Help me diagnose intermittent transmission behavior (Volvo / Aisin content)

I've noticed slightly odd behavior in my Volvo V50 lately. When I come to a stop with more than gradual brake pressure (meaning anything normal people would call stopping abruptly, but not full-on threshold braking), the Aisin AW55-50 trans will shift itself into first gear with a distinct thud. This thud is enhanced if I get on the throttle at all before the shift occurs. It's not violent, but it's certainly not smooth. All other shifting is normal. Cold or hot doesn't seem to make a difference.

I have two theories. One, the fluid level may be slightly low - I had a small leak (ironically from a line I replaced proactively - no good deed goes unpunished) that has been remedied; I was waiting to do another 4qt drain-and-fill cycle with my next oil change, which would top it up. I doubt it's down very much, but the dipstick is virtually useless on these due to lack of access, so I'm not sure.

Two, a transmission mount has failed. I've replaced the upper and lower engine mounts, but not the trans mount. Not sure if I would feel something during other phases of driving if this is the case, as I have very little experience with both automatics and transverse-mounted drivetrains.

Finally, it's worth noting that I had noticed this shifting behavior previously, but only on the rare occasions that I use the manual shift function. Only recently has it manifested when allowing the box to shift itself.

Happy to hear any suggestions or ideas.

My thought was drivetrain mounts.

I have no experience with this vehicle, that's just my go to to check.

I've ordered the trans mount - I figure even if it's not the problem here, at 217k miles, it's due. I'll see if it makes a difference and go from there.

My parents have a V50 that presumably has the same transmission and based on your description was doing the same thing. I've only had it happen a couple times when I was driving it and couldn't intentionally reproduce it, and it struck me as feeling like a solenoid problem, like either the converter clutch was dragging on release (at least on theirs, the converter is locked most of the time once into second gear and beyond) or some other solenoid that maybe was leaking somewhat so a pressure rise wasn't being applied or released fast enough. I had a solenoid eventually fail in the trans in my Silverado and had the same kind of behavior (it was also the 2-1 shift) before it failed completely, which was kind of nice since it made the source of the problem obvious.

I know they did fluid and filter, but I don't remember if they replaced solenoids or not. They definitely didn't go any further than solenoids, but it's been a long time and I didn't do the work. One of those two things seems to have fixed it though.

Plug in a good scanner that tells you the trans temp.  My guess is that it's reading -273F.  Common thing with Aisins, and it makes it do all kinds of weird things.

Here's hoping it's just a mount, but solenoids and temp sensor are pretty common failures.

02Pilot said:

...the Aisin AW55-50 trans will shift itself into first gear with a distinct thud. ... It's not violent, but it's certainly not smooth. All other shifting is normal.

FWIW, our '04 Saab 9-5 with AW55-50, ~230k miles and a tired drive-train mount does the same thing. As with others, I also can't reproduce it.

Also FWIW, I'd fixed a slow trans-cooler leak sometime ago, but after topping off the fluid, the issue continued. It's so intermittent that I haven't worried about it, but I'm interested in finding out the cause.

My 2017 V60 does the same thing. 

I remember it being a common complaint on SwedeSpeed forums, even under warranty. So far, no one has found a fix

It happens 1-2 times/week, enough to be irritating but not bad enough for me to do anything about it.

I have a scanner that will read trans temps, so I can easily check that tomorrow. I'll see if it can do live data logging from the solenoids - that might reveal something if I can get the problem to occur while monitoring.

I've got the mount and 4qts of fluid on the way, so I'll get the mount in and do another flush-and-fill (the fluid was pretty dark when I got the car, but it's almost back to looking nice and clean after several cycles). May not help, but it won't hurt.

I scanned the transmission and everything seems normal. Both Temp at Start and Oil Temperature readings are plausible and seem correct. I can also monitor solenoids and actuate them for testing. I shifted into Drive as well as manually shifting (this was all done stationary in the driveway, so not really more than checking the capability) and watched the solenoids actuate what seemed like very quickly; none of them were lagging behind. If there is any specific test program for the solenoids, I'm happy to try it; all I know about automatics is that they work on voodoo (or possibly black magic - I can never remember which).

Yep.  For about 40,000mi with my current one, if I accelerated hard and let off the throttle at just the right time during a shift, something would go wonky in the valve body and the transmission would shift harshly as if line pressure were jacked up to maximum, on every shift.  I'm fairly sure that it was hydraulic, because it would only stop doing it if I shut the engine off while stopped and restarted.  Some accumulator somewhere getting its signs reversed maybe?

Then it stopped doing it.

If your issue were inside the trans, I'd scratch my chin and wonder if the trans had a low/reverse brake and sprag setup like an old 3 speed, which wouldn't have engine braking in 1st/Drive which combats the 1st gear bang issue, and go look up powerflow info.  If you're braking heavily the trans controller may be asking for engine braking in 1st.

I'd also look for loose motor mounts.