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MG Midget and Sprite Technical - Selecting 3rd Gear

Hi,

As part of my rebuild I have a transmission specialist rebuild the gearbox. They fitted new bearings, seals, gaskets and layshaft.

I filled with Dynolite Gear 30 oil and for the most part it has been fine changing gears.

I’ve not driven more than 30mins straight yet, but it does sometimes not like changing from 2nd to 3rd.

There is resistance there stopping me from pushing the stick all the way. I can really force it and it will go, after that it is fine again.

Certainly happens more when it is all warmed up.

It will only happen occasionally, perhaps once per drive. Not more than that.

I can always select back to 2nd again. I tried releasing the clutch and trying again but unless I force it, it won’t go.

The specialist said I could try different oil, something like Dexron 4, before returning the car to them to pull out the gearbox and checking it over.

Any advice or suggestions are most welcome

Thanks

James
James Paul

I can only say from experience if you have to take it back for them to remove the gearbox to photographically document the state of your car and engine bay as I had a failed silver seal gearbox replaced under warranty by Hartwells in Bath and they bent the front of the battery tray. Apparently a common issue back in the day but something I never did on the various occasions I'd changed the engine and gearbox.
David Billington

James
Does it change easily from 4th to 3rd?
Bill Bretherton

Hi,

So I could be in 4th or 2nd and try to select 3rd it won’t unless I really force it.

Once I’ve got it into the 3rd it works fine again
James Paul

My initial thought is a worn 3rd gear synchro ring - the ring helps the sleeve to engage with the dog teeth on the gear and should have been changed if worn. 2nd and 4th rings probably ok.
Bill Bretherton

If it were worn wouldn’t it be more of an issue. Why does it change gear perfectly for most of the time?

James Paul

James,

What a (expletive deleted ) pain after finally getting it looking so good !

I would echo David’s advice- in fact if you decide to remove it I would still do it my self as nobody will be as careful as you !

I run mine on a not dissimilar oil ‘Penrite GB30’
Oils are a subject that gets a lot of very fixed views on the bbs!
You could try going back to 20/50 as per handbook (enter Nigel !!!) and see if it helps - I personally doubt it but maybe ?
The stuff they advised to try seems more of an ATF so not sure about that.

Could try an Italian gearbox service if it’s coming out any way!!!

R.
richard b

James
It may be partially worn and work better when cooler. You could, as Richard says, try 20/50 oil. Synchro rings are sensitive to oil viscosity AIUI. That'll be why the reconditioner suggested it as an "easy" fix. Hopefully someone like Willy will chime in later.
Bill Bretherton

Richard,

I know what an Italian engine tune-up is but what's an Italian gearbox service?
David Billington

A worn or loose fitting syncro ring would normally result in 'grinding' or 'crunching' as you select the gear.

I ended up rebuilding my 1500 gearbox twice due to poorly made modern replacement syncros. They are sometimes too big in diameter and too loose on the cone. In the end I bought some forged syncro rings with carbon friction surface from a guy in the USA to get round the problem.



Chris Madge

There’s no grinding or crunching going on.

It just won’t engage fully unless I force it.
James Paul

"There’s no grinding or crunching going on.
It just won’t engage fully unless I force it."

Maybe the gear selector mechanism is the issue?
Chris Madge

Does it select 4th gear satisfactorily? If so its likely to be the baulk ring on 3rd gear. I would take it back!
Bob Beaumont

I'm tempted to agree with your gearbox man initially
Easiest fix first
Your oil is fairly heavy duty at 20/60
I'd be tempted to drain a cup full(250ml) of oil and then top up with that amount of atf (dexron) It's a known fix when the lube is a bit heavy.
Is your reverse lockout correct as in can you still move the gearlever back and forward with the lever resting against the reverse spring loading(but not compressing it)
William Revit

I agree William but James says the problems are worse when the gearbox warms up which possibly could negate the impact of thicker oil. He says It is also intermittent which sounds like something is worn or broken?
Bob Beaumont

True Bob, but worth a try, a bit of atf usually fixes oil related shifting issues -and- If James does have a mechanical issue, at least he's done what they asked him to do for a try which should keep them on side if it does have to come back out-
William Revit

I'm wondering if there is an issue with the detent spring, or its little peg. I think the end is rounded, to locate into the notch on the selector shaft. If the peg is sticking or inserted the wrong way round it may not retract smoothly as the selector shaft slides past it, causing it to initially refuse. But then work once it has been pushed back a little for later changes.
At least it us something that can be checked in situ.
GuyW

This thread was discussed between 01/06/2023 and 02/06/2023

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