Knock knock whats there?

I don't know what is knocking, but here is what I do know.
1 I feel/hear it in the body. Can't tell if it is in the rear or front.
2. If I put the brakes on, accelerate without moving, i get this knock or clunk.
3. If I put the brakes on, put it in reverse after 2 above, i get this knock or clunk.
4 happens occasionally while going around a corner and going over bumps.

Suspects:
drive line U joints
Ball joints,
Front axle u joints.
control arm bushings
Leaf spring bushings.
broken leaf - no visible cracks
TRE's

It is not
Shock mounts - checked those

What is your your list of suspected parts starting with the most likely and working down the list?

loose trans mount bolts, cross member bolts...

a collapsed trans mount will allow the exhaust to touch the cross member under load

I'll check it out, but I don't remember ever loosening those. Hmmmm.

Knocking????? Is it one knock per occurrence or multiple.

One

sjx40250 said:

I'll check it out, but I don't remember ever loosening those. Hmmmm.

Click to expand...

you don't have to have been working around them for them to be loose.

I just acquired a '99 xj that had a similar clunk during rev to drive shift. The 2 bolts attaching the trans mount to the trans were just loose enough for the mount to shift under load. Didn't look like anyone had ever touched them before.

Sounds like driveline ujoints (or as mentioned above, something in the trans mounting). I bought a jeep a while back that would let the rear of the trans lift off the trans mount under heavy acceleration. It was the peice between the transmission and the trans mount. It had ripped apart. (Manual transmission)

For driveline u joints, get under there and physically shake the driveshaft at the joints. Ujoints bad enough to do this, will be obvious.

xcm said:

Sounds like driveline ujoints (or as mentioned above, something in the trans mounting). I bought a jeep a while back that would let the rear of the trans lift off the trans mount under heavy acceleration. It was the peice between the transmission and the trans mount. It had ripped apart. (Manual transmission)

For driveline u joints, get under there and physically shake the driveshaft at the joints. Ujoints bad enough to do this, will be obvious.

Click to expand...

Checked those already. They feel tight. Not sure about the ones in the hubs.

You don't mention if stock or not...

If stock, with no after market SYE; then the clunk you may be hearing is a result of dried out splines on the rear driveshaft slip joint (where it mates up at the transfer case).

Remove driveshaft, and lube/grease the splines....

If it's in the drive line then maybe it's the axel. On my 85 XJ there was a clunk I couldn't find finally watched as it was put in gear the yoke on the rear axel where the drive shaft attached would leach forward banging the drive shaft.
I forgot the proper terms for all this it was a very long time ago, years before we welded a ford 8.8 in. Basically the original axel was wore out and the pinion, carrier bearing (or whatever else it's proper name is) would lash out banging the drive line.

If all else fails I'd check the axel as it engages. I've seen this happen in a few different vehicles with worn out axels but I have got to have my terms wrong because I can't find a video of it.


More likely it something simple like broken exhaust hanger, broken mount or ujoint.

Thank you all for your suggestions! What an invaluable resource this forum is! Been a long time since I have spent any time here but it is good to see some of you still on line!
@digger87XJ wins the solution award.
So far driving around the neighborhood validates the lower transmission mounts weren't tight enough. It didn't take much, about 1+ revolution to tighten them up. Had to remove the skid plate to get to two of the nuts.

So this is a 1990 XJ Laredo nearly fully loaded and stock, from a suspension POV. The only modifications to it are helper springs in the back, rear axle from an earlier ('88?) rear end with traclock diff and 10" drums, finally, an extra set of spacer over the top of the front springs. Oh and the track bar broke right at the top of the bend for the diff! I replaced it with an adjustable one in anticipation for a lift at some point.

AW4, NP272 with 215K miles. I bought it new in May of 1990.

As I have mention in other threads, it has aftermarket injectors, MAP adjuster circuitry, Borla header to tail. Still running the original cooling system, having to replace the tank every once in awhile.
I have had the head done and replaced the rings with cast rings and new journal bearings. That was over 125K miles ago. Went through 4 water pumps before finding one that didn't fail, FlowKool.

Anyway, I think the knocking is solved. I will validate on here in a couple of days to validate.

@Green Mesa XJ - Thanks for your suggestion but that was the first thing I checked - the entire driveline for slop. There is a little clunk when shifting into drive, but not anything significant. I think the pinion bearing is nearing term as it does howl a bit when accelerating. Hard to tell with the Borla muffler.

@Ivan - I do frequently lube all the joints. About time for them to be hit again. I noticed that the TRE boots are failing. At some point I should replace them. Steering is great with no slop.

Those axels can howl for decades without dying.

Glad you found the problem.

Yes they can and have!

Validated that it was the transmission mount!

Congrats :thumbup:

:clap: