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MG MGA - Gear box oil leaks

So, I now have the gearbox out of my car and for many years it parks in my garage with an oil drip pan underneath it collecting pools of oil...leaks. If you had your gearbox out with this symptom what would you replace to stop the oil drips and leaks?

Steve
Stephen Lofaro

Front and rear seals! No other places to leak except the rear section joint in the case and the side inspection cover and you will renew these gaskets. On mine I had to have the rear sleeve polished as the seal had worn the face.
Of course, the oil on your floor is probably from the enginge side, behind the flywheel.
Art Pearse

The speedometer drive is below oil level in the tail housing. It has a small (5/16" ID oil seal that may need to be replaced. When this seal fails it can run oil all the way up the speedo drive cable an into the back of the instrument. If the cable jacket is not liquid tight it can leak oil on the ground. A new seal should fix that, but do drain the oil from the gearbox before removing the speedo drive.
Barney Gaylord

Art et al.,

I found one of the bolts missing on the housing for the remote lever on the rear gear box extension. There are two short bolts and two long bolts that secure the housing to the gearbox. I am wondering if this could be a cause of a leak into to the tunnel over the gearbox?

Steve

Stephen Lofaro

Have you got the later type of gearbox with a proper lip oil seal on the input shaft ?

Andy
A J Dee

I am not sure if I have a 'later type gear box'. Also, I am not sure what you mean by the 'input shaft'? I will be replacing the standard gasket kit...front cover, side plate, rear extension, and the gaskets on the remote lever housing. My big question is about the special seal on the rear of the gearbox to the shaft into the propeller, expensive seal of rubber, steel, felt combination about $75.00. Just wondering if that one is usually a problem?

Steve
Stephen Lofaro

There were five different gearboxes used in the MGA. See here: http://mgaguru.com/mgtech/gearbox/gt101.htm
Early 1500 production used an external rear seal, quite expensive as a replacement part today.

Late production 1600-MK-II gearbox changed the front cover to use a rubber lip seal (where earlier units had a mechanical scroll seal). A substantial number of the earlier gearboxes may have been converted to the later front cover with rubber seal.
Barney Gaylord

By input shaft I mean the first motion shaft, ie the one that goes into the clutch plate. The front cover, as described by Barney, is where this shaft goes into the gearbox. I have a spare MkII front cover if interested.
Andy
A J Dee

Barney et alia,

I have a mid 1500 gearbox from what I see and it takes an expensive ($75.00) part to replace my rear seal. I don't know if they are the same seals as in the early gearbox or not. But what I am really curious to know is why there has been so much oil built up on my gearbox? I had the motor and gearbox rebuilt the year after I bought the car, in 1976. Strangely, there are two apparent things to me that seem missing. One, as I mentioned, is one of the long bolts on the remote lever housing to the rear extension. It appears to me that the gaskets were also not fitted to the housing! I will go ahead and replace all the gaskets...but I am still curious about the rear seal. I am not sure even how to remove and replace it. And, if dominic clancy is reading this, I did not see it in the Workshop Manual, which I am reading almost daily these days. I had a new gearbox mount pressed in after doing a thorough cleaning in one of those coin type pressure wash establisments. What a hobby!

Steve
Simi Valley, CA
Stephen Lofaro

Only the very early boxes had the metal seal, yours should have a standard rubber oil seal which costs just a few dollars. I can't remember if you can replace this without dismantling the box, but after 40 years I guess you are going to replace the synchro rings while it is out of the car so that means a tear-down anyway. My gearbox is in the cellar, so I can take a photo of the rear end tonight so you can see if you have the same type.
dominic clancy

dominic et alia,

Well after 40 years I have put about 30,000 miles on this car. Would you be replacing the synchro gears, dominic? I don't think it needs it, at all. If mine the rubber seal and I wanted to replace it, do you know how to remove and replace it? Is it a machine shop duty? My point is just this, the amount of oil is unacceptable and I would like to get to the bottom of this issue. If the rear seal is likely most culpable I will do it. I have posted other issues I would like to hear your feedback on those. You seem very knowledgeable on this series of MG.

Steve
Stephen Lofaro

I think it would be wise for me to report the gearbox number for all to reference. And I will endeavor to do that.

Steve
Stephen Lofaro

Steve, -- Check again which gearbox and propshaft you have. Early 1500 uses the (now) expensive external seal. All other renditions of the gearbox use a relatively inexpensive internal seal.

The early gearbox should mate with the early propshaft with the cylindrical welded dust cover on the front coupling, and 1 inch diameter spline. The mid 1500 gearbox should mate with the second type with the bell shape sheet metal dust cover on the front coupling, and 1=1/16" inch diameter spline. It is possible to assemble the second type propshaft (1-1/16" spline) with the early gearbox (1" spline), but definitely not a good idea.

