No overdrive - AW70

Baweesh

1989 740 GL- I thought this was a simple fix but I am clearly mistaken. I’m starting to lose it!

Last weekend had an issue I noticed for the first time, I didn’t have “4th” on the highway. I stopped for about half an hour and I had overdrive again! Another half an hour later I downshifted into 3rd and couldn’t get back into overdrive after that.

Now I’ve confirmed that my solenoid is working. I removed it and connected the positive straight to the battery and earthed it on the negative pole. Solenoid clicks as it should.

I’ve installed a new bullet connector on the overdrive button wire and it’s a snug fit on the solenoid power. With the ignition on I can clearly hear the solenoid click when pressing the button. The light comes on the dash as normal when disengaging the solenoid and turns off when re engaging. I’ve tried swapping the relay with another one just in case.

None of this worked, so I’ve confirmed I’m getting battery power to the solenoid (13.95V at idle) and I’ve even removed the solenoid and started the car to see if it was blocked up, and fluid spilled out at decent pressure. Note: when I removed the solenoid, no fluid leaked out, however checking the dipstick (correctly!) at operating temperature reveals that I’m at max level on the hot side. I’ve also adjusted the kickdown cable to what Volvo recommended.

I did a new mesh filter and changed the fluid about 6 months ago, the fluid is still a clear red colour with no abnormal smell.

After all of this, I still cannot get the car to shift into overdrive. I’m sitting here typing this in my car absolutely defeated. Does anyone have any advice?

ramrod

Fuse, relay, wiring, solenoid, switch.

What’s missing?

Can you get the solenoid to energise at all?

Baweesh

ramrod Solenoid is indeed energising, I can hear and feel it de energising and energising when pushing the button. As far as I’m aware, electronically it’s working. I’ve checked all that you mentioned.

ramrod

Baweesh

It might be bypassing fluid internally then.

Put a new one in it with new o-rings.

Baweesh

ramrod Not sure where I’d find a new OD solenoid nowadays? I might try one of those overdrive bypass plates from IPD.

There two things I’m still unsure about: even though I’m getting good voltage, am I getting sufficient current? I tested the resistance of my solenoid by removing it and measuring between the terminal and body of the solenoid. I had 19 ohms, I believe it should be around 13 ohms. Not sure if that would affect it.

Secondly, even though I know it’s not blocked on fluid input passage, I’m not 100% it’s clear on the other side.

ramrod

Do not buy the stupid, pointless and idiotic pathetic excuse for a repair IPD sells.

Fix it properly.

Would you like me to organise a new solenoid for you? As I say the solenoid could be working electrically, but may be leaking internally.

Baweesh

ramrod Yes please, I’ll PM you.

jamesinc

Do not buy the stupid, pointless and idiotic pathetic excuse for a repair IPD sells.

Strong words! The only thing stupid about the IPD kit is that for even less money you can take your broken solenoid, notch it so it can't close the fluid circuit, and spend more like $0.

If you want an O/D defeat then obviously you need the solenoid. If you don't, it doesn't matter. It doesn't harm the transmission or anything like that.

ramrod

jamesinc

What the IPD plate does is eliminate the solenoid.

What this means, is that you will never be able to manually select third gear ever again.

The transmission will shift directly from second gear to fourth. You will have no control over it.

I don’t know about you and anyone else reading, I like being in control of my transmission, and for me, the repair is a new solenoid.

jamesinc

Blanking the solenoid does not eliminate 3rd gear or leave you with some weird 1-2-4 pattern, you just get a normal 1-2-3-4 progression. It's identical to normal driving mode (no orange arrow on dash, all 4 forward gears available).

ramrod

jamesinc

It’s road speed dependant.

The transmission will, if road speed is high enough, go straight from shifting from second to third, to just as quickly shifting from third to fourth.

That’s why I say third gear becomes inaccessible. Say for arguments sake, you shifted into second gear at 30 km/h. Then, second to third shift took place at 60-65 km/h. By that time, the road speed is high enough to allow overdrive. So, driving like this, you lose the choice of staying in third gear.

Another example, you were towing or carrying a large load. Driving in the mountains. You do not want the transmission choosing the gears unnecessarily and too often.

You want the choice to be in whichever gear you want to be in, and keep it there.

And, you’ll also lose the ability to adopt engine braking in third gear, because you simply won’t be able to access third gear if you were to remove the solenoid.

I hope this helps everyone understand the scenario.

Brad

The only thing stupid about the IPD kit is that for even less money you can take your broken solenoid, notch it so it can't close the fluid circuit, and spend more like $0.

This is what we did on my mum's 740 a few years ago. Trans works just fine but it can be annoying when you want/need to lockout overdrive to stop it hunting between gears.

jamesinc

You are writing it like gear is decided by speed. If that were true, your transmission would be useless on anything other than flat ground at a constant cruise.

Actually, in "D", the gearing is a function of two components:

Output shaft RPM (via the governor)
Load (via the kickdown cable, which is used by the transmission at all times, not just at WOT)

This results in:

As you speed up, the governor more authoritatively commands a higher gear from the transmission
As you press the accelerator pedal, your foot more authoritatively commands a lower gear from the transmission

These two opposing forces are resolved in the valve body to a desired gear.

Like I said in my first post:

If you want an O/D defeat then obviously you need the solenoid. If you don't, it doesn't matter.

ramrod

jamesinc

Your explanation makes sense, as does mine. You could look at it either way, same outcome in the end.

Ramrodfunk

Anyway.... Baawish, I'd disconnect the hard line to the radiator, I think it's the top one, & make sure the ATF is flowing through the rad. Sounds like it's the only thing you haven't checked.
I'd also clean out the small passages in the solenoid & where the solenoid sits on the transmission. If that doesn't work I would cut the small channel between the inner & outer rings on the solenoid till a replacement can be sourced. There's plenty of info on how to do it. This is what I did.

Baweesh

Ramrodfunk I fixed it I fixed it! I sacrificed my old solenoid and made a cavity between the two ports. I now have overdrive however I do agree with ramrod that this isn’t the right way to “fix” it and as someone that lives in a hilly area, I actually do use my OD button occasionally.

I fell victim to believing the solenoid I took off my parts car was ok, but I ended up with two broken solenoids. Even though it electronically tested well, it clearly had internal issues that I couldn’t see or diagnose.

jamesinc

I've had luck flushing them out with brake cleaner and power cycling them at the same time

Anthony

Hows it going transmitting power in 1-3?

Absolutely normal power delivery ?

Any odd metal clinking sounds?

Consider the rarely mentioned but critical ‘Torque Converter’s’ role in the whole 4th gear overdrive process.