elliotgr

Hey all!

This is my first post here and am pretty stoked. I drive a '97 XJ 4.0 6cyl and love it.

ISSUE: Today I began noticing a roar/growl whenever I accelerare, and you can feel the vibrations in the floorboard. U-joints? 🤔

Thanks!

jordan96xj

Welcome!

Yes, u-joints are one of the things that can cause a "howl" or "roar" when they are going dry/failing. They will typically produce more noise when under load, such as when accelerating. However, you owe it to yourself to check the fluid levels in your front and rear differentials as well as your transfer case, if you have never done that before. They should all have fluid up to their holes, so that by sticking a finger in you get oil on your finger.

Roars and growls can also be caused by failing wheel bearings, but those are not so sensitive to acceleration or loads. They tend to be more sensitive to turning, such that when the weight of the vehicle shifts to them they get louder, so if the noise is sensitive to rocking the steering wheel back and forth at speed...bearings are more suspected.

Provided the fluids have been checked, you can attempt to get underneath and push the drive shafts around to see if there is any movement in the u-joints. Some rotational movement against the differential is normal (a small amount) but the joint itself should not be able to be moved, or produce any type of clunking when you are handling it. However, when a cap on a u-joint is just starting to go bad, and make some noise, it is very common for the u-joints to have no play at all, so they can be difficult to find by hand sometimes...unless they well and truly failed (normally you would have terrible vibrations by this point).

Here is what I did. I took the front drive shaft out (yes, just take it out). Then I drove and tested to ensure the problem was in the rear drive shaft. Which it was. Then I simply took the rear drive shaft out and replaced both u-joints (since I was in there any way). But, if you take the front driveshaft out, and the noise completely goes away, then the problem is in the front. Redoing the joints on that shaft is not too much harder, but it has a double-cardan joint which is a little more tricky for first timers. There are many good videos on how to replace the joints and centering-yoke on that as well (just a small cup/plate that sits between the joints).

Worn out rear driveshaft u-joints are more common, and because you hear it under acceleration, it is more likely to be one of the rear u-joints.

elliotgr

Jordan,

Thanks so much for your response, I really appreciate it. 👌

I'll get on it!