Fourth gear not engaging
 

Hi.

My 1994 940 wagon was having problems changing from 2nd to 3rd. A friend of mine rebuild it ($600) and it's working pretty good 1, 2 and 3.....but now the 4th gear (overdrive) it is not engaging. I sent it back to the mechanic for a full review. He said it's nothing inside the transmission, maybe an electrical issue.
I had read a lot of treads about this issue and applied all of the solutions found and still not working.

-I replaced the overdrive selenoide with a new one ($100) and doesn't work; the activation click test was performed. We test with other used selenoide.

-A new Overdrive Relay ($40), doesn't work either.

-A by pass to the new selenoide was made to have a permanent solution and doesn't work.

-The kickback cable was inspected and adjusted in various ways and nothing.

Is there anything else that could cause this problem? :confused:

Thank you in advance.

What specific transmission do you have, I assume Automatic with OD AW71 as its most common, but there is the M90 but I believe its a 5 speed


at any rate, if the OD solenoid is bypassed, you will have OD (4th) all of the time, even if your kick down cable is broken, it just wont shift into it when you expect. There is definitely something inside the transmission that is incorrect, probably the valve body or gunk in the passages. The OD hydraulic circuit is relatively low pressure, but if you take of the solenoid or bypass plate, then start the car, fluid should rush out of one of the two ports.

Mine did the same exact thing, eventually I sold the car because I got to the point of simply swapping the transmission.

Nichals: FALSE. if the OD solenoid is bypassed via cutting a notch, or installing a bypass plate, the engine will automatically shift into 4th/OD as needed same as when the OD light is off on the dashboard.. with the solenoid in place and the OD button switched, then it will shift 1-2-3 normally but never go into 4th.

fyi, the solenoid is powered when the light is OFF, and the solenoid is turned off when the ligth is on. when the solenoid is powered, it connects the passage from the inner to the outer ring, this allows ATF to flow under pressure to the OD control valves inside the transmission, which will energize the OD 4th gear when the rpms are high enough and the throttle setting is low enough.

Sorry if it was confusing, as that’s what I thought I said. I assume then you would concur with me that it must be something internal to the transmission, as in his case the solenoid is bypassed (at least at one point in time) therefore so long as the transmission is sound, there is no reason why it wouldn't be able to shift into 4th.

I am guessing that it is a blocked passageway because there are 2 valves inside the valve body of the transmission, 1 for ears 1 and 2 and another for gears 3 and 4(OD), therefore if you had something else wrong, then you wouldn't have 3rd gear either.

I also don’t suspect a pump issue in the form of hydraulic pressure, because the drive pressure is about 150 PSI but the Reverse gear hydraulic pressure is 250, so much higher PSI, if it was a pressure issue, then Reverse wouldn’t likely work

yeah, a bit of grit gets into the passages that solenoid connects, and blam, no OD. Anecdotally, some folks have had luck sucking the passages out and/or poking them with a wire.

could try to loosen the by pass plate and run engine for a couple of seconds to try to get the junk to blow out/passages clear. it's messy but this worked for me.