Black & Tan

I've got a 2001 XJ that is totally stock and 170k on the odometer. It drives well but I get an occasional "thunk" from the rear end after I've come to a stop and let off of the brake pedal. When you stop, the weight transfers to the front and the rear end goes up. It appears that the brakes are holding the rear end up and when I let off the pedal, the rear end drops and goes "thunk". I think the front and rear springs are original but not sure (I bought it with 160k on it). I don't drive aggresively and usually only hear it when I come to a more abrupt stop, not the smooth, slow stops I usually make. Any ideas what it could be? It's going in next week for a full service from a guy who services my cars and want to put it on my "things to do" list.

tinytrax78

steelybill

Your mechanic can check the rear springs and the U bolts, to see if something has come loose or broke under there...A check of the universals on the drive shaft may be another item to look at...

tech

You can also check the slip joint on your drive shaft . remove the drive shaft and put some grease in the slip joint just some grease to help the slip joint slide .

jordan96xj

Your rear drive shaft slip yoke needs to be cleaned/lubed. Its extending, but then binding when trying to compress, ultimately "thudding" back into place.

Black & Tan

Thanks for the quick replies. I'll point these out to him and see if it gets better.

The drive shaft slip joint is probably the culprit but I'll look at the springs while it is up on the lift. They may need replacement since the rear looks like it is a little lower than the front. 170k and 17 years can cause a droopy rear end. After 64 years, my rear end is getting a bit droopy too!

tinytrax78

so is it fixed?

Black & Tan

We checked all of the above but everything looks good. I think the rear springs may be old and need replacement but my mechanic says they are okay. He is conservative and feels if it isn't broken, don't break it. Even though I'm a little OCD I have to remember that it still runs well and gets me where I want to go reliably.

Oswalla

Just throwing it out there, a bad tranny mount can cause a "thunk". It's been a few years, but I remember it was making a part of the exhaust bang on something. You can use a small pry bar and try to lift tranny in the area of the mount, it will be obvious if its torn/bad.

PatHenry

Did you lube the rear driveshaft?

unidentifiedbomb

I had a thunking once with hard braking, replaced the rear drum setup and everything went away, can't explain why it happened. But also could be worn leaf spring/shackle bushings, tranny mount, motor mounts, worn u joints on the driveshaft. I doubt it's the slip yoke seal.

Password12345678

+1 on what unidentifiedbomb said. I had an occasional thunk from the rear end when braking. I replaced the drums with this set from Rockauto. They sent me 10" drums at first I think, but we got the kinks worked out eventually. If you're going to replace the drums though, you might as well use a conversation kit to have discs in the rear.

Saygoodbye41

Hi guys. I'm new here and I have this similar thing going on. Any takeoff it feels like a bowling ball is being sent to the back of my 2000 xj. I saw a writeup elsewhere on common problems with these things and greased the crap out of my slip yoke. It still does it and ... I'm here because it sounds like there are two slip yokes? Does anybody have any pics?

PatHenry

The slip yoke on a rear driveshaft is the part where the driveshaft connects up to the transfer case (or in 2wd vehicles, the transmission). On a 2000 XJ there is a rubber boot that covers the transfer case output shaft and the yoke slides forward and back on the shaft. This is the OEM setup, there are aftermarket "slip yoke eliminator" kits that modify this. 96 and earlier XJ's use a design with a cone so the transfer case lubricates the shaft.

In order to keep the driveshaft moving correctly, you need to occasionally put some lubricant on the shaft. To do this, remove the u-joint straps at the rear axle and push the shaft back out of the axle yoke, then you can slide the driveshaft off the transfer case side by pulling it straight off the shaft. Lube the shaft up (I'm not sure of the recommended lubricant, I believe on my TJ I used wheel bearing grease, but don't quote me on it.) and then install is the same thing in reverse.

The front driveshaft is a double-cardan shaft and the front section of the shaft slides in and out. There's a zerk for greasing the shaft.

Saygoodbye41

Awesome, ok. That sounds like what I ended up doing. It wasnt the problem. I ended up using lucas red and tacky (like the writeup I saw recommended) but did everything, from this thread, thought maybe I was missing something