TR2/3/3A Overdrive solenoid sticking

[vickxxx]

So I just got the OD in my 1959 TR3A sorted and enjoying the cruise when I realized the OD was engaged even with the switch off. Once I had a chance to stop and raise the car back at my garage. With trans in 4th gear, i flipped the switch on and off with no clicks at all. The amp gauge showed a high draw with it on and would not come down till I clicked it off. I did what many British auto mechanics do and that was to break out the ball peen and gently tap the solenoid. I then flipped the switch and relay and solenoid were clicking just fine. I then took the car for another spin, engaged the OD and disengaged the OD a few times during the cruise. When I got it back home, the solenoid again was sticking. Another love tap fixed it, but I'll probably have to replace the solenoid. Before I do this, has anyone run into this problem, is there an adjustment I'm overlooking, can the closing switch in the solenoid be accessed and repaired?

 

[Mstanleyfl]

Others may know more but I would be very careful about using reverse until this is corrected....

 

[vickxxx]

Others may know more but I would be very careful about using reverse until this is corrected....

Yes. I've heard about that. Ive opted to not use the OD till it's rectified. The 15amp draw when the switch is on is scary enough. I'd hate to have the solenoid melt on me Thanx!

 

[TR3driver]

Good point about reverse. Backup slowly, and if it feels like you're trying to run over something, STOP! Call a wrecker if you have to, but don't force the car backwards with both rear wheels on the ground. Backing up with the OD engaged puts the OD between a rock and hard place; usually the sprag clutch will be what breaks and it may take the annulus and possibly even the housing with it.

There is an often overlooked "adjustment" for how far the solenoid plunger can extend when released; if it drops out too far the solenoid may not be able to pick it back up. The earlier units actually had an adjustable stop there; but later ones just had a rubber buffer that frequently falls out. Here's a shot of my substitute stop (the number of washers can be changed for adjustment)


It is possible (at least with most solenoids) to access the pull-in contacts. But they are pretty basic, so I'm doubtful that is where your problem lies. More likely the plunger is not pulling all the way up, either for the reason above or something is causing it to bind. Last time it happened to me, there was a bit of errant gravel that had found it's way inside the solenoid. Here's a photo that shows the contacts (along with the transient suppression diode that I added)




PS, I also added an in-line fuse near the relay, so the fuse will hopefully blow before the solenoid (or wiring) melts. I used an MDL 8 (8 amp slow blow) but I believe that even an AGC 5 would work.

 

[CJD]

15 amps means the solenoid is no good. It has an energizing circuit that may draw that much, to forcefully close the OD valve...but once engaged, there is a contact within the solenoid that trips, so the holding current should be closer to 1 amp. If you are drawing a constant 15 amps, then either the solenoid is not reaching the full stop position (for which there IS an adjustment), or the internal contact is inop.

At 15 amps the solenoid will fry itself within 10-15 minutes.

Edit...

I took my solenoid apart, and was able to adjust the plunger and contact. It is not difficult, so long as the 2 coils are still functional. Sorry, I just looked for pics, but I didn't take any...

 

[vickxxx]

Good point about reverse. Backup slowly, and if it feels like you're trying to run over something, STOP! Call a wrecker if you have to, but don't force the car backwards with both rear wheels on the ground. Backing up with the OD engaged puts the OD between a rock and hard place; usually the sprag clutch will be what breaks and it may take the annulus and possibly even the housing with it.

There is an often overlooked "adjustment" for how far the solenoid plunger can extend when released; if it drops out too far the solenoid may not be able to pick it back up. The earlier units actually had an adjustable stop there; but later ones just had a rubber buffer that frequently falls out. Here's a shot of my substitute stop (the number of washers can be changed for adjustment)


It is possible (at least with most solenoids) to access the pull-in contacts. But they are pretty basic, so I'm doubtful that is where your problem lies. More likely the plunger is not pulling all the way up, either for the reason above or something is causing it to bind. Last time it happened to me, there was a bit of errant gravel that had found it's way inside the solenoid. Here's a photo that shows the contacts (along with the transient suppression diode that I added)




PS, I also added an in-line fuse near the relay, so the fuse will hopefully blow before the solenoid (or wiring) melts. I used an MDL 8 (8 amp slow blow) but I believe that even an AGC 5 would work.

Many mahalos for your in-depth diagnosis of my sticky solenoid. I think you just saved my transmission! I'll remove the tunnel cover so I can do a proper visual, removal, clean and adjust. Hopefully that will rectify my situation. The inline fuse is a great idea.

 

[vickxxx]

15 amps means the solenoid is no good. It has an energizing circuit that may draw that much, to forcefully close the OD valve...but once engaged, there is a contact within the solenoid that trips, so the holding current should be closer to 1 amp. If you are drawing a constant 15 amps, then either the solenoid is not reaching the full stop position (for which there IS an adjustment), or the internal contact is inop.

At 15 amps the solenoid will fry itself within 10-15 minutes.

Edit...

I took my solenoid apart, and was able to adjust the plunger and contact. It is not difficult, so long as the 2 coils are still functional. Sorry, I just looked for pics, but I didn't take any...

Thanx for the info. I think between you and Randall I'll be R&R'ing the solenoid for a much closer inspection!!