driveline thunking...

[ghettocruiser]

Hey all. I have a 94 XJ Sport. 2 door, 4.0, auto etc. When Im starting off, I can take off with no problems. No noises or anything. While I'm moving, if I let off of the gas suddenly or get on the gas suddenly (i.e. not easing into the throttle) I get a pretty heavy metallic bang from what I think is the rear of the jeep. At first I thought it was the transmission mount. It was pretty messed up. So I replaced that, and I thought it made it better, but it still does it. I dont think its a motor mount issue because of where the sound is coming from...unless someone here tells me different.
Anybody else have this issue? Its got around 175,000 miles on the body... Could u-joints cause this? I felt the drive shaft play and it didnt seem bad. Or could it be a problem in my diff? Let me know what you all think. If anyone has some more ideas on diagnosing let me know too. Thanks in advance.

Justin

[PaulJ]

It's worth checking the u-joints again. There should be no perceptible play in them. Make sure the rear joint is tight in the straps too.

[HossHoffer]

I wouldn't discount the motor mounts. I had a similar problem though that turned out to be the exhaust clunking.

[bchulett]

Anybody else have this issue? Its got around 175,000 miles on the body... Could u-joints cause this? I felt the drive shaft play and it didnt seem bad. Or could it be a problem in my diff? Let me know what you all think. If anyone has some more ideas on diagnosing let me know too. Thanks in advance. Justin

My '91 did this for years ... seemed to get worse as time progressed. I had a guy I knew that owned a driveline shop take it for a spin and said it was the rear diff ... wanted several hundred to take it apart and tighten things up. I sat on it due to other priorities.

Well, last year I had a new lift installed that required a SYE and new driveshaft that significantly improved that "thunk"---but is still evident.

Now I'm not suggesting that you go out and install a SYE kit ... with all those miles you need to ask yourself if you can live with the "thunk", or if you want to risk chasing a problem that may wind up costing you big bucks with marginal results.

If I recall, I read somewhere that you can pull the shaft and grease the slipyoke to improve the "thunk" ... I'll try and dig up the info.

[ghettocruiser]

Thanks for that info. I re-checked my U-joints and it doesnt seem like they are bad. I yanked and twisted on them best I could and they were pretty tight. Im pretty sure its in the rear. You are right...I think Im going to just deal with it for now. I dont think its something that is going to strand me or anything. Besides, Im gettin a lift and some bigger tires soon, so Ill be doing a gear change then anways. Ill be putting in a locker so most of everything in the rear will be new anyhow. Keep the ideas coming if you have them! If you find that site post it and Ill check it out!

Justin

[bocaj]

i have a 93 manual same problem i havnt even started to try to diagnose it but ill try tommarow

[jeepguy97]

Your gonna get some noise if you let off while moving and then mash it again. This is normal, you are asking the driveline to slow down and then speed up again in a hurry.

[ghettocruiser]

JeepGuy97: Yeah I gottcha. I dont think I explained myself all that clear from the beginning, but I know I will get some thunking if I do that. It does it even if I left off the gas...coast for alittle bit, then just try to get on the gas again normally. I dont even have to mash it. The only way I can get it to not do it is if I ease on to the gas really slowly. Which is fine late at night or on a back road. But in traffic when you are trying ot make lights and merge and all its kind of hard. Im guessing something in the rear is worn. My Trans AM clunks alittle if I get off and get on the gas real fast...but no where near this kind of thunking. Thanks

Justin

[4wheelnjeep]

I have had my 94 sport auto for four years and it has had the same sound. I first thought it was the DS u-joints (replaced) and it was no help. Had the rear end (8.25) reworked , no help. I just read the lubing of the DS splines, I'll be trying this next. Hope someone comes up with a fix!!!!!