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MG Midget and Sprite Technical - Smoothcase gearbox

As it's come up a few times lately and is the sort of thing people might search for in future I thought I'd start a new thread.
To avoid the known shortcomings and scarcity of parts, Heathrow Transmissions can now supply a smoothcase box with ribcase internals.
davidsmith

Interesting. I have a frogeye with, I think, the original gearbox and was contemplating removing it at some stage to see if I could service it myself as it jumps out of gear very occasionally.
Are you saying that I may have a problem getting parts?
It's quite an ambitious project for me anyway so might be best to leave well alone as it is not a major problem as not too bad. In fact someone told me they did that from new, so if that's the case, it may be a waste of time anyway!

Graham
Graham V

I have had a couple of smoothcase boxes in my frogeye. Neither has jumped out of gear but one wailed terribly in first and reverse whilst the other had no effective synchro on 2nd gear. I replaced with a rib-case because, at the time, replacement parts were unobtainable.

Heathrow Transmissions seem to have been offering rebuilt and re-geared smoothcase boxes for some time now - has anyone on here bought one of their offerings? Any good or bad comments to share?

Simon
Simon Wood

The conversion of internals has been offered for a while and I have not heard of any problems. The ratio's are superior to the original smoothcase ones. the baulk ring synchromesh of the rib case gearset is much better too.
Bob Beaumont

I suspect that many of us have a smooth case lying around that we'll never use. The ribcase is superior in all respects, as I understand it I.e. better gears, better bearings, better synchros. If you want to maintain exterior originality with a Frogeye, Mk2 Sprite or Mk1 Midget you're probably best with a smooth case fitted with ribcase internals.

Bill
W Bretherton

So repairing a smooth case is not a sensible option?
Graham
Graham V

Graham, it might be sensible if you can get the parts, but that is unlikely according to extensive reading I've done. Parts for rib case gearboxes are still available although you take a chance on whether the box will work properly e.g. if mating new gears against old.

A major problem with a smooth case is the synchronisers which you probably can't get whereas you can get new baulk rings for a ribcase (which has better synchronisers anyway) and other parts are available. By the way, I'm no expert on this, I've just done a lot of reading (and have rebuilt an, as yet, untested ribcase).

Bill
W Bretherton

As Bill says the smoothcase has different synchronisers. They are brass and shrunk and machined onto the gear. I guess they could be made but would be outrageously expensive. The factory supplied gears with the syncro cone already machined on it, occasionally NOS come up on the usual sites. Second gear goes first usually and I can't recall ever seeing one. Third and the first motion shaft do pop up.

The smooth case also uses plain bearings for the gears but the ribcase sprite/midget one uses needle rollers. the conversion makes sense particularly if you intend to use the car.
Bob Beaumont

Does conversion require machining of he casing?
GuyW

Yes I believe so. The first motion bearing carrier is slightly different
Bob Beaumont

Sorry remiss of me for not thanking Bill and Bob for the helpful responses- thanks appreciate it
Graham
Graham V

Sorry remiss of me for not thanking Bill and Bob for the helpful responses- thanks appreciate it
Graham
Graham V

Sorry remiss of me for not thanking Bill and Bob for the helpful responses- thanks appreciate it
Graham
Graham V

Wow three thank yous! Not sure how that happened
G
Graham V

This thread was discussed between 22/02/2017 and 28/02/2017

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