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Old 04-15-2010, 12:40 PM   #1
Inc3pt
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Default M46 Overdrive Relay Pinout/Wiring Diagram?

Hey all,

Having a bit of an issue with M46 overdrive. At first it will engage and then drop out after a few seconds, (the light turns back off, etc). After trying to engage it several times, it stopped wanting to engage at all (the light wouldn't even turn on). Because the light wasn't turning on even for a moment, I started to guess it had to do with the relay.

The next time I drove it, it seemed like it was ready to try again, and it would go in, then drop out again after a few seconds. The next time I tried holding the momentary switch for ~30 seconds just to see what would happen. Sure enough it stayed for the rest of the drive.

It started acting up again this morning when not even holding the switch for a while helped. I pulled over the freeway and changed the relay out with another one I had. I tested it with the car off, worked "normally".

Once I got on the road, it sort of acted the same way. Then, when it wouldn't want to do anything at all when pressing the button, I tried wiggling the gear shift to see if maybe the fourth gear switch was acting up. Immediately after, the OD came on and stayed on the rest of the trip.

So, this leaves me with two questions:

1) Do the symptoms I describe sound like its relay/fourth gear switch related? Or could it still be mechanical (ie: solenoid, tranny fluid low, etc)?

2) Does anybody have the pinout for the relay? I would like to take the fourth gear switch out of the equation. I'm assuming the switch just grounds a pin when the car is in fourth, so I could just ground it at the relay if I know what pin it is.

Thanks!
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Old 04-15-2010, 06:58 PM   #2
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It definitely sounds like an electrical problem- if the problem were mechanical, the overdrive light would go on, and stay on even if the overdrive cuts out. It sounds like either your overdrive wire is shorting out, or the 4th gear switch wires are shorting out or broken. Jack it up and inspect the wires on the tranny...
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Old 04-15-2010, 07:21 PM   #3
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Quote:
Originally Posted by casioqv View Post
It definitely sounds like an electrical problem- if the problem were mechanical, the overdrive light would go on, and stay on even if the overdrive cuts out. It sounds like either your overdrive wire is shorting out, or the 4th gear switch wires are shorting out or broken. Jack it up and inspect the wires on the tranny...
Exactly the reasons I assume it's electrical. To be honest, I really don't like the fourth gear switch that much, I'd rather just bypass it. The M46 won't be in the car forever and it's really unlikely that I would ever replace the switch if I found out it were bad.
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Old 04-15-2010, 07:57 PM   #4
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its pretty common for the OD wires leading up to the switch to chafe/rot around the shifter. if you wiggled the shifter and the OD stayed on i would take a peek around there first.
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Old 04-15-2010, 08:56 PM   #5
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Quote:
Originally Posted by mrk24018 View Post
its pretty common for the OD wires leading up to the switch to chafe/rot around the shifter. if you wiggled the shifter and the OD stayed on i would take a peek around there first.
The wires for the actual switch have been moved into the dash already. They're solid/tested.
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Old 04-15-2010, 09:25 PM   #6
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have you inspected the wires at the transmission?
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Old 04-15-2010, 09:29 PM   #7
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Quote:
Originally Posted by mrk24018 View Post
have you inspected the wires at the transmission?
The wires look fine. While I appreciate the help, I'm really hoping for someone to tell me the pinout of the relay so I can continue diagnosing the issue.

Thanks!
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Old 04-15-2010, 09:34 PM   #8
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have you checked you exhaust bearings? headlight fluid?

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Old 04-16-2010, 06:04 AM   #9
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Quote:
Originally Posted by Inc3pt View Post
The wires look fine. While I appreciate the help, I'm really hoping for someone to tell me the pinout of the relay so I can continue diagnosing the issue.

Thanks!




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Old 06-04-2022, 08:52 AM   #10
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Since the forum died a lot of the recent thread progress has been lost. Here's the recap on my progress so far.

My 1983 M46 only sometimes will activate OD properly, when it does it generally holds but also sometimes drops it. The light on the dash is always the first indicator of dropping OD, whether it never really engaged the solenoid or properly engaged but then fell out. Since the OD light is connected to the same pin that supplies the solenoid, the OD light is just a fast indicator of what the solenoid will be told to do.

This also means that the solenoid is not the problem, but something else is causing the relay to turn off prematurely. When I replaced the gearshift switch I did patch the wires that go to it, but those are also fairly firmly in place so likely don't have much of a way of moving to only sometimes jump connection.

I had pulled the 4th gear switch and put it back on with dielectric paste (I know, the wrong type of paste, haven't cleaned it off yet). In previous testing I had connected the pin (85) to ground and reliably got the relay to hold. When I was running voltage checks on that pin with a multimeter while driving in 4th there were points where it seemed like the voltage would quickly change briefly then return, but the multimeter wouldn't update in time. I don't have an oscilloscope on hand to properly watch it/trigger while driving.

As a result, the next suggestion was to pull the 4th gear switch (22mm socket I believe) and clean the contacts / wiring cup in hopes that a poor connection there was the issue. I have not yet done that.
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Old 06-04-2022, 05:26 PM   #11
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There is no cleaning of the contacts in the 4th gear switch. It either works or it doesn't. The wiring does decay and turn to crap and you can buy wiring pigtails to fix that. Just put a new 4th gear switch in.
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Old 06-04-2022, 05:48 PM   #12
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Yeah, pulled the switch out (had to drop trans crossmember (14mm on the bolts) to be able to get a socket and wrench on it. Need like a medium depth 22mm to have space without moving trans) and beyond cleaning off the dielectric paste on the banana looking plug, there wasn't really anything to clean on the inner side (nothing to access really). BUT I tested the contact and it seemed to work fine, and when moving the shifter I never had it not contact properly, so I think short of the wire fatiguing, the drop out was due to the female plug on the pigtail being kind of loose. Squished it slightly with pliers and now it grips the male plug end much better.

