Vibration Under Load

Sounds more like the 45-50hz range for sure, and at highway speeds its like that all the time. At lower speeds i really only notice it around 30mph or so then between 40-60 its pretty quiet then picks up again badly at highway speeds.

The thing drives beautifully other then that, trans shifts great, T-Case is perfectly operational...

Its really hard to describe how it changes.
 
well if it's the higher frequency then it's probably something rotating at output shaft speed.

The advice about the motor mounts is good, check all of those, especially the trans mount.

then I'd start pulling driveshafts to try and figure out if it's front or rear.
Did the yokes look damaged when you pulled the old u-joints? Any wear marks on them? Did you try to deflect the pinion to the side? Have you pulled the cover off te rear axle and had a look?
 
Had it up on the lift this weekend. Engine mounts look good, they dont seperate when i tried to jack the engine up so Im assuming there good, old, worn, but good.

Trans mount does have one of the 4 bottom mounting bolts snapped off but the assembly appears to be solid still. There is a decent amount of play in the rubber mount itself though, how firm is that rubber mount supposed to be? Could that one broken bolt on trans mount actually be the problem?

Yoke at the pinion does not seem to have any play side to side or front to back in it.

Output shaft at the transfer case does have play in it but I dont know what they consider acceptable? The output shaft bearing looks to be very easily replaceable as that tail section is seperate from the rest of the housing, or am I missing somthing.

Anyways, thats where im at....
 
output at the T-case should have minimal deflection, how much does yours have? I'd say my max tolerance for somehting like that would be 1/16" of an inch. Anything more than that could be the vibe. Yes you can replace just the output bearing and it comes off with the tailhousing.
 
87manche said:
output at the T-case should have minimal deflection, how much does yours have? I'd say my max tolerance for somehting like that would be 1/16" of an inch. Anything more than that could be the vibe. Yes you can replace just the output bearing and it comes off with the tailhousing.
Click to expand...

You dont happen to have a part number for that bearing and whatever new seal I may want to install do you? I might as well just replace it and see.
 
Hey there, I'm having almost the same prob as breecher7, vibrates at low speeds and again between 35-55 but drives nice and smooth at other speeds. This happens when under load but as soon as I let off the gas it goes away. Mine is a 90 xj 4.0 aw4, np231. So far I've ruled out:

Motor mounts(replaced)
Trans mount (replaced)
Not the fds because its not in
All new u joints
new front hum assemblies
Thought it might have been the d35 but did an axle swap and didnt go way
Changed the t case
Had tires balanced

And still vibrates, I don't seem to be missing any weights on my rear driveshaft but i'm still thinking of taking out and taking to see if it needs balanced. Not trying to thread hijack or anything but I'm intrested to see what you find breecher 7 because I've been having this for awhile and I'm lost and want to be done with it! Thanks
 
Had this happen to me. Front DS u-joints no good. I didnt suspect it at first either. Just remove the front DS and drive it around the block. If it doesnt vibrate, there ya go. Besides, if you replaced the rear DS u-joints, do the fronts as well. Makes keeping track of maintenence alot easier
 
groovyjeepster said:
Hey there, I'm having almost the same prob as breecher7, vibrates at low speeds and again between 35-55 but drives nice and smooth at other speeds. This happens when under load but as soon as I let off the gas it goes away. Mine is a 90 xj 4.0 aw4, np231. So far I've ruled out:

Motor mounts(replaced)
Trans mount (replaced)
Not the fds because its not in
All new u joints
new front hum assemblies
Thought it might have been the d35 but did an axle swap and didnt go way
Changed the t case
Had tires balanced

And still vibrates, I don't seem to be missing any weights on my rear driveshaft but i'm still thinking of taking out and taking to see if it needs balanced. Not trying to thread hijack or anything but I'm intrested to see what you find breecher 7 because I've been having this for awhile and I'm lost and want to be done with it! Thanks
Click to expand...
U using a SYE? Maybe rear DS angle?
 
Yeah I thought about that too, and no sye but I've been driving around with it lifted for almost year with no probs. Then these vibes started happenin. I forgot to metion this started after I had to get a new trans, but it shifts fine and the fluid is topped off and clean.
 
breecher_7 said:
You dont happen to have a part number for that bearing and whatever new seal I may want to install do you? I might as well just replace it and see.
Click to expand...

no, but I wouldn't start replacing parts until you've diagnosed it. Have you tried pulling driveshafts?
 