Gearboxes are often changed ad may be replaced with a different type. Do not depend on the model year of the car as the only guide, but check the gearbox itself to see which one is in your car. If you do have a mid 1500 type gearbox, the rear seal is about $9 (or maybe less if you shop around). The expensive early type rear seal is a little tricky to replace in situ, but can be done. The other two are pretty easy. See here: http://mgaguru.com/mgtech/gearbox/gt113.htm
Barney Gaylord

While I haven't replaced rear seals on the MGA tranny, I have done internal-type rear seal replacement on "B's", and judging from photos of the mid and late trannys, I would say the method is similar....
Sadly the easiest way to get the old metal-cased seal out, is to destroy it...(This assumes, of course , that you don't have the external seal).
What I have done is drilled two holes in the rear of the seal housing (on the metal ring), one on each side about 180 degrees apart....You must use a center punch to start the drill, and use a drill about have the width of the seal ring...If you are going to drill through both sides of the ring (front to back), then do it on a bench, with the tail shaft slightly downward, to help prevent particles from getting into the case....Some will enter, but you should wipe it out thoroughly, before installing the new seal.
You will need a slide hammer to then screw into the holes, and pull the seal out, a little bit at a time on each side.
Once the seal is out, clean it up, and use a hard wood block, and a dead-blow hammer to install the new seal.Lightly grease the outside of the seal, and the inside rubber part....Slip it over the shaft. Lip on the inside.
I use a 4x4 block, with a large hole in the center, to allow for the length of the output shaft. Place it over the shaft, and give it a few good whacks.
I have never found a seal puller that will get into the small space between the shaft and the seal ring, that would not damage the shaft, when pulling out the seal.
If anyone has a better method, I'm open to new ideas.
Edward
Edward Wesson 52TD

Something clicked in my head about the gearbox in my car when I had posted a recent query about the engine number of my motor that was in the car when I bought it...a replacement motor with number 15K 926. When I removed the gearbox one of the long bolts was missing from the remote lever gearbox housing and I ordered one from Moss motors, part 322-460 which is a fine thread bolt and does not fit. So, the gearbox most likely was a replacement fitted witht the mystery 15K 926 motor that uses course threaded British bolts. Does the gearbox stamping provide me with a clue to where the gearbox is from? Maybe this is the key to where the motor came from....in any case, I am still searching for the long bolt.

Steve
Stephen Lofaro

The threads changed from fine to coarse once during production. Different fasteners changed threads at different times, so there were actually several different variations of 1500 type gearbox housings (front and rear housings). See here: http://mgaguru.com/mgtech/gearbox/gt123.htm

When these things get disassembled periodically for long term maintenance, the female threads in the aluminum housing can eventually be damaged. This is one of those School Of Hard Knocks lessons. Any time a bolt comes out of an aluminum thread it should get a Helicoil before reassembly.

I once had a starter motor bolt strip out of the bell housing, resulting in starter motor falling out, jamming up the flywheel (at 4000 rpm), breaking the crankshaft, and lots of other internal engine damage. It was a long tow home, and a very expensive repair. Since then I always Helicoil the threads for the starter mounting bolts, and also the threads on top of the rear housing for the shift extension mounting (as a matter of convenience). Now all of these bolts are fine thread, regardless of origin, and I don't have to hunt for bolts when doing a gearbox swap.
Barney Gaylord

Barney,

It's such a sensible comment that it is brilliant.

Steve
Stephen Lofaro

If you DO have the early back seal, it is available here for a great deal less than 75 US - about $20 including shippin in fact

http://www.leacyclassics.com/11g3147.html
dominic clancy

dominic,

I have a mid 1500 gearbox with the inner seal. That's a good break for me. But if you noticed my previous thread, I do think this gearbox may have been part of the motor replacement that was done prior to my purchasing the car by one of the previous owners. I am not sure. I did make a note of the gearbox number and while it is now in the shop I will make a note to report it here at a later date when the seals have been redone and I get the gearbox back to see what the community may know about the originality (or the geneology) of my gearbox. It's a good gearbox, a little tight out of second which has been previously reported by other members...not surprising then I guess.

Did you read Barney's solution to the long bolt thread issue on the remote lever housing? Brilliant.

Thanks for your comments. Very helpful as I do my best version of the tortoise moving along, keeping a high standard. My brake drums and front suspension pieces are due back next week from powder coating and the exhaust manifold along with it, done ceramic as suggested by the community. You guys are the best and it is truly great to have the live chat going on this site. I am working by myself but I am not doing it alone thanks to the MG Enthusiasts!

Steve Lofaro,
Simi Valley, CA
Stephen Lofaro

This thread was discussed between 24/04/2013 and 11/05/2013

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