A type Overdrive

[Graham Harris]

I have had ongoing problems with this unit and wonder if anyone else has come across the same situation.

I purchased the box and OD from TR Bitz as part of my restoration project and took it apart for inspection and replacement of any damaged parts. One of the last items to take out was the accumulator and piston and to my surprise found the O ring had what looked like a bite taken out of it so it would not have had any oil pressure and would not have been working when last in a vehicle.

This unit is from a TR6 with the heavier casting and the smaller accumulator piston (one and an eighth inch diameter) and after fitting to the car it performed as i would expect it to for about 1000 miles then it stopped so out it came and would you believe the same thing had happened. A piece chewed out of the O ring. Again replaced and another 1000 miles and its stopped working again and i am sure i will find the same problem.

What could be the cause,once the accumulator is fitted it is held in place by a tube so it has no movement the only pressure on the O ring is oil Penrite hypiod 80W-90 gear oil.

Any ideas welcome thank you.

Graham

Edited November 16, 2015 by Graham Harris

[AlanT]

Is this the O-ring that seals the housing, for the sliding piston, against the main casing?

 

If the oil pressure is blowing this apart then you need to measure the pressure.

I'd guess the relief valve is stuck.

[Drewmotty]

Could be that the o-ring is sitting against a defect in the cylinder wall. A slight leak will erode the o-ring pretty quickly.

Alternatively the o-ring may be catching on a defect (sharp bit) when being assembled and again being subject to subsequent erosion.

Andrew W

[Graham Harris]

Yes Alan this is the O ring that seals the cylinder for the accumulator piston which is in itself the relief valve. As the piston is compressed it reveals relief drillings in the cylinder which take the excess oil through internal drillings to between the main bushes and then into drillings in the input shaft for lubrication to the rest of the works. In order to create excess pressure the internal drilling would need to be blocked which is quite possible . I was hoping to avoid taking the box out and just replace the O ring through the side cover with unit in the car. I may be able to apply air to the oil way to see if it is open, if it is it could be a sharp edge as Andrew suggests catching the ring on installation.

Thanks for your input.

Graham