I have a '68 1800 with M41 tranny. OD works fine untill after driving on HWY w/ OD about 20 min. then it will pop in and out of OD. Usually after a couple minutes it will start working ok again for another 20 min or so. I rigged a voltmeter so I could check voltage at solenoid while driving and voltage checks good. I checked the tranny fluid and it is full (using 30 wt oil). Any ideas? Planning to pull off cover to check filter. I can't be sure if the solenoid is acting up during the periods when it pops out, only that voltage is at the solenoid.
Thanks,
Russ

"Asp" is almost certainly right, however, just on the slight chance that he isn't, and if you haven't done so already, I'd check, clean, and tighten all electrical connections, including ground.
Bob S.

All of you will have to replace the actuating piston O-rings. Pulling the OD off the tranny is the hardest part of the job.

All your problems happen when the fluid is hot. New fluid helps for a while but is not a cure.

Time to R&R the OD.

I'm afraid I can't help with that one... but I'd guess its the OD unit (presumably a D tipe unit?) is headed south.

I was southbound on the interstate when mine started doing the same thing. Wasn't long afterwards that it quit working entirely, and hasn't worked since. I did take the bottom cover off and cleaned things, changed fluids, checked electricals... to no avail.

I hope someone has some suggestions, as I'd be curious to hear them too. Good luck with it!
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-Matt I ♥ my ♂

A possibility is that the little aluminum connecting rod on the OD pump has cracked/broken causing nothing to pump regardless of fluid and solenoid action. Found that on my OD during the rebuild.
Not really a solution you want to know about.
-Erik

My 63 has the same problem that you guys are having. I've done the same things, checked electrical, fluid, filter etc. I figured since I have nothing to lose, I put 90 wt gear oil in and that helped some, but it still kicks out when the oil heats up. I'm afraid unless someone comes up with a better answer we're all in for a rebuild.
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Bill (63 P1800 - 69 Triumph GT6 - 74 Triumph Spitfire - 79 Chrysler Cordoba)