overdrive not working - fourth gear switch?

[dahicori]

Hello ,

So yesterday my overdrive stopped working. Relay is ok, I have good values on the button of the shifter. Good oil level. So I started cheking the wiring. I pulled the wires from the shifter and without giving it any force two wires came right off, completly rotten. I red somewhere that fourth gear switch have a single pin, so I dont know what I picked up but I guess the fourth gear switch is not receiving any electricity att all . Access from underneath the car is very limited. Can you tell me if it s feasible to change the wires? I saw many guys on youtube giving tips to bypass the solenoid, the relay etc

But for some reason I'd rather changer the wiring.

thanks!

[ngoma]

The 4th gear lockout switch I have seen are one wire. Looks like a bullet connector. It sticks out of the RH side of the top cover. The switch for the rear backup lights is on the other (LH) side, two wires.

It is possible to repair the wiring, I would say necessary in your case. As you say, access is more constricted in the 2xx series so you may want to drop the rear of the trans as low as possible.

Sorry I don't know anything about bypassing the solenoid or relay, no idea on how that would even work or reasons why.

LATER EDIT: Maybe you're talking about modifying the earlier sliding switch type of OD control?

[ngoma]

This photo might be helpful (thanks to Dave Barton):


Find the connector for the 4th gear switch here:
https://www.prancingmoose.com/blackvinyl.html
Search for "Special FEMALE 1-POLE BULLET Sealed Plug Housing with terminal insert and wire pigtail."
Fair pricing or OEM part, fair shipping.

[dahicori]

Hello Ngoma,

thank you very much for the photo, very helpful. So if I understand correctly, the single wire of the 4th gear connector provide ground for the relay ?

about modifying the circuit : I saw plenty of videos on youtube about that

like : https://www.youtube.com/watch?v=AxyWeP5Gsxs

But I'm not looking for it

Plus, I was mistaken : I tested the relay, and it doest work (I hope I was choosing the right pins: 31 for ground and 85 for power supply ). I bought it second hand from an old 240 and it lasted like 6 months! So I just ordred a brand-new one.

[v8volvo]

Those relays are common for failures. That might be the only issue.

One time I was on a road trip from Washington State to California in the western US, and the OD relay failed in my 760 along the way. I had a "good used" one onboard in the car and put that in, then it turned out to be bad also. Had to finish the trip using a pair of makeshift jumper wires sticking out of the dashboard, having my passenger manually connect/disconnect them when we needed overdrive! New relay fixed it when we got home.

The relay does a lot of work over the course of the car's life, changing in and out of OD multiple times every time the car is driven, so they do wear out.

Test the wires and 4th gear switch though. Also make sure the single ground wire that attaches to the main OD solenoid on the bottom of the transmission is connected, tight, and in good condition.

Check the wires at the base of the shifter too, they get moved repeatedly and like to strip/break. Many people give up on having the switch or button in the shift knob, and change the system to a switch on the dashboard where the wires are not subjected to constant motion every time the driver moves the gear lever.

[ngoma]

OD relay: The small internal logic PCB stands vertically on the connector base, connected by what looks like the legs on a common IC chip. Vibration can break one or more of those legs loose from the thru-hole. With a good light and magnification, wiggle the PCB and watch the legs at their connections for what looks like a cold solder joint. I was able to resolder and bring mine back to life, still going strong several years later.

[dahicori]

thanks for all these tips and advices. V8, the same thing happened to me (but I couldnt turn my passenger into a relay as I rode alone at this moment) , I bought a second hand relay like 5 months ago, I was so convinced that the culprit would be something else that I lost almost a day looking for a solution. Then I ordered a new relay and here I go.

About resoldering the relay, I think I dont have the skills to visualize what would cause failure on a relay : the old one looks good to me, but if I understand the very basics theory, I have no deep understanding on how these devices work.

I have an auxiliary question : at what speed do you activate the overdrive? On my car book, it is said that one can launch the OD at 50km/H. Must be incredible for having a great MPG, but I feel like the motor is asking for less revs at 70 km/h. And maybe the handling of the OD is different with the turbo cars?