AT problem with shifting from 2nd to 3rd gear, 1997, S70

[Kinimoden]

Hello,

usually I have been able to solve all my problems by scouring the endlessness of the Internet, but this time I get the impression that I am already reaching the limits of information resources and my patience. Anyway

The patient is a Volvo S70, 1997, 2.5T 5452T engine, AW 50-42LE automatic transmission.

The problem that keeps me up at night is shifting from 2nd to 3rd gear. However, the problem only occurs with the first gear change after the car has been parked for a while. I park in an underground garage. When leaving for work in the morning, I always drive gently, calmly, without unnecessarily squishing the gas. It looks more or less like this, from gear 1 to 2 the shift is timely and very smooth. Gear 2 is already heavily dragged, and the change to 3rd comes after random, unspecified moments, with some jerking. Sometimes it's a few seconds, and sometimes when the revs already exceed 3k, I let off the gas, and here the reactions also vary. Sometimes after letting off the revs, the gear is able to jump in, and sometimes I can roll like this for a few hundred meters, adding and taking off the gas until the shift occurs. Once 3rd gear has jumped in, the change to 4th is timely and smooth. After such a situation, all gears are already working smoothly, I can stop and start as many times as I want, the change from 2nd to 3rd gear is no longer a problem, it is at the right moment and smooth. I drive about 20km to work, mostly on the highway.

After about 9h at work I get into the car, which was under a cloud, and drive home. The problem is exactly the same as in the morning. Also the same as in the morning, once it engages that first time, there are no problems after that. I get home, the car stays in the underground garage. If I need to go somewhere in the afternoon/evening, there are no problems, the gears shift nicely right away.
Another symptom is an error that the transmission throws out when I keep my foot on the gas all the time, and it can't shift from 2nd gear to 3rd. It happens quite often. The error code is 323, and is described as “Fault 3rd gear AT.” The transmission then goes into limp mode, which causes 3rd gear to engage. All I have to do now is delete the error and the transmission is already working properly, changing all gears without any problems.

I've been looking at LiveData lately, and everything indicates that the TCU wants to shift gears correctly. The computer shows that a shift to 3rd gear has occurred, but nothing has actually happened. According to the information I found and what I see on LiveData, it is in 2nd gear that solenoid valve S1 and S2 are open. When shifting to 3rd gear, solenoid valve S1 remains open and S2 should be closed, but it looks like this is not happening. However, I can't figure out how it happens that once its closure occurs, after that there are no problems with it.

The last part of the whole story is what I've been doing with the transmission for the last while. A few months ago, the transmission while driving threw me an error specifically related to the S2 solenoid valve. It turned out that the resistance of the solenoid valve had gone high beyond what was specified. So I ordered a new piece, unfortunately from no-name company, because the price of the genuine one scared me a lot. The replacement went without much trouble, although it was not pleasant. A topic from the forum describing the whole procedure was very helpful. I did a dynamic oil change and the transmission worked very well. Unfortunately, more or less after 2 months the above-described problem began.

I have no idea what to do next anymore. Should I blindly replace the solenoid valve again, but this time for the genuine one? Here, however, I am strongly discouraged by the price, because in this amount, I can already have a whole used gearbox. What and how can I else diagnose? The only error that the gearbox throws is the one described above, nothing else. Looking for explanations of this error I find that it could be anything and nothing, but the best thing is to replace the whole box.

It came out a little long, but I wanted to describe as accurately as possible everything that seems relevant to me. To the persistent, thank you for making it to the end, and please give me some wise advice. I try to do everything myself, because I like it and it gives me a lot of satisfaction. Putting it away in the workshop will be a last resort for me.

[Clemens]

Just to get this right:

Did the weird shift into thirs begin before or after replacing the S2 solenoid? If it begann after, I'd try to find an S2 solenoid out of a used transmission.

If you can, I'd try searching for a wrecked parts car or a used transmission. The ugly truth about these AW transaxles is that they are more or less sealed throwaway items with no real service information and basically no parts available.

Your TCU seems to work from your data readout, so I'd try to plan ahead a tranny swap rather than be stranded and have a non op car.

My AT in my 96R was well maintained with regular drain and refills, worked like a charm. Then, one day it misshifted 2 or three times, and a few km later I had no drive. Turned out a needle bearing had failed. It took me almost a year to gather all parts for a manual swap.

[Kinimoden]

Thanks for the quick reply.

The strange shift into 3rd gear started about 2 months after replacing the S2 solenoid valve.

Almost everything indicates that the S2 solenoid valve is to blame, but I can't understand how it is that only this “first” gear change after a longer parking is problematic, and then everything works smoothly. However, I realize that not everything in such cases is obvious and logical.

I will try to contact automatic transmission workshops. Maybe they will have solenoids from disassembly of old transmissions. If not, I'll look for a used transmission and replace the S2 solenoid valve for the moment. And if in the future something happens then I can do a complete swap. There are still quite a lot of first-generation V70 driving in my country, so I hope there will be some used parts.

[Clemens]

Could it have to do with line pressure? I am no AT expert at all, but I think that the solenois allows fluid to flow somewhere and cause the shift of gears. If the solenoid opens too slowly ot might take a while to get the fluid where it should go. Once the fluid is in that line, the pressure is high enough to shift nice for the remaining drive.

But this is only my theory, I never quite understood how automatic trannies work in detail.

[abscate]

It’s the magic of oil pressure. In a manual you move gears mechanically, in an automatic the gears stay meshed , but they freewheel unless oil (ATF) pressure forces a series of clutches into contact, and thus the gears transfer power from engine to wheels. The torque converter is a two fans thst face each other in a bath of the same oil , and so power is transferred by engine coupled fan swirling the oil and turning the wheel coupled fan. . This lets you come to a stop without declutching, as the fans can turn independently and just swirl oil. Our Volvos all have “ lock up torque converters “ where one of the solenoids ( using the same kind of oil pressure clutch) forces the two fans to lock together and provide direct coupling of engine and transmission, you get another 3% on your mileage with this feature.

7 minutes of video here

[Clemens]

No, it's witchcraft, Steve. You're old enough to know it's true

[abscate]

I’m always in awe of how cheap a transmission is when you consider it takes the full power of the engine every day and last 300k miles on these cars with minimal intervention.

[Clemens]

Sometimes I wonder if the humor over here on MVS scares some people away.
If you wanna know how stiff and uptied fora can be, skim through any large German language Audi forum. It made me sell my 2001 A6B4 as soon as the electronics got bonkers.