Separate TR6 gearbox and J type Overdrive/oil leak

[Steve Morris]

Having replaced most of the gaskets and O rings I have narrowed down the oil leak to the gasket between the gearbox and overdrive.

I was hoping to avoid separating them but it seems unavoidable now.  Is this likely to be a problematic exercise?  Any pitfalls to watch out for? I’ve heard that spline loading can be an issue.

cheers.

 

Edited May 2 by Steve Morris

[Lebro]

Is the box out of the car ? A type or J type ? 

Bob

[John Morrison]

Steve, how bad is the leak?

because thats something I would be trying to leave until the winter, 

also to say it is almost impossible to make these old girls oil tight, 

experience tells me you fix one only to soon find another.

If you can live with the leak, then enjoy the car, also are you certain

that the leak is between the joint, and not for example from the GB top

and the selector rods?

John.

[RogerH]

Hi Steve

This is an Autumn/Winter job as I believe you will need to remove the GB and OD in order to separate the two.

That adaptor plate can warp and can crack at the 6-o-clock position.   Spares are availabel from ORS in Sheffield.

Be absolutely certian tis is the issue and not (as John pointed  out) not coming from above.

It is also very very difficult to bodge a repair insitu - I've tried. many ways.

Roger

PS - having just had a look at the Moss schematic the above may not be true for the 'J' type OD.  It does not have the same adaptor plate.

Edited April 24 by RogerH

[Steve Morris]

Thanks for the replies chaps.

The box and O/D are out of the car and most of the seals and gaskets have been replaced.

The two have been sitting level since done while I finish the engine and I’m certain that this is the only spot it can be coming from.  I wiped the oil away and checked again and it is the same spot.  If it’s leaking like this when cold then I suspect it’s going to be worse when hot, in operation.  Oil level is full, btw.

While the box is out it would be the best time to tackle it I think but only if it’s not a nightmare proposition.

 

[Steve Morris]

Bob, it’s a J

[AlanG]

No big deal to split the J type O/D from the G/B. 

FWIW a J type can be removed from the G/B insitu.

Alan.

[Steve Morris]

So drain the oil, undo the nuts and pull?

[wheeler]

Steve,

All you need to know about J type overdrive.

Bill

https://www.buckeyetriumphs.org/gearbox

[Steve Morris]

Thanks Bill.

[Malbaby]

Are you positive that the leak is exiting the gasket and not from one of the bolts...I have a vague recollection that there is at least one bolt somewhere that is in contact with the inside oil in the case.

[Mike Collins]

To remove the J from the gearbox it needs to have been driven from the propshaft end or the two sets of splines will have locked together. It should then separate easily.

If last rotation was from the clutch end it will be near impossible.

Found that out the hard way.

Good luck, Mike.

[Ian Vincent]

FWIW, I didn’t find it straightforward to connect my gearbox and Type A overdrive with both on the bench.  I wouldn’t even think about trying it with the gearbox still in the car.  Maybe a J type is easier.

Rgds Ian

[Steve Morris]

21 hours ago, Malbaby said:

Are you positive that the leak is exiting the gasket and not from one of the bolts...I have a vague recollection that there is at least one bolt somewhere that is in contact with the inside oil in the case.

I shall investigate - that would be a perfect scenario…

[Steve Morris]

2 hours ago, Ian Vincent said:

FWIW, I didn’t find it straightforward to connect my gearbox and Type A overdrive with both on the bench.  I wouldn’t even think about trying it with the gearbox still in the car.  Maybe a J type is easier.

Rgds Ian

the box and O/D are on the bench.

[Steve Morris]

11 hours ago, Mike Collins said:

To remove the J from the gearbox it needs to have been driven from the propshaft end or the two sets of splines will have locked together. It should then separate easily.

If last rotation was from the clutch end it will be near impossible.

Found that out the hard way.

Good luck, Mike.

 

11 hours ago, Mike Collins said:

To remove the J from the gearbox it needs to have been driven from the propshaft end or the two sets of splines will have locked together. It should then separate easily.

If last rotation was from the clutch end it will be near impossible.

Found that out the hard way.

Good luck, Mike.

This is what is putting me off an attempt.

[Mike Collins]

It does not have to be driven hard, rotation by hand or drill may well do it. Make sure the direction of rotation is correct though.

Mike.

[Lebro]

For what it's worth  I rebuilt a Sunbeam Alpine gearbox, with J type O/D. Was not a problem getting it off, or back on.

Bob

[Steve Morris]

I’ll give it a try and see what happens.

[Steve Morris]

On 4/24/2026 at 11:37 PM, Malbaby said:

Are you positive that the leak is exiting the gasket and not from one of the bolts...I have a vague recollection that there is at least one bolt somewhere that is in contact with the inside oil in the case.

This might well have hit the nail on the head - looks like oil is exiting from the two lowermost bolts attaching the adapter to the gearbox.  This makes sense as they are the ones sitting below the filler plug level so I guess the holes go through to the main gearbox casing.
Will put some thread sealant and a copper washer on these and wait and see.

[Steve Morris]

Confirmed.  Removed one of the lowermost bolts and oil flowed out so this is looking very promising.  Up-ended the box and after carefully cleaning out the threads with a pipe cleaner have re-installed with high temp thread sealer and a copper washer on both.  I did hesitate and consider using the locking washer in addition to the copper but thought better of it.  Will monitor the bolts for tightness once she’s running again.

[Steve Morris]

Bingo - completely snuff dry today.

[stillp]

Result!

[Steve Morris]

Yep, still oil free.  Thanks for all your help chaps. 

[RogerH]

Who is a lucky boy then - well done.

 

Roger