Looks like I have got bigger OD issues...

[tdskip]

...than the solenoid wiring on the '66 TR4a. I rigged up a tie to the lever the solenoid operates and just took a drive. Lever down, everything is fine. Happy car, happy gearbox.

3rd or 4th gear at speed, pull up on the tie to operate the OD and RPMs jump like a badly slipping clutch. Uh oh.

It will disengage on its own in a second or so once I release pressure on the tie used to pull the lever up.

First checks is low oil level not allowing the unit to generate enough pressure, right? Not sure I want to hear about 2nd or 3rd things to check here - ha.

[TR3driver]

Won't hurt to check, but I doubt low oil is the problem.

Taking a "second or two" to disengage sounds like a problem as well; perhaps not the same problem. I'd check the tiny drain hole in the side of the operating valve stem (shown somewhat larger than actual size).

[tdskip]

Thanks Randall. I topped up the gearbox oil and it still slips if I have the throttle one, but if I lift off it will hold the OD engagement. So, as you suspected, something else is up.

Is it worth cleaning the filter before pulling that valve stem?

[TR4nut]

Tom-

Its probably been asked, but do you have a gauge for the od? It will help a lot to see what pump pressure you are getting.

Randy

[tdskip]

Hi Randy - why instrument something when it can remain an unknown but critical variable?
















Ha.

[TR3driver]

Same as before, it can't hurt to check, but I doubt that is the problem. IMO you're going to wind up doing just what you're trying to avoid : buy a gauge, check the pressure, then pull the unit apart to find out why it won't build/hold pressure.

The hole in the valve (shown above) only affects dis-engagement. It's basically the drain hole that lets the oil back out of the pistons when the valve is closed.

[tdskip]

Yeah, sigh, kinda of expecting that it needs to be pulled apart. Wasn't really in the game plan. Oh well.

[JerryVV]

Do you have any idea how long it's been since the OD worked? Has the car been driven much, oil warmed up, changed, etc? Cheking the valve that Randall suggested is pretty easy and does not require pulling the gearbox and disassembly. It does sound like you are bleeding pressure and that valve is the likely suspect. I'd refill with Redline MT 90. Expensive but best that I've found. Pull the plug at the bottom and clean the filter too if you have not done so already.

[TR3driver]

I'd refill with Redline MT 90.

I wouldn't. I like MT-90, use it myself and it is great stuff.

But it's not cheap and it is not going to cure this problem IMO, so you would be just throwing your money away. I actually use cheap motor oil while troubleshooting; then once it all works right, drain & refill with MT-90.

[tdskip]

Do you have any idea how long it's been since the OD worked? Has the car been driven much, oil warmed up, changed, etc? Cheking the valve that Randall suggested is pretty easy and does not require pulling the gearbox and disassembly. It does sound like you are bleeding pressure and that valve is the likely suspect. I'd refill with Redline MT 90. Expensive but best that I've found. Pull the plug at the bottom and clean the filter too if you have not done so already.

Hi Jerry - it has been years. She sat for 5+ years. At this point I have only topped off the oil. At this point I'm going to check the valve that Randall pointed out and then try (per your idea) taking her on a longer run and then changing the oil. Not expecting too much out of that, but occasionally Hail Mary pass plays work out.

[tdskip]

I'd check the tiny drain hole in the side of the operating valve stem (shown somewhat larger than actual size).

Randall (and guys) - is it normal for oil to come welling up when the top bolt for this assembly is loosened?

EDIT - Yes, normal. Especially if you ready the Buckey guide afterward and it says to actuate the lever several time before loosening the valve nut.

[tdskip]

OK - pulled that assembly. The hole on the shaft is about 1/2 the size in the picture but having the location enlarged definitely helped find it. Oil did flow through it, but I cleaned it just in case.

What I did find, however, is that the oil seemed dirty on shaft. There was darker oil that was not sludge but heading that way. May not be my problem, but can't be helping anything.

[JerryVV]

After 5 years that sludge will settle into all the wrong places. It may be as simple as that. Have you solved the solenoid issues? Maybe changing the oil before you go for a good run with some GL4 or even 30 weight. Get it cleaned out and then replace with Redline MT90. Using MT 90 as a quick cleaning oil gets expensive. be certain to clean the screen before you make the warm up run too.

[TR4nut]

Apologies to Tom for slightly stealing this thread, but I have a closely related problem - I put in a spare gearbox/od in my TR4 - the overdrive bench tested ok but I find it frequently won't disengage in overdrive. Cleaning the operating valve, whacking the brake ring, jiggling the solenoid linkage etc eventually will free it up.

Like Tom, the od sat for several unknown years before use. Old gear oil was old. I'd like to flush it with something, it has been recommended to put in a little diesel fuel and try to dissolve some of the sludge. Horrible idea? I've already put in MT90 so that will be a loss but at this point I need to get it to work reliably - its taking me to the Mitty!

