Driveline thump...?!?

clehmann · **Joined:** Sun Sep 16, 2012 7:53 pm **Posts:** 24

Hello all,

I've got a 2005 Liberty CRD with ~134k on it. I've got 2 sounds that I'd like to describe and see if you guys have any thoughts. I think the sounds will turn out to be related, but it's hard to say. I'll just present as much info and feedback as I can and we'll go from there....

First problem - everything sounds mostly fine around town, but when I hit the highway, somewhere around 65mph+ it feels like I am constantly going over small bumps - not as frequent as the grooves in the road, but constant thumping. Maybe 2-3 thumps per second and it varies with speed (subject to calibration of course ;-)

So I had it in the shop for a diff service a few weeks ago and asked the shop to take a look at it and they said tires. Hmmm.... Ok, so I took it to Discount Tire who put on new Hankook Dynapro ATM's last March and told them the story. They checked out the tires and rebalanced them all and said everything looked within spec. Took it back to mechanic for a hose replacement and told them that the tires were clear, please check driveline again, and AGAIN they told me that it was the tires and that they needed to be load tested. Ok, fine. Went BACK to D. Tires and they load tested them, swapped the front tires and did a road test with me. ...it's not the tires.

Second sound - sometimes, when the Jeep is cold, when I start down the neighborhood street there's a pronounced thump from something underneath. The high speed thump is subtle, but noticeable, this thump sounds like someone is under the car hitting the chassis with a hammer. Scary? Yes. Here's the fun part - it goes away after ~1/2 mile driving. Also, the frequency is slow. Moving ~20mph the thump is maybe once per 1-2 sec. Certainly not in time with the tires on the road, hard to tell in terms of driveshaft rotation with the gearing of a given gear speed. Also, if it's doing this and shift into Neutral while moving, the thump continues.

Other notes - I'm definitely fighting the transmission fluid check valve issue, in that sometimes if I don't "prime" the fluid for long enough, when I put the car in Drive it just sits there. If I don't catch it back into Neutral in time, the gears "crash" and it stalls the motor. I'm more and more careful, but it's definitely crashed a few times. Related? Possibly. If I prime it up and it goes, the transmission shifts nicely and seems to be fine. Also, I've been underneath to see what I can see for myself and the driveshaft U-joints seem to be solid (though it's hard to know for sure). I did notice that if I move the rear drive shaft side to side with my hands, I can move the transfer case on the mounts enough that it taps the undercarriage somewhere. Hard to tell exactly, but that's what it feels like.

Any ideas where to start? Transmission issues? Transfer case? Joints? It's a lot to take in, so let me know if I can supply any further info. In general I'm diving around town and it hasn't been too bad, but I'm on the highway about once a week and I'm starting to get nervous taking it up to speed. Might be fine, might be really bad. =/

Thanks in advance for your feedback!

Chad

tommudd · **Posted:** Mon Jan 27, 2014 5:13 pm

Have they or you checked the rear boot on the front driveshaft yet?
Boot goes bad, junk gets inside rusts or tears up the bearings
They have been known to cause a thump, rotational noises and all kinds of weird things
worth a look and if it is, easy/cheap repair
Could be something else but start there

clehmann · **Joined:** Sun Sep 16, 2012 7:53 pm **Posts:** 24

I'll take another look tonight and look closely. I poked around underneath over the weekend and specifically remember looking at the front boot of the front shaft, but I'll have to double-check on the rear boot. Thanks for the tip.

clehmann · **Joined:** Sun Sep 16, 2012 7:53 pm **Posts:** 24

Finally got under the Jeep last night and took the following photo:

Definitely looks like a failed boot. Great call tommudd! There's another thread for swapping this joint, so I'll follow that and see how things go. The front boot looks in excellent condition, so hopefully I can just do the rear and it will clear up a lot of these mystery noises.

Thanks!

clehmann · **Joined:** Sun Sep 16, 2012 7:53 pm **Posts:** 24

OK, finally an update. I've successfully installed the new joint. The old one was definitely full of dirt and debris and lacking in grease. So far the repair seems to have fixed the highway "road bumps" problem. However, the louder, less-frequent sound when running at low speed is still there and getting more frequent. It seems to be worse if the Jeep is cold. This morning it was ~17 F and the thump was pretty bad. Once I drive around for a while it goes away. Also, it doesn't thump when I engage 4WD Full Time. Once I release 4WD, the thump comes back. Hopefully these are useful pieces to the puzzle. Nothing has failed as yet, but it's a pretty disconcerting sound first thing in the morning for the first few miles. Bearings? Transfer case? Pretty stumped at this point. Worst case is I'll just drive it until I have enough noise to better diagnose the source.

HoosierJeeper · **Joined:** Sun Feb 15, 2009 8:23 am **Posts:** 1218

If it gets less pronounced in 4WD then I'd think it could be in the rear, since "pressure" is taken off in 4WD from the rear. What about U joints?

clehmann · **Joined:** Sun Sep 16, 2012 7:53 pm **Posts:** 24

U-joints are not out of the question. The notes I have from the previous owner say that the rear u-joints were replaced at 44k, so we're sitting at less than 100k on them, but anything can happen. Is there a good way to check them? Any tips for diagnosis? Thanks for the help

Driveline thump...?!?

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