Talk Morgan Forums Morgan Sports Cars Classic Morgans (pre-CX) Gearbox groans

The problem is there are no groans and really, there should be. Some of you will have read of my overheating episode on a Swiss motorway on the way back from LMC. In short, a very hot gearbox, smoking hot, pulled over, poured water over it, crept into a service station, cooled it down again, filled it with oil (it wasn't empty) and then drove on slowly to the overnight train to Vienna.

Today I took TWP out for the first time since the return, about 12 kms, and there is no sign of overheating and no unusual noises are to be heard. Any thoughts?

The heat appeared to come from towards the rear of the box i.e. the extension. Have I run a bearing on the main shaft where it exits the extension? The gears themselves seem fine. Will this thing overheat again if I take it on a long run at motorway speeds? Will I ruin the shaft if I keep driving it?

Any thoughts on diagnosis or is it out with the motor and gearbox? Kerry

How much oil did it take? I think the 4spd box only holds just over 1 litre.

2.1 imperial pints or about a litre. I'm guessing but I think I put less than one third of a litre in. Guessing, because this was happening on a busy service station forecourt, and when I had pumped quite a bit in I checked and the box was full and there was at least a third of a litre on the ground. If you've ever filled a gearbox you'll know how this happens. And there is still a third of a litre in the bottle.

I did the last gear box oil change and filled it about two years ago but I had not checked it since. Maybe thrashing it around Le Mans for two laps has caused an issue.

I don't think much can generate heat like that. If it was a bearing seized, I think you would get vibration, especially at the propshaft end. Conventional (classic) gearboxes usually run in top gear by connecting first motion (input) shaft directly to the third motion (output) shaft, so the lay-gear and gears are freewheeling.

Way back in time I had a 1275 Midget with a really badly worn gearbox. Much noisier and looser than was good for it, but I just used heavy duty oil and molyslip in it because I couldn't afford a repair.

That gearbox also got really hot on the M way. So hot that the gearstick was too hot to hold, and it tended to stick in4th, needing a sharp swipe to come out of gear. But it never let me down.

So I would check the feel of the propshaft where it enters the rear of the gearbox. If it seems OK, just see how it goes. Maybe do another oil change and see what comes out? Assuming you have a drain plug!

So not a ridiculous amount, but still potentially 1/3 empty.

If gears are selecting OK, it's not making any new funny noises and it's not overheating straight away, perosnally I'd be inclined to leave it for the time being, but keep an eye on it.

Random thought regarding generating that much heat without rattling ... could a bearing have seized and the bearing itself be spinning in the casing ? ... until it ovaled its seating in the alloy case it would just run like a not very good plain bush.

As TBM says .. maybe something tightened a bit under the Le Mans lap abuse and now it's cooled and loosened with decent lube it may well just run for years ... maybe some increasing test runs keeping an eye on the g/box temp might he in order ... I use one of those cheap laser I/R thermometers for my temp checks but your hand will tell you well enough (if the skin comes off it's probably a bit warm 🙂)


K

Thanks Dave and Tim. The incident occurred after 5 hours of fairly hard motorway driving so perhaps it is just wear and accumulated heat. No vibration detected and drain plug still in place.

Propshaft was overhauled about 3,000 miles ago so should be fine but when I get it on a lift I will double check it.

Exactly - a thought I was just hatching. An infrared thermometer should tell me if there is a specific hot point. Thanks. I'm starting to feel more confident about driving it.