I'm in process of rebuilding the failed tranny on my 98 VDP (145K miles). I have the tranny on the bench and am just waiting on parts to finish the rebuild. The fault was in the A drum, with a section of about 2" broken away in the classic failure mode. Based on mileage, I'm also replacing the frictions & will replace the F piston while I have it opened up as it has also been an identified failure point over the years. The frictions are a precaution only as I can't see / measure any change in the originals - pretty impressive after all those miles. As a note of interest, no codes were ever set post failure even though it immediately went to limp home when put into gear post failure.

My question is this.
I see a lot of info on an updated main pressure regulator in the valve body (p/n 1058-327-030) & an indication that scoring of the bore may cause pressure spikes that contribute to the A drum failure. However, I wasn't planning on doing anything with the valve body as there were no shifting issues apparent up to the time of the failure. I would have expected pressure spikes to have caused shifting symptoms that were noticeable (harsh shifts etc). I had thought the issue with the A body lay primarily in a fatigue failure, so was comfortable to only do only that replacement as the A drum has also seen upgrades in both the lip design as well as in an the addition of another lubrication port to overcome what I expected were recognized design deficiencies.

Am I correct in this line of thought or Would there have been symptoms apparent if the bore had scoring & pressure spikes were occurring?

Thoughts and input much appreciated

 

Apparently ZF USA tech support is pretty decent. Maybe they would know.