Shift flare from 3-4

[colovolvo]

Hello,
I understand that most people have problems with shift flare from 2-3 but I am experiencing it from 3-4. Any idea which valve controls this operation? Thanks!

[MoeB]

I would assume the S3 and S4 solenoids are the primary controls on the 3-4 shift, but as I understand things (I'm not a Volvo tech or trans expert by any stretch), it may not be as simple as saying "3-4 shift flare = S3 and S4 solenoid issues." Besides the S1-S5 solenoids in the valve body, the transmission also has a throttle solenoid, a lock-up solenoid, and a clutch disc pressure solenoid, all of which affect shifting depending on the specific operating situation. The TCM is also fed various adaptive data from other modules and sensors and controls shifts according to the data.

If it were mine, first thing I'd do is check to be sure the ATF fluid is good and at proper level. If that's ok I'd have it diagnosed on a VIDA system to see if the TCM software is up to date or if any error codes are being thrown. If you're lucky, a TCM adaption reset might be all that's needed to fix it.

[colovolvo]

I just recently (6 months ago) flushed the fluid and the dealer said that the software for the transmission was up to date. The problem was intermittent for a long time but now has become commonplace. I can modulate the throttle and reduce the 'flare' somewhat, but it is still noticeable. I would have to say it was one of those solenoids, since under heavy acceleration it does not happen. Only under light or moderate acceleration is it noticeable, which I would assume would involve lower fluid pressures in the transmission.

[MoeB]

What year is it and how many miles on it?

[JRL]

Change out the B4 servo, (cheap) this not only controls the 2-3 shift but the 3-4 shift.
Easy and cheap enough to try, part is 15 bucks or so and about 1/2 hour labor

[colovolvo]

Well, okay, left out a piece of info. I think I replaced that valve (if it's the one that's behind the left tire toward the top of the tranny case) but I did not notice a difference.

[MoeB]

If you're talking about the B4 servo, you probably mean you replaced the cover and some rubber o-rings. I don't think you can replace the servo piston itself...apparently calibrated to the unit or something.

Anyway, you never said whether or not the TCM got an adaptive reset. That's about the last relatively cheap thing I can think of that might fix the 3-4 flare. There's a TNN on it somwhere. Search for AW 55-50 Adaptation Procedure or some such. If that's been done, then it's starting to sound like you might be a candidate for a new valve body...or worse. Good luck.

[geo]

Mine has had the problem, cured at the moment by a software mod (so the dealer say's)

[colovolvo]

Yes, I replaced the B4 cover and o-rings. I think maybe I'll head to another dealer in town to get some feedback from their service manager. Thanks for the suggestions!