View Full Version : So maybe its not a rear seal

02-14-2008, 09:51 AM
All this time I've been assuming that the oil that was pouring out of my engine at the back was from a poorly sealed rear crank seal. But last night in the chat room, alana, suggested what might be happening is a leak from my gearbox running down the bellhousing and out. I'll admit that thought had crossed my mind before. Well, now that I have the gearbox sitting on the floor: If the seal on the input shaft is good, if I tip the gearbox up on end (set the bell housing opening on the floor) I should not see oil leaking? ANd if it is a bad seal, I would see oil leaking? Does that sound logical?


02-14-2008, 09:55 AM
You can usually smell or feel the difference, motor oil and g/box oil is usually different oils

Don Elliott
02-14-2008, 10:33 AM
There always seems to be some oil stuck to the inside surface of the bell housing. The oil inside the bell housing usually has a radial "spread" pattern which results from the spinning flywheel/clutch assembly. This radial smear is always oily black.

If the oil comes from a leaking rear seal of the engine, one would logically imagine that this engine oil would usually stay between the hidden side of the flywheel and the back of the block. I always imagined that this oil inside the bellhousing was from the front gearbox seal because the hidden side of my flywheel was always dry and dusty. This is still a mystery to me. I have checked my front gearbox seal and changed it too and this still came back.

I changed the rear seal for the crankshaft to the modern lip seal design about 1996 and I still had to add about a quart of oil every 600 miles - just like before. So was it engine oil in my bellhousing? It was black. And where did all that oil disappear to ?

Last spring, I had the time, etc. so I rebuilt the engine. I wanted to fix the leaking oil problem once and for all. I had driven 94,000 miles on it since I had done it in 1990. I don't know what I did right but there are no leaks anywhere now and I can drive 3,000 miles without topping up the oil. How can I explain that ? I can't. The mystery continues. Either you got it or you ain't!

Zblu is right. If you find some golden oil in there, it's from the gearbox. If it's black oil, it's from the engine. I can't see what colour the oil is. If you can't verify the oil colour, it'll be a mystery to you as well.

I can't say that tipping the gearbox up on end will result in any oil coming out the front gearbox seal. It will if the seal is really leaking, but maybe you can have a problem here where it may need heat and spinning rotation at 3000 RPM to cause it to leak. Possibly the input shaft has a groove in the OD, worn by the old seal and this is causing the leak. You might want to consider using a "speedi-sleeve" and a new seal. Check if you have the copper flat washers under the bolt heads holding the front casting onto the gearbox. Steel flat washers will not seal. You need copper washers. And use the lock wire to keep the bolts tight.

As Andy says, "a Triumph never drips oil, it's just marking its territory". Most owners will tell you that if it drips, let it drip. It's easier to check the oil now and then, than to pull it all apart and still be confused.

And now you know the rest of the story - or do you ?

Don Elliott, Original Owner, 1958 TR3A, Montreal

02-14-2008, 10:39 AM
Also gearbox oil has that smell - from the sulfur additive. One sniff and you should be able to tell from the unique bouquet - GL4 with just a hint of syncromesh.

02-14-2008, 10:50 AM
Just out of interest - the original box from my TR6 upended leaked oil all over the place.

It looks - and smells - indistinguishable from regular 20w50, regardless of what is supposed to be in there.

That's one reason why the box is Japanese now...

02-14-2008, 12:00 PM
Also gearbox oil has that smell - from the sulfur additive. One sniff and you should be able to tell from the unique bouquet - GL4 with just a hint of syncromesh.

I run Non-Detergent 30 wt motor oil in my gear box, because John Esposito told me to.

I changed the rear oil seal on my engine and the front oil seal on my tranny. I still get oil from the tranny. I think it is supposed to be that way.....

02-14-2008, 12:03 PM
Take the flywheel off. If the oil is on the back of the flywheel(engine side) it's coming from the engine, either the rear main or an oil galley plug on the back of the head.

Most of what you;ve been told about the oil difference is true. But do you know what the previous owner installed in the trans. He may have installed gear oil, he may have installed engine oil.....

When the trans input shaft seal is leaking you will usually (notice that disclaimer usually) see a newer, fresher trail coming from the bottom of the seal. And when the trans fluid sinks below a certain level, the leak mysteriously stops, but is soon accompanied by noise from the transmission.

02-14-2008, 12:15 PM
Not sure which gearbox you're working on, Basil, but some of them have vents near the front that will leak if you stand them on their nose. There's a big oil slick in my attic from a TR6 box I forgot to drain first ...

And perhaps I'm being naive, but it seems to me that if you had oil "pouring" from the gearbox, you'd quickly notice that it loses a lot of oil. A half-pint spread over an oil change interval (when I also check gearbox level) isn't much of a leak.

Synthetic gear oil doesn't have "that smell", or at least not nearly as strong. Many LBCs are supposed to have motor oil in the gearbox anyway.

But if you've got it out, change the gearbox seal anyway, IMO.

Dave Russell
02-14-2008, 01:29 PM
It's a bit late for this if you already have things apart.

With things together & running, the dye tracer systems work well to find mysterious leaks.

Systems such as the "Tracer Products LeakFinder Kit" can be had from many auto parts stores for around $50. They consist of a bottle of dye & a 12V portable ultra violet light.

If you suspect the engine is leaking, wash as much oil off as possible. Add some tracer dye to the engine oil & run the car for a while. View the various engine parts with the UV light & any oil coming from the engine will glow brightly under the UV light.

The same works for transmissions & engine coolant.

Newer kits use a flashlight & goggles. Cost much less.

02-14-2008, 01:33 PM
When we first got our TR-3, It too leaked oil {even after an engine rebuild}. We changed the front transmission seal {Twice} to NO avail! Come to find out the front mainshaft trans bearing was worn along with the pilot shaft bushing. causing the mainshaft to woble just enough to beat out the seal in short order. After replacing the 2nd gear syncro, pilot shaft bushing and front tranny bearing the leaking stopped!

{the reason we tore into the trans in the first place, poping out of 2nd on acceleration} CAUSE: The worn front mainshaft bearing and or syncro or both.

The copper washers are a must have item.
Any leaking after that was very minor if any.

Don Elliott
02-14-2008, 01:42 PM
If you decide to change the seal at the front of the gearbox, cover the splines in the input shaft with a couple of vinyl milk bags so you don't cut the new seal as you slide it over the splines. Other ideas are to wind masking tape or black electric tape around the input shaft splines - over these shaft edges before you slide on the new seal. If you don't it will leak right from the get-go. Maybe that's what the DPO forgot (or neglected) to do. Then remove the tape or bags and make sure that the front retaining casting is oriented as per the repair manual.

02-14-2008, 02:44 PM
If you decide to change the seal at the front of the gearbox, cover the splinesGood point, Don. I use black (vinyl) electrical tape, being careful to wind it from back to front so the seal doesn't catch on the edges, then smear it with a bit of grease. The seal gets greased as well. Afterwards, clean the splines with solvent to ensure there is no trace of adhesive from the tape.

Someone, Ken Gillanders I think it was, also wrote of finding a "new" shaft that didn't run true. If it continues to leak for no apparent reason, might be worth running the shaft between centers to check for straightness.