Rattle-Grind Noise Below XJ w/ CC, Downhills, and Foot off Throttle

As described in the post.

Not sure if I want to know this answer or not. Here goes...

My 90 XJ 4.0 is now running solid, however when I either let my foot off the gas, am coasting downhill, or have the Cruise Control engaged and it slows there is a rattle/grind/vibration noise below the bottom of the vehicle. Anyone know off hand of common noises like this in that circumstance. I don't know if it's transmission related or what. The XJ has no issues with transmission and shifting.

Thanks guys.

I have a 92 with a similar problem, havent really looked into it yet, but your not alone

driveshaft ujoints

mine did exactly the same thing, got even noisier after i replaced my sagging transmission mount.

X2 on the u-joints. Easy repair, and 2 ujoints will run you b/w $15-$20 depending on if you get the kind you can grease or not.

If it's not the U-joints then it might be the ring and pinion. I had a ZJ that did the same thing and had to replace the R&P. The reason it didn't do it on accelleration was that the teeth mesh on one side of the ring gear teeth and when you let off or coast downhill then they mesh on the other and that is where you hear the grinding noise/vibration. On the upside if it is the R&P that's a good time to regear to a different ratio as you will be halfway there expense wise.

Cheers!

Have you lifted your xj? if so how much have you lifted it? If it's lifted then it's probably because the slip yoke is pulled out on the output shaft and when under acceleration the shaft keeps force on it but when gas is let off it's allowed to vibrate some. I've got the same problem on mine and currently saving up to put in a sye.

dave92cherokee said:

Have you lifted your xj? if so how much have you lifted it? If it's lifted then it's probably because the slip yoke is pulled out on the output shaft and when under acceleration the shaft keeps force on it but when gas is let off it's allowed to vibrate some. I've got the same problem on mine and currently saving up to put in a sye.

Click to expand...

Mine is lifted 3" I believe. I bought it from a cousin, so I don't know everything that was done to the vehicle.

I got underneath yesterday noticed minor leaking around the transfer case, not enough to pool on the ground. The rear driveshaft didn't make noise when turned but could be pushed a little into the transfer case and could forcibly create a minor knock. The front driveshaft when turned could create a little more noticeable clank.

As I was driving around, I noticed it wasnt just when slowing down that I heard it, it just simply was a more exagerrated and 2-3 sec rattle. It would still do it a little when first accelerating just not as prominantly.

so that's where i'm at.

found this - http://www.fullsizexjgear.com/Tom Woods/Install.html