BT7 Overdrive

For years my overdrive unit will only stay engaged for about 5 miles then kick-out. It is as if the oil gets warm and it quits working. I thought for sure I had figured it out after reading an article about not using detergent oil in the transmission/O.D.. I changed the 10/40 Valvoline to a straight 30W non-detergent but it had no effect. Could lever setting or a weak solenoid do this and be so consistent?

royandale3000 said:

For years my overdrive unit will only stay engaged for about 5 miles then kick-out. It is as if the oil gets warm and it quits working. I thought for sure I had figured it out after reading an article about not using detergent oil in the transmission/O.D.. I changed the 10/40 Valvoline to a straight 30W non-detergent but it had no effect. Could lever setting or a weak solenoid do this and be so consistent?

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Hi & welcome to the forums,
If it works when cold I doubt if the lever setting or solenoid are the problem. It's barely possible that the solenoid is letting go when things get hot. You could drive the car with the transmission tunnel removed & observe the solenoid's action. Don't get your shirt tail in the drive shaft. You can even manually operate the operating lever to see what happens.

I think it just isn't holding pressure or the pump is not building pressure. The problem could be as simple as the operating valve is not completely seating/sealing or that the pump intake screen (under the drain plug) is plugged. Other possibilities are the accumulator piston seals leaking, the pump check valve leaking, or the operating pistons not sealing. The operating valve, the accumulator, & pump check valve can be checked without removing the OD. Other problems would require disassembly.

First check the operating valve & the pump screen. The ball has to seal on a bottom seat and seal on the end of the valve spindle. The next easiest thing would be to have someone knowledgeable check hydraulic pressures with a gage.

These OD's are pretty complex so you may be into learning a whole bunch, or finding someone who really knows these OD's. I hope it will be easier.
D