A different issue with the B4 servo piston

Post by **precopster** » 01 Dec 2016, 03:41

I agree with whatever you say JRL. It just doesn't match up with literally hundreds of threads regarding what the B4 servo was able to achieve in the field. Engineer or not he may not be a transmission engineer or had anything to do with the design of the AW55/50 or AW55/51 series transmissions.

The B4 servo's function is to brake the 3rd gear drum. Transitions to and from this gear (adjacent ratios) would naturally be affected by its timing so to me and to many others here that makes a whole lot more sense.

Post by **abscate** » 01 Dec 2016, 08:16

Mike - double check your fuses - the B4 servo power shares a fuse with the third seat heater - a lot of people miss that one.

Post by **vtl** » 01 Dec 2016, 11:25

Senior tech in #1 New England Volvo dealership told me several times the front camber can not be adjusted on P2...

We debated good half an hour, he admitted it still has 1 degree of slack in bolts, but that's not what it called adjustment. Sigh...

Volvo says B4 may cause to-gear-3 and from-gear-3 problems: http://www.volvoxc.com/0/resources/how- ... -cover.pdf

I'm going to replace it too on my 2005 XC70, plus I'm switching back to OE ATF as since I moved to Amsoil/Mobil/Idemitsu/Valvoline/Aisin ATF 4 years ago it never worked really well. My diagnosis points to a low torque transfer in converter, Volvo might have more friction additives in its branded ATF.

12 litres of Volvo ATF is still cheaper than valve body replacement, which I'm almost sure is fine.

greffel · Post by **greffel** » 12 Apr 2020, 05:14

So on my S60 2.5T (my2003) i have 3-4 upshift flare / slip. Should I look into the B4 serve cover or just first try the oil flush?