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Overdrive OD'ed

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Norton47

Jedi Warrior
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Question, we are off on vacation and drove up to Port Angeles, WA. Gorgous drive and day, sunny, with the top down. The car (74 TR6) is running well, the new overdrive nicely keeping the revs down and the mileage up. However, once we got to town and I selected the OD to off, it did not disengage. I tried going to second gear as, this does not have a enabling switch, so all power should be removed from the soleniod. Making sure the selector switch was off, I then went back to third gear, still in OD. At a stop light, I shut the engine off, still in OD, when I went back to third gear. So I drove in second gear for awhile and after a several minutes the transmission shifted out of OD.
Now 2 questions, if the voltage is not present, what actually disengages the OD?
The second, on a J type OD, can it be harmed, if in OD and reverse is used? I thought I read this somewhere and the was the reason for the OD enabling switches on 3rd and 4th gear.
Thanks
 
First, the easy stuff: check your gearbox oil. Low gearbox oil can cause a wide range of Jtype problems.

Many electrically-related problems with Jtypes are associated with the solenoid. Check the electrics there.

Good luck, let us know.
 
I will double check the oil. I just installed this newly rebult trans on OD about 2300 miles ago. It was filled then and no leaks beyond a dime sized stain on the concrete once in awhile. I have been monitoring closely as it is newly installed and when delivered had a leak, which I called the rebuilder and we found the problem and repaired.

This is a simple electric circuit(to me). I will discribe in case I am missing something. This is a 12 volt actuated soleniod that has 2 switches wired in series with it. One is the selector switch (on/off switch)on the column, the other is the switch mounted on the trans that is closed when in 3rd or 4th gear. These 2 switches apply the 12 volts to the solenoid and completes the circuit through the soleniod to ground or return.
As the soleniod engages just fine, I would say the switches and wiring are ok, and since it will not disengage, when selected off and in second gear, and when selected off and in first gear doesn't disengage with the ignition switch off, this would mean 2 switches are shorted and not opening. Double failure is fairly unlikely.
Would seem to me that what ever the soleniod actuates is not releasing when the power is removed. What is that part and if stuck in OD can I harm my OD if I select reverse?
 
Could be any of several problems. One thing, NEVER attempt to shift into reverse if the overdrive is still engaged. Major catastrophe. Ask me how I know. Also, if the OD won't disengage, stop the engine and let the car rest for half an hour or so. The pressure from the OD will eventually bleed down to where you can drive the car w/o overdrive till you find the problem.
 
From your description, I doubt the problem is electrical in nature. The power comes from the ignition switch, and you know that is shutting off.

It's possible that the solenoid itself is jammed (there is a tiny hydraulic valve built into the end of the solenoid), or that the dashpot inside the unit is jammed; but IMO it's more likely that the clutch ring is stuck into the OD brake ring inside the unit.

One way to find out is to remove the test plug located on the bottom near the solenoid. If you find lots of pressure under the plug, it's a hydraulic problem of some sort. But if not, it's a mechanical problem, most likely a stuck clutch.

If it's the clutch ring that's stuck, usually it can be freed by rapping the unit sharply all around the brake ring (visible as a black stripe around the body of the unit) with a soft-faced mallet.

And yes, backing up with the OD engaged will do serious damage to the OD unit. The car won't want to back up, should feel like the wheels are against a curb; but if you force it, it will likely break the outer ring of the one-way sprag clutch and ruin the tail housing.

A short synopsis : the pump runs all the time, and the pressure is controlled by a relief valve operated by the dashpot. When the solenoid is energized, it applies pressure to the bottom of the dashpot, which increases the force on the relief valve and runs the pressure up to maximum (about 400 psi for a TR6). The pressure causes a pair of hydraulic pistons to extend and move the clutch from the non-OD position against the annulus, to the OD position against the brake ring.

When the solenoid is de-energized, it vents oil from under the dashpot, removing spring pressure from the relief valve which in turn vents the hydraulic pressure back to 20 psi or so. There are 4 springs that oppose the hydraulic pistons, and move the clutch back to it's non-OD position against the annulus.

PS, are you sure the OD is staying engaged, rather than staying in direct drive ? I wouldn't ask, except I know someone that spent a long time trying to figure out why it wouldn't disengage, when the problem turned out to be that it wasn't engaging at all and his speedo was wrong.
 
TR3 Driver
Reasonably sure it's engaging. On the first part of the trip, I engaged it and disengaged it several times. I usually use the clutch when doing this, however these times, I did not. There is a difinte egagement and disengagement. Also when I went to pass a car, 3rd gear just did not have the acceleration it should have. Also when driving in second there was a definte shift and an increase in RPM when it came out of overdrive. I would not pay much attention to the speedometer, but do watch the RPM's closely.
Ok this test plug would it be located on the small plate where the filter plug is? How much oil may come out? Or just crack it to get it show if pressurized or not. I assume this could be used to bleed off pressure,unless it vents a lot of oil.
Either way mechanical or hydralic it sounds like one would need to pull the unit to effect repairs to get it to operate correctly?
Thanks
 
The test plug isn't on the plate, but next to it. It can be seen on the far right in the attached photo (the solenoid has already been removed, but would normally be hanging down below the test plug head in that view).

I haven't actually tried it, but I don't think you would get more than a tablespoon or two of oil out under pressure. Unlike the A-type, there is no accumulator and the pistons should only move a tiny amount (less than 1/8") under pressure. However, it will continue to slowly dribble as the passages drain (so put the plug back in).

Both the solenoid and the dashpot/relief valve can be serviced without removing the gearbox from the car. However, you'll need some special tools to do either one.

The solenoid takes a very thin 1" wrench, which at least on my Stag also had to be quite short. Trying to turn the exposed body of the solenoid is a strict no-no, since it's just a coil housing and not strong enough. I started with a cheap 1" open end wrench, milled away the sides of the jaws to get it thin enough, then cut through the handle with an abrasive cutoff blade. Had to rap on it with a hammer to loosen the old solenoid.

The dashpot plug (like the pump & pressure filter plugs) is under the cover plate, and takes a special pin-drive wrench. Nelson's version is shown in the photos. I didn't want to take the time to make that square hole, so for mine, I used some flat rebar (approx 3" wide by 3/8" thick) from Home Depot that I had on hand, and drill/reamed it for hardened dowels to form the pins. A hole 12" away and a fish scale turned it into a torque wrench /bcforum/images/%%GRAEMLIN_URL%%/smile.gif
 
Sounds as if you have a newly rebuilt J-type overdrive. And from the way you describe the operation of the unit, you had it done for you. Just like me. I had my unit professionally built and installed on my own newly rebuilt tranny by Quantum.
At great trouble, I my self installed the unit (by myself) and found that the new overdrive worked flawlessly, one time. It engaged and never would disengage. At great frustration, many, many, many phone calls, a trip to a local professional transmission shop, and pulling everything apart in the above photos that you see, I pulled the whole unit out and shipped it back to Quantum. He installed another unit and returned it. I works great to this day, 3 years later. John Esposito was at big a loss as me and, bless him, has no idea why my unit didn't work. He did the correct thing and replaced it post haste, but I pulled more than a few hairs out. Talk to the guy that built it.
 
Randall
Thanks for the quality input and the time to put together such detail. What a great forum.
I will check this out and see which direction to go.
More tommorow.
Thanks again
 
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