It is not too often that you see a no-reverse concern caused by a bad solenoid or by a valve-body problem that does not affect any forward upshifts. Generally you’ll see this only on valve bodies that have a reverse-inhibit function, such as the 5L40 or JF506. There are always exceptions, though. We recently had an FNR5 do exactly that. In this instance it was a bad shift solenoid, but not one obviously connected to reverse.
A friend of mine who owns a local transmission shop called me recently to see whether I could help with a difficult problem he was having with a transmission. He had taken in a Ford truck with a 4R100 transmission that had no fourth gear. The fluid was badly burnt and there was a lot of clutch material in the pan.
The 6F50 and 6T70 transaxles were developed as a joint effort between Ford and General Motors. Because this was a joint effort, as you can imagine many of the internal parts are very similar or almost identical. In this article we talk about the solenoid body and what is similar but different.