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MG MGB Technical - 'Clunky' Rear-end
|I have a 1970 MGB that has a real clunk in the differential. I have talked with a ,proportedly, very good mechanic on old Brit cars. He tells me (without inspection) that my car has a Banjo type rear end. I have looked at it and the illustrations in Moss and it looks like a tube type rear end.|
Moss holds that it is a "fairly easy and in expensive" process to replace the thrust washers. The mechanic says it takes special tools to do this proceedure and he does not have them.His suggestion, replace the rear end.
My concern is, how do you know if you are getting a used rear end that is any better than the old one and where in the heck do you find another.
Any suggestions, comfort or information would be appreciated. I am a fairly good mechanic but really reluctant to tear into the differential,
|I'm a very amateur mechanic by the standands of this board, but can tell you that changing the thrust washers in the tube diff (standard cause of clunk) takes me a long afternoon. Nothing tricky if you follow the excellent instructions that are in the archives. Parts cost next to nothing. A 1970 certainly should be tube (Salisbury) axle. There are lots of items archived about diagnosing the source clunk before setting about it.|
|I just replaced the thrust washers in my differential, with the axles still in place. No fancy tools - just a socket set, a big hammer, and a little patience. I have an extra pair of the thrust washers too, so email me if you plan to replace yours.|
|Your mechanic offering to replace the rear end at your cost, I presume? As others have said just not needed, see this for a step-by-step: http://www.mgcars.org.uk/cgi-bin/gen5?runprog=mgoc&a=&p=emg/emg010302.html|
|Steve is right -- replacing the thrust washers|
is an afternoon's job (but watch out for the
crownwheel teeth, they are very sharp.) Lindsay
Porter's mgb restoration book has good pictures of
However, after replacing the copper and fiber
washers about 10 thousand miles ago, my B's clunk
seems to have returned to its old self. Check the
archives, as others have had the same problem,
and a suggestion was made to double up the
Also double check other sources of the clunk
,including u-joints, loose u-bolts and broken
shock links. (I had a broken shock link that
was only evident on jacking the car up.)
|Hi John. I assume you talked with Don. Don't give up -- he's a good Brit-car mechanic. Call Don and tell him that you have the tube-type axle. No special tools are required to replace the washer sets-- it's just a laborious process. I just did this on my '72 bgt restoration project.|
|If the plate on the rear of the differential is bolted on then you have the tube type. As was said a good afternoon with the car jacked up in the rear all you do is drain it ,pill off the rear palte and then follow the easy directions to replace the shims. It does not take a rocket scientist to do this . It is just common sense. Do not get talked int a big and unnecessary tab for this simple job.Make certain you have the shims , gasket and oil on hand.|
|And a new roll pin.|
|As one or two others have alluded to, a 1970 car would not have had a Banjo axle when new. It should have the later tube type Salisbury diff. Fitting the washers is an OK job so long as you are careful and think about what you are doing. The kit should not cost more than about 10 dollars.|
|And diagnosing a rear end clunk sight unseen is a neat trick. Years ago, the clunk in my 72 bgt resulted from rear bearings in the driveshaft that were toast. Safely support the car on jackstands and have a look see. Also verry common.|
You can also replace these bearings yourself if you are handy. I did it on an emergency basis with inadequate tools and a BFH in lieu of a vice. Fortunately I had an ample supply and assortment of swear words on hand to manage it.
|If, under hard acceleration, I completely let off the pedal I get a knock from under the car. And, immediately after, if I return to the pedal I get the same knock. I don't tend to hear this under normal driving... just the occassional heavy foot.|
Would this be a symptom for the same problem?
Jack up the rear and support the car safely. Get underneath and turn the drive shaft with your hand. There should be very little free play before it starts trying to turn the back wheels. If there is a lot of play (mine had about a quarter of a turn) make sure it is not the two universal couplings, one at each end of the shaft that are worn. If they are OK, it is in the diff and the thrust washer job is definitely worth doing.
On the other hand it could be loose bolts in the rear suspension, so check them while you are under there. Then again, it could be much more simple, like the exhaust banging on the floor. Plenty to keep you busy.
Do you have wire wheels? If so, bad splines can make a lot of clunking. Charley
|C R Huff|
|Is thrust washer wear occasionally accompanied by a speed sensitive vibration? The vibration comes in around 60mph and is gone by 70mph. It started all of a sudden and is possibly a wheel balance issue, but I've since noticed a power on / power off clunk felt through the gear lever. I wonder if they're related? The u-joints are okay, I checked.|
|Even when mine was really bad there was no symptom except the clunk. Certainly no noticeable vibration.|
|Obviously, check the for loose items next to your spare tire as a source of clunk as well. I have a block of wood in the boot(long story why its there) that likes to shift upon acceleration and deceleration that produces a nice clunk noise. If you have wire wheels, jack up each wheel, have someone apply the brake, and see if you can rotate the wheel one way or the other, could be a source of a clunk as well.|
|Posted 08 January 2004 at 11:27:52 UK time |
I changed the diff. thrusts quite successfully in an hour or so and found I only needed to ease the (near side) half shaft bearing about two-thirds out of its housing on the axle tube outer end. This can be done without resorting to violence by using a pair of bolts on two diagonal shaft flange holes with washers and nuts arranged to bear on the axle tube end. This allowed me to draw the bearing and shaft part way out until enough space was obtained at the inside end to lift the diff gears out. It is then an easier matter to simply tap the bearing back home rather than remove the shaft...unless you need to of course.
Re: "...a speed sensitive vibration? The vibration comes in around 60mph and is gone by 70mph."
A clonk plus a speed sensitive vibration are classic signs of a bad u-joint. And in fact, those are about the speeds my car vibrated when the spline in my driveshaft wore out. I know you said you've checked them, but I'd take the trouble to take the shaft completely out of the car and check again very carefully. While you're there, check the splines. There should be no radial play.
Granted, this could be something else, like a loose wire wheel spline coupled with a tire out of balance. But if I were in El Paso, I'd bet a free lunch you've got a u-joint on the way out.
If you were in El Paso you would owe me a lunch because I replaced the U-joints first and that didn't fix the problem.
This thread was discussed between 31/10/2004 and 13/11/2004
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