[tdskip]

After 5 years that sludge will settle into all the wrong places. It may be as simple as that. Have you solved the solenoid issues?

Hi Jerry - thanks for the help.

I'll get the gearbox oil warm and then drain/change it today and see if it makes a difference.

I think I've narrowed my solenoid issues down to low power at the relay, but that troubleshooting is on hold until I get the OD to function.

[tdskip]

Apologies to Tom for slightly stealing this thread

You are going to have to try harder than that to need to apologize Randy - especially since you question is directly related and you have been such a huge help over the years.

I'm curious to see what comes back on that question as well.

[Guest]

What about ATF as a flush?

[JerryVV]

Like Randall said, use an inexpensive motor oil as a flush. A 5W-xx might be good for a short period. I would not put a lot of stress on the gearbox using a thin oil. (slow starts, easy slow speed driving around town enough to get it warmed up) but I would change it before making the run so as to drain as much of the old stuff out as you can before trying to clean with a new fill.

Randy, hope to see you at the Mitty (Royal Blue 4A with Surrey top) I'l be mostly hanging with the FOT crowd in the pits. Hard to say what your problem might be. I'd do the light oil flush too and put fresh MT 90 back in. Be careful in reverse if it's sticking too as that will fix your problem in all of the wrong ways. A friend who rebuilds these has had good luck using MT 90 when freeing up a stuck clutch

[KVH]

I'm still learning on my OD, and just tore it apart again due to bearing alignment issues, but it would seem to me that if the pistons are working when you manually operate the OD operating lever, that would mean that the clutch has disengaged the annulus head, thereby locking the sun gear and allowing the OD to operate, with the planet gears turning inside the planet assembly.

That being the case, high speed RPMs like a slipping clutch may indicate issues in the planet gear assembly or the roller clutch. Though, I suppose if the sliding clutch doesn't properly disengage from the annulus, and fully engage with the brake ring, the sun gear might not be locked properly, and that may be the problem. And, I guess, that's why a gauge may be necessary now. I suppose the problem could be the accumulator springs, the piston rings or the accumulator piston rings, or not enough washers between the piston the accumulator springs. Maybe not difficult fixes.

I could imagine another scenario where the clutch springs are shot and the OD sliding clutch is always slipping. I'm not sure what the symptoms there might be, but the symptoms might change depending upon the gear you're in and the speed you were going.

Someone with more experience please take over, but the issue is interesting.

I'll wait for a more insightful analysis.

[TR3driver]

Maybe I'm not following your argument, KVH. The pistons do pull the clutch away from the annulus; but until the clutch locks against the brake ring, it will just spin uselessly and there will be no power transmitted through the gears. The sprag (roller) clutch inside the annulus normally covers this transition, since it keeps the input shaft from turning faster than the output shaft (so effectively the OD stays in direct drive until the OD clutch locks to the brake ring).

However, if the pressure in the pistons is too low, the clutch doesn't fully lock to the brake ring and can slip back to direct drive (through the sprag clutch) when extra torque is applied. I assume that's what tdskip is talking about when the "RPMs jump". Could be a mechanical problem, but most likely is low pressure IMO. I got some slippage at around 250 psi, but only at full throttle in 2nd gear.

Experiences will vary, but mine has been that for there to be a lot of sludge, the OD is coming apart internally and the sludge is actually very tiny bits of metal. I don't know why Jerry thinks it will accumulate in the wrong places, as it normally accumulates at the lowest point of the reservoir, which coincidentally gets removed every time you drain the oil. Or on the magnets, same story. The only tiny passage is that one in the valve stem, which is also easily cleaned.

Way I see it, if you pull it apart and it only needs gaskets, seals & thrust washers, then the job is cheap. But replacing hard parts gets expensive very quickly. Thus if you know it's coming apart, it's best to service it now rather than wait until later. Broken thrust washers let the gears start touching in bad ways, which will eventually tear them up even though the OD is still working. Somewhere, I've got a ruined annulus that came out of a "working" OD.

Randy, have you checked the hydraulic pressure? One cause for repeated clutch sticking can be too much pressure. And your DPO/M may have made the same mistake I did, by shimming up the pressure just a little bit too much, so it tests fine on the bench (at relatively low rpm), but the spring reaches coil bind before the relief port is fully uncovered (meaning that at higher rpm, the pressure rises until something breaks). Not the only possibility of course, but one of the first things I would check.

IMO, ATF would work fine as a flush. That's even what Herman van den Akker used when testing on his stand. But I would definitely avoid using full throttle in lower gears (or even doing a hard launch). The countershaft thrust washers in the main gearbox are the Achilles heel, and the lower gears are when the forces are highest on the countershaft. 4th gear should be fine, though, as it doesn't send power through the countershaft.