AW55-50SN / AW55-51SN -one of the most famous and reliable 5-speed automatic transmission Aisin Warner, since 2000 it was installed on almost the entire Volvo lineup, and a little later - after running-in and several upgrades - and other major manufacturers (General Motors, Renault) began to install AW55 series boxes on their front-wheel drive cars with an engine capacity of up to 3 liters.

We can say that the AW55-50SN is a representative of the "old school" automotive industry, when the engineers were interested not only in the race for the number of gears and their shift speeds, fuel economy and following environmental standards, but also in the reliability and maintainability of the unit. AW55 can easily depart 150-200 thousand km. run without any complaints, of course, if the oil changed regularly and the driver did not overload the transmission.

At the same time, when such a mileage is reached, problems usually begin to appear, since no matter how reliable the design - wear of such automatic transmission components as friction discs, bushings, brake bands is just a matter of time.

Generation also appears in the hydraulic control unit of the box - solenoids clogged with dirt begin to wedge, the plungers and channels of the hydraulic plates wear out (as a result of which tightness is lost and the valve body does not work as usual).

Malfunctions of the valve body are expressed in the following symptoms:

•  pause and thump when DRIVE mode is activated;
• thumps when braking from 3rd to 2nd gear;
•  slippage when switching from 2 to 3 and from 3 to 4 gears;
•  malfunctioning of auto-neutral

We will onsider the valve body repair on a real example. This valve body has a small background, it was repaired before us, and after installation on the car and a test drive, it turned out that after the repair it became worse than it was before the repair.

Let us consider pricing. The cost of valve body repair at Maktrans, as always, consists of 2 components - consumables and work, which means that it is better to carry out the repair when the first symptoms of the  failure appear - it will be cheaper. Below is a table with a calculation of the cost, it turns out $ 350, but options are possible - it depends on the condition of the hydraulic plates.

We proceed to disassembly and troubleshooting.

Here, the professionalism of those who repaired before us is immediately noticeable. The plate that fixes the PWM solenoids is screwed on the contrary, and in order to screw it so - you need to apply serious force and bend the solenoids.

It is necessary to unskrew  and remove the solenoids. The AW55-50SN has 3 PWM (PWM) solenoids and 5 ON / OFF's

We unscrew and disassemble the plates. Before removing the plungers - we check them for jamming, the standard procedure.

Taking out the plunger and plugs - it is convenient to use a magnet

We carefully remove all the springs, plungers, plugs, booster valves - in no case they should be lost. Such a mistake was made by the master who repaired the valve body before us - a few errors in the assembly; paper gaskets of the valve body were not installed on all separator plates. To understand the problem, the photo below shows the entire contents of the valve body plates. If you repair yourself - we strongly recommend photographing each step of disassembly, it will be easier to assemble.

Disassembled hydraulic plates are sent to an automatic sink. While they are being washed, we will begin to check and repair the solenoids. As mentioned above, the AW55-50SN has 3 linear solenoids (SLT, SLS and SLU), dirty oil destroys them much faster than the shift solenoids S1, S2, S3, S4 and S5 due to the higher load:

• SLT solenoid - pressure control in the entire valve body, that is, the oil coming from the pump passes through this valve;
• SLS solenoid - gear shift control;
• SLU solenoid - torque converter lock

Starting test on the stand

 We get such a schedule. It indicates serious problems with the plunger, this can be either because of severe contamination (if the box burns out), or mechanical wear - bushings, washers or plunger.