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MG MGB Technical - A wheel bearing lesson please

79 MGB-LE
What are the symptoms of a rear wheel bearing being/going bad? I’ve been chasing a clunk…clunk…clunk for over 2 months (it starts at about 30 mph and is continuous, every 5 to 8 seconds, until I slow below 30, then stops—no change when shifting or breaking; same rhythm continuous sound at 40 or 60 no change). I have replaced motor mounts, trans mount, checked the u-joints, checked the main shaft nut, checked all the shock/spring attachment points, and I now have the half shafts out and the differential cover off, awaiting new thrust washers from Moss…however I feel no slop in the gears, and I think I understand that thrust washer clunk only happens when shifting/change in speed. One friend said that sounds like a wheel bearing may be going out…same friend that had me changing/checking the other components. SO, what are the symptoms of a bad bearing?
Joe Walck

I had a rear bearing problem a few years back - not in an MGB but a front wheel drive car. Symptoms were an intermittent low "growl"coming from the back somewhere. testing showed that it usually occurred on cornering hard (ie more than parking speed) and usually with some weight in the back seats.
I tightened the bearings a little and checked if any change. This fixed the problem but I guess i caught things before they became irreversible. I don't recall any clunking at all.

Have you checked wheels and tyres for any problems?

John
John Minchin

My experience of bearing failure is a moaning sound. You can provoke it by swerving so as to load that wheel.
Art Pearse

This sound is on a straight road/freeway, steering/turning into a curve doesn't change it...slowing down to make a L or R, turn the noise stops (because I'm under 30 mph again). It doesn't sound like I have a bearing problem.
Joe Walck

Is the prop shaft touching something? Although one would expect this at all reves? Are you sure it is coming from rear of car, not front discs out of true? Mike
J.M. Doust

Worn bearing would be a growl IMHO. If the noise is every 5 - 8 seconds at whatever speed above 30, it surely cannot be related to something revolving unless it is winding something up that then lets go with a clunk? But what I can't think!
Michael Beswick

"5 - 8 seconds at whatever speed above 30, it surely cannot be related to something revolving " etc.

My thoughts exactly. Do you have OD? Does that make a difference in or out? You don't mention gears, is 40 in 3rd different to 40 in 4th?

Other than that I'd consider supporting the rear of the car wheels off the ground SAFELY AND SECURELY, then running the wheels at 30+ and see if you can locate the source of the sound from outside the car. DON'T position any part of your body under the car or in front of the rear wheels while doing this. Try using a length of pipe poked under the car AS AN 'ear trumpet' to locate the sound more precisely.
PaulH Solihull

No overdrive. I usually notice the sound when I'm in 4th, but it may start in 3rd, but engine/wind noise masks it...I didn't notice it when I purchased it, but the DPO test drove it with me, top down...I didn't notice it until I put the top up about 200 miles into my trip home. I figured the broken engine mounts were causing it to happen.
I moved the tires from front to rear, sound stayed in rear. I thought the drive shaft might be hitting something, and with broken engine mounts that was my first thought and attempted fix...no change.
As soon as I change out the rear thrust washers I will test drive again and let you know results.
I would/will try the ear trumpet, but was afraid to start the car on jack stands and get wheels spinning to 30+...
Joe Walck

Update-
When I removed the differential pinion, one of the thrust (cupped copper/brass)washers was missing-giving me a little slop in the one of the pinion gears. The 2 thrust washers(flat ones) on the differential gear looked okay, but I'd ordered a set anyway...better safe than sorry. Waiting for the parts postman now...
BTW there is a very good video of the thrust washer change out on youtube: "MGB Differential Repair Part 1 & 2"
http://youtu.be/9cFanj0iSMA It gave me the confidence to try it by myself...so far, so good!
Joe Walck

The noise was still there after reassembling the rear end.
I ordered a wheel bearing for the RH rear, and after changing it out...THE NOISE IS GONE!!! Thank goodness, my next idea was a bad driveshaft...
I sure learned alot during this evolution!
Joe Walck

Joe, thanks for the update and well done tracking it down.
As said by others, the wheel bearing is the last part I would have expected! Just goes to prove the saying "if you've replaced all the likely sources, whatever is left, no matter how unlikely, must be the problem".
I'm just pleased you found it before changing the wheels, the suspension, the shell, the hood, the lights... or the whole car...LOL

Now go enjoy..

MGmike
M McAndrew

...now to check on those other two thumps/clunks my wife told me she heard yesterday.....SMILE!

Joe Walck

"I'm just pleased you found it before changing the wheels ..."

Reminds me of the restoration advice

"Step 1: Raise car by radiator cap, rotate everything suspended from it one quarter turn clockwise, discard and replace.

Step 2: Buy a new radiator cap."
PaulH Solihull

This thread was discussed between 16/10/2011 and 11/11/2011

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