Gearbox Re-seal

[colin3511]

Hi,

I have a rebuilt A type overdrive gearbox that, now fitted, has a couple of leaks from the overdrive unit and one in the bell housing. Pretty competent mechanically but never touch a gearbox before. How straightforward would it be to replace the paper seals? Is there anything I should be aware of?

Alternatively I'll get it done professionally but I've tackled everything else.

Thoughts?

Thanks, 

Colin

[Drewmotty]

Go for it. It’s not rocket science or even a complicated gearbox.

Follow the WSM be methodical and keep everything clean. 

Don’t hit anything with a hammer, use quality seals and the correct gaskets with a bit of grease or some Welseal if the faces are less than perfect.

Avoid silicone sealant. 

Ask if you’re not sure. 

You’ll be fine. 

[Chilliman]

Quote

 Is there anything I should be aware of?

One of the culprits for an o/d leak is the adapter plate that sits between the units, they tend to get distorted along the bottom edge if someone has used force previously to assemble everything, it's worth checking with a straight edge as it's not always apparent to the naked eye & it would be a shame to go to all the effort of replacing the gaskets only to still have a leak..

[Mike C]

Make sure you have access  to a manual and the Buckeye Triumph site. There are things like the bolt tightening sequence's and torques you need, especially for the solenoid cover plate which is under potential  load all the time.

[Litespud]

6 hours ago, Chilliman said:

One of the culprits for an o/d leak is the adapter plate that sits between the units, they tend to get distorted along the bottom edge if someone has used force previously to assemble everything, it's worth checking with a straight edge as it's not always apparent to the naked eye & it would be a shame to go to all the effort of replacing the gaskets only to still have a leak..

Agreed - the adapter plate is prone to warping or cracking if someone tried to muscle the O/D onto the tranny without having all of the gears lined up. When I overhauled my A-type O/D I found that the plate had a major crack. A new plate was available for ~$130, IIRC. Apart from that, scrupulously clean the mating surfaces. I think I used black Hylomar - use sparingly, because most of it will be squeezed out, and you don't want extruded chunks breaking off and floating around inside the unit

[Chris59]

You'd better check if the breather is not obstructed….

[John L]

You might find that a lot of the leaks of the overdrive actually come from the selector shaft seals, and then it runs down that overdrive joint.

I think the O rings that are provided for the selector shaft seals are actually too small to fill the cavity where they sit, There are other options to use a quad ring seal, but even that will need some packing to stop it being too loose, the seal must be held tight to stop it pumping oil out. There is a lot of info on the forum about these rings a search is needed I'm afraid.

The same applies to the input shaft seal, you need to make sure that the input shaft doesn't moving in and out once it snout is bolted up to the gearbox, you may have to leave out the paper gasket and use a sealing compound, usually the bearing will rotate in the housing and will wear its outside circlip ring, which should hold it tight by the snout when bolted up.

Also the side cover operating shaft seals need to be the square section type, but all the usual suppliers seem to be just O rings that don't seal, this has been on the forum recently also.

John

[Mike C]

I can only find O rings available for the operating shaft seal. To seal a proper O ring seal joint needs to incorporate  a groove to pressurize behind the O ring. 

The usual suppliers' seals are just O rings which are probably a waste of time in terms of long term durability.

If you have a leak from these seals you need to find the proper replacements- I'm still looking for a source for these.

[RogerH]

9 hours ago, Mike C said:

I can only find O rings available for the operating shaft seal. To seal a proper O ring seal joint needs to incorporate  a groove to pressurize behind the O ring. 

The usual suppliers' seals are just O rings which are probably a waste of time in terms of long term durability.

If you have a leak from these seals you need to find the proper replacements- I'm still looking for a source for these.

Hi Mike,

ORS in Sheffield England do a seal kit for the OD. It contains what should be the two square xsection 'O' rings. If you only want the rings then it is expensive ( £20 or so.).

A couple of years back I phoned them and they gave me a number which turned out to be Osection rings. These grip the shaft too much.

I hope the kit is better.

I'll have a look at the kit this morning and get back to you.

 

Roger

 

[Mike C]

Thanks Roger. I'd really appreciate confirmation that the rings are square section. I need new seals  for my winter work program but I don't want to use O rings just because just  they are readily available.

Given the effort involved in replacing the seals I'd much prefer to pay a bit extra for parts  that work permanently.

[RogerH]

Hi Mike,

sorry for the delay.

The square section O rings from OSR are in fact ROUND. This doesn't make them bad, simply round.

They are 1/2" O/D with an I/D of (apprx) 0.305". It is a little difficult to get a precise figure as the rubber deforms when you move the vernier. 

It should just nip onto a 5/16 shaft.

 

Roger

[Mike C]

Thanks Roger. I'll see what I can get locally if there's any question over the local product's suitability I'll order from ORS.

[RogerH]

Hi Mike,

I recall that last year I fitted the seals that ORS recommended (nothing special) - these were round section.

I noticed with the engine not running that I could engage overdrive but when deselecting the rigging lever stayed where it was.

I wrongly (I think) interpreted this as the O rings holding the shaft too tight.

But thinking about it  there would be no pressure forcing the rigging ;ever back.

The ROUND O rings should work.

When i get my TR4 back to the house I'll check this (maybe next week)

 

Roger

[Mike C]

No hurry Roger. It's nearly time for me to start winter work in S E Australia and the driving weather could be miserable for months.

As I see it the operating valve stem is exposed to oil pressure when the overdrive is engaged and the sealing  ball is closed. When the lever at the bottom goes to direct drive this pressure forces the valve stem to follow the lever down.

The system needs the OD oil pump operating to switch  reliably.

If round O rings will work I'll try to get them in Viton, Shore 70 hardness.

[Mike C]

My winter works are approaching completion. About 6 weeks ago I replaced the overdrive operating valve seals with 7.60mm x 2.62mm , Shore 75 ,BS 109 Viton O rings. In the garage this has stopped the leak and the A type OD is switching reliably. I won't know for sure that this has fixed the problem until the car is back on the road later this year.