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Triumph Repair/TR6 Overdrive


 I have a 1975 TR6 that the overdrive will not engage on. At first I thought it was an electrical problem but now I'm not so sure. I attached test leads to the connections on the servo on the overdrive and connected my volt meter to them. With the ignition on and the transmission in 4th gear, and the overdrive switch in the off position, I was receiving a reading of about 9 1/2 volts. When I switch the overdrive switch to the on position the volts read zero. Off 9 1/2 on zero. Is this correct? Should I be able to hear the overdrive engage when the switch is moved to on from under the car? (I'm not) What else can be done to test why the overdrive is not engaging?
        Thanks Ken

Hi Ken,

The overdrive solenoid is suppose to receive power with the Overdrive switch turned on and the ignition on and the gear in 4th gear. You should disconnect the solenoid and test the wire to it for voltage. If you have 12+volts then touch the wire to the solenoid and listen for a "click" from the solenoid.

There were two different types of overdrives used on the TR-6 and to ID which you have is easy.
The earlier was the "A" type and it had the solenoid on the left side pointed straight up. The later was the "J" type and it had the solenoid on the lower left side pointed toward the rear.
Both types operated the same.

The car needed to be moving at a cruise speed for the pump to supply sufficient pressure to shift into overdrive. When the oil was cold it often took a while to shift into overdrive. You also need the oil level to be up to spec too.


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Howard M. Fitzcharles III


Triumph TR-4 up & Spitfire, and Engine theory


Dealership line mechanic on MG, Triumph, Jaguar for 15 years, Instructor in commercial mechanics school 2 yr. Product information manager for piston and valve manufacture, Instructor & hotline answer man for import car parts importer 15 yrs.

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