Gearbox oil leak

[PaulFinch]

I entered my third race meeting on Saturday at Donington and I am describing it as a successful failure!

Managed 17 laps in qualifying, which is about three times more than I've previously completed! I was 10th out of 28 entries and there was definitely more time to come.

Unfortunately I discovered a huge gearbox oil leak when parked after the session. It was bad enough, along with a charging issue that I think is simply a broken alternator, for me to have to withdraw and not take part in the race.

Leak is coming from the rear seal. Interesting thing is this is a virtually brand new box (New ally casings, new dog gearset and only run for an hour) so really shouldn't be happening. I guess it could be caused by one of a few possibilities. The seal could just be knackered from incorrect installation, maybe a prop shaft vibration has damaged the bush and the seal, or there's too much pressure in the box and the breathing vent isn't sufficient for the heat being generated.

Interested to hear other people's thoughts. Does anyone run a dedicated gearbox breather system?

[rgh0]

The standard box has a vented bolt on the top do you have that installed ?

The fit of the nose of the tail shaft into the sleeve bearing in the tail housing is critical. The tail housing also needs to be concentric and aligned with the output shaft and the splined end a good fit also into the nose of the tail shaft. Getting all this aligned and fitted correctly is essential for minimum oil leaks out the rear. Lots of opportunity for machining errors and alignment issues with all this.

I use a standard iron box in my racing class and don't have any problems with gearbox oil leaks.

cheers
Rohan

[Lyn7]

Hi Paul, Rohan is right as usual, you would have less trouble if you used the original cast iron parts. I am currently using magnesium casting for the gearbox and after quite some time the tail housing developed a leak.
After investigating further it was obvious something was wrong with the rear bronze bush. Gearbox out to discover the bush had moved forward into the housing. The conclusion I came to was that it had come loose because of heat transfer/expansion and probably a bit of wear from fitting replacement parts. I solved the problem with a Loctite product recommended by the company. No problems since. I think It's worth you looking into this a little closer. Cheers, Lyn...

[PaulFinch]

Thanks guys.

I do have the breather bolt on the gear shift cover. Does the location of the bolt matter? It's currently on the left side facing the bell housing.
I've drained the remaining oil and the leak wasn't as bad as I'd initially thought, it's lost around 150ml.

I've also discovered by brand new (one event) Brise starter motor is also knackered, along with the alternator. I'm reconsidering my summation, the weekend is now just being described as a failure...

[toomspj]

I once had an Elan that kept destroying the tail shaft seal. It turned out that the propshaft was too long and the weld on the yoke was running in the seal. I didn't understand how that happened but the fix was simple - i just got the propshaft shortened and no more leaks.

Other than that I've never had a problem with tail seal leaking, either in ally or cast iron housings.

I had a run of starter motors fail - it was a wire on the field windings that would break. I haven't had that problem for years but I still religiously carry a spare with me to race meetings.

Is it an ACR type alternator? If so, again it's most likely a broken wire in the control circuit which is easy to fix. They fail regularly and it seems to be a function of the twin cam vibration at high revs, rather than the rpm of the alternator itself.

Paul

[PaulFinch]

Thanks Paul, I'll check the yoke mesh depth.

What make of starter and alternator do you use? My starter is a Brise item and I was really impressed with the quality prior to fitment and also how well it spun the engine but if they fail after 28 minutes of track time they're no good.

My alternator is a cheap Denso copy and so I probably shouldn't have expected too much. Will take it apart and have a look.
I see TTR have a 'Special' vibration resistance item, any thoughts on this?

[rgh0]

You may want to also check that the Welch plug in the end of the yoke shaft that fits in the gear box is still in place. if this is loose or falls out you loose oil down the spline.

I also have had problems over the years with vibration affecting the starter and especially the alternator when using 8000+ rpm . I use a Lucas 17ACR alternator and a Bosch pre-engage starter from the early 70 escorts made here in Australia. Since I started taking a spare of each to race meetings the problems have gone away

cheers
Rohan

[boxer]

Hi Paul,
Have just suffered a identical seal failure to yours after 1 hours testing 26R.
New gearbox just built from TTR parts but using original alloy tail case.
The new seals supplied by TTR seem noticeably different from the ones pictured on his web catalogue.
Past seals have been very difficult to remove new ones fairly easy.
Have manufactured a collar to fit over machined section of tailcase to retain seal. Testing again this week so will report findings.
FYI have tested breather system from gearcase in endurance races with no significant loss of oil through breather.
Biggest problem is you're putting 175HP+ through a casing designed for 40 HP!

[PaulFinch]

Thanks Boxer,

I've had some very busy weekends and haven't managed any further investigation yet but would be very interested to hear how you get on with the modification.
Out of interest, have you ever managed to replace a seal with the box in situ or is it always an engine out job?

[PaulFinch]

Well Lyn was right, tail bush was dislodged and floating up and down the shaft.

Will be replaced with a top hat style bush from MKF engineering which will hopefully be the end of it.