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M46 overdrive issue

2

245TICSweden

New member
Joined
Aug 13, 2023
Hi all,

I've searched and read the majority of M46 overdrive issue threads here, but couldn't find one that properly matches my issues and would be delighted if I could get some pointers at where I should start.

I bought a 1985 245 Turbo B21ET with a manual M46 with OD about 2 months ago with around 350k km on it and the OD has now stopped working:

  • The OD was not working when I bought the car, I changed to a new OD relay and shifter button and it started working
  • The OD light on the dash has never lit up, even when the OD was working
  • The reverse lights have never worked and neither the seat belt warning lights (if this is at all related?)
  • I drove the car on a long journey recently and when slowing down for roundabouts, traffic lights, etc. suddenly the OD would not work when I tried to engage it
  • I managed to get it working intermittently for a while after some juggling of the cables inside the shifter and also putting the shifter button off/on, although I'm not 100% sure if this helped or if it was just random when it started working again
  • But ultimately the OD stopped working and I can't get it to work at all, cold, warm, when pushing the gear leaver back when in fourth, etc.
  • I noticed a couple of oil drops on the exhaust right beneath the gearbox when I got home after the trip and those were not there before. Although it's not dripping any oil when parked. The drops were also showing to have come when driving, as they had run downwards at an angle.
  • I've measured the connector for the relay with a multimeter and I get current through it when I press the overdrive button, the OD relay does however not click
  • I get no measurable values when I have the gear leaver in fourth gear which makes me think the issue might be with the fourth gear switch or wiring?
  • I've not yet checked the oil level in the gearbox, but I plan to drain it and refill with new
Based on this, where shall I start?

Any help is appreciated, and sorry if this has been posted many times before, I just haven't been able to find it in that case.
 
Sounds like an electrical problem if the relay isn't clicking. Make sure the wire from the lockout switch is getting a ground when in 4th gear.

It could also be a bad solder joint on the relay board. Replace the relay or try soldering the connections.
 
hiperfauto said:
Sounds like an electrical problem if the relay isn't clicking. Make sure the wire from the lockout switch is getting a ground when in 4th gear.

It could also be a bad solder joint on the relay board. Replace the relay or try soldering the connections.
Click to expand...
Thanks for the input.

The thing though is that I didn’t get the replay to click when having the car stationary and in 4th gear before either when the OD was working when driving and obviously clicking when engaging then… and that makes me even more confused.
 
I assume you have access to the wires that head towards the transmission. I would suggest popping open the one that goes to 4th gear switch and directly wiring it to the same ground the relay uses. That way you can pretend your switch is working regardless if it is or not.

Similarly, the push button can also be simulated - basically each time it 0-->1 (circuit connected) the relay should change states - so get a good fat toggle switch to make it very clear where the 0-->1 is (avoids button chatter potential issues).

Make sure you're getting a good supply voltage to the relay, and basically check out the relay itself - make sure it's toggling properly. Fix supply and ground wiring as needed. Make sure you have a good connection on the fuse that supplies it.

Then start looking at the connected stuff - What is the resistance to ground via the 4th gear switch? How much change in value depending on how the shifter is positioned in 4th gear?

If all checks out, relay is toggling, current flows to solenoid but you don't get OD engaged, then you have some form of a hydraulic path problem and I don't know much detail about that. There's methods to shock it, and of course hotter coolant should flow more easily....
 
Those are symptoms I've encountered when the oil level was low. I've also had those symptoms when I had a bad 4th gear switch. It can lose the ground connection for the relay over big bumps.
 
dl242gt said:
Those are symptoms I've encountered when the oil level was low. I've also had those symptoms when I had a bad 4th gear switch. It can lose the ground connection for the relay over big bumps.
Click to expand...
Interesting, thank you for the input.
And do you mean the 4th gear switch on the gearbox itself? Did you replace it and is that possible without lowering the gearbox?
 
Yes, the switch on the gearbox. Easier to access that switch if you lower the gearbox some by dropping the crossmember and letting it all tilt down a bit. I've also been able to slip a socket over the switch that has a hex on the top of the socket and used a wrench on that hex to unscrew the switch. 22mm if I recall correctly.
 
dl242gt said:
Yes, the switch on the gearbox. Easier to access that switch if you lower the gearbox some by dropping the crossmember and letting it all tilt down a bit. I've also been able to slip a socket over the switch that has a hex on the top of the socket and used a wrench on that hex to unscrew the switch. 22mm if I recall correctly.
Click to expand...
The fun part is taking the boot off the switch and trying to get it back on in one piece.
 
