Hello again all...

Here's a new mystery I need to solve, hopefully with the help of your advice.

I drove home to Brooklyn from Philadelphia today (about 110 miles), without once depressing the OD switch (M46 manual trans w/ OD switch). Unfortunately, the OD seems to come on by itself once the transmission is nice and warmed up, but only if I'm driving along at 55 mph or faster for any appreciable amount of time. Now this wouldn't be so bad if it went back out of OD when I downshifted to 3rd, but it seems that the OD sometimes stays engaged all the way down to 2nd gear! I was driving through clogged Brooklyn traffic with the OD kicking itself in every time I shifted up from 1st to 2nd. The car moved along OK, but it was pretty sluggish. Most of the time I found myself driving along at 35 mph in 2nd gear at only 1800 rpm.

This is another one of those problems that will never present itself for a mechanic, as they usually don't spend an hour driving at 65 mph as a test drive. I know I'm on my own with this one. So....

Any suggestions on how to fix this? I would be perfectly happy to completely disable the OD and consider the car a 4-speed, as I don't take long expressway drives that often. I've also noticed that the old brick is perfectly happy roaring down the road in 4th at 75 mph and 3500 rpm. It'll do it all day (on those rare occasions when the OD doesn't kick in 'automatically') and still get 25 miles per gallon. So disabling the OD is an OK option, if that's the only inexpensive way to get around this problem.

I'm not an auto mechanic by any stretch of the imagination. I don't have good jackstands or even a high-quality ratchet set (I have a cheap one), but I'm at the point where I'll do what it takes to get this thing sorted out once and for all. I have a Haynes manual and I'm about to get a Bentley manual. If anybody has the Bentley manual handy, can you tell me if this sort of problem is described in there?

Now I'm off to the 700 FAQ to do some research. Feel free to email me with any suggestions (I'm all ears).

BTW IPD has a pretty good OD troubleshooting flow diagram in there latest catalog (not sure of original the source)....

Sounds to me like a dual problem or as Duane says (basically) find out why (when hot I guess) there is always power to the OD solenoid. I was thinking along the lines of an electrical problem....with both the 4th gear switch (or wiring) and shift button sticking on (or something else that puts +12V to the solenoid when not wanted )...

I have trouble visualizing it as a hydraulic problem if you are in 4th (OD not engaged at all, button NOT pushed) and suddenly it pops into OD????

Yeah, it's weird. It pops into OD all by itself after I've been cruising along at highway speeds for a while -- OD button NOT pushed and "5" light on dash NOT lit.

Once it's decided that it likes to have the OD on, it'll keep it on through all the gears, even after I've gotten off the highway and am in stop-and-go traffic. Once it's had a chance to cool down it goes back to normal operation. According to what Duane said, it may be a piece of gook in the OD itself, which sounds like a fairly major job to clean out. That's why I was hoping I could just disable the OD completely until I can get the tools and info together for attempting the repair. But from what Duane said, it looks like the fluid backing up in the OD can cause the OD to self-activate even if the solenoid is disconnected.

I'll be disconnecting the ground wire to the solenoid and taking a drive back to Philly this weekend (110 miles). If the OD kicks in by itself again then I'll know it's a fluid flow problem in the OD itself. At least I think that's what Duane was describing (I hope I got that right).

Wish me luck, and thanks for the info!

Does the dash OD light come on when it's doing the schizo come on thing?

No, the dash OD indicator light stays OFF unless I depress the OD switch on the shift knob. OD indicator is a number "5" in a green square, in the instrument cluster just above the red Brake indicator light.

Does that shed any light on the situation?

Then it would for sure eliminate a faulty shifter knob switch as a cause (it's not shorting closed) and anything else electrical before the relay...and really points to the situation as Duane describes!! (Duane's had me munch crow many times with my spouting off about OD's!!)

I would now do as he sez with the o-rings and do the mini OD rebuild, clean the screens, replace seals, flush the thing through with petroleum ATF type F and then change over to synthetic ATF type F. (Click on my link to read about it)

Ron, Three areas to check.

To isolate the problem area, remove the ground connection of the solenoid at the OD. IF the problem goes away, trace the wiring and repair the constant power feed to the solenoid.

When the above does not work, you will have to remove the solenoid and replace the O-rings inside the solenoid after you have drained the fluid out of the solenoid. After many miles and age, fluid gets pushed past the seals on the solenoid piston into the coil area where it forms a black goo which then at times creates a hydrostatic lock of the piston not allowing it to return to the OD off position until the fluid drains past the seals.