Need to drive and test still, but if it continues to be a problem I'll likely rework the wiring harness - a few chunks were crumbling off the coating near the plug cover. Then if that fails I'll get a new switch.
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Old 06-05-2022, 05:04 PM   #13
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Drove it today and now the OD light comes on and stays on robustly. However, each time I activated it, the ratio never changed or tried to change. It used to change, at least when the 4th gear switch circuit was properly connected to a ground.

Beyond checking for appropriate resistance through the solenoid to ground, and circuit continuity, what else could/should I test initially that doesn't require disassembly? I could rig up a switch and listen for actuation of the solenoid (key position 2, engine off, shifter in 4th, switch jumpered in the activation circuit).
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Old 06-05-2022, 11:05 PM   #14
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I'd recommend getting a power probe, it will make diagnosis much easier. with that and the wiring diagram you can just systematically move through the circuit and power components to test them.
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Old 06-06-2022, 07:00 PM   #15
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Checked electrical today. Solenoid receives 12V when relay is activated. Solenoid makes slightly audible noise when activated and can be felt with a finger on the solenoid body. This was done with engine off.

With vehicle up on front jack stands I checked trans fill level and it's still to the bottom of the fill plug like it should be.

This all points to something very recently happening with the solenoid hydraulics, unless I'm clearly overlooking something. Could a drain and refill be the cause? Gasket on Overdrive unit was replaced, filter didn't fall down or come off easily so left it in that position. It had worked at least sometimes after the drain and fill, and haven't done anything to internals since drain and fill.
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Old 06-09-2022, 03:08 PM   #16
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The next test is to rent or buy the gauge to measure the pressure. Put the car up on four jackstands and go into 4th and engague o/d. Record the pressure. You could also use a very long hose on the gauge and watch the gauge while driving. The greenbook has lots of info and it's probably in the ozvolvo archive.

Should see a 600rpm drop when o/d works.
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Old 06-09-2022, 10:01 PM   #17
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Found a couple of green books for J type on ozvolvo, and here's a bit more on the troubleshooting I can do

Sources
Document A: TP 30058/3, 6000.05.84, Overdrive 1976-, Section 4 Group 43 - locally saved as Green Book _overdrive.pdf
Document B: TP 30941/1, Reconditioning manual, Section 4 Group 43 - locally saved as Green Book M46, M47, M47II and Overdrives.pdf
Document C: TP 10487/1, 500.5.69, Overdrive Type J, Part 4, 43b- locally saved as Older highly detailed overdrive_type_J.pdf - very good detail on pressure profile and internal function.
Document D: P/N - 7777943-7 - MAD magazine cartoon diagnostic style

1. Doc A, Doc B - Activate Solenoid with 12V battery and check current draw. Should be 1.5-2A. Doc C - 2A.
2. Attach Volvo Pressure Gauge 2834 (like dl242gt mentioned) and check pressure when engaged and check for appropriate pressure (various target levels depending on vintage). Doc A - off - 0.15MPa (21psi), On at 45mph (turbo) 3.7-4.0MPa (526-568psi). Doc B - off, ditto, On - asbestos-free friction linings <3.4MPa, old type 3.9-4.2MPa. Doc C - 25mph, Off 40psi, 510-550psi for 164 model. Doc D, 25mph - off 21psi, on - 285-500
3. Doc A - Possibly Clutch sticking to shaft. Drive at ~50mph, turn overdrive on. Disengage clutch, rev to 5k engine rpm, quickly engage clutch
4. Doc A,B,C,D - remove solenoid, make sure oil ways not blocked. Try to blow air through. Energize solenoid and try to blow air through other holes.
5. Doc A,B,C,D - check control orifice between solenoid and relief valve is clear - clear with toothpick to avoid damaging metal.
6. Doc A,B - clear groove in front of ring gear in output shaft.
7. Doc A,B,C,D - Remove / clear pressure filter

Tool 2834 (pressure gauge)- where do I find this tool / a similar pressure tester / appropriate fittings for the tester port? No luck even finding super expensive results when searching. This guy made his own gauge and hose connection, but I would likely need to make a much longer hose to reach into the cabin while driving - he had the luxury of a test stand.
At least for Tool 2836 you can fabricate your own to remove the plugs (IPD apparently used to sell a tool but it also looks like Harbor Freight has a pin wrench that may do the trick.
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Old 06-09-2022, 10:41 PM   #18
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Update - it looks like if http://www.geocities.ws/jholekamp/ still works then there's a reasonably priced source.

Still probably going to try #1,3 above first, since there's less time spent under the car (and I know the OD was working recently).
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Old 06-10-2022, 12:01 PM   #19
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Check in with Hiperfauto. They may rent you the tool.
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Old 06-21-2022, 05:22 PM   #20
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heh. Whatever was stopping my OD from working before is clearly not stopping it right now. Didn't even have to do the 50mph slapper.

There's more delay at 2000rpm than at 3000rpm for engagement, but whatever. shifter switch and 4th gear detection working properly and solenoid at least mostly doing what it's supposed to.

Case closed until it isn't.
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Old 06-21-2022, 09:20 PM   #21
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I recently helped a friend wire up the broken wiring to fix o/d
in his 740T wagon. It hadn't worked in ten years. It acted funny
at first going in and out of engagement. Then after he flushed the oil a couple times it has been fine.
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