Success! The overdrive transmission is back on the road, and working fine....but there's a bit of a story:
Using the Borg-Warner overdrive manual, some good advice from rfs56trk, and considerable online info (including the link from Gdads51), I started to disassemble one of my spare OD units to see how the one that's in the truck would come apart. Looking at the B-W manual, I was expecting to gain access to the two sets of bearings/races in the tail of the OD, as indicated in figure 3. As I was disassembling the OD, I noticed there was only a bronze bushing at the output shaft, not bearings. I ran an endoscope down the tail to make certain. I couldn't find a date of publication of the B-W manual, but I guess there were production changes throughout the years.
I then scoped out the OD unit in my truck, and discovered that the bushing was completely missing! I ran the scope through the oil drain hole and both fill holes, checking for debris. It seems that whoever last worked on this OD failed to install the bushing. The collar where the bushing goes had been gradually wearing away the yoke, and had worn it down by 1/64". I got a bushing and rear seal set from NAPA for about $32. I drove in the bronze bushing, replaced the seal, and refilled the transmission with oil. When I replaced the yoke, I went ahead and replaced both U-joints. (If the bushing were damaged rather than completely missing, it can be pulled from the rear with the correct puller)
Basically, I was able to make the repair without having to disassemble or remove the OD from the truck. The test drive was smooth! This trans has had a bit of vibration for as long as I owned it...I attributed it to being old and worn. The vibration was generally only noticeable when driving down the interstate at 75-80mph. It had gotten worse lately, which is what led me to start checking into it.
Thanks to everyone who contributed information!
The other issue I encountered is regarding transmission identification. The internet is replete with opinions and assertions about what is a Saginaw or Muncie transmission. The tri-five forums are a dumpster fire of conflicting opinion and partial information. There isn't even universal agreement on the years of production, while some conflate the characteristics of the 3-speeds with 4-speeds. It's a hot mess.
From what I can tell: A Chevy transmission made at the factory in Saginaw Michigan in 1960 is not a 'Saginaw', while a Chevy transmission made at the Saginaw factory in 1966 is? I'm painting with a broad brush here, but the early 'Saginaw' transmissions were just known as 'Chevy', as there was no need to differentiate. Later transmissions (3 & 4 speeds) made in Saginaw were known as 'Saginaws' to differentiate them from the 3 & 4 speed transmissions made in Muncie, Indiana. The term 'Saginaw' was retroactively applied to the earlier Chevy Saginaw-built transmissions as casual reference. (Borg-Warner transmissions have a uniquely-identifiable case, and transmissions made in Dearborn seem to be BOP applications)
Ultimately, casting numbers will tell you what era and model of transmission you have. Use primary references, not just what someone posts. Some people will argue with you, to satisfy their need to be 'right'. Just get the parts you need that fit your transmission, fix it, and drive it! If someone feels compelled to argue, they can find all the verbal judo they want at the tri-five forums. They have people there who seem to enjoy tearing each other down, rather than buoy each other up.
I hope this story and info helps!
-Kevin
