That was a good effort Guy
Practical Classics have just completed a series of articles on rebuilding the Borg-Warner 35. Good series too and it helped me understanding how an epicyclic autobox works.
You're spot on about ekaftan's (and my) problems stem from lack of oil pressure in the 'box. It is believed the filter does block but what causes it remains to be resolved. Soon we'll know as my duff 'box is coming ever closer to coming off the car due to good progress today.
The filter in the 4HP20 is a pad of felt essentially and filters to about a micron as I understand it. It does not take a lot of debris from the clutches (6 of them) to block it in a "sealed for life" 'box that cannot be fully drained. The one I've already stripped was 40K old and that had enough very fine debris in it so it'll be interesting to see what my 150K one looks like. I'm guessing it'll do a fair impression of coal-hole or an explosion in a pencil factory...
In addition to the 6 clutches in the 'box itself, the torque convertor has a "lock-up" clutch inside it (something the BW35 never had) and it seems there is a chance this breaks up and fills the 'box and filter with blocking debris.
It is a good idea to replace the TC even if it seems OK, along with the transmission cooler and the filter itself.
Watch my blog (Brief Encounter II) for more news as it happens...
Nah... the truth is that I am having back and neck pain and it looks like the culprit is the low roof. I am tall enough that a sunroof equipped car makes me bang my head or drive crooked.
