Rhythmic Rear End Noise

Post by **ARCHINSTL** » Mon Apr 17, 2006 1:14 am

OK - please bear with me...
The car has developed a rhythmic, almost knocking, barely-audible sound from the rear axle and/or driveshaft. This is also barely detectable tactilely while putting a hand on the driveshaft tunnel. It is present while under load or while coasting and whether in FWD or 4WD in straight-ahead driving. The frequency increases with speed. There is no shaking or juddering at any speed.

The rear end is full of lube. When the axle is lifted, the wheels can be rotated/shaken with nothing noteworthy happening. The braking is steady, with no funny noises.

This is gonna seem naive - but here goes: I thought about disconnecting the driveshaft at the axle and suspending/anchoring it to see if the noise disappears (FWD operation only). Or - should I pull the drums and check them first, even though nothing appears wrong?

Has this happened to anyone else? Universals or center bearing? Worrisome, or just do the other already-planned stuff first (struts-mounts-CV axles)?
The 6-speed car has 171K miles, and probably has never been "off-road."
Thanks to all.
Tom M.

takza · Post by **takza** » Mon Apr 17, 2006 4:09 am

I'd take a look at the drum brakes in the back...also check the rear wheels/bearings for play?

Post by **Mattel** » Mon Apr 17, 2006 5:48 am

I Had exactly the same trouble with mine, check this thread and see if if helps..

I still goto fix mine though.. haven't been driving much lately though

good luck with it

viewtopic.php?p=13122#13122

still check your bearings anyway

Matt

Post by **ARCHINSTL** » Mon Apr 17, 2006 10:00 am

Thanks for the answers.
I feel sheepish for missing the earlier thread.
When I get home this week, I will check, in order, the tightness of assorted fasteners, the wheels, drums, bearings - and then the shaft. I will add to the literature.
It appears that the U-joints are not replaceable, per the AZ site.
Tom M.

shogun · Post by **shogun** » Mon Apr 17, 2006 10:26 am

if its bearings dont let them get too loose, i once lost all braking capacity because of bearing play, it mooved too much so it came apart inside the drum

MootsMan · Post by **MootsMan** » Mon Apr 17, 2006 10:32 pm

Arch,

Both of my rear axles are out right now, already have the new bearings and seals installed on the axles. I was hearing the same type noise you mentioned, it would gradually pick up in speed as the speed of the vehicle increased, until it was just a loud roar. I parked on a side-to-side incline at the junk yard last week, and when I got back to the car, there was a puddle of gear oil around the left rear wheel. Left axle bearing was shot, so I decided to do the right one as well.....going to do the rear brakes while I have the drums off, too. Hope to get it all back together in the next couple of days.

Keep us posted !

MM

Post by **ARCHINSTL** » Tue Apr 18, 2006 12:40 am

MM -
OK - apart from the noise - did the wheel assembly feel loose or ? when you moved it? When the wheel was removed, did the drum move around/feel loose horizontally or radially? Would it compare to loose axle cones on a conventional bike hub?

The AZ site refers to special tools/press to install the bearings - dunno about the FSM, as I am not home right now. In fact, the AZ site recommends taking the axles to a machine shop for installation - is this what you encountered as well?

What was your source for the bearings and seals? Big bucks?

THANKS...
Tom M.
P.S. Went to the Bike Pedlar, et al, sites the other night - very impressive sites and stores!

MootsMan · Post by **MootsMan** » Tue Apr 18, 2006 8:39 am

I didn't really notice much sloppiness before I took the drum off, but once I got the axle shaft loose, there was some play in it.

I ordered the bearings and seals from a local parts store. They also have a machine shop, so I had them install the bearings on the axles for me as well. Altogether, parts ( bearings and seals ) and installation of the bearings on the shafts was a little over $100. I think the bearings themselves were around $35/ea.

Hope to get it all back together today !

It's a pretty cool store to work at. The running joke among the employees is that when any one of us puts our bike on top of our car, it quadruples the value of it...

Typrus · Post by **Typrus** » Tue Apr 18, 2006 10:38 am

Also check your carrier bearing.
Grab the driveshaft and push/pull it to try and move it. If it has significant back/forth movement, loook at the center bearing thing. Its the carrier bearing. If it is the source of the movement, it is shot.
As long as you are moving forward, the axle is rotating. It free-spins inside the transfer case. So, if it is rotating and the carrier bearing is shot, it can let out a low rumbling and vibration.

Fingers · Post by **Fingers** » Tue Apr 18, 2006 3:07 pm

Don't forget to check the center support bearing. My bearing was fine, but the rubber around it was worn and it caused a similar problem.

As far as replacement of the rear bearings, if you do replace them, take the axels out and bring them and the bearings to any machine shop to have them done. I used St Louis Auto Parts on Gravois, I took the old bearings off (cutoff tool and a chisel and big hammer) and I think they charged like 15 a piece to press the new ones on. Any shop could do it though, I just like using those guys.

Fingers

Post by **ARCHINSTL** » Tue Apr 18, 2006 3:20 pm

Thanks for the words on the center bearing, guys. I had wondered about that as well.
And Fingers - really Thanks on the local outfit. Nice to know who has some experience in the area for the right settings/positionings.
I will certainly post my results to help the next person.
Tom M.

Soutthpaw · Post by **Soutthpaw** » Tue Apr 18, 2006 6:51 pm

That seems like a driveshaft problem, either u joint, carrier or bent driveshaft or you may have lost a balancing weight off the driveshaft. Wheel and Diff bearings usually will be a constant noise, vibration. Check your diff fluid and make sure you are not using Hersheys Syrup in there (means you got water in the diff)

Post by **ARCHINSTL** » Wed Apr 19, 2006 12:37 am

WELL......
I pulled the drums - and discovered two leaky cylinders and shoes worn to 1mm+... So - I'm doing a brake job on the rear.

The axles do not move in and out or up and down, so I am presuming for now that the bearings are OK. Also, there is no indication of fluid having leaked past the bearings. The diff fluid is OK.

However - I can move the intermediate (front) drive shaft up and down (and horizontally) almost 1/4" in the center bearing, and the rubber mount looks pretty perished; it is intact, but has a lot of cracks and seems soft. So - I presume this is the origin of the noise. Any thoughts on this diagnosis?

I will have to wait a bit for the center bearing replacement, as this brake work was not anticipated - I presume the rubber cannot be replaced separately - at least it appears so in the wonderful FSM. I presume this replacement will not be an "A" item ? ? ? Other than being an annoying sound ? ? ?

Thanks to all - will post a followup.
Tom M.

takza · Post by **takza** » Wed Apr 19, 2006 3:01 am

Sounds like my center bearing...all I get is some rumble from it when going into 4WD at speed now and then. I'm leaving mine alone...ain't broke....don't fix.

My guess is that the noise will be gone once the brakes are done...but maybe not.........

Typrus · Post by **Typrus** » Wed Apr 19, 2006 10:10 am

Sounds shot.
I'd do mine if it weren't for the price... Guess I've just grown tone-deaf to the rumble.