5HP18 – Hard shift when changing gear from 3 to 2. Cause and solution

[whiskychaser]

The following is quoted from an article which appeared on the German forum, 7-forum.com. Any mistakes in the translation into English are likely to be my own:

''On 5HP18 transmissions built before 1995, there is a design weak point which can cause a harsh shift when changing down from 3 to 2. There can be a strong jerk when braking for a traffic light and the change takes place at a speed of around 25 kmph.

This is caused by a small valve piston that over time works its way into an end cover in the valve body. When the piston has worked its way into the end cap, the ATF can no longer wash behind the face and thus cannot actuate the valve.

ZF recognized this sometime between 1994 and 1995 and changed the cover plate, the valve piston and the associated compression spring. The new end cover has a deeper pocket that offers a 3-point support for the piston on the inside. In addition, the material of the piston has been changed. Since then, it is no longer made of steel, but of the same (dark) material as the rest of the valve pistons.

Since the piston no longer rests over the entire area on the bottom of the pocket in the end cover, but rather selectively, ATF always comes behind the face and the piston is always actuated in a secure manner.

The old cover has the part number: 1056 427 116
the new cover has the part number: 1056 427 175

The change was made sometime in 1994/1995

You can recognize the design of the cover by means of the additional port or the part number when you remove the oil pan. So you can check whether the old or new variant is installed.

Caution: if you have a 5HP18 with an old cover and without the shift jerk (piston has not yet worked into the end cover) and reorder all compression springs according to the parts list to overhaul the valve body, you could cause the shift jerk. ZF replaced the compression spring, piston and cover and only uses the new part numbers without any indication of when they should be used. If you install the new, longer compression spring (ZF 0732.042.581) together with the old piston and end cap, the piston can no longer be operated due to the higher spring force. The important note that the compression spring should only be installed in connection with piston "X" and cover plate "Y" is missing ...
You will not immediately recognize from the parts list that you are installing a modified spring which does not match the old components. But you have just "built in" the jolt.

If you otherwise have the problem with a hard shift from 3 to 2 and thus a 5HP18 with an old housing cover, you need the following parts to remedy the problem:
COMPRESSION SPRING: 0732.042.581
PISTON: 1056.327.177
COVER: 1056.427.175

For 5HP18 with the old components from the factory, the piston works its way into the lid at some point as described and the jolt occurs at some point.

With a little skill and caution, the parts can be exchanged without removing the switch gear. The affected cover is located at the very back of the valve body, towards the rear of the vehicle. Unclip wiring harness, pull off metal clips and then unscrew the cover. Be careful not to let the content fall out uncontrollably. Then swap the piston and spring in the affected channel and mount the new cover, reconnect the wiring harness clamps and wiring harness - done.

Otherwise the valve housing can be unscrewed and removed individually. I did it that way. The complete valve body does not have to be taken out. When reattaching you just have to be careful not to move the part of the valve body which is located above the one you are working on.

So far there is no information about the problem with the shift jerk and the above-described measure by ZF, so I am posting this post in various forums. I bought a second valve body from m a 730i V8 E38 and meticulously compared all the components that are responsible for the 3 to 2 switching process. Then I was able to understand the whole thing in the parts list (high and thus newer part number = changed parts after / during the construction period).

In photo 1 I have marked the affected piston including the compression spring.
In photo 2 you can see the new and old covers side by side. The new one on the left with a deeper pocket for the piston marked in red.'' link with larger pic https://imgbox.com/QhiqzFLQ




original German article https://www.7-forum.com/forum/showthread.html?t=242114