I just installed an M41 trans and B20 (both from a '73 1800ES) into my 122. The trans appears to work fine EXCEPT when I try and switch from 4th to OD. Without fail, the OD solenoid will click on for a second (w/ an immediate, audible drop in RPM), as though the OD was trying to engage, but then immediately "slips" back out of OD. Another strange finding is that this only occurs EVERY OTHER time that I flip the OD switch on- otherwise it doesn't appear to engage at all. It doesn't matter if I switch back and forth immediately or wait several minutes- it only momentarily engages everyother time I "flip" the toggle switch. The wiring is fine to/ from the switch and relay and to the solenoid. The oil (30W castrol) level is fine also. I purchased this trans as well as the accompanying/ attached B20F (retrofitted w/ my SUs) and was told that everything worked fine from the PO prior to taking them out of his ES. Any ideas onthings to check or is the solenoid just beginning to die? Is the toggle an acceptable (although temporary)switch to be using or do I need to consider a momentary contact switch to engage the solenoid/OD? Thanks, SJA

the reverse light relay,or any other cheap on/off relay is what you need. You also need a multimeter and to spend some time looking at the wiring diagram. Elelctrics used to be one of my weaknesses aswell, but a little time and now I'm decent. The o.d. circuit is very simple, and a 60 volvo is very simple so it's a good place to start.

I'm pretty sure a momentary switch should solve your problem. Go to http://216.160.8.21/RWD/index.htm?id=695288 for a really neat way to hook up your OD wiring.
Bob S.

It kinda sounds like you DO have a momentary switch.
Can you describe your switch, relay (how many prongs), and wire routing?

Thanks for your reply. The switch is an illuminated rocker switch, the relay is a 240 headlight relay (suggested by Rusty from RPR). We used the VClassics article on overdrive conversion in an Amazon as a reference, esp the wiring instructions, as this is-admittedly- my weakest automotive skill. We copied the "wiring it up" instructions that are at the end of this article when we did the installation -if that helps any.

Ah, there's the problem. You're using a relay that's not compatible with the VClassics wiring diagram.

The 240 headlight relay is meant to be triggered by a momentary switch, not a rocker -- steady voltage applied to it tend to burn them out.

It works momentarily every other time because it's a bistable relay, meant to switch between two outputs (high and low beams). You're solenoid is getting momentary power from one of those outputs. Next time you turn it on, the relay switches to the other output, where nothing is connected.

Your simplest solution is to get a simple, on-off relay from your generic auto store and use that instead of the headlight relay.

Save the headlight relay, because there's a cool thing you can do with it that moves the high-low beam dipper from the floor switch to the turn signal stalk...

Ah - its wired to the 'high beam' side. And when switched to the low beam he gets a brief 'high beam flash' function?
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I'm JohnMc, and I approved this message.

Something like that... here's how that relay works:

31b = momentary ground to armature (steady ground burns them out)
15 = fused power in (used only for high-beam flashing)
81a = 12V to relay armature (jumper with 15)
56 = main 12V for headlamps
56a = output to high beams
56b = output to low beams

You can see it's meant to toggle one power input between two outputs, not to act as an on/off relay. It IS the relay used for OD in older 1800s that have a momentary switch on the steering column or later cars with a momentary pushbutton in the shift knob, which is no doubt why Rusty suggested using it -- but it does not work with a rocker switch.

If it is rigidly every-other as you describe I'd be suspecting the relay or the switch driving the relay. You might try temporarily wiring in a simple on/off switch straight to the OD solenoid just to rule out anything funny with it.
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I'm JohnMc, and I approved this message.

My understanding was that with the J-type overdrive, a simple on/off switch with no relay is fine. But not with the d-type overdrive unit...

I never got the right idea as to why though, but I've got just the on/off switch in my 145 and its never been a problem.

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-Matt '70 145s, '65 1800s, '66 122s wagon, others inc. '53 XK120 FHC

I've got a J-Type in my PV. And I just took out the cigarette lighter and put a matching old Volvo switch in it's place. No relays, just 12 volts to the switch and through on to the 4th gear switch on the trans. Only slight problem is that is isn't self cancelling - every once in a while I'll leave it on and get a 3rd-to-OD shift. I think you'd have to get a little clever with the wiring of a bi-stable relay and that 4th-gear switch to get that setup to be self cancelling though.

I'm already using the turn signal pull-back switch to dim the headlights - I replaced that wretched floor dimmer switch with a 140 relay.
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I'm JohnMc, and I approved this message.

Thanks much for all of your responses. I think I can handle this fix. Pardon my cranial thickness but did I understand correctly that I can also wire the set-up to go through the existing turn signal switch on the steering column? If so, it would certainly "look" better than an add-on switch or lever. Again,thanks to all for sharing your expertise/experience w/ this eager novice.

Yes - there is a switch built into the turn signal lever that was used in other markets to flash the highbeams. In the US it wasn't used, and the wire (attached at the switch) just pokes out of the wiring loom under the hood with a plain unstripped wire end. It gets a momentary ground when ever pulled back. I'm not sure where it emerges from the loom on a 122, on the PV it was on the left hand side of the engine compartment, about 1/2 way between the firewall and the radiator. If I had to choose, I'd pick the headlight dimmer as the best use for it over the OD switch - unless you happen to like the floor mount dimmer.
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I'm JohnMc, and I approved this message.