle.

Also, if you know where to get a steel rather than aluminum 2* shim I'd like to know that too!

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Rod here's what I did this morning;

I added a 2.5 degree shim with the fat facing forward. That brought the front of my pinion down just a bit. There is now not any vibration rumble or grumble that I can tell. It's a noticeble improvement to me and I knew when I put those springs on I should have slipped those shims in. Mine were some used aluminum ones that were given to me by FNJeep in colorado Springs when I bought another part.

I believe without using a precise instrument to measure the angle of the two diffrent u-joints that they are running pretty close to parallel again. I do about 100 miles per day so it's important to me.

My rig is a 2001 on stock shackles without a TC drop. I'm running 31's that I balanced myself on our machine before the changes so I know it wasn't a tire balance issue.

I can't believe I found this thread!!! I just did a bastard pack too and have the same issue, only mine is about the reverse. Acceleration is fine but deceleration is where the vibe starts and is worst @ 40-45.
I too thought pinion angle but haven't crawled under to figure it out. I know TC output shaft and pinion must be nearly the same angle to get rid of vibes. There is an equation that is available from spicer but I don't have it handy. It is shaft length dependent in determining the overall allowable angle difference. Some situations are pretty tight with no more than 3 degrees delta.

I have to admit that putting the fat enf forward seems counter-intuitive but it seems to work for people. The theoretical/mechanical basis for doing it this way (keeping the axial projections of the pinion and TC output shaft parallel) is briefly discussed in the link I provided a few posts up. They also discuss how to determine through basic trigonometry the appropriate degree shim to use.

I'm actually beginning to think that putting in the shim in either way can be better than no shim, obviously for very different reasons...as long as you understand what degree shim to use. It'll be interesting to see what everyone tries and what is or is not effective. I'm ordering a 2 * shim ASAP although I expect it won't move till Monday or Tuesday. I still have my front end lift to do.

Where's the best place to get some steel shims? Rustys are $30.00/pair compared to under $10 for his aluminum ones. Does that seem high to anybody else?

From TW's website.
http://www.4xshaft.com/driveline101.html