The third possible cuase is a particle of something, usually a part of an O-ring, blocking the fluid return port from the pressure application dashpot. This is inside the OD, accessable for cleaning after removing the OD sump pan, the far left plug under the sump pan, and the solenoid.

Cost factors. First, your time. Second, two routes: A; dealer will not have O-rings, will tell you solenoid is not repairable and sell you solenpoid for $180+. B; get seal kit from me for $5.90, make tool to remove solenoid from Craftsman crows foot, $8.00 or so, NAPA tool to remove spring ring from end of solenoid, $35 or so and some electrical contact cleaner about $3.50. Reduce cost by whatever you have in your tool box. Time wihtout making the solenoid removal tool about an hour.

Duane

OVerland Park, KS

ODGuru (Laycock only)

Duane,

I would like to purchase this:

>get seal kit from me for $5.90

as I have two bricks with M46's.

The tool mentioned:

> to remove solenoid from Craftsman crows foot, $8.00

is it made by ginding the crows foot to make it very thin?

This item

>spring ring from end of solenoid

removal tool.. is that just a cir-clip or C ring type spreader pliers type thing-a mo-joe-whatcha-ma-callit remover's. If so, I have them.

Let me know how or what to do to get 2 seal kits send to Cleveland TN.

Thanks

Bill

Keeping up my '83, and '85 the wifes '87 all 24x's and moms '95 -850

Bill,

The seal kit I mention contains only the five O-rings just for the solenoid.

Replacement of those seals only cures the self actuating symptom of the OD. Any other problem will not be cured.

The crows foot is indeed ground thinner, to just under 1/4 inch, but is necessary only from the middle of the part number on the crows foot out. Leave the socket portion full thickness and keep the tool cool with frequent dips in water.

The spring clip in the end of the solenoid is an internal about 1/4" NAPA tool #3050 or equivalent.

I'll need your address so forward it to me at: ODGuru@kc.rr.com

Duane

Duane,

Ok, Yea, I understood that the seal kit contains only O-rings for the solenoid.

>Replacement of those seals only cures the self actuating symptom of

>the OD. Any other problem will not be cured.

My '85 is acting strange, and I thought the seals might cure my problem but, it's not really a self actuating problem. It's more of a hard to get to actuate problem. I have to speed up and slow down, while switching on/off (kinda like pumping it) trying to get it to ingage, sometimes several time's before it actually go's in OD.

Any thought's

Bill

Thanks Duane!

I forgot to mention that the solenoid was replaced about a year ago. Unfortunately, I feel that I can't trust the shop that did this, so I have no way of knowing what the condition of the solenoid actually is.

> To isolate the problem area, remove the ground connection of the

> solenoid at the OD. IF the problem goes away, trace the wiring and

> repair the constant power feed to the solenoid.

Is the ground wire black? Looking in the Haynes manual I see mention of a yellow wire, so I assume yellow=positive and black=ground.

Just so I get some idea of how this works -- Am I correct in assuming that with the OD switch OFF, there should be zero volts on the yellow wire to the solenoid? If so, how many volts should appear on the yellow wire when the OD is switched ON, 12V?

I would then assume that if the above is true, that if voltage is appearing on the yellow wire even with the OD OFF, then I have a short circuit between pos and ground somewhere upstream of the solenoid?

Since I'm somewhat experienced in electronics, I'll hope that the problem is electrical. I can relate pretty easily to that. I'll let you know what happens... and thanks again!

Answers to post from Ron and others.

Battery voltage at solenoid with relay activated. Current draw 2.2 amps. Once under the car it will be obvious which is ground.

Disconnnecting fuse 11 may also cause your car not to run. And it is not the same as disconnecting at the ground. Disconnecting the ground eliminates ALL electrical capability of the solenoid even if it is receiveing power from other than the correct circuit. You are trying to isolate a cause of OD self actuation. ie. is it electrical or mechanical?

The 4th gear switch on the trans is a ground for the relay coil. It controls the relay in the 83, which when closed will also cause the dash light to light. If your dash light stays on all the way to stop, then look at the 4th gear switch or the wire to it finding a more convinient path to ground.

How the OD stays on with no power to solenoid.

Hydraulic pressure is always present anytime the trans is rotating, being pumped anytime the trans output shaft is rotating. It then flows through the filter, behind the actuating pistons, behind the pressure control valve, then to the solenoid which when OFF does not allow it to flow any further. Pressure builds up and the pressure relief valve opens dumping fluid onto the pump cam and follower. OD is not activated as pressure is limited to 15 psi or so. At this point all that is holding the pressure back in the solenoid is a small spring about half the size of those used in retractable pens. When power is removed from the coil, this spring is all that returns the piston to its original blocking position.

