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TR4/4A Overdrive Solenoid issue TR4

thechileman

Jedi Hopeful
Offline
I need some help with troubleshooting this problem. I bought the car about a year ago, the Overdrive was intermittent. The Solonoid looked like it had overheated significantly, and was actually melted on the plastic end. I put in a new Solenoid, and it fixed the problem. Cut to this week, about 1500 miles later. My Overdrive stopped working. The new solenoid again looks overheated, (the plastic discolored this time.) And smells like burnt electrical. Voltage seems to be normal (Checked with a multi tester...) What else do I need to look at?? I hate to put another solenoid in, only to have it burn up as well. what am I missing? (The car is still positive ground, if that makes a difference.)

Any help would be appreciated!
 

TR3driver

Great Pumpkin - R.I.P
Offline
Anything that blocks the plunger from moving all the way into the solenoid can cause the solenoid to overheat and burn up. There is a high current "pull-in" coil, and contacts inside that take it out of the circuit when the plunger hits the top.

So, look for grit or anything that has found it's way inside the solenoid.

Also check the lever adjustment carefully, both in the 'operated' position with the plunger fully seated, and how far the plunger can fall down.

On some A-types, there is a rubber stop below the plunger that can get crushed or disappear, others have an adjustable stop that can come loose or fall out. If the plunger falls too far, the solenoid may not be able to pull it up, and will burn out as above.

Check out Nelson's articles on the Buckeye Triumphs site for more information.
https://www.buckeyetriumphs.org/

I also advocate installing a fuse in the circuit to the solenoid. That way, if something does keep the plunger from hitting the contacts to open the circuit, the fuse will blow and you get a chance to try to correct the problem. As I'm sure you've noticed, replacing solenoids gets kind of expensive!

I used a MDL-8 (8 amp, time delay) fuse just because that was what I had on hand. But I believe an ordinary 5 or 10 amp fuse would do fine. The pull-in coil draws close to 20 amps, but the contacts should open before even a 5 amp fuse can get hot enough to blow.

Early Stags had A-type ODs, and used a 10 amp Lucas fuse, which is roughly the equivalent of a 5 amp fuse (eg AGC-5) in the American system of rating fuses.
 
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thechileman

thechileman

Jedi Hopeful
Offline
Thanks Randall! That definitely gives me something to look at. There was no dirt where the plunger slides, but I can definitely check the adjustment, to make sure It is traveling all the way up.. Your advice make a lot of sense...

The knowledge on this board is awesome!!
 

Don Elliott

Obi Wan
Offline
If your solenoid has a small round accordian type rubber boot at the bottom of the plunger, that may be preventing it from falling all the way down. I removed mine years ago.
 
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thechileman

thechileman

Jedi Hopeful
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It did have the boot. I will leave it out when I install the new part... Thanks!
 

TR3driver

Great Pumpkin - R.I.P
Offline
Don Elliott said:
that may be preventing it from falling all the way down. I removed mine years ago.
However, "not falling all the way down" is not likely to be a problem, IMO. The lever has a moderate amount of freeplay, where only gravity pulls the plunger/lever down ... it doesn't actually matter if the lever moves down this far or not. But when the ball in the operating valve is actually being held off it's seat, there is a good deal of hydraulic force (plus the spring over the ball) that pushes the lever down.

IMO, it's better to leave the boot in place, to try to avoid getting crud inside the solenoid.
 

jessebogan

Jedi Knight
Offline
I believe there is a small "switch" in the top of the solonoid body. The plunger has to rise enough to trip this switch. It changes from a high amp "pull in" current to a lower "hold in" draw. Check that the solonoid actually moves up all the way to trip the switch.
 

Geo Hahn

Yoda
Country flag
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I used Randall's suggested solution to (hopefully) assure I never cook the solenoid due to failure of that cut-out.

Here's a wordless workshop on how it went together. Made so it was easy to put in or remove later:

SF_Fig_1.jpg


SF_Fig_2.jpg


SF_Fig_3.jpg
 
OP
thechileman

thechileman

Jedi Hopeful
Offline
My new part will be here Friday, I already have the inline fuse wired in... Thanks for all the help everybody!
 
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