Overdrive advice? Solenoid problems

Hi folks,
Can anyone give me an advice with this strange Overdrive solenoid behavior. Mk2 3.8 -61

Symptoms: OD solenoid has stopped working about every 1-2 years, a slight knock to solenoid
has “freed” it and it has worked again another year or two. But last Fall it stuck and knocking did
not anymore help. During winter hibernation I changed a new solenoid. It clicked fine every time I
tried. Also the old one works fine when testing on table. Now after hibernation I went for a test drive and OD does not engage. I stopped and listened solenoid: no clicks. Next day I tried and solenoid clicks every time in garage, then on test drive and again no OD engage, no solenoid click on road.
And next day same again, fine in garage, no click on road or in garage after drive.

It seems like something jams solenoid when driving and after cooling(?) it works again. What could cause that? And what is the cure?

I have not checked OD solenoid adjustment as it is very difficult to access that setting hole on the other side when OD is in situ. But it worked fine up to last fall, so at least then the setting was ok. There is enough oil (Redline MTL, I have been using it for years without problems). OD light goes on every time, even when solenoid does not click.

Any ideas?
Köpi, Finland

There is a switch on the gearbox top cover to ensure the overdrive only engages in top gear, wired in series with the solenoid. Perhaps that is at fault. If you take the console off, you can short out the top gear switch terminals and bypass the switch to see if that is the fault.

Perhaps you have already done this: stop the car (warm after a drive) in the garage and try to operate the solenoid as the car cools down at half hour intervals. If it is heat related at some point in the cooling cycle it should begin to work, I expect? It could be a simple wiring problem, earthing should be solid through the gearbox/engine return.
Also, if you are able to get under the car when it’s still warm, perhaps you could run another 12 volt test wire (direct from battery) to the terminal on the overdrive and see if it operates this way when warm? Then it’s a supply wiring intermittent fault. Paul.

Also what Kevin said.

This may not be related to your issue but it is worth stating. At least on the later compact overdrive (post 1964 full syncho box) the adjustment is very critical as there are two coils in the solenoid, one is a relatively high amperage draw pull in coil and the other a low draw hold in coil. As i learned decades ago if the adjustment is incorrect it may run all the time on the pull in coil and will fairly rapidly burn itself out.

Or maybe if hot will not fire the strong coil but both are unlikely as he has the new solenoid and the old issue… I believe it’s not only the compact type that works that way.

Check the engine earth strap as well.

Thank you for the ideas, I’ll try to check those. Somehow I think this is an adjustment problem or something inside OD when OD pump operates. If it were electrical, OD light in steering column would not turn on like it does, right? E.g. if top speed switch were broken, the light would not lit.

In addition to the earth strap suggestion, It could be the condition of the hot wiring going to the solenoid… A few poor joins would increase resistance and then the solenoid wouldn’t get enough current to effectively activate.

When you tested it, it was on a bench, so not “in situ” and probably hooked up to a spare battery with only a short cable run.

The light and solenoid are not in series but parallel so the light can operate with a 12V “hot” wire at the solenoid and the solenoid not able to operate (in your case). The 4th gear switch and the overdrive (column) switch are in series - both “on” to engage - of course. .

Some new info/measurements:

  • earth strap ok, no voltage drop between battery minus and chassis/engine.
  • OD solenoid adjustment OK, I was able to check the opposite side lever/hole

I added an external wire from solenoid to cockpit so I can measure solenoid voltage while driving.

  • ignition on, engine not running: Battery 12.4V, Fuse box 11.8V, Solenoid 10.8V and clicks ok.
  • Driving: Solenoid 11.3V, later on 12.8V, no click, no OD engage.
  • After driving, ignition on, engine not running, Solenoid 11.5V, no click.
    So clearly there is a voltage drop somewhere. I checked OD switch and Top Gear switch, no voltage drop in those, so somewhere in wiring/mid connectors.

Could it be that when OD has pressure on (driving and shortly after), there is so much mechanical resistance that this slightly dropped voltage is not enough to move solenoid? After the pressure releases, it starts to work again even with lower voltage. So not temp related but OD pressure related.

I’ll try to feed external voltage straight to solenoid to see if that helps. And change OD oil, in case there is some dirt resulting additional mechanical resistance.
EDIT: Even with straight wire from battery (12.8V) to solenoid it does not click after driving.


The voltage drop seems perfectly normal to me!
I guess you have something in your OD binding while hot. I’m afraid that’s comparatively bad news but I don’t know how bad since I haven’t plunged into one yet.

The OD pumps up a reservoir (a piston with a large spring: the accumulator) and this keeps the pressure constant. If it was oil pressure related, here’s how to find out: the accumulator should be ready after driving around the block. If it’s already not switching, go in and out of overdrive about ten times. If it starts to work again it’s a pressure thing.
If it doesn’t, it must be heat related. Did you find and go through a fault finding chart? I’m thinking a sticking brake ring for example but as I said, I don’t know the internals well enough. And that’s not it because the solenoid would still click…

What you can rule out for now is an electrical issue. It has to be inside the unit I’m afraid.


Thanks David. I hope oil change helps.

I know little about these Kopi but I do have an incomplete one in pieces in my garage.

If you get stuck for parts let me know. I’m in Australia but I’m happy to send you whatever you need for postage cost only.

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Thanks Andrew, I’ll keep that in my mind.

It works! Oil change helped, after it OD works 100%. Either there was some dirt (filter was clean though) or I have accidentally added wrong oil into gearbox. It leaks (both gearbox and OD) a little so over the years I have added oil every now and then. I do not have can anymore, but I may have added Redline MT-90, now I filled it with Redline MTL, which I think is better for older type OD.
Anyway, problem solved, driving season beginning (we just got rid of snow), car working fine.
Thanks to everyone for ideas!
Jaguar Mk2 Restoration Project

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When we had our family 3.8 MK2 from 1963 until 1985 we always used the factory recommended gearbox oil, SAE 30, non-detergent and never had shifting or OD issues.

SAE 30 is correct for the 1963 ‘family 3.8’. Once the all synchro box was introduced in September 1965, correct oil was SAE 90. When I visited my mechanic awhile ago with my 1967 Mark 2 3.4 equipped with the all synchro box with overdrive, I asked him to check the oil level, he said it was a bit low, but he did not have SAE 90 oil, but, owning a Shell service station, he said he carried Shell SAE 80/90 which should work well. Gearbox and overdrive have operated ok since.

Not sae90, ep90 gl4. Not that different in viscosity. I believe the synchros are far more picky, they determine the oil type. The 80w90 seems fine.