UPDATED: Triumph gearbox selector shaft seals. The dreaded rear of the gearbox oil leak. 😠

[Niall Power]

A member asked me about this yesterday and I dug out some further detail so have updated the post here in case its of use to anyone else. Most everyone with a Triumph will have had or most likely does have an oil leak at the rear of the gearbox, let's face it it can be soooooooo many things given those cars propensity to leak oil but a really common one is caused by the gear selector shafts.

Oil drips down the back of the overdrive casing, its visible there and of course its visible as a modest little puddle on the ground. There is a gasket on the gearbox/overdrive mating face but unless this has been disturbed then its not the most likely source for an oil leak. The selector shaft seals are the most likely source for an oil leak in that area, it can be the lip seal on the O/D output shaft as well but there is a way to determine which it is, if you put your hand up beside the box to the underside of the gear selector extension then you will feel whether there is oil there or not, equally if you remove the transmission tunnel cover you will be able to put your hand underneath the selector shaft extension and feel if there is any oil there, you'll see it in fact having dripped down onto the O/D. I'd recommend this route, removing the transmission tunnel cover, whether the oil leak is at the output shaft lip seal or the selector shaft seals the tunnel cover is going to need to be removed in order to fix the leak so nothing lost at this stage in removing it.

The selector shaft extension is the highest point on the box so the only reason there would be oil on its underside is if those shaft seals are leaking, it wouldn't be there from any other leak. If the underside of that extension is dry and yet there is a drip underneath the back of the box/overdrive then its likely the output shaft lip seal. If this simple test shows the leak as coming from the selector shaft seals then its a simple but fiddly little job to change them, the original seals and arrangement don't work well and are very well known to leak even when relatively new. There is an improvement that doesn't add any difficulty or cost to the repair and that's quite simply to use quad rings and PTFE backers instead of O rings as Triumph did, its not a good application for O rings.

 

Selector Extension exposed, 8 bolts holding it down, 6 visible here.                                                                                                       

 

With the selector extension removed its clear here that an oil leak from the extension is dripping down

onto the overdrive area.

 

Selector Shaft extension removed and turned up to expose the shafts. 

The retaining plate for the selector shaft seals visible here, using the quad rings and backers this plate

becomes a compression plate and fulfills a more effective role.

Image here shows the selector fork fixings removed to allow the shafts to be withdrawn, also shown here

are the receiving holes for the springs and ball bearings used for the selector detentes (the mechanism that

gives that nice positive little "snick" when a gear is selected and holds it in that gear). Be careful when 

when withdrawing the shafts that those little detente springs and balls don't get lost, the only fiddly part of

the whole job, just make sure you have them out before pulling the shafts.

 

A rotating cuff keeps the gearshift in position, unbolt and rotate and off that pops, the final obstacle 

to pulling out the shafts.

 

New quad rings in position and PTFE backers going into position, what was the retaining plate now 

acts as a compression plate to keep a mild compression force on the quad rings through the PTFE 

backers.

All ready for the retaining plate and shafts to go back into position. You can see here that the PTFE 

backers are slightly proud of the housing thus providing for that mild compression that makes for a 

long lasting and effective seal.

 

My gearbox has done 4K now without a drip and many others in the TR Register have tried the same mod and report the same. Its not a difficult job and can be done from the top of the car easily enough, removing the carpet and transmission cover is probably half the job. I'd buy the output shaft lip seal at the same time and that way if its not the selector shaft seals one could just go on and do the lip seal as all the access work would be done anyway. The selector shaft seals are pennies. 

 

Supplier: This one is English but they should be available in Ireland too and the spec is detailed here. Abbey Seals in Dublin would be a good bet.

 

 

 

 

Rgds 

 

Niall

 

 

[Niall Power]

Updated with some additional detail and photos as requested.

[Luke Fenner]

Don't seal up all the leaks....the car will have no character left!

 

[Patrick Duffy]

Very nice mod niall! Looks very neat. Fairly amazing that they probably knew it would leak back in the day but pushed ahead with the design anyway. Jay was showing me pictures of his spitfire diff earlier. He changed the breather assembly for a more effective one. The factory breather was a cost saving...washer and a split pin😄

[Bren Walls]

Perfect timing, was unsure what to get her indoors ( or mine is more of a Great Outdoors kinda Girl) so three of these will be just what she has always wanted.........!

[Bren Walls]

Great tip, Niall, are they readily available?

pibren

ps well done on using the forum!

[Niall Power]

Yeah I'll dig out the suppliers I used if anyone wants the details.  Off the shelf available in ones and twos for buttons.