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MG MGB Technical - Rear end rebuild

Hey all,
I just finished installing the Doug Jackson composite leaf spring/anti tramp bar kit, with really good results. Love the way it rides and handles.

While working on the back half I decided to take a crack at curing my MGB's axle clunk. Note: the driveshaft and u-joints were checked first to ensure they were not the source of the clunk. The flange off the pinion would not move in/out or up/down, but when rotated had a bit of play before it would begin to spin the wheels.

So I did the thrust washers (thanks to some help from the archives it was a snap), but the clunk/clank is still there.

I've had a pinion bearing fail on me before and take out the whole rear end in my B GT, so I'm thinking about going in and redoing the pinion bearings.

First of all can this be done?

Secondly since it uses a crushable collar how do you set it up without buying a multiple collars?

Lastly there doesn't appear to be any shims on the pinion side of things, do all the adjustments come from changing the thickness of the distance collar on the ring gear assembly?

Hopefully I can make this work as I really don't want to track down another wire wheel axle.

-Bill
Bill Mertz

The crushable spacer is just that, it crushes to the required size. This is done by tightening the pinion nut a little at a time and then checking with an inch pound torque wrench to the required pressure needed to rotate the pinion. The pinion will require shimming to get it to ride in the correct position on the ring gear, if yours had no shims it just happend to come out not needing them. The backlash won't likely change unless you replace the bearings holding the the ring gear carrier assembly. The backlash is adjusted by shims between the carrier and its bearings to locate the crown wheel for the correct backlash. Once set correctly it is typical to add a couple thousand's to each side for preload.
John H

John,
The reason I didn't think my pinion had shims was that I didn't seem the part listed in the shop manual or on the moss website. Is there a good source for the pinion and carrier bearing shims?
Moss sells distance collars in different thicknesses for the carrier bearing but I didn't see shims.

Also how do you determine the shim thickness for the pinion? It seems like you would have to test assemble everything a few times to get it right, but that would mean crushing the crush sleeve?

Maybe I should just take it to a professional shop.

-Bill
Bill Mertz

I think they call it a pinion thrust washer. See #75 p. 49. There are about 5 different thicknesses. I'm surprised you didn't have one. It looks like the side bearing distance collars are N/A.

If possible I'd farm this out to a shop. They can make shims or have them in stock. Bearings and seals are no problem. Of course none of the MG specific tooling will be available but they can work around that.

I rebuilt a tube-type differential on a 67 Mustang. I had to make shims, the collapsible spacer was not available so I used shims to crush it more to meet preload requirements. I also had to make differential gear thrust washers as the old one were pounded into pieces and also not available. The design of this axle did not require a case stretcher. I used Prussian blue to check the gear tooth contact and a dial indicator for backlash. It came out pretty good. Just a little gear noise on coast. There was still some slop in the axles because the splines on the axle and differential had wear.

BTW, I you can check backlash and gear mesh without destroying the collapsible spacer. Just torque it down a little to pull the pinion and bearing into correct position. At the end torque while checking preload. At that point the spacer cannot be reused.
Robert McCoy

Yes you may have to assemble/disassemble several times to get the spacing correct. Assemble the pinion without the collapsible spacer and just snug up the pinion nut, this will hold the pinion and bearings in the correct position to check the gear mesh.
John H

Yeah this may be over my head. I've done a few Alfa diffs, but they were a bit easier as the diff case splits open for easy access to the pinion and carrier.
Just talked to a local gear shop and they said they completely refurbish MGB rearends for $425 plus parts.
Unless a wire wheel axle pops up locally for a lot less I'll probably take it in for a full overhaul and call it a day.
-Bill
Bill Mertz

Bill, We have done a LOT with the B,C,V-8 rear & thay are heavy duty for that 4 banger & hold up O.K.,Good with the V-8, if you are not a kid & drop the clutch to see the tire smoke. I have 425,000 miles on one V-8 3.07 & 300,000+ on 3 other M.G.s & all that has been changed is the axel bearings, the V-8 wear them out every 100,000 miles when you pull a trailer that is 2,000 to 2,500 lbs every weekend going to M.G. car showes. There is a lot of bearing on the pin. shaft & carrier & the only way you will have problems hear is if you run it low on oil or never change it. Were I would look is the brass thrust washers at each end of the spider gears, thay wear! I have seen the pin shaft that goes through the spider gears egg shap the carrier & make the clunk. I use the brass or stainless steel thrust washers, not the fiber, card board junk that was O/E. A good speed shop will have them in there pile of parts thay have gotten over the years, for I think it is used in a chev. rear. I had a 4.8 V-8 with a T-56, 6 spd. with 215/60/15 on a STOCK 3.9 rear, wouid turn a 13 sec. 1/4 mile@ 103 mph & put 100,000 miles on her & then it got real hot! The paint shop burned down on it 3 years ago.
Glenn Towery

Bill- I think Glen has the word,and you could reset the 4 thrust washers. When I did the 71 splittail, I reused the remainder of the top copper spider thrust lapped in to the top of the new one. It was tight and the clunkectomy was 100% successful-all gone: no whine, no clunk on go or backup. The last one, on the 77 SC car, had eaten both spiders' copper thrust and the fiber sides and the oil was kinda like a jam. I doubled the side thrust this time as the spiders were quite intimate after, and flushed the case and went back with 70-140 synthetic. It too is now a quite puppy. For the 2 hours, you may just save that $425 . Luck Vic

PS- Bill- I used to live on 47th in Oakland. Fun time. I bought the 71 in 1970 off the floor in Alameda for $1900. Oh what a feeling- close to 1 million miles in 38 years!
vem myers

You can reuse a collasaple collar over if you mic it's length then, using a ballpeen hammer, lightly tap against it's center while resting the collar on a vise or anvil. While tapping, rotate the collar, perodically rechecking the length of the collar until it's length has increased by .030".RAY
RAY

Many years ago I had a B come in with a horrible "ping" sort of noise every time you went on & off the throttle. Tried everything until I removed the pinion & put a few drops of loctite on the spline - hey presto. noise was gone. It was the flange moving just the few thou clearance & echoing back through the drive shaft because with the collapsable spacer the flange is not locked onto the pinion. This problem has occured many times since & usually only happens with the later cars with a rear sway bar or anti tramp rods fitted.
Garth
Garth Bagnall

This thread was discussed between 09/07/2008 and 19/07/2008

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