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MG MGB Technical - OD Tranny rear seal leaking

I recently put an overdrive transmission in my '69 BGT. I did the front seal and gasket but forgot to do the rear, so naturally it leaked out the back and blew all over my exhaust at freeway speeds. I just popped in a new rear seal with the gearbox in the car. It went in pretty straight forward with no big issues. I drove to work today and oil was still dripping from the rearmost (non-removeable) cross member, and there was a bit of oil on the exhaust. It was probably about half as much as before I did the seal, but still a decent and annoying leak. Any ideas on how I can further reduce it. I haven't crawled back under yet, but my suspicion is that the rear flange might be scored on the seal surface. I though about pulling it back off and seeing if I could smear a smooth bead of rtv around the sealing surface of the flange, but it seems like it would be too difficult to make a smooth bead.

I'm open to suggestions.

thanks

-Bill
Bill Mertz

Just started looking into Speedi-Sleeves as a possible solution for the long term, but anyone have a short term fix in the mean time?

-Bill
Bill Mertz

Hi Bill. There is a breather on the top of the overdrive make sure it is clear. I have never seen a drive flange so badly worn that a modern oil seal can not seal. Did you polish off any build up of gunge? You could also try installing another new seal but don"t drive it all the way in, about 1/8 of an inch protruding, the seal can then run on an unworn surface. Regards Jim
jim soutar

Good ideas Jim.
I'll take a look at the breather, although it's probably a bear with the gearbox in the car. The seal idea is also a good one. I may order up a second seal just in case the breather isn't plugged up.

-Bill
Bill Mertz

Just get the speedi sleeve. They are sold by size at most any auto parts house. There is nothing special needed just because it for an MG.
J Heisenfeldt

Yeah i just found a shop that has them and I'm going to pick one up. But I think I'll go after the vent as well.
Is the vent on standard and O/D trannies in the same spot?

Also the Speedi Sleeve I ordered is Part #99168 from Chicago Rawhide. I'll verify fitment once I get it tomorrow.

-Bill
Bill Mertz

Bill,

You might check to ensure that this oil is not 'old' oil spill remains just working ther way down. Also check that the OD is not leaking at the service plates or from the speedo takeoff.

When I did my rear box seal it was on the bench, but I do remember it took some work to get the seal properly inserted, with its end matched to the flange lip. is it possible you might have under/over pressed the seal?

Good luck, at least it is a seal that we can get to - even if it does mean taping our glasses to our foreheads to manage the task!!

regards
Roger
Roger T

It's the gearbox that has the breather (immediately in front of the extension that carries the gear lever), the OD when fitted vents through that. FWIW it's the same part as for the tube axle.
Paul Hunt

Got at the breather with an allen wrench and dental pick to clear any unseen blockage.

I also installed the speedi-sleeve. Just for future reference Part #99168 from Chicago Rawhide was the correct part and fit perfectly. I've since reinstalled and only driven about 20 miles. I haven't had a chance to get the car in the air yet, but the leak has certainly been minimized at least (possibly fixed but can't confirm).

It is possible that I pushed the seal in too far. I pushed it in until it was flush with the surrounding aluminum case. Is it supposed to protrude slightly?

Just in case I ordered a second seal from Moss that I can throw in tonight if need be (event starts early tomorrow.)

cheers,

-Bill
Bill Mertz

No Bill, from your description you probably have it in correctly.
Regards
Roger
Roger T

Don't you slide the speedi-sleeve over the flange and then fit the flange to the gearbox output shaft?
Paul Hunt

Paul,
That is how the speedi-sleeve works. And I'm happy to report after 800 miles of really hard driving on twisty back roads this weekend, the speedi-sleeve did its job and the leak is no longer.

Unfortunately my overdrive is having an issue when it gets hot where it engages on its own off throttle. But I'll save that for another thread.

-Bill
Bill Mertz

Is it engaging OD or moving between normal drive and slipping? If it is pulsing then it can be difficult to tell which of the two is happening.
Paul Hunt

Hmmm,

Paul I'm not sure. When engaged in overdrive it performs flawlessly in both third and fourth gear. But when the outside temp got really hot and we had been driving the car for awhile (so the component temps were up as well) in 3rd and 4th gear the revs would drop about 500 rpm when off throttle and not in overdrive. It may have even happened in second gear once or twice. As soon as you got back on the gas it would engage back into the proper gear. This made engine breaking problematic. It really felt to me like it was engaging overdrive, not slipping, but I couldn't be sure. I did check the fluid level multiple times and topped it up. And the problem was totally gone when I drove in cooler temperatures along the coast, still wailing on the car.
Bill Mertz

This thread was discussed between 03/09/2008 and 10/09/2008

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