Knocking Sound coming from the Rear

[Jdub76]

Hey Yall. Just the other day i started to hear this knocking sound coming from the back of the Jeep....

It only makes the noise at LOW speeds (10-25 MPH) And only when I let off the gas (coasting).

I can make it go away if I shift into Neutral.

So this leads me to think there is a problem with the Rear Drive Shaft???

Or U Joint?...
Need some help here.. what should I look & check for?

Thanks guys!

[Mudderoy]

Hey Yall. Just the other day i started to hear this knocking sound coming from the back of the Jeep....

It only makes the noise at LOW speeds (10-25 MPH) And only when I let off the gas (coasting).

I can make it go away if I shift into Neutral.

So this leads me to think there is a problem with the Rear Drive Shaft???

Or U Joint?...
Need some help here.. what should I look & check for?

Thanks guys!

Well I guess it could be a u-joint. Best thing to do would be to get under there and twist the drive shaft by hand and see if you have any play. Get a flashlight so you can look at the u-joint carefully.

https://lh5.googleusercontent.com/-8LVeQlDFaWI/TnwRLjdWtwI/AAAAAAAABP0/AGNKREglfFU/s1024/2011-09-22%252022.20.49.jpg

[xj4life2]

Does it clunk louder when you first put it in reverse ? If so than a ujoint is very possable. If it only does it in gear when driving it could still be a joint but not likely in my opinion. Little more info please

[Jdub76]

I wouldn't even call the sound a "Klunk" but more of a hard Low Tone Tape that gets faster the faster you drive. But the sound fades away as you get above 25 MPH. and also I just recently installed my 3" Lift.(about 3 weeks ago). could this sound just be Drive Line Vibration due to the different angles???
I dont know maybe i am being to picky about the noises coming from the Jeep.

And Remember this is only during Deceleration (slowing down)

Also I never did recheck Nuts on the U-Bolts on the Leaf Spring. Or the ones for the rear shocks. I guess it wont hurt to check all those?

I am definitely going to do some inspection with that Drive Shaft... Is any play at all normal while trying to Rotate it by hand? And what about Play moving Back to Front?

[nickxj94]

Sounds like the u joints to me,

Sent from my LG-LW690 using Tapatalk

[KH96XJ]

Also I never did recheck Nuts on the U-Bolts on the Leaf Spring. Or the ones for the rear shocks. I guess it wont hurt to check all those?



You want to check those nuts regardless. I learned that lesson the hard way on my full size Cherokee about two months after I did the lift.

[Jdub76]

You want to check those nuts regardless. I learned that lesson the hard way on my full size Cherokee about two months after I did the lift.

Oh please tell us the Lesson you learned... What happen?

I did check everything in the front, and glad I did to. 2 of lower control arms bolts were way loose.

[KH96XJ]

Oh please tell us the Lesson you learned... What happen?

I did check everything in the front, and glad I did to. 2 of lower control arms bolts were way loose.

Pretty severe case of death wobble. The u-bolts on the front axle had come loose and some of the nuts were about 1/4 inch away from the spring plate. I don't know how I drove it for almost two months before it got that bad and never had one problem till that day. I was only going about 30 mph when it started and I was pretty glad it didn't happen on the hwy and nothing broke. I was paranoid about them after that and would check them once a month for the next 4 months till I was satisfied that I had them torqued correctly.

[Jdub76]

Pretty severe case of death wobble. The u-bolts on the front axle had come loose and some of the nuts were about 1/4 inch away from the spring plate. I don't know how I drove it for almost two months before it got that bad and never had one problem till that day. I was only going about 30 mph when it started and I was pretty glad it didn't happen on the hwy and nothing broke. I was paranoid about them after that and would check them once a month for the next 4 months till I was satisfied that I had them torqued correctly.

Well you have convinced me to Check and RECheck every thing!

I am also paranoid about getting the death wobble even tho I have never experienced it, I hear it's Hell to go thru!

Thanks Man! :)

[Jdub76]

Well I checked the Drivshaft & both universal joints, and all of it is really tight no play at all. But I have reason to believe the sound is coming from my Rear wheel Bearings. I think they are totally worn out...

I have never replaced these before, So this will be a learning experience!! :confused:

[Mudderoy]

Well I checked the Drivshaft & both universal joints, and all of it is really tight no play at all. But I have reason to believe the sound is coming from my Rear wheel Bearings. I think they are totally worn out...

I have never replaced these before, So this will be a learning experience!! :confused:

You may need one of those bearing removal tools, at least to get it out easier. I'm wondering if its the ring and pinion now though. Have you checked the fluid in the rear diff?

[OrangeXJ]

Just throwing this out there if you have a auto it could be a cracked flywheel.

[bluedragon436]

I would say try jacking up the rear end, and spinning the wheels by hand see if you can get the sound to happen... if it does, remove the DS and try again, see if you can't figure out where the sound might be coming from that way... If nothing else while you have the rear end up in the air, make sure you are in 2wd, and put it in gear and have someone slow down the tires every so often using the brakes, and see if you can hear where it is coming from while moving around the rear end.... obviously supporting the vehicle with jack stands, and being very careful while moving around...

[Jdub76]

You may need one of those bearing removal tools, at least to get it out easier. I'm wondering if its the ring and pinion now though. Have you checked the fluid in the rear diff?

I removed the rear wheels & Break Roters, Got the axle spinning pretty good and i couldn't really hear much out of the ordinary. This thing is making me CRAZY :crazy:

I guess it's time to pull the Diff Cover and check the Fluid???

I have a stock Dana 35 in the rear with a rubber cap on it, Can I just pull that cap off and try to top off the Fluid?