Based on what you've described, it is highly likely that it's driveshaft vibration.

Do what others have suggested and pull the rear driveshaft, throw it in 4HI, and get it up to highway speeds.

One question, specifically in relation to the slop/play you described in the slip yoke (rear transfer case output)... When transitioning from loaded (under throttle) to unloaded (coasting) at highway speeds, do you hear a different sound/vibration? Almost like a grinding? If so, it's time for an SYE.
 
Still not figured out but I havent been working on it either... Only gets driven about 500 miles a month if its lucky, just a winter beater...

I bought a new trans mount, gonna replace that and see if it makes a difference. If that doesnt do anything, im gonna start playing with the driveshafts.....

Its pissing me off though!
 
Swapped out the trans mount today. What a pain in the ass. 3 of the transmission crossmember bolts/studs snapped off in the frame and there wasnt a chance in hell of getting them out. Ended up drilling and tapping new holes, hopefully it holds up as good as stock. Anyways, vibration hasnt gone away, might actually be a bit worse now!
 
may not care to hear this but mine is doing the exact same thing and it is the rear end itself. my pinion sealblew awhile back, and last week this vibration just started. when you grab the rear driveline at the pinion housing, im getting quite a bit of movement up and down. this would explaing the vib under load. the rear end needsto be rebuilt. im doing mine this weekend. i would reallyrecommend you doing that befre that vib ends up eating your gears.
 
breecher_7 said:
Trans mount does have one of the 4 bottom mounting bolts snapped off but the assembly appears to be solid still. There is a decent amount of play in the rubber mount itself though, how firm is that rubber mount supposed to be? Could that one broken bolt on trans mount actually be the problem?
Click to expand...

FYI... I tried to replace my transmission mount this past weekend. I ended up breaking off 1 of the 4 mounts that go to the body. I did notice extra vibration when driving on the highway after breaking that bolt.

Just to give an idea of the force from the engine torque, I can feel a loud thunk in floor boards because I have a bad transmission mount. If you think about the force that causes that thunk, and the flex that could be caused by only having 3/4 transmission mounts, that could be contributing towards your vibration.

Just an idea and a cheap, but somewhat time-consuming fix to replace that bolt. It'd rule out one more issue.
 
Well I know the trans crossmember is not the issue as it vibration was pre-existing and even though i snapped 3 of the bolts I tapped them larger and used new grade 8 hardware to re-install it, so it is rock solid. If it loosens up Ill weld the trans crossmember up. I should have no reason to remove it now anyways since the mount is new, unless for some reason i have to remove the trans in the near future.

Now, onto the thought of the rear axle being trash. Dunno, could be. I never checked to for play in the rear axle pinion bearing. I know I have quite a bit of slop in the T-case output shaft though. I guess it could be that. Id really have a hard time believeing that a pinion bearing would be trash at 140K but its possible.

Also, im now noticing that if I snap the throttle at moderate to high speeds that I feel and hear a slight "clunk" both when I snap the gas on and when it lets off, has to be done quickly though. Unsure what it is, but im sure its related to the problem at hand. When I put the vehicle in gear it sometimes makes a "clunk" as well and considering that ive already replaced the driveshaft u-joints im assuming this is coming from play in the spider gears. But I dont think thats part of my problem.

Anyways, problem/vibration still goes away when you let off the gas. If your on the highway under throttle it vibrates very noticeably, let off the gas and its gone.

Still open to thoughts on this.

What is acceptable play for the t-case output shaft on these things?
Acceptable play in the pinion?
How much spline should be exposed at the slip yoke at ride height?

This issue is truly pissing me off. I have tons of extra parts on hand from a totaled 01 XJ. I have a extra trans, T-case, and front and rear axle assemblies.... Just dont want to waste my time replaceing it all!
 
I have maybe 1/16" play in my T-case yoke after much abuse and 20 years.
Pinion on the axle should be about the same. Too much more than that and it's likely the bearings are worn.

No idea on what a stock shaft shows for slip yoke, that was a long time ago.
 
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