Manual gearbox oil leak

M

Mangozac

Senior member
 QLD, Australia
So my blue Zed has found a new owner, but before I can hand it over it needs to pass a roadworthy inspection. They pulled me up on the front brake discs (as I had expected) but also, unexpectedly, an oil leak from the 5spd manual box.

Let's see if this link to the pictures works:
https://goo.gl/photos/FV6Y6zNx43hTUkYm8

The oil has pooled in three spots along the bottom of the gearbox, including the bottom of the drain plug. It's clear and clean, so definitely isn't engine oil. The sides of the gearbox are dry so it's definitely not coming from the fill plug or the selector seal. No oil has been flicked onto the transmission tunnel or around the flex disc area, so I doubt it's the output shaft seal.

One of the three pools is at the bottom of where the bell housing meets the engine block. I'm assuming that's just migrated there due to being lower, since there's nothing around there that could leak.

The drain plug seems pretty tight, but apparently it does use a crush washer so perhaps that's failed? Leaking oil there could be more around with movement of the car...

Has anybody for any suggestions? I've just degreased and cleaned the area so hopefully it will show up again quickly at the source.

The buyer has offered me $300 less to take it as is and have it fixed themselves. I guess that's a good deal if it turns out to be something that the gearbox needs to be dropped to fix!
 
Take the fill plug out and see if there's any oil coming out of it (to see if someone somehow saw a possibility to overfill the box).

If the box is not overfilled, my guess is the input shaft seal.

If you don't do the repair yourself, take the 300.
The gearbox has to come out to replace the input shaft seal.
Also with any leakeage in the bell housing: the clutch may be conterminated.
 
Thanks guys!

GuidoK, with the location of the fill plug how would it be possible to overfill? And even if it was, where would it overflow from? It's definitely not leaking from the fill plug - the area under it is dry and very clean. Input shaft seal is possible. If it was the input seal I would DIY for myself, but obviously the buyers are keen to collect the car so I don't have time.

I have been reading that it's not uncommon for the drain plug to leak but it seems pretty tight. I'll put a torque wrench on it tonight and see...
 
Update: after cleaning up the leak last night and driving the car today I slid underneath and took another look. It seems like the gasket between the bell housing and gearbox is weeping! Is that plausible?
 
Mangozac said:
GuidoK, with the location of the fill plug how would it be possible to overfill?
Click to expand...
Jack it up on one side and fill. The car has to be level.
Something like that (people do the stupidest things so who knows), but checking if the gearbox is overfilled is the first thing you do as it is just loosening 1 bolt, so maybe 30sec work?

If it's overfilled, it would probably leak from the input shaft or the output shaft.
Typically the lowest dynamic seal f there's no spill hole.

Mangozac said:
Update: after cleaning up the leak last night and driving the car today I slid underneath and took another look. It seems like the gasket between the bell housing and gearbox is weeping! Is that plausible?
Click to expand...

That might be possible. The gearbox doesnt have a real bell housing. Afaik its 2 pieces: the front has the bell housing integrated and the faces split the gearbox in half (so you open up the gearbox, not remove just the bell housing.
There is obviously a gasket inbetween. So potentially leaky. (and if that's the case..... :o )

If the inputshaft seal would leak, I think it would be coming out of the lower breather hole (where also clutch dust comes out)

Drain/fillplugs can leak too, as there is a rubber seal in the plug. If that's damaged, no torque will help I think.
 
GuidoK said:
Jack it up on one side and fill. The car has to be level.
Something like that (people do the stupidest things so who knows), but checking if the gearbox is overfilled is the first thing you do as it is just loosening 1 bolt, so maybe 30sec work?

If it's overfilled, it would probably leak from the input shaft or the output shaft.
Typically the lowest dynamic seal f there's no spill hole.
Click to expand...
Ahh yeah makes sense. Unfortunately that would mean a lot of work for me putting the car on stands so that it's level to check. Either that or jack up one side, unscrew the fill plug, put a pan underneath, drop the car back down and see if anything dribbles out!

Either way, after my last check I'm certain that this isn't the issue.

GuidoK said:
The gearbox doesnt have a real bell housing. Afaik its 2 pieces: the front has the bell housing integrated and the faces split the gearbox in half (so you open up the gearbox, not remove just the bell housing.
There is obviously a gasket inbetween. So potentially leaky. (and if that's the case..... :o )

If the inputshaft seal would leak, I think it would be coming out of the lower breather hole (where also clutch dust comes out)

Drain/fillplugs can leak too, as there is a rubber seal in the plug. If that's damaged, no torque will help I think.
Click to expand...

Correct, the bell housing is integrated into the front of the gearbox: RealOEM diagram. As you say, if the input shaft seal were leaking the oil would have exited the bell housing at the lower breather hole.

The more I have thought about it the more obvious it becomes that this has the be a leaking gasket, which is a big headache. Have you ever heard of methods to fix such a leak that don't require disassembly of the gearbox? A quick google showed up this product which is designed to soften up seals, but I'd be skeptical whether it would have any effect on the gasket. The purchaser is aware of the issue so I'll be best to just let them deal with it if the weeping ever becomes bad enough!

Edit: One final thing I might try is to retorque the transmission case bolts. They're 8mm thread and TIS specifies 23 11 1AZ "Transmission housing, rear section/front section" as 22Nm. I can try the torque wrench set to 20Nm and see if any of them move at all (particularly on the side of the leak).
 
The bolts are in an aluminium housing, so they are usually corroded stuck (being on the underside of the car especially), so I dont think they'll move with 20Nm. In fact I suspect they'll be a pain to get loose, risking stripping the threads. This is common on the bolts that hold the bell housing to the engine (so these have to come loose for a clutch job) and that is a similar situation. But you can try.

I'm not a fan of all additives that try to repair leaks (or try to 'fix' things in general), but splitting that box and replacing the gasket (is it a paper gasket or a liquid gasket?) would be quite the job.
If you have a lift and you're a trained mechanic, it's still half a day minimum. Especially if the exhaust bolts are rusted in place, that can be a pain too.
 
GuidoK said:
The bolts are in an aluminium housing, so they are usually corroded stuck (being on the underside of the car especially), so I dont think they'll move with 20Nm. In fact I suspect they'll be a pain to get loose, risking stripping the threads. This is common on the bolts that hold the bell housing to the engine (so these have to come loose for a clutch job) and that is a similar situation. But you can try.
Click to expand...
That's a good point, however in the past when doing maintenance I've never had any issues with typical "trouble" fasteners like that (the exhaust bolts being a prime example - mine came off first go). I assume that not having to deal with sub-zero winters is a big part of that.

I'll try backing off the bolts slightly on the weeping side first, before retorquing (one at a time). If they back off without any issues then the retorque should be reliable.

If I was keeping the car I would attempt a DIY gearbox repair. Replace the clutch, the gasket and probably the seals while I was at it.
 
Final update:

Since cleaning the gearbox almost a week ago there has been no further weeping. It's obviously extremely slow! To be sure, on the weekend I one at a time cracked the gearbox bolts that I could access and retorqued them. As I had suspected there was no problem in doing so as we just don't get as bad corrosion of underbody components here. The roadworthy inspection has passed this morning so I'm set to hand her over to the new owners tomorrow. It will be sad to see her go and I'll finally have to get around to updating my signature ;)

Thanks for the advice, GuidoK!
 
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