This is a fix for transmission slip/flare on 2-3 upshift at partial load for 722.3,722.4 and 722.5 automatic transmission
If your automatic transmission shifts fine with the exception of a flare on the shift up from 2nd to 3rd, and you've exhausted all your adjustment options, then the K1 Accumulator Spring Kit might be the solution.
The spring kit (part number 126 270 44 77) will cost you less than $10, and is a drop in replacement for the K1 accumulator's spring/piston assembly in your transmission's valve body. While you're buying parts, you will also need several quarts of transmission fluid and a new gasket for the pan. You might as well change the filter while you are in there too.
Before you begin. Get some old newspapers/cardboard underneath the transmission. Fluid will be constantly dripping while the transmission pan is off.
Begin by draining the transmission fluid. On my W126, I also had to remove the front cross member (by undoing 3 bolts on either side) to get the necessary clearance to unscrew the K1 accumulator cover. NOTE: MB recommends replacing these bolts. You
may want to support the crossmember with a small jack to avoid it clattering to the ground.
Once the fluid's drained, unbolt and remove the transmission pan. Again, you might want to use a small jack to support it. Also, bear in mind there will probably still be fluid in the pan.
Locate the front of the valve body. You will be unscrewing 4 screws and removing a rectangular cover.
The picture above should help you get your bearings. It was taken from the left hand side of the car. The transmission pan and front cross member have been removed. You can see that the K1 accumulator cover has already been removed, revealing the green plastic end of the piston/spring assembly (highlighted in red).
NOTE: The four screws for the cover are very tight. I ended up using a 1/4 inch driver with a flat-headed socket to unscrew them.
This was especially useful for the top screws, since the curve of the torque converter housing made it difficult to turn a screwdriver.
Pull out the spring/piston assembly from the valve body. It'll look something like this.
Go ahead and pull the spring assembly out from the tube. You'll notice that there is also a small spring left at the bottom of the tube. Remove that too.
Put the old springs aside and open up your new parts. First of all, drop the new small spring into your old tube.
Next, loosely assemble the rest of the pieces from the kit (2 springs, 2 plastic rods) like so. NOTE: It may not be obvious from the picture, but the smaller spring goes on the white rod, and they are then inserted into one end of the big spring.
Now the fun part. You're going to have to squash that loose assembly of springs and plastic rods together. Carefully.
The white rod will fit into the black, but it does take a fair bit of pressure to do this. Once the 'head' of the white rod is in all the way, the entire assembly will hold itself together (just like the old one does). Just be careful and take your time. Remember, your dealing with springs under pressure, and parts can go flying if you're not careful (don't ask me how I know).
Before putting everything together, make sure everything is nice and clean. When you're ready, drop your new spring assembly into the tube like so.
Now put the entire assembly back into the valve body, and screw the cover back on, nice and tight.
From this point on you are effectively following the same procedure as a transmission fluid/filter change. If you are
also replacing your transmission filter, now's a good time to do so. Put your new seal on the transmission pan, and bolt it back up (don't overtighten it either). If applicable, bolt your front cross-member back on, and fill up the transmission, being careful not to overfill it. NOTE: The transmission dipstick under-reads when the transmission is cold.
Before going for a test drive, start the car up, and with the brake on, run the gear selector up and down the gate, pausing a few seconds at each position, so the gear engages/disengages, and the fresh transmission fluid gets a chance to circulate properly.
Hopefully, you should notice an improvement in the 2-3 flare. You may find that you have to make some adjustments, since it's possible that the transmission was previously adjusted to try and compensate for the flare. Refer back to the other articles.
Note: the photos were lost years ago. Why don't you take new ones and send them to me?