I need help with J Type Overdrive

[Simmo]

I acquired a Triumph 2500TC (1976) Gearbox and J type overdrive in order to fit it to my 3A.
After cleaning the outside I ran it up on a test rig and the Overdrive seemed to behave properly showing 410PSI. Maybe a little low but intend to add a spacer to the accumulator spring later on.
I removed the Overdrive, rebuilt the Gearbox and at the same time removing the Overdrive Sump, cleaning both oil filters and replacing the “O” rings.
Everything seemed very clean but now when I run it up it won’t engage.
I have had another close look under the sump and everything seems all good.
People talk about the operation of the Solenoid but never explain in detail. Mine draws 2.2Ampres and moves only about 1/16” and is rather quiet in its “Click”. Is that the normal operation?
I’m happy to buy a new one but reluctant if it isn’t the problem.
Is there any chance I could have put the Oil Pump Cam on backwards or something like that and the mistake would not inhibit the rest of the assembly?
I'm really stuck and look for someone with great knowledge and wisdom.

 

[titanic]

Are you familar with the Buckeye tech articles? They have a lot of info on the ODs, including a trouble shooting checklist. I don't believe the J type used an accumulator. The amp draw for the sol. is about right at 2 amps. and they are quiet compared to the A type sol. I doubt if the pump cam is backwards. Did you replace the o rings on the sol.? Good luck
Berry

https://www.buckeyetriumphs.org/technical/technical.htm

 

[Simmo]

Thanks Titanic. I have read the Buckeye article and although very good it doesnt seem to go into any fault finding that I havent already tried.

After writing this post I pulled the Solenoid apart and am trying to find someone who can provide the solenoid seals. I am thinking that after replacing those there are few options left

 

[TR3driver]

All of the seals inside the J-type solenoid are common size O-rings. I forget the sizes offhand (but thought they were in the Buckeye articles someplace).

Are you seeing no pressure at all, or are you getting the normal 20 psi 'idle' pressure? If it's nothing at all, then something is wrong with the pump or (more likely) the relief valve/dashpot is stuck or not properly assembled. On the J-type, the solenoid does not control the pressure below 20 psi.

In the direct drive position, the solenoid blocks oil flow through the port closest to the coil (which leads to the pump), and vents the middle port (which leads to the dashpot under the relief valve) to the end port (which leads to the sump). Thus there is no pressure under the dashpot, and the relief valve is controlled by a relatively weak spring to provide the 20 psi. (There were a couple of different designs for the dashpot, I'm not sure which one a 2500 would have. The original design in my Stag was much more complicated than the one from the Volvo unit I bought for spares.)

For overdrive, the coil causes the solenoid to extend (yes, that is opposite to the way most solenoids work), which opens the passage between the two side ports and blocks the end port. That allows oil under pressure to feed into the dashpot, lifting it up and increasing the force against the relief valve. More force on the relief valve lets the oil pressure go higher and so on, until the dashpot is fully up and the relief valve is regulating at high pressure.

410 psi should be plenty behind a 2 liter motor. The 430-460 spec is for the 2.5 liter TR5/250/6. Stags (3.0 V8) use 510-550.

 

[Simmo]

Hi Randall,
There is no idle pressure but that well could be the fault of the cheap Ebay Gauge - I hope.
Is the Dash Pot, of which you speak, the centre screwed plug under the sump, the one with the spring and ball? If so I had it out this morning and everything seemed clean and good so I changed the "O" ring and put it back.
The Accumulator piston and springs are the configeration without the nut which holds them together, if that makes sense.
Cheers
Ian

 

[TR3driver]

No, that is the check valve for the pump outlet, what the Brits call a non-return valve. The dashpot is probably what you are calling an accumulator, under the plug nearest the solenoid. It's function is not to accumulate oil, but to change the pressure at which the relief valve opens.

Sorry, I've forgotten how that dashpot piston works. It wasn't hard to dope out, but that was a few years ago. I do remember that trying to shim up the idle pressure (in hopes it might engage faster) was a mistake.

