940 m46 to m90 conversion

[knuckledragger]

No. I will tomorrow. Wouldn’t the dash light still illuminate if it was low though?

[Laird Scooby]

Originally Posted by knuckledragger

No. I will tomorrow. Wouldn’t the dash light still illuminate if it was low though?

It won't let the relay oeprate if the oil level was low and the relay operates the lamp..................

[knuckledragger]

Ah I see. Where’s the O/D level sensor though? Couldn’t see it in any wiring diagram..

[Laird Scooby]

Originally Posted by knuckledragger

Ah I see. Where’s the O/D level sensor though? Couldn’t see it in any wiring diagram..

It's shown on the diagram as an oil pressure switch. Not all models have it but certainly worth checking you have enough oil in it anyway.

It might simply be once you've topped up the gearbox, it needs a few on/off flicks of the switch to get things moving.

[knuckledragger]

Crawling around under there today I couldn’t see one. But a top up/change wouldn’t hurt. I gather ATF-G non Dextron type is the stuff to use..? Same fluid as BW35 transmissions IIRC

[Laird Scooby]

Originally Posted by knuckledragger

Crawling around under there today I couldn’t see one. But a top up/change wouldn’t hurt. I gather ATF-G non Dextron type is the stuff to use..? Same fluid as BW35 transmissions IIRC

There's no "T" in Dexron - GM can be heard revolving in their grave!

I believe for your year car you can use 10W40 engine oil, ATF-F, ATF-G or Dexron II-D. Personally i'd use ATF-U as i've had extremely good results in auto boxes, some of which are little more than hydraulically shifted manual boxes with clutch packs instead of synchro rings and not a brake band in sight! Shift faster and smoother than a manual with all the other benefits normally associated with a manual over an auto so they're one auto that is faster off the line and past it than the manual equivalent.

You should also find Mercon -IV is also backwards compatible with ATFs F & G and is slightly better than the Dexron II-D.

[knuckledragger]

Managed to do the test light trick yesterday, which showed (as I had suspected) that no power was getting to the solenoid when overdrive was selected.

Also checked oil level, and its right on the level bung, not low.

Next thing I will do is check the 4th gear switch since this earths the relay, so could explain the lack of relay click. Presumably I could test with the car parked up in 4th gear, ignition on, gear lever button pressed, and with the relay removed use a multimeter to check continuity between terminal socket #85 and a good body earth?

If the 4th gear switch does prove to be the issue, how hard is it to remove/replace? I gather its on the top RH side of the gearbox with one brown wire going to it I think? Do I need to drop the transmission (and prop, exhaust front pipe, gear lever etc too)?

[Laird Scooby]

Originally Posted by knuckledragger

Managed to do the test light trick yesterday, which showed (as I had suspected) that no power was getting to the solenoid when overdrive was selected.

Also checked oil level, and its right on the level bung, not low.

Next thing I will do is check the 4th gear switch since this earths the relay, so could explain the lack of relay click. Presumably I could test with the car parked up in 4th gear, ignition on, gear lever button pressed, and with the relay removed use a multimeter to check continuity between terminal socket #85 and a good body earth?

If the 4th gear switch does prove to be the issue, how hard is it to remove/replace? I gather its on the top RH side of the gearbox with one brown wire going to it I think? Do I need to drop the transmission (and prop, exhaust front pipe, gear lever etc too)?

Just link out the earth to #85, also link out the 4th gear switch and take it for a drive. You'll need the mass inertia to ensure that overdrive drops out again when you switch it off.

If it doesn't disengage, don't reverse the car until you get it to disengage, it can damage the overdrive and/or gearbox if not.

[knuckledragger]

Found the problem. I went over the relay pin sockets again, checking voltage and continuity in accordance with the diagram. This showed the 4th year switch to work. Then I removed the relay cover and checked the continuity of each pin of that, which all seemed fine. I closed the relay contact by hand and discovered the solenoid clicked!!

Turns out the wire from the gear lever switch to the yellow connector in front of the gaitor had broken. I rigged a temporary toggle switch up and went for a spin and I had overdrive!!

[Laird Scooby]

Glad you found the problem!

Didn't you say that you checked that with the multimeter on resistance setting though? I'm sure you did and also that it gave continuity. This highlights one of the drawbacks of using a multimeter - they're fantastic tools but have their limitations.

While the wire may have been intact enough to pass the multimeter currrent, when it needed to pass a heavier current for the relay coil, it couldn't. This is where a test lamp comes in handy. It presents a load to the circuit under test that mimics (to a point at least) real-life situations.

However there are times you can't use test-lamps as they present too much of a load and can damage the circuitry by putting too much load on.

Now you have overdrive, are you still thinking of converting to M90?