1946-1949 Hydramatic Help Needed - Rear Band Issue

[Joe Jensen]

I was driving my '49 6207 yesterday and experienced first gear slipping and it got pretty bad fast. I drained the fluid and removed the lower oil pan.  I found the rear band out of adjustment.  The band adjust screw was threaded fully in.  I suspected something happened in the rear servo so I removed the front and rear servo to tear down the rear servo.  Unfortunately, I found no major issues.  I have one piston ring gap out of spec that will be replaced.  All of the springs measure less than spec but I am not sure it is enough to be cause of the issue.  It seems that the band may have skipped off the adjustment screw (if that is possible).

Does anyone have any suggestions or see any issues?

Thanks,
Joe

[Joe Jensen]

More pictures

[1959Fleetwood]

Hello Joe, i just saw your question regarding the transmission you're working on. I have rebuild many Cadillac transmissions for my customers in the past. Seeing that the screw for adjusting the front brake band is turned in all the way, to me it can mean only one thing namely worn brake band(s) In the 4th picture of your 1st posting you can see the end of the friction material from the brake band, it's very thin. To my opinon if take the brake band out to check it you will see that the friction material is (almost) gone. And old friction material can not do the job as it should because of age. Just a few weeks ago i had a 1954 Packard in my shop with same issue, slipping in first gear. Readjusting the brake band adjuster bolt didn't help so i took the transmission apart and discovered the problem of slipping. The friction material had come to such and end that it was almost steel surface that was left. Renewing both brake bands and adjusting the bolts by means of the shop manual solved the problem. My experience also tells me that specifications of the springs for the servo's can be a little bit out of specs what the shop manual tells you but that it isn't give a problem. Also at the other side of the brake band there's a strut that is held to the case side and the brake band end. Unless you turn the band adjuster all the way out and/or removing the servos this strut cannot fall out of it's place.
Hope this helps.

[Joe Jensen]

Thank you for the reply.  After checking over the servo and reinstalling it I found the rear band ends collide before achieving proper band adjustment.  The rear and front bands were replaced in late 2020.  Even when the rear band went in new in 2020 the adjustment screw was nearly screwed in as far as it would go.  I confirmed that the band was the correct part number for a 1949 Hydramatic.  I am going to remove the transmission and remove the band.  Something is wrong besides a worn out band.  I will report back what I find it case it could be of help to anyone else.

Joe

[Joe Jensen]

Update...

For any of you that are interested, I ended up replacing both bands.  The replacement rear band was identical (but much more wear material than the one removed).  I ended up with a lot of adjustment on the adjustment screw after setting the rear band according to the service manual.

I ended up installing the rear band and the rear servo right after installing the assembly with the front and rear drums.  I wanted to see if I was going to end up with no adjustment before I put most the transmission back together.  I would recommend this to anyone putting a Hydramatic together.  You can see the rear band much better without the extension housing in place.  Once tested, I removed the rear servo and continued per the assembly instructions in the service manual (note, adjustment screw screw must be backed out at least 7 turns, just like the initial disassembly.

I am left with the conclusion that I somehow had the rear band installed incorrectly when I rebuilt the transmission in late 2020.  I can't understand how that could happen.  However, since the bands were identical (new versus old) that is the only possibility.

The transmission has been working well.  My 2-3 shift is much smoother.  I suspect the broken compensator piston ring in the rear servo was making shift harsh.

I hope this might help some else digging into one of these Hydramatic transmissions.

Good luck!
Joe