When the coil is activated, an iron slug is pushed into the end of the solenoids piston overcoming the spring and moving the piston about 1/8 inch. This movement allows fluid to flow through the inside of the piston and on to pressure amplification valving and controls inside the dashpot area through a small metering port between the solenoid area and the bottom of the dashpot. Pressure increases to +370 PSI and OD actuates. When voltage is removed from the solenoid, the spring returns the piston to the OFF position and the fluid drains back through the port and solenoids piston.

This high pressure over time eventually bleeds past the two O-rings on the solenoids piston into the coil area, which then fills the space where the iron slug needs to return into when the power is removed from the coil. Since the fluid behind the slug prevents the solenoids piston from returning to a position where fluid can drain from the pressure amplification dashpot, pressure is maintained and the OD stays engaged until the fluid behind the slug drains out.

I think I covered all.

Duane

Let me second Paul's "WOW!". I think you covered it extremely well. Both the Haynes and Chilton manuals explain removal and installation of the OD solenoid, but explain nothing about what it does or how it works. I appreciate your taking the time to explain.

Now for a question -- I've removed the ground wire to the solenoid and the OD is no longer actuating itself -- but I've only been able to test in short duration city driving. Is it probable that this problem would only happen when the transmission and OD are very warm, as would happen on a 100+ mile drive?

Thanks again!

Ron, it may only happen after the OD has been actuated for a time.In the city, you probably do not use the OD enough to get it "hot" and it sometimes takes quite a few miles to push enough fluid past the solenoid piston O-rings to cause the lock on or self engagement.

Another process may be occuring, and diagnosing this takes a tach and lots of familiarity with your car. If the solenoid is locked "on", the OD would self actuate during the transition from second to third. It would be so subtle that it would not be felt, and would show up as not engaging when the button is pushed. Only a tach and familiarity with what rpm's at what speed in what gear to truly diagnose without removing the solenoid. and once you have the solenoid off you are 1/2 the way to repair.

Duane

"I think I covered all"

I'll say!

Again thanks, makes sense to me...I was more thinking the reverse action of the spring was a tad stronger and the valve was a bit more "positive off"....but I see how with the pump in constant motion this would happen.

BTW, got any good used OD's for sale?

Paul, I do not sell used OD's. I have a few rebuilt units for sale though.

Got to keep my reputation intact!!

Duane

Ron -

Sounds like a never-a-dull-moment trip. If the o/d is engaged in the lower gears, especially reverse, enormous additional stress is put on various transmission parts, so you should disable the o/d to avoid that. Pull fuse 11 if you don't need the heated rear window. Otherwise pull the o/d relay off its base. You will need to remove the glove box for access. Be careful about over-tightening the little screws when re-installing the box.

The o/d is limited from engaging in other that 4th gear by the gearbox switch in the transmission and it has apparently become unstable. It is a replaceable part.

You may also have a now-and-then o/d relay that could use re-soldering. Don Foster is the guru on such, and while I've not yet done one, it sounds simple.

Good Luck,

Bob

BC -

Fortunately, the OD has never engaged in reverse (I did try it while the trans was hot from the trip and the OD was sticking ON in the forward gears). Does pulling fuse 11 do essentially the same thing as disconnecting the ground wire to the OD solenoid?

> The o/d is limited from engaging in other that 4th gear by the

> gearbox switch in the transmission and it has apparently become

> unstable. It is a replaceable part.

That sounds like a likely candidate for replacement too. What is the name of this part, and does replacing it involve dropping the transmission? I'm afraid that would be beyond me. I looked in the Haynes manual for this part but couldn't find it. I'll look again.

Thanks for the info.

Ron -

No, pulling fuse #11 removes power from the O/D relay and the gear shift switch. The O/D solenoid receives power from the relay, terminal #87, and is grounded at its mounting on the trans housing. The gearbox switch allows another part of the relay to ground to the trans housing.

Pull the relay to disable the O/D. If you go looking for a relay in a boneyard, get one cheap as that may not be the problem. Remember that the manual one won't swap with an auto one. I think they are very different colors.

The other posts are good. You have a unique problem that offers challenge. I'm not one to attempt repair in the solenoid, though that may be the problem.

We, as Volvo fans, (freaks? geeks? cult members?) have to learn what sorts of things go bad in a car that's 2 or 3 times older than the design life.

What a deal, and what a ride!

Good Luck,

Bob