RudeXJ

Hey guys,

Got a stock XJ, no lift 175k miles.

There seems to be a grinding vibration when I accelerate from standstill, but only when under load i.e. With passengers in the back going up a hill and if I swing the wheel from side to side it tends to move.

Im pretty sure it's U Joints, what do you guys think? How do you know if they're shot and am I in any danger driving the vehicle like this for a little longer?

Jeepin'_Aint_EZ

Free and easy to check and see if it is the u-joints. Get your noggin under there and poke around

mo8414

You essentually want to bench press your drive shaft and see what's loose

RudeXJ

so after I've successfully bench pressed my driveshaft, what would I be looking for? Any common issues I can look for around the slip yoke?

mo8414

It should be solid. Look at your u joints while doing it and see if u can see any play in the direction you are pushing. Look at where the drive shaft connects to your differential also to make sure that has no play in it too. A bad pinion bearing usially allows that to move a lil bit.

If the u joints are bad it should be kind of obvious when you push and pull on the drive shaft. You could always take a couple hrs and just replace them anyway since they are pretty cheep and easy to do.

Check your differential fluid level also while your at it since that's free to do. That's how my pinion bearsing went on my mustang 300 miles from home. No oil after it all leaked out the wheel bearing seals.

cruiser54

I'd look here and see if the exhaust pipe is touching the crossmember. If so, check your engine and trans mounts.

RudeXJ

Cheers for the info guys.
Rear pinion bearing was replaced just before I bought it 6 months ago, but will defo check oil level!
Thanks for all the U Joint pointers, might just do me all anyway and will definitely check those mounts!
Anything else that could be causing a grinding vibration under load when accelerating from standstill?

OldTires

Probably not what you have but worth checking. I too had a rattle, grinding noise when accelerating from stand still. It turned out to be the mechanical fan blades jerking forward with the engine and hitting the fan shroud - the fan shroud was loose a little. Check your motor mounts for cracks. Transmission mount too.

Waynerd

I too have a noise when accelerating hard from a dead stop. My mechanical fan is hitting something but I haven't figured it out yet. No shroud so it's not that. Only thing that looks close enough is the AC lines.

What I was thinking of doing is holding my foot on the brake in drive and hitting the throttle hard and maybe have someone outside the vehicle to try and pinpoint it.

RudeXJ

I'm pretty positive it's not coming from the engine bay, but will check anyway.

It it just occurred to me that when I first bought the jeep and knew even less than I know now, I took it to a mechanic to check all fluids, they topped up the oil in the rear diff. I did mention the slip diff, but could the wrong oil perhaps be causing that noise? When the slip diff is semi engaged under load and up hill!!!??? Shizzle, think I might just change that oil anyway!

BwanaBob

Not sure what you mean by slip diff.

As for the grinding noise, check the pinion nut. Is it tight? Is there any leakage
around the pinion seal? By the way, there are two pinion bearings, the inner (also
called the rear) and outer (the front). Do you know if both were changed?

From the factory service manual:
Pinion gear bearings have a constant–pitch noise.
This noise changes only with vehicle speed. Pinion bearing
noise will be higher because it rotates at a faster
rate. Drive the vehicle and load the differential. If bearing
noise occurs, the rear pinion bearing is the source of
the noise. If the bearing noise is heard during a coast,
the front pinion bearing is the source.

RudeXJ

[QUOTE=BwanaBob;3384608]Not sure what you mean by slip diff.

Sorry I meant Limited Slip Diff.

Theres not really a bearing noise, just as I mentioned a grinding vibration, but only when there are extra passengers in the car and going up a hill and only from stand still to acceleration.

Will definitely check though, and great info thanks a lot!