Saab 9000 - Governor Valve Seal Replacement, ZF 4HP18 Automatic Gearbox
(reference discussion and procedure to carry out this job here -> :


Photo of the transmission end cover removed. 

Removed the 36 mm bolt (right side bolt in the pic above) with an impact socket and it came off fairly easily after 2 to 3 knocks. Here's the bolt after removal :

View of the governor with the gear removed.

View behind the gear and the bearing outer race. In my case, the bearing outer race didn't require heat to come off, and just slid off with finger pressure.

Discovered a crack in one of the O-rings on the Governor valve.

The seal is a square profile O-ring, inner diameter measures up at 51 mm, with 2.5 mm width and 2.5 mm height.

I was in a hurry to get the car going and did not source for original ZF parts, but decided to source off the shelf rings from an O-ring specialist. Unfortunately, they did not have the correct profile square O-rings, but had X-profile oil resistant rings of the correct dimensions (I'm not sure how to explain it, but if the ring were cut, you would see an X like profile at the cross section). I decided to get them anyway, but cannot recommend them as it was a trial and error solution - in the worst case, I was prepared to disassemble again.

Comparison between the original and off the shelf O-ring :

With both new O-rings fitted to the Governor valve :

Photos of the re-assembly :

Replaced the worn transmission mount while I was at it :

Final view before re-fitting the plastic inner wheel housing :

Took the car for a drive. I had to loosen the kickdown cable, as I had previously tightened it up when the erratic upshifts occured. The gearbox has never felt so good since I acquired the car! Gear shifts are absolutely correct now and amazingly smooth :)