A gearbox question

[CarlS]

I have a 1071 Cooper S with the engine built by Richard Longman, putting out 74 bhp at the wheels but since I have bought it I have had a few gearbox problems (a lost tooth on 3rd before I bought it, a collapsed bearing causing a hole in the casing and now a hole worn in the back of the casing caused by (I think) using the original type rubber crosses instead of the uprated nylon ones).

The gearbox is 3 synchro in a 22G333 casing.

Now before I rebuild it into another casing am I just have a run of bad luck or do you think this has something to do with the state of tune of the engine and I should consider moving to 4 synchro which are apparently stronger boxes.

All help gratefully recieved

[cooperman]

At that power I would go for a straight cut close ratio gear set, a 3.9: 1 diff ratio and a comp clutch plate.You don't need s/c drop gears though. The 3-syncro boxes are OK, but use Hardy-Spicer couplings. I shattered the nylon ones on my 112 bhp Cooper 'S' and the rubber ones are useless.

[CarlS]

Thanks for that.

I'm already running straight cut gears and uprated clutch but a chat with somebody at Silverstone who had moved from 3 to 4 synchro beacuse "they are stronger" got me thinking.

Time for another rebuild then (as soon as I can find a 333 casing that cost less than my left arm)

[Cooperman]

There is a school of thought saying that the 3-sync boxes are stronger as the gears are wider. I don't know as I've always rallied with 4-sync in my big-engined cars - well, since 1995 that is. In the 60's I did use 3-sync boxes without anything more than the normal problems.
With any powerful engine the potential for transmission probs will always exist, after all the box was originally designed for 34 bhp and, although we may fit better gears and roller bearings in place of plain bushes, the physical constraints of size do exist. All the probs with my rally cars seem to centre around the transmission (I've broken drive shafts, drive-shaft couplings, diffs, transfer gears (on a 112 bhp unit), selector shaft, etc.