Yeah, I got a closer look at the wiring for both the 4th gear switch and the reverse lights and they were in poor condition.

I managed to put new isolation on the reverse light cables and wrestle it back on the switch and it actually worked - I've got working reverse lights now for the first time since I bought it! Although the cables are not in a good condition, so wouldn't be surprised if it fails later - so have ordered new cables just in case.

I tried fixing the cables for the 4th gear switch, but still no luck. So I've ordered a new 4th gear switch and cables, will give it a try to replace it.

I will also change the gearbox and rear axle oil as there is no record on when it was last done. Just need to head into the jungle of deciding on which oil, there are so many different recommendations. ATF, Dexron or not, etc.

From what I can work out, the most recent recommendation from Volvo is 75W GL-4 for the gearbox:
https://imgur.com/Dm7Lg77
 
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So, it seems there are two different 4th gear switches:

Kontakt

www.gcp.se www.gcp.se
www.skandix.de

Interrupt switch, Overdrive 1324496 (1019603)

Interrupt switch, Overdrive Volvo 200, 700, 900
www.skandix.de www.skandix.de
And I ordered the first one, but it seems the one on my M46 is the second one, which isn't available to buy anywhere...
Has anyone here got any insight, could the first one be used/modified or are the completely different?
The main thing visually in terms of difference seems to be the connector and the wiring I've got is adjusted for the second one.
 
I don't know if the threads are the same size but if they are you can run a wire off the second pin of the switch and ground it to the transmission. The later style switch just grounds through the threads while the earlier 2 prong switch carries 12v across for the solenoid.
 
dl242gt said:
Your car should use the push button on the shifter with relay which means it uses the single contact grounding version of the 4th gear switch.
Click to expand...
Yeah, I've got the push button and that relay.
The issue is just that the single contact grounding version (https://www.skandix.de/en/spare-par...overdrive/interrupt-switch-overdrive/1019603/) isn't available anywhere while, oddly, the 2-pin version is available at plenty of sources, including Volvo: https://www.gcp.se/products/1235353

I found this old thread where someone had encountered a similar issue: https://www.brickboard.com/RWD/volv...ut_switch_m46_1980_242_dl_od_200_244_245.html

The early M46 OD circuit did use a two pin fourth gear switch, Volvo PN 381251-8 (1975-78) or 1235353-8 (1979-80). The switch on the shifter was a slide switch (ON/OFF), Volvo PN 1234508-8. One wire of the slide switch was connected to fuse 11, the other wire was connected to one side of the fourth gear switch (and the OD indicator). The other side of the fourth gear switch was connected to the solenoid. You can see this circuit in the Green Book TP30057-1 available at www.k-jet.org. Navigate to the 200 series Green Books. It is the first book of wiring diagrams listed. The OD circuit is on pg. 98 of 145.

If the shifter setup you have has a push button you can use that but you will need to configure the OD wiring to use a relay. But not just any relay will do. Because the push button is momentary, the relay is an electronically latching relay that also has an AND function. (Button pushed AND fourth gear TRUE will turn on the solenoid.) The relay is Volvo PN 1259750-6; it should be easily obtainable at a pick and pull. (In a 740 the relays are behind the fuse box. In a 240 the OD relay is up behind the Heat/AC controls.)
Click to expand...
 
I would try one of the venders here on the board if you can't find a good used switch. Hiperfauto and planetman may be able to help you get a switch. GCP says the part is expired so they are not going to make new ones.
 
So, it's finally been solved!

And the issue was the switch:

I started by changing the gearbox oil, the overdrive gasket and the wiring to the relay, the gear leaver and the gearbox/switch. I had replaced the relay earlier.
That did not solve the issue.

I then, as stated above, encountered the issue of that the older version of switch - which I had and that my wiring connectors were adapted to - is not available to buy anywhere.

The newer version is however and after modifying the cables to the two pins of the new switch and adding a ground wire which I connected to the overdrive ground, the overdrive works!

Worth to note is that I was able to replace the switch without lowering the gearbox.

It was a bit of a pain, but you can either do it with a deep 22 mm socket and a thin wrench or remove some of the plastic of the connector on the old switch and use a regular 22 mm socket and normal wrench.
 
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