Triumph Repair: TR6 ( 1975) Overdrive, automatic transmission shops, clutch pedal

Question
My 1975 TR6 has o/d in 3rd and 4th gear. When engaged it "kicks in" but the RPM's increase, is this correct as I am of the opinion the RPM's should decrease? When disengaged it kicks off. Also, when the car has run using o/d and been parked for a short while. ( 20 minutes) I go to use o/d again and it does NOT kick in, there is no change in rpm's. Any ideas? Many thanks.

Answer
Hi Peter,
Your symptoms are of no use except to tell you that something is wrong.
The RPM should drop when the OD engages. However, there are many other factors to consider and the first is to make a test of the clutch first by running up to a fast cruise speed without OD and just step on the clutch pedal momentarily and release it quickly and note if the clutch grabbed solidly. If it jerked the car then the clutch is ok and you can start running tests on the OD. If you skip this test you are wasting your time going further.

Now you can check the transmission oil level. It would be a good idea to change the oil at this time too. And for this test use engine oil in the transmission. (the OD is just a two speed automatic transmission) The level must be up to par or the OD will not operate. Once you have changed the oil and put the level correct. Take the car out and drive it (no OD) for 30 minutes or more and then go out on a highway and take the car up to at least 55 MPH in 4th gear before you engage OD and set the throttle steady and turn on the OD. If it does not drop in RPM you need to have it's oil pressure tested. This is not something a Do-It-Yourself person should do. You need to find a British car specialist or ask some automatic transmission shops if they can pressure test it. If you get it working correctly on the engine oil you can either leave the engine oil in (in cold weather) or switch back to gear oil. Either one works well.
Howard