Overdrive Not Engaging

[60TR3A]

I flip the switch and nothing happens. Any ideas how to troubleshoot the problem before I take her in to the mechanic?

 

[RomanH]

Start with some basics. First make sure that the transmission if filled with oil. If the oil level is too low the OD will not engage. If that is fine check to make sure that the solenoid is operating correctly. With the ignition in the "ON" position but the engine not running place the transmission in 4th gear and engage the OD switch. You should be able to hear the solenoid click. If not you will need to trouble shoot your circuit for the solenoid. I'm sure someone more experienced will chime in with a preferred method of doing this as I'm not familiar with the TR3 electric system.

 

[hondo402000]

check the switch on the transmission to see if you have a close circuit when the transmission is in 4th gear, could be the switch too

 

[60TR3A]

I put it in 4th, turned on the key and dropped the switch and no click and no movement on the ammeter. I assume that means it's electrical in nature. Either the switch or the solenoid, I guess. Is there a fuse? The light in my garage is rather dim so it's hard to check the fuses but I'll rule them out once I get some decent light. As far as I know, there is no transmission switch (at least, not one that's visible) though I recall back in the 60's that my friend's TR4 had a button on the gearshift that put it into and out of overdrive. Is that the switch you're referring to, Hondo?

 

[Toners]

I just solved a similar problem on my '74. The best advice I had was that the problem was more likely electrical than mechanical. It turned out to be the transmission interlock switch. That is a switch mounted on the transmission that completes the circuit to the solenoid only when the transmission is in 3rd or 4th gear.

The oldest wiring diagram I can find is for a '69 TR6. There the OD electrical circuit is complicated with a relay and two lockout switches, in addition to the column switch. If you want to work on tracking it down yourself, then check for voltage drops from the battery to the fuse block, the column switch, and on down to the solenoid. I found that cleaning up connections along that path was part of the solution.

If you go straight to a mechanic, then make sure he checks electrical issues before tearing the OD apart, or replacing the solenoid.

Cheers,
Tony

 

[TR4nut]

You may also have a bad relay - the relay is located on back of the battery box, nearest to your gas pedal foot. So if its electrical, it could be switch, relay, interlock switches on the gearbox top, or solenoid.

 

[TR3driver]

No fuse originally (on a TR3A), but it's possible someone has added one.

I would start checking voltages at the relay unless you've already got the tunnel out. IMO the relay, lockout switch, dash switch, and solenoid are about equally likely to be the problem. Oh, and FWIW, the overdrive circuit is supposed to be connected on the battery side of the ammeter, so you wouldn't expect to see anything happen on it anyway.

FWIW my "intermittent" lockout switch proved to have been improperly adjusted, by a "professional". Removing the "as required" gasket fixed it right up.

 

[MDCanaday]

There is an Achilles heel to the A type OD.After you have eliminated all of the easy stuff,and know that the lever on the trans is moving,and the unit has clean oil/filter,now for the tough stuff.Down in the bottom of the accumulator well under the huge spring is a little plug.This plug holds a checkball that lets the high pressure oil into the well,and keeps it from bleeding back to the pump.If there is so much as a speck of dirt,swarffe,crud,or dead bugs this valve will not let the pump make the 390psi minimum to engage the clutches. Clean and re-assemble. I have seen it often...
MD(mad dog)