My M41 with J Type OD has been giving me problems.

- Initially, the OD engages and seems to work fine.
- After shifting out of OD it appears not to reengage when I flip the OD switch to the on position.
- However, based on the RPMs, the OD appears to be engaged in 4th gear regardless if the OD is switched on or not. In other words, the OD appears to stay engaged.
- The RPMs are also reduced in 2nd 3rd gear too. I'm not sure about 1st gear.

Can it be that the switch that is supposed to ensure the OD only engages in 4th gear (part # 662292) is the problem? This is the switch that mounts on top of the M41 gearbox.

Thanks in advance for your advice.

Jerry
1969 123GT

Jerry,
Don't drive it. Don't even back it out of the garage. Follow ODGuru's advice. I think, I repeat, THINK (if I'm wrong, please, someone correct me), that if you remove the solenoid, the OD should disengage. Shake it vigorously - you should hear a distinct rattle. If you don't, it will be full of oil and you can proceed as per ODGuru's instructions. You can also test it by touching 12v to the terminals - the piston should move instantly with a distinct click. If it does all of the above, your problem is most likely electrical (relay or switch). If you want to drive the car temporarily without the OD, you can disconnect the OD wiring and, if the piston in the solenoid has retracted, put it back in till you get a chance to make repairs to either the electrical components or the solenoid. Check oil level and top off, if necessary, before you drive. If the solenoid repair doesn't work out for you, let me know - I may be able to dig up a used replacement.

Bob S.
--
'62 PV544 (B20, M41), '71 142E, '93 240 Classic Wagon.

You will need to remove and refurbish the solenoid as long as there is no power getting to the solenoid when the switch is OFF.

If your wiring includes a power relay between the switch and the 4th gear switch, if the relay and 4th gear switch gets stuck on, power will get to the solenoid and you will be ON all the time after the first use.

What is probably happening is fluid is getting pushed past a set of internal O-rings on the control piston within the solenoid and not allowing the control piston to return to the off position.

Usually after sitting a while, the fluid will drain out of the solenoid and for the first one or two uses all acts normally until the fluid again gets past and locks the solenoid ON.

http://www.brickboard.com/FAQ/700-900/TransmissionManual.htm#ManualM46OverdriveSelfEngages

is a set of tips on refurbishing the solenoid.

Duane

My understanding is that the switch on the top of the gearbox is closed circuit when in 4th and open circuit in any other gear. The power from the OD switch (or relay - depending on how it is wired) runs through the switch on the top of the gearbox so that the power only reaches the solenoid on the OD when the gearbox is in 4th.

It may be that the switch is stuffed and permanently on but that would not explain why it stays in OD when you switch OD off. I think it is more likely that your solenoid is jammed on.

Whatever you do, make absolutely certain that you never drive in reverse with OD engaged. Reverse is certain and sudden death to overdrives when engaged. If it were me, I'd go for a drive in 4th gear and try an get it to a state where you know that the OD is definitely off, then disconnect the wiring until you sort out what the problem is. It might be necessary to take the M41 out and bench test it. A tacho is a good diagnostic when driving. There is also a port in the side of the OD that you can connect a pressure gauge to. When driving with OD off it should show about 20psi. Switch OD on and it should climb to about 500 psi as the hydraulics pump up. I have used a pressure gauge to bench test an OD. It would take a bit more setting up for a road test - piece of brake pipe running up to a gauge clamped to a front door maybe.

One easy test of the solenoid is to listen for the click as you work the switch when you are parked up in 4th gear with the engine stopped.

If you want to bench test your M41, ask me for more info. I developed a simple bit of gear for a cheap and crude but very effective test rig.

First of all - regardless of whatever others will say: Don't drive your 123GT untill it's solved - running 1.st. gear with OD engaged WILL wear out your OD.

Your problem is probably not the '4th. gear-switch' - your problem is, that your OD doesn't dis-engage! (Sorry - it's obvious).

- What oil are you running in gearbox? (Your problem is not related to low level of oil (that will give slow engage of OD and fast dis-engage of OD), but to 'fat'/'sticky'/wrong oil).
- Your solenoid may have a problem retracting.
Check that electrical is fine - meaning: check that OD switch, switch current on AND off (at the solenoid).

Oil or wear in solenoid preventing the solenoid to function as should is your problem.

The the solenoid switch involves oil pressure and YES low oil will cause odd performance. Check with any of the other members if you doubt this.

Don't take things personal.

Problem is obviously (as per describtion) not odd OD performing. - but non-dis-engaging OD.

Low oil level will never course non-disengaging OD.

The problem is related to that the oil-pressure stays on = faulty electric system, faulty relief valve or blocked oilways. (Or at worst, internal fault/sticking clutch).

Re-read his post, he says that the OD does not re-engage after switching it off. Based on that it, is obviously NOT stuck on - at least not all the time.
He does later say that it appears to be in other gears, but does not really clarify

I totally agree that he ought not to drive it if it really is stuck on, and that driving with the OD on while in reverse is quick death for an M41. I also agree that it's probably not the 4th gear lockout switch.

A stuck solenoid makes sense if it is really stuck on. low oil makes sense if engagement is sporadic

First, be sure that you have the proper amount of fluid in there. My M41 OD would not engage reliably when the gearbox "juice" was too low. Toping it off made it run perfectly.

You might have a problem with your 4th gear lockout switch (on the top of the case). If it is always engaged, then the switch may be stuck closed. These are $20.00+ so it might be worth changing just to be sure. Check the wiring on it if possible. It's a sort of series-type wiring and the switch breaks the current to the solenoid shutting off the OD. You might have some bare wires touching or something. Then again, your OD would always be on if that were the case.

Your engagement problems may also relate to the wiring at the solenoid These are just simple push-on spade connectors and they work loose over time.

You might have a problem with your OD relay. It is is faulty your OD will not engage or do so sporadically.

When you are sitting in the car, with the ignition turned on (but NOT running), and in 4th gear, do you hear a little "click" when you flip on the OD?? Confirm this before you do anything else.

Check that you get a click and rule out the wiring to engage the solenoid first. Check your fluid second, check the wiring to the switch and solenoid, and then worry about the 4th gear switch. My gut says your fluid is too low, but it could be any number of things.

Thanks for all the good advice. To answer a couple of your questions:

- I am using the same oil in the transmission as in the engine.....30W.

- Yes, I have checked the oil level and that is not the problem.

I highly suspect that the O rings in the solenoid are the problem as Duane wrote since the OD always works after the car has sat for a three or four hours.

I'll check the wiring too.

Thanks again for the help.

Jerry