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MG Midget and Sprite Technical - Jumping out of third

Our 1275 fitted with a standard box has started jumping out of third, g/box has about 20000 miles on it but has had a hard life (classic rallies).

Anyone got any ideas? Yes it does have the right amount of the right oil in it.

TIA

David
d brenchley

Have you had any problems with weak synchro? Crunching?
Dave O'Neill 2

Hi Dave,
No problems with anything else (its as good as a midget box gets - MGOC refurbished).

David
d brenchley

I remember 1100/1300 boxes used to jump out of second but not Spridgets out of 3rd

obvious thing to say but sounds like something is worn

I might be wrong but I think you'll need to ask the racing/rallying people on here for advice on this
Nigel Atkins

Maybe the little pointy-ended screw that locates the selector fork onto the selector shaft has come loose. A loose selector fork might vibrate and "nudge" it out of gear. Should be possible to check them through the little cover plate without removing the gearbox, but it is close to the chassis rail so visibility isn't good!

Guy
Guy Oneandahalf Sprites

Doesn't do it every time - if you back off the power that tends to make it happen.
d brenchley

I think it happens when the selector hub doesn't properly "latch" into position - then power on / power off tends to thrust the hub and gears out of mesh. Either the hub isn't moved fully into the engaged position - possibly because the selector fork is loose on the selector shaft as suggested before, or maybe a worn selector fork. (except you say it was rebuilt not long ago).
The other "maybe" is a problem with the detent balls or springs that hold the hub in position. Could be a broken / weak spring or maybe your balls have dropped out!

I started with the easiest to check as with some patience, it is possible to remove the side cover plate and check that those set screws are still tight without removing the gearbox. The other possibilities require removal and at least a partial strip down.

Guy
Guy Oneandahalf Sprites

another a bit off-the-wall idea but it can happen - it happened to me and a mate

rubber gear lever gaitter too tight a fit especially if it's not the standard one
Nigel Atkins

Well there's another idea that doesn't require gearbox removal! Definitely check the easy things first!!

Guy
Guy Oneandahalf Sprites

This thread was discussed between 18/09/2010 and 19/09/2010

MG Midget and Sprite Technical index

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