A-overdrive slow to disengage

[TR4nut]

I had my first glitch with my overdrive today while heading to the Saturday morning Triumph breakfast club here in Houston - after some pretty spirited highway driving, my overdrive failed to disengage. I eventually got it to come down when I took off at a stop light.

Normally the overdrive response is nearly instantaneous both on and off. On still seems good, in fact quite often too good if I don't pay attention and keep the foot on the gas too much.

Today is very hot here, car was at its temp limit for sure. Also, I changed out oil about 2 months ago (30 wt non detergent). Although the oil seemed to work before I'm suspicious of it and am considering swapping to 20W50 Valvoline racing oil.

Anyone experience similar problems? I read up on Nelson Reidel's diagnostics on the Buckeye site and it is a good read but has me worried a bit - is my oil theory just wishful thinking?

Randy

 

[Guest]

What kind of overdrive? A-type and is it original to the car and has it been ever rebuilt or J-type add-on? Solenoid might need changing out. Filter clean? Passageways clogged? Call John at Quantum for advice.

 

[TR3driver]

Offhand, I can think of a few possibilities, in roughly decreasing order of likelihood :

1) Crud in the return port of the operating valve stem. There's a tiny hole in the side that sometimes gets clogged with wear particles from the clutch.

2) OD clutch is getting mechanically jammed into the brake ring. This could conceivably be caused by the wrong oil, but seems unlikely to me. Usually it's a symptom of weak return springs or something interfering with clutch motion.

3) Mechanical hangup in the solenoid, possibly a piece of rock from the road jammed in between the solenoid plunger and it's bore. This can be expensive if it jams the solenoid open rather than closed, since then the pull-in contacts will not open and the solenoid will quickly lose it's smoke.

4) Electrical problem allowing some current to keep flowing in the solenoid. Never seen this on a TR, but had an Audi once that would turn on it's rear window defogger due to leakage across the base of the relay (likely a salt film on the phenolic).

 

[TR4nut]

Its an A-type, original. When I changed the oil, the filter was relatively clean, at least no large chunks of metal greeted me. Typical brass sludge that I've seen before from synchro wear.

My hope is a fluid change and cleaning of the operating valve will straighten it out.

 

[Tomster]

Sidebar, is this a factory original od or did you by one and install?
I ask because I "think" I "need" one

 

[TR4nut]

quote=Tomster]Sidebar, is this a factory original od or did you by one and install?
I ask because I "think" I "need" one[/quote]

Its original to the car. Didn't get to it today, but it is high on my to-do list at this point. If you can source a reliable A-overdrive, I still recommend it, up til now it has been great and I do like running at those lower revs on the highway.

Randy

 

[TR4nut]

Just a followup. Appears to have been a plugged control valve. Very simple to clean out, just a pain to access. Much better than a bad overdrive though!

Changed fluid to 20W50 VR-1 while I was there, everything looked good so I think I'm okay. I am amazed at whoever initially designed that overdrive, it is one interesting & robust piece of equipment.

Randy