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MG MGB Technical - Oil Leak

I have a 77 B and after a drive I have oil leaking from behind the rubber boot which surrounds the clutch withdrawl lever on the side of the gear box. It's not coming from the slave cylinder as that is new and recently replaced. I would say after a drive it will leave a spot a little bigger in size than a silver dollar on the ground. Is this the rear main or something else and can I let it go until it becomes worse?
JCH Hibbard

hi, it could be the front oil seal in the gearbox,or rear main seal on the engine,keep toping up engine and gearbox to see what one is dropping the most,
my car did the same so i put both seals in,
all the best
dave
da wright

Thanks Dave, there's been no drop in engine oil levels I'll crawl under the car this week and check the level in the gearbox, it;s about time to change the gearbox oil anyway.
JCH Hibbard

The rear main usually drips out of a hole at the lowest point of the bell-housing, and should have a split-pin in it to keep it open. Oil leaking from the release arm almost certainly is one of the gearbox input shaft seals. There are two - a round seal runs on the shaft and sits in a housing, and the housing has a paper seal to the main gearbox casting.
Paul Hunt

Sounds like work cut out ahead of me as oil is leaking from the lowest point as well as from the release arm. I guess the question is how long do you let it go before it become imparitive to replace?
JCH Hibbard

When you get fed-up with the mess or topping-up! On my Mini at least when the crank seal went it contaminated the clutch - it was either in or out - and that took the CV joints. The begger with all these seals is that there's really no way to check the new seals are effective until you get it back together again. When replacing the clutch the conundrum is always "do I replace the old seals as they might start leaking with the disturbance, or will the new seals not be as good as the old ..."
Paul Hunt

The good news is the drop is no bigger than a silver dollar. For you young ones who have never seen a silver dollar and are cousins around the world, a silver dollar is only 1 1/2" in diameter. There are many owners of MG's that would love to have a leak that size.

The rear seal on MG's often leak. Unless you notice a significant loss of oil I do not think there is a major cause for concern. You might want to climb under and make sure all the bolts on the bell housing and the pan are tight. To remove the engine and transmission to repair a drop of oil ---- why?
Lee

Since my last post the leak has gotten worse. After a 40 mile run the leak is about grapefruit size now and it looks as though there is also a leak developing at the timing cover seal as well. Should I stop driving the car until I can repair it? I've done a lot of work on the car myself but never pulled an engine and gearbox. Anyone know the approximate cost to have a job like that done to replace seals?
JCH Hibbard

Again, it depends on what you are prepared to put up with as far as mess and topping-up is concerned. This is more of a pain with the gearbox, especially side-fill. Did you check the level here and is it dropping? But with an increase from a silver dollar (whatever size that is) to a grapefruit I think you are looking at getting the engine out sooner or later. Gearbox leaks should just run out, it's engine rear main seal leaks that usually contaminate the clutch

Parts cost for seals should be pretty negligible, although you should factor in a new clutch kit as well unless it is very recent. If you have to pay commercial labour rates you are probably talking hundreds.

Getting the engine out is pretty straight forward, getting the splines between the first motion shaft and the friction plate seems to be the biggest problem people have, but ours just pushed together. You *must* use a clutch alignment tool to centre the friction plate with the pilot bearing in the end of the crankshaft before bolting up the cover plate. You might like to have a look at my experiences at http://www.mgb-stuff.org.uk/wn_clutchframe.htm and click on 'Clutch Change'.
Paul Hunt

JCH,

Have you made sure that your crankcase ventilation system is working properly? If not, excess pressure can cause or increase a leak that might otherwise not be an issue.

Charley
C R Huff

Thank you Paul and C R. Just changed the gearbox oil I do that on a regular basis and it was down I'd say half a quart but always seems to be when I change it. To my knowledge the crankcase ventilation is OK. Everything appears open but is there a specific way to check it that you would recommend?
JCH Hibbard

At what mileage do you change your gearbox oil? I have to admit that I didn't change mine in 19 years and 50k on the roadster and 15 years and 80k on the V8, but only topped up the first a couple of times in that period.

The crankcase has two openings for ventilation, both would have to blocked and there be blow-by for the crankcase to pressurise, and that would only affect engine oil anyway, which you have previously said hasn't been dropping.

You can check the suction side of the crankcase breathing by simply removing the oil filler cap with the engine idling. Not only should there be a change in idle speed (more noticeable on cars without the charcoal canister than with it is true) but it should also suck down a sheet of paper layed across the oil filler. Only if neither of those things happens is the suction side is blocked, which either comes from the PCV valve on 64 to 68 engines, or the carb port(s) after that. But for that to cause crankcase pressurisation and engine oil loss (which you don't have) the crankcase inlet would have to be blocked as well, but that is more difficult to check. For pre-canister cars the oil filler cap should be the vented and filtered type - coppers to replace, and a service item. For canister cars there should be a restricted port on the back of the rocker cover which you can check is clear with a wire. The hoses from there to the canister and the canister granules can also get clogged, but you should be able to detect suction with the engine idling on the fresh-air inlet to the canister with a smoke source.
Paul Hunt

I just received an email from a local mg shop here in Florida, the owner says they can change the rear main without pulling the engine on a 77 B providing it's not an overdrive. Is this the case and how hard would it be to do without taking it to the shop. Anyone had any experience changing the rear main without engine removal?
JCH Hibbard

It's said to be possible to remove the non-OD gearbox without removing the engine, but you almost certainly will need a pit or a lift, I'd hate to have to do it crawling around under the car, even if I could get it high enough. How tall is the bell-housing at its highest point? The chassis rails would have to be at least that much off the ground without a pit. From your description it sounds more like the gearbox is leaking than the engine, but with that removed instead of the engine you can still change both, of course.
Paul Hunt

This thread was discussed between 15/03/2009 and 29/04/2009

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