Output Shaft seal?

[chasgrips45]

After a nice ride today ,I notice transmission oil seeping pretty heavily in the seam between the main transmission housing & rear cover. That cover has a gasket,& it seems to me that that gasket should have more ability to stop a leak ,or seepage from the transmission no?. the seepage is getting worse.Is there really that much pressure ,or agitation in the rear of the transmission by the output seal to cause such seepage through the gasket? Isn`t there a small pressure relief hole atop the transmission? Could that be plugged up? Then again ,where would transmission oil go if it`s leaking from the output seal? Oh yeah,the transmission oil level is proper,& as far can tell the bolts holding the cover are tight.

[dougie]

Check the bolt where the battery ground cable is attached to the gearbox. It has a hole in it to allow the gearbox to breath. Make sure the hole hasn't become plugged.

[Jean]

Or has THAT bolt been replaced with one that does not have a hole?
(It's also the bolt that captures the speedo-cable.)

[chasgrips45]

No, the bolt is the original. It could be that the 13mm on top of the transmission is loose. I can`t feel any excess oil in the u joint boot. Wouldn`t there be a build up of transmission oil in the boot if the seal was leaking?

[chasgrips45]

So in fact it was the speedo bolt.Had grease in it. It`s always a good idea to look for the easiest solution first. I keep reminding myself of that ,why don`t I practice it.

[chasgrips45]

Well in fact ,although the little speedo bolt had some grease in it ,& I blew it out, the seam still leaks! Again it only leaks at the seam between the tranny rear cover & main transmission housing. Above the output flange,it seems. I guess it is the output seal after all? I guess the oil has no place else to go ,if the boot is not leaking,so it goes out at the gasketed seam ,no?

[Deleted User 62]

Chas, are you sure the oil's not coming out the gap between the airbox and the top of the transmission? A cracked or leaking breather hose can leak oil and the only place for it to go is down...

[Duane Ausherman]

Chas, if the output seal leaked, it wouldn't show there. The purpose of the transmission output seal is to keep the oil in the swing arm. That keeps it from transfering from the swing arm into the transmission. The usual reason is that someone installs it backwards. In no seal situation that I can think of will it show oil on the outside.

Check Tim's excellent suggestion first. Then consider cleaning it well and watching for the first sign. If it really is coming from the cover mating surface, then I would suspect that the surface has a defect. This would be most likely if the transmission was recently repaired.

There is one very unlikely possibility. Sometimes a casting is porous and the oil just appears to go through the metal. This has been most commonly found in final drive covers. This is not likely your issue, but it is possible. It has also been seen on a lower fork casting.

Are you sure that the oil isn't coming from under the rubber boot that is over the U-joint? They like to leak.

[chasgrips45]

Thanks for thew clarification Duane.So I would assume that the oil in the transmission would rise & the oil in drive shaft would fall,if something was leaking? No the boot is nice & dry. BTW ,I hope I don`t start an argument here ,but I just started using synthetic oil in the transmission. I`ll be damned if it didn`t start to seep shortly thereafter.

[Major Softie]

Thanks for thew clarification Duane.So I would assume that the oil in the transmission would rise & the oil in drive shaft would fall,if something was leaking? No the boot is nice & dry. BTW ,I hope I don`t start an argument here ,but I just started using synthetic oil in the transmission. I`ll be damned if it didn`t start to seep shortly thereafter.

No, that isn't uncommon (at least, anecdotally). Although a tight engine won't leak synth any more than it will conventional oil, lots of people have found that a non-leaking motor with worn seals may leak synth, and may even return to non-leaking status if you go back to conventional. The synthetic seems to expose worn seals before conventional oil does.