Overdrive Problems.....

[Lagnakeil]

Hello,
i have just had my overdrive rebuilt and I have just finished reinstalling the box. It is a j-type overdrive. The electrics work correctly, the inhibitor switch stops power going to the solenoid in first second and reverse. The gear knob switch works switching power through when on and switch off the power in the off position. The solenoid can be heard firing and releasing when the power is provided and removed.

The problem is that whilst driving, the overdrive can be switched on but not off. It remains constantly on. Even when the car is switched off and the battery disconnected for a week the overdrive us still on. The only way to release it is to put the car in reverse. This has the effect of raising the back of the car as if the hand brake is on. Then there is a loud "BANG" and the car will go backwards. Drive forwards and the overdrive is off. Switch in again, and the overdrive comes on and stays in. The only way to switch off is to put the car in reverse.

Any ideas before I take the car back?

or should I throw in the towel and buy a Daf Vario-matic?

Richard

[TR5convalescent]

Please DO NOT reverse the car again in OD. You will destroy the unit if you haven't already. The clutch in the unit is unidirectional.

If this isn't a wiring fault, it is possible that the solenoid is sticking because the shaft isn't true, or the o rings are swollen or there is corrosion on the the solenoid shaft.

Other more knowledgeable people will be along soon but please don't reverse the car or even allow it to roll backwards with overdrive engaged.

David

[stag8manod]

+++1 with TR5c, take it back.
Cheers Ian A

[Guest]

That sounds suspiciously like a seizing overdrive cone clutch.
If it seizes in the OVERDRIVE IN, position it will give those symptoms and NO it won't damage the unit like that, despite what people say.
The clutch is forced back onto the annulus with 4 heavy return springs, but they may not be sufficient to overcome the stiction once it's stuck IN.
The reason why there's a BANG when it come back to normal, is because the PLANET gears also play a role in returning the clutch back to the internal clutch (non OD condition).
The moment torque is applied a fight will take place between the unidirectional clutch and the planet system forcing the outer OD cone clutch to disengage from the brake ring and the inner one to re-engage on the annulus.

Apart from possible problems with the relief valve and solenoid it does sound to me like the problem is mechanical not electrical.
(Btw I have been repairing overdrives since 1982.....when I got featured in a magazine repairing one on a GT6 in under one hour.....)

[Marco Polo]

I've had similar symptoms as you, can I suggest changing the O-rings in the solenoid shuttle valve? It happens a lot more regularly Down Under due to the higher ambient temperatures. Unfortunately the commercially available O-rings don't last long, however the use of aerospace items has improved time between replacement considerably. you may find that in the UK you don't need to go to such lengths, especially if you don't have access to such !
regards,
Raoul

[davidf]

I don't think it can be hydraulic (or electrical) because the overdrive system needs pressure generated by the internal pump, which in turn needs a minimum speed of rotation (usually stated as equivalent to around 20 mph). So, it does sound as though it is mechanically stuck in.

[Lagnakeil]

Hello all,
Thankyou all for your input. It transpires that the diagnosis is a sticking clutch cone. I took the car into the garage today and they will bed the clutch in over the next few days. When I arrived, there was some confusion as another Triumph was on its way up with the same problem.
I hope that they can sort it and that the uni directional clutch is ok. I'd hate to have to remove the box again as I do it with the car on axle stands and car ramps. Space is not in abundance.
keeping my fingers crossed........
Richard

[Guest]

Sounds like our gut alt friend "fawlty machining" ja?

Most people aren't aware how accurate an OD clutch has to be machined.
It's to a few minutes of a degree.
Get it wrong it sticks, or slips under load.

Then of course there was all the Volvo J types they made with the EXPLODING clutches.
That was cured by shot peening the alloy clutch member before cooking the linings on.

Finally came Ford and some Triumphs with the slipping unidirectionals......wow that generated some work and quite a lot of cash.
I reckoned I could turn one around and get the car back out working properly in under 2 hrs....

[mole42]

Ello Rich, tell yer co forum member that it could well be the bigg circlip on the frunt of the inner OD
it,ll have sprung oot of its groove, as not been tapped concentric,

the bit under the brass wesher on here

https://www.google.co.uk/search?q=j+type+overdrive+parts&client=firefox-b&dcr=0&tbm=isch&tbo=u&source=univ&sa=X&ved=0ahUKEwi61LDr9L7XAhUqKcAKHQDiBiwQsAQILg&biw=1368&bih=810&dpr=1.25#imgrc=CDNWtM5PNhan3M:

or this, the split washer / circlip, first one after the sun wheels on top pic

https://www.google.co.uk/search?q=j+type+overdrive+parts&client=firefox-b&dcr=0&tbm=isch&tbo=u&source=univ&sa=X&ved=0ahUKEwi61LDr9L7XAhUqKcAKHQDiBiwQsAQILg&biw=1368&bih=810&dpr=1.25#imgrc=IoiY5TFVLZCnqM:

had a few like this
rgds M