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MG MGB Technical - Help with rear end - MGB

I need the collective wisdom of this group. The rear end in my 1974 MGB GT has the dreaded clunk and all of the drive line has been replaced and the wire wheels are not the problem. I have ordered all of the bits required to re-shim the gears and I have a replacement rear end to work on prior to installation in the car. I have also reviewed all of the material available on the Internet, including a rebuild done by the Chicago MG Club. A 2 hour job!!!

The problem I am having is removing the "planetary gear shaft". The roll pin is out but I have been unable to get the shaft to move in either direction more than about 1/16 of an inch. I am trying t drive it out but don't want to hit it too hard in case I am missing something.

Can anyone shed any light on how to remove this shaft??

Brian
Brian Smith

Brian,

Just what you DIDN’T want for an initial responder, something less than good news.

I had the exact same problem with one that I was trying rebuild before putting in my car. The roll pin was out but I could not get the shaft to move in either direction. Seem to recall someone saying that this job could be done in the car and was thinking to myself, while getting larger and larger hammers and working off a set of jack stands, there is no way that I would want to try and do this in the car. I eventually ended up pulling the axles out of the unit and turned the carrier, with shaft and gear still in place, to a machine shop to try and remove it(the shaft). I figured I could use the same carrier bearings and shim in their original position when I got it back from the machine shop so as to not worry about setting the ring/pinion interface set up. It was not pretty to get apart and DEFINITELY could NOT have been done in the car!!! Actually considered the unit to be completely wasted/trash because there was nothing left of the shims and the gears had worn into the carrier such that it was not a smooth interface anymore. The problem is that the shaft has a ridge on it that was caused by the gears. This ridge is what is preventing you from being able to slide the shaft in either direction. You might try and turn the shaft, if possible, or may be move the gears around while someone tries to drift the shaft out. Hopefully, you will have better luck than I and not end up with a housing that is pretty much scrap due to excessive wear. I found another unit and rebuilt it before even trying it in the car and that one may have been done in the car. It came apart very easily and probably wouldn’t have given the familiar “CLUNK” but thought it better to go through the unit before installing it in the car.

HTH

Fred
Fred Wright

Ditto, although I was practising on an old axle out for the car so didn't have the mass of the car to lever against. OTOH you wouldn't want to pull the car off stands! In my case the shaft started moving easy enough but then got tighter and tighter. I removed the diff cage bearing caps and lifted the whole thing out, then drifted the shaft out on the bench. The books say you have to use an axle-case stretcher, but that is probably when fitting new bearings. If you do this be careful to get the caps back on the right sides and the right way round. The pinion and its bearing and spacer aren't touched.
Paul Hunt

I must have been lucky for I did it with the axle in the car. It was tricky but not the most difficult thing I have done on the MGB. I don't recall it being especially difficult to move the shaft. I had the fuel tank out anyway which gave easier access.
Mike Howlett

I don't remember having any particular problems either but then I also had the diff off the car. That definitely makes it easier!
Simon Jansen

I've been able to do this on both my cars, in situ, and seem to remember the shaft came out easier one way than the other. I have a vague recollection of putting something through the roll pin hole to pull it rather than push once it had moved a bit and I wouldn't spare the hammer; it's a good solid bit of metal.
Steve Postins

All of which makes me thankful that my cars mostly have the lighter banjo axle that will never have this problem (except the MGC, about which I shal cross my fingers).

Good luck with it, Brian.
Bill Spohn

Thanks Guys, everything I have read about this job is that it should easily tap out! The rear end that I am working on is on the floor in my workshop and I resorted to removing the whole cage as the shaft will just not move. The roll pin is definately not in there and the shaft is locked solid. I will take it to a shop on Friday and have it pressed out and hopefully be able to report what is wrong. I am just glad that I didn't disable the "BGT" to do this job as it is supposed to be a 2 hour job if the shaft comes out easily but sometimes everything doesn't go quite as well. I am still driving the car and have the luxury of working in a dry shop with good lighting while I get this figured out.

Bill, good to hear from you, its been a few years! I am working with Mike Zbarsky and hope to have him out at the end of the month to tell our local club about vintage racing in an mga twin cam!

Brian
Brian Smith

"everything I have read about this job is that it should easily tap out!"

BTW it definitely *won't* tap out all the way with the diff unit in the casing, it has to be pulled out once you have tapped *a small amount* enough to get a grip on it. If you tap it too far it fouls the casing when you try to turn the diff cage, and then you *have* to remove the diff from the case.
Paul Hunt

Paul

I would have been happy to get it to move even a 1/16th of an inch. For some reason the shaft is locked in there solidly. I agree that you should only tap it far enough to get something in the roll pin hole and then pull it out, all of the articles are pretty clear about that. My hope now is that the shop can get it apart without doing any damage and that there is not too much wear to reuse the gears. Hopefully tomorrow will tell the tail.

Brian
Brian Smith

Took the gear set to the machine shop and they advised today that the pinion pin had actually turned and had jammed in the two smaller gears. They told me I could have pounded on it all day and not had it move, it required a great deal of pressure from a hydraulic press. Can't pick it up until Friday so don't know what shape the parts are in but at least it is now apart and I can start putting it back together ( probably with a lot more new parts than I had originally planned).

Brian
Brian Smith

Picked up the gear set today and what a mess. The pin had spun in the gears and "welded" itself to the two small gears. From the looks I would guess that the rear end had been run with no oil. One of the small gears fell into two pieces and the other is so marked up that it is unusable, as is the pin. The large ring gear and the two gears that slide onto the axles appear to be fine. The rear end was free, machine shop $40. I think that I will actually check the one currently in the car and rebuild it in place as the parts neede to replace those that are ruined will be more than it is worth.

Brian
Brian Smith

This thread was discussed between 11/11/2008 and 21/11/2008

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