 

[titanic]

https://www.6-pack.org/j15/index.ph...7594-J-Type-Solenoid-Rebuild-Project-Pictures
Here is a link to a 6pack forum posting on rebuilding the sol. No explanation as to how it works, but you might find it helpful.
Berry

 

[RomanH]

Randall may be on to something with the relief valve. I was assisting in the rebuild of a J type several weeks ago and it would not develop pilot pressure and would not engage when the solenoid was energized. A quick inspection of the relief valve seat (the disc under the ball) revealed some minor pitting and a bit of damage. After grinding the seat smooth and slightly peening the ball bearing (tap the ball with a hammer into the seat) pilot pressure returned and the OD was operational.

 

[Simmo]

Thank you for that positave feedback. I'll remove the sump, once again and have a very close look. Just waiting on a new gasket kit to arrive. I'll post the results.

 

[MDCanaday]

Everyone has overlooked the real problem,the J type is a poor choice for a tr3.It mounts deep into the X
frame where you might also like to have the exhaust pipe.On a tr3 there is VERY little room to run the pipe under the frame
which will be the only other option.If you have a plasma cutter and dont mind ruining the frame,large holes can
be cut and the emergency brake removed........????
MD

 

[TR3driver]

Everyone has overlooked the real problem,the J type is a poor choice for a tr3.It mounts deep into the X
frame where you might also like to have the exhaust pipe.On a tr3 there is VERY little room to run the pipe under the frame
which will be the only other option.If you have a plasma cutter and dont mind ruining the frame,large holes can
be cut and the emergency brake removed........????
MD

Not overlooked, we (I) told him about that before. But at some point, you've got to play the cards you're dealt. And I'm guessing that A-types are kind of thin on the ground in NSW.

 

[Simmo]

I have a perfectually good TR3A gearbox and "A" type Overdrive that I have removed. I and many others have suscessfully fitted later model Overdrives and gearboxes before without the aid of industrial equipment.
My request for help is with regard to the hydraulics.

 

[Simmo]

Suscess.!!!
My friend Peter Cox, in the UK, who rebuilds lots of race gearboxes and OD's said to look at the gallery between the Pump Housing and the Solenoid. Sure enough there was a small bit of something that poked out of that fine hole. He also told me to open up the hole by about .005" to a size of 1mm. This I have done and now its runnig with a pressure of 580"PSi.
Thank you everyone for your contributions

 

[TR3driver]

Does opening up the hole help it shift faster? Or just less likely to get clogged?

I'd like to see a photo of your installation when you're done; still can't quite see how it will all fit in there but I'm always willing to learn.

I'm also curious as to why you would remove an A-type to switch to a J-type? Are you doing a lot more power than stock or something?

 

[Simmo]

The opening up of the oil galery is to help it not getting blocked so easy. The J type OD is 20 years of engineering improvements ahead of the A type and operates more quickly and more reliably. Here is an artice under the heading "Fitting a 2500 Gearbox to a TR".
I hope that the information will assist.
https://www.tr-register.com.au/Files/technical.htm

 

[TR3driver]

"More reliably" maybe. But I have driven both A and J types, both professionally restored, and no way does a J-type shift even as fast as an A-type, let alone faster. The A-type carries high pressure oil all the time, and the solenoid controls the high pressure oil directly. When the solenoid moves, the 400+ psi oil is dumped directly into the operating pistons, which move and engage the clutch in a matter of milliseconds. They actually had to reduce the accumulator size on the later ODs (for IRS cars), so that it wouldn't shift so fast (the pressure drops during engagement, making the engagement more gradual).

But on a J-type, the oil pressure is low and there is no reservoir of oil under high pressure. After the solenoid moves, the pump has to move enough oil to displace the dashpot, then build up enough pressure to overcome the return springs and then move more oil to move the operating pistons, before the clutch will engage. But the pump piston is much smaller than the operating pistons or dashpot and only acts during part of a driveshaft revolution.. So it takes a minimum of several driveshaft revolutions before the OD is engaged. The time can be minimized by modifying the OD to reduce the clutch movement as much as possible, but there is no getting around waiting for the pump to move the oil.

That's also why the J-type does not work in 2nd gear, while the A-type (except for very early ones) does.