What causes Moke gearboxes to jump out of gear?

[bnicho]

One for the gearbox gurus.

What causes Moke gearboxes to jump out of gear?

Once you have eliminated the shifter as the fault, what else can make a Moke gearbox consistently jump out of second gear when you back off on the throttle?

I'm thinking 1st-2nd selector fork, but I've seen references online to detent springs.  The only detent spring I can see that affects shifting is the one in the diff housing that acts against the selector rod.  But surely if that was the fault, then it would jump out of other gears too??

Thanks,

[Newie]

I'm certainly not a gearbox guru and it's probably not your issue, but for the sake of the discussion I was having trouble with mine jumping out of gear because of cracks in the body where the top engine mount attaches. This obviously allowed too much movement in the engine/gearbox which would cause it to jump out of gear - especially under sudden deceleration.

This issue has been fixed and it doesn't jump out near as often, but does still occasionally do it, so I'm thinking the engine mount may have been exaggerating some other problem.

[melbournerob]

My old gearbox jumps from second gear on deceleration too.......did for ages (at least 7,500km...) - I swapped engine and gearbox recently for a complete newer assembly but the old one is up for reconditioning one of these days so I would love to know the answer too...

No other gearbox issues, no funny noises or whining....just second gear.

Rob

[bnicho]

No other gearbox issues, no funny noises or whining....just second gear.

Mine was exactly the same Rob.  Other than the second gear issue it worked perfectly fine and was quieter than any other Mini gearbox I have driven. 

EDIT:  The steadies and jmounts were all tight as a drum and no cracks in the firewall or brackets.  Also it jumped out of second once in the donor car but I thought I had knocked the gearstick.  I only drove the donor car a couple of times around the block. 

[shorty 68]

Not a guru but in the gears there are  springs that move the gears along a shaft and alot has to do with the borc rings too.
Cheers shorty

[Tim]

I'm told that the part of the selectors that go round the gear can 'spread' which can let it happen. A mechanic told me that you can close them up a bit to prevent it happening, but I think I'd rather replace them.

Tim

[bnicho]

I'm told that the part of the selectors that go round the gear can 'spread' which can let it happen. A mechanic told me that you can close them up a bit to prevent it happening, but I think I'd rather replace them.

Tim

They are the selector forks I was referring to. 

http://www.minispares.com/product/Classic/TSP100390.aspx

For 45GBP I'd rather replace them than try squashing them and get it wrong.   

Cheers,

[Tim]

Yep, they are made of some kind of brass/bronze alloy, I don't know how well they'd take to getting squeezed in a vice. They do wear a lot, so I'm sure that there's a specification for how worn they are allowed to get before they are no good.

Tim

[Tim]

I just noticed that they say "now held in place by a roll pin" does that mean you need a new shaft too?

Tim

[bnicho]

I just noticed that they say "now held in place by a roll pin" does that mean you need a new shaft too?

Exactly the question I was going to ask them.  Also which roll pin size. 

By the way, I have found watching these videos a couple of times invaluable in understanding how everything works and fits together.  Highly recommended.

http://www.minimania.com/Classic_Mini_Gearbox_Rebuild_-_Mini_Mania_Video

Also these pics are a great quick reference guide:

http://www.minimania.com/Gearbox_Rebuild

(Admins, it might be worth putting the above links in the FAQ's.)

Cheers,

[Nzdraughty]

Worn synchros can also cause it to jump out of gear, mine used to jump out of third when going over railway crossing etc...

When I rebuilt the gearbox in my mini I took the time to replace the 3 small ball bearings & springs in each synchro, and why wouldn't you when they're so cheap....http://minisport.com.au/mini-4-speed-all-syncroa-ball-and-spring-kit-does-1-selector-hub-2-hubs-per-gearbox

[Terry]

Hi,

I have worked on a problem of the gears disengaging a few years ago and it turned out to be the single row bearing for the input shaft was moving because someone had used the large circlip from an older 3 synchro box and it wasn't staying put and had just enough movement to let the assembly move about and knock itself out of gear.

It would be a long shot if the cause was the same, the wrong circlip, but still look for movement at that end.

Terry

[dumb]

Exactly the question I was going to ask them.  Also which roll pin size. 

By the way, I have found watching these videos a couple of times invaluable in understanding how everything works and fits together.  Highly recommended.

http://www.minimania.com/Classic_Mini_Gearbox_Rebuild_-_Mini_Mania_Video

Also these pics are a great quick reference guide:

http://www.minimania.com/Gearbox_Rebuild

(Admins, it might be worth putting the above links in the FAQ's.)

Cheers,

the roll pin size is 1/8" but forget that idea. buy a long series 1/4" unf tap and thread the hole like the original ones and screw the needle nose bolt in as per original. by the way the new ones are soft as brie cheese not like the old manganese bronze ones.

[FNQ]

Hi


the sources are identified as above. Best solution take apart rebuild etc  but if trying to avoid that for a while


check the upper rod hasnt become detached from diff casing ( answer courtesy guessworks) and secondly alignment, sometimes a worn engine mount or engine steady can allow an incomplete engagement, so get everything tightened up to reduce any play  Good luck

[bnicho]

Hi,

It seems in my case it was down to a well worn 1-2 selector fork.  When operated out of the car it was clear that second was not enagaging fully and hence it was dropping back into neutral when I backed off on the power.  When I stripped the box down I found the selector for had loads of play on the hub.  The rest of the gearbox appears to have been recently rebuilt, so I guess they did not pay any attention to the selector forks. 

Cheers,