Thanks Mudderoy xjtalk :yourock:

[bluedragon436]

I'd pull the cover, check your gears and such, as well as look at the fluid for metal flakes... and then just replace it with new fluid... Or even better pick up a 29spline Ch.8.25 to swap in!! LOL

[Mudderoy]

I removed the rear wheels & Break Roters, Got the axle spinning pretty good and i couldn't really hear much out of the ordinary. This thing is making me CRAZY :crazy:

I guess it's time to pull the Diff Cover and check the Fluid???

I have a stock Dana 35 in the rear with a rubber cap on it, Can I just pull that cap off and try to top off the Fluid?

Thanks Mudderoy xjtalk :yourock:

Yeah, I'm a little concerned you may have a problem with the rear axle. The best way to do it would be to get you some diff fluid, some RTV and remove the cover. Check for debris and clean it out with brake cleaner.

[Jdub76]

Yeah, I'm a little concerned you may have a problem with the rear axle. The best way to do it would be to get you some diff fluid, some RTV and remove the cover. Check for debris and clean it out with brake cleaner.

Thanks, I just keep on crossing things off the list...LOL

Is there a diff fluid that your or anyone else recommends???

[Carves]

X 3 with bluedragon436 & Mudderoy re getting the cover off for a look.



Is there a diff fluid that your or anyone else recommends???


Normal driving use oil is 80w/90

Heavy duty driving and towing use ... the factory specs 75w/140 synthetic ... but I just use a 85w/140 dino gear oil front & rear.

... and you need to add friction modifier for the clutch packs in the rear diff ... if the oil doesnt already have it in the mix.

Oil brand is your choice ... but as a suggestion .... Cheap stuff replaced regularly - if you like to splash around in big puddles ... ;)

[Jdub76]

I picked up some Oil & Hi Temp RTV Last night. So I will be removing the Diff Cover this morning. I will take pic or video if I find anything strange or out of the ordinary...

I'm hoping my Diff is just Low on oil causing this noise. I really appreciat everyone thoughts & guidance!!!
I Love xjtalk

[xj4life2]

it's probably not the rear end unless the pattern is off on the coast side only, you said you jacked it up and it sounded normal , I would do the following,
1. remove rear shaft and drive in 4wd any noise ?
2.replace rear shaft and remove fron now drive 2 and 4wd drive any noise ?
you probably have noise and its comming from the middle of the rig.on #2 leave shaft out of the front , jack it up and run the rear wheels listen carefully as you let off the gas or coast , now head for the noise , you can use a piece of rubber hose to your ear to isolate it (like a stethascope). My guess based upon what you have said is transfer case chain slap on decell.

PS good luck hope you find it !!!

[Jdub76]

it's probably not the rear end unless the pattern is off on the coast side only, you said you jacked it up and it sounded normal , I would do the following,
1. remove rear shaft and drive in 4wd any noise ?
2.replace rear shaft and remove fron now drive 2 and 4wd drive any noise ?
you probably have noise and its comming from the middle of the rig.on #2 leave shaft out of the front , jack it up and run the rear wheels listen carefully as you let off the gas or coast , now head for the noise , you can use a piece of rubber hose to your ear to isolate it (like a stethascope). My guess based upon what you have said is transfer case chain slap on decell.



Everything went good today. A friend of mine stopped over while i was under the XJ. He is a retired Engineer from the Chrysler Plant here in Ohio. He took a real good look at the Gears and said that look great!

And after putting the HD Lucas Gear Oil in, It is MUCH Quieter. If I do need to work on the Transfer Case, do you recommend buying a Rebulit one, Or an Upgraded Case?

Or just my current NP 241 rebulit?

But on a whole new note my friend seems to think I just have Drive line Vibration & Noise due to lifting the Jeep???? any thoughts on this?

[Mudderoy]

Everything went good today. A friend of mine stopped over while i was under the XJ. He is a retired Engineer from the Chrysler Plant here in Ohio. He took a real good look at the Gears and said that look great!

And after putting the HD Lucas Gear Oil in, It is MUCH Quieter. If I do need to work on the Transfer Case, do you recommend buying a Rebulit one, Or an Upgraded Case?

Or just my current NP 241 rebulit?

But on a whole new note my friend seems to think I just have Drive line Vibration & Noise due to lifting the Jeep???? any thoughts on this?

Well it wouldn't hurt to check the angle of the drive line, however with a 3" lift a transfer case drop shouldn't be necessary.

[4.3LXJ]

There is an article in the tech section on how to set up driveline angles. You might want to check them. The angles need to be within 4° or you will get a vibration. What could be happening is that you are close to having a vibration under acceleration, but the spring is flexing a little allowing the pinion to go up enough to not vibrate, but under deceleration it flexes just enough to drop the pinion and get a little vibration. But you won't know until you check those angles.

[Jdub76]

Well I guess it could be a u-joint. Best thing to do would be to get under there and twist the drive shaft by hand and see if you have any play. Get a flashlight so you can look at the u-joint carefully.

https://lh5.googleusercontent.com/-8LVeQlDFaWI/TnwRLjdWtwI/AAAAAAAABP0/AGNKREglfFU/s1024/2011-09-22%252022.20.49.jpg

Well here is an Update on this Problem. :happy:

First of all you were Right Tony!!! Bad U-Joints were the source of the sounds I was hearing.

Even tho I had no play in u-joint, they still needed replaced. I gusses you cant always tell by checking them for play.

I went with the Gold Seal (http://www.4xshaft.com/GoldSeal.html) U-Joints...

I took her up to 90 MPH and NO Vibration, Humming, Knocking, Clunking or anything from the Rear... Now to do the front of the Jeep!

Thanks So much xjtalk :thanx: