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MG MGB Technical - Oil leak

My 72 roadster. It has an oil leak that I think is coming from the gearbox or overdrive. Whenever it has been out for a run it leaves me a little puddle on the garage floor and I do have to top up the gearbox with about a cup full of oil each year.
The engine and gearbox will be coming out this winter as I have acquired another engine that has only done 27,000 miles so should be in good order even though it has been laid up for about 20 years and my old one is getting a bit tired.
So my question is where is the gearbox most likely to be leaking from and any suggestions on what to check over or replace on the engine prior to fitting. I will change the timing chain and tension er but would welcome further advice.
Trevor Harvey

My 1980 GT drips gearbox oil too. It shows itself at the point where the gearbox joins to the engine so presumably leaks from thereabouts.
Geoff Everitt

Trevor

The speedo drive is source of small leaks. Just make sure all is clean before reconnecting speedo cable etc.
The rear seal on the overdrive can leak too and as Geoff has said there is potential for a leak on the gearbox fornt seal. Only inpection when out will tell where the oilis coming form.

George
G R Wilder

When I pulled the engine/gearbox from my GT this year to replace the clutch, i noticed oil leaking from the front of the gearbox. I didn't have a replacement gasket and didn't want to wait on one, so I tightened down the bolts- none were tighten down. I think it took care of the problem.

so get a front gasket- easy job while it's out.

don
don g

Look straight up from the centre of the puddle! Better still put some clean paper under after a run and check when there is only a drop or two. Without any clue where the puddle is we cannot say where it might be coming from, could be anywhere from the 1st motion shaft oil seal or bearing plate gasket (drips through the release arm hole or drain hole forward if that), the output shaft oil seal, or any joint, drain/filler plug or other aperture between those two points of which there are many particularly on the OD. If you get the general area but still can't see on the gearbox where it is coming from (clean oil is difficult to see on clean metal, red ATF is said to be easier) puffing baby powder or somesuch can help to reveal the exact source.
Paul Hunt

This thread was discussed on 01/11/2009

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