Transmissions are complicated. Really complicated. Really, very complicated. Building a good one takes years of engineering experience and expertise, and often times due to the cost and complexity, the same models of transmission are used in a huge variety of cars and engines. Often times, because of the development cost of designing and building a vehicle’s transmission, car manufacturers will hand the baton to the guys that really know what they are doing. This includes manufacturers like ZF, who designs and builds transmissions for German companies like BMW, MB, and Porsche. Aisin (which used to be called Aisin-Warner before ’87, when a partnership with BorgWarner ended) is another company that has a huge transmission division that focuses solely on how to put the power to the ground. If you have any early 2000’s Volvo, this is where it gets important.
When Volvo redesigned their powertrains to consolidate their model ranges, they invested heavily in a transmission called the Aisin AF33 family. With a few modifications to accommodate their specific needs, they renamed the transmission the AW55-50/51SN and started slapping that puppy on everything that left the assembly line. However, there was a problem. Something about the transmission was causing issues in relatively low mile cars, and suddenly the warranty division started forking over the big bucks when cars that were just a few years old started getting complaints of hard shifting.
The problem manifests itself as a hesitation, and then a bang when the car finally finds a gear. That gets worse as time progresses. Sometimes this can be cured by a transmission flush (don’t let the term “Lifetime Fill” fool you, these cars should have new fluid every 30-50,000 miles), and more radical instances got a transmission ECU reflash to reprogram shift points and sensor tolerances, thus improving shifting. However, none of these are considered end-all solutions, and eventually Volvo came up with a mechanical update to these transmissions.
Caution, Jargon incoming!
The update is commonly referred to as the B4 servo update, which basically replaces a component of the valve body that was under designed, causing hard shifting. The component is a cover for one of the main servos that actuates the valve body valves, the updated version ensures that sufficient hydraulic pressure is built up to enable the servo to push open the valves, and actuate a smooth gear change. That wasn’t too hard to understand, right? If you want to read more about how an auto transmission works, specifically with the valve body, check out this blog, which is a crash course on the slush box. Moving on!
The servo cover itself is accessible on the transmission from the driver-side wheel well. It is held in with two o-rings and a snap ring, so with a little patience, it is possible to do this update yourself in your driveway. Just remember to accompany with a trans flush, and an ecu adaption afterwards. The third o-ring is for the B4 servo piston, which will come out.
The updated servo covers didn’t start making it into cars until around 2004, so 2000 and up models would be affected by the early style part. Here is a list of cars that had the AW55-50 transmission installed, there may be more as Volvo installed these transmissions into TONS of cars..
2006–2013 Volvo C30
2000–2004 Volvo C70
2006–2013 Volvo C70
2000–2013 Volvo S40
2000–2007 Volvo S60
2000–2006 Volvo S80
2000–2004 Volvo V40
2004–2013 Volvo V50
2000-2007 Volvo S/V70
2000-2002 Volvo V70XC
2003–2005 Volvo XC70
2003–2006 Volvo XC90
If you have flushed the trans, installed the update, reflashed the TCU and STILL are having rough shifting problems, your only recourse is most likely installation of a new transmission valve body.
That is not to say that all of these cars will have transmission problems, and like I mentioned before, after around 2004, the transmission hardware and software was getting substantial upgrades to avoid Volvo hard shifting problems. Later cars that are experiencing shifting problems could benefit from simply flushing the fluid, or getting a software update.
The fluid is not exactly cheap, but it is worth it, and even at this price we have trouble keeping it on the shelf due to the order volume. I guess that means people are catching on, and that is great news to help keep as many Volvos as possible on the road. The part number for the Genuine Volvo Fluid is 1161540 and eEuroparts.com has it IN STOCK.
So if you are enticed by the low resale prices on these otherwise high quality cars, but are wondering why they are so cheap, this is why. Be sure to be extra careful when gauging the quality of the transmission, and make sure the seller knows what you are talking about when you mention valve body servo updates. If not, run. Run like hell. You may need to install an entirely new valve body soon.