I recently bought a 1956 Cadillac sedan deville and it starts up and reverses out the drive way with no problem but after driving for a couple minuets when I put the car into reverse it makes this awful banging noise if I feather the gas it will go into reverse and the noise will stop but it sounds awful going into gear. Any ideas what this could be ? All the other gears work fine and I've added a lot of transmission fluid but it did get driven a little with very little fluid I'll try to get a video of it making the noise later.
If it needs overhauling you need a spe******t or someone who really cares about them today. The last time I did on I had to supply 2 extras for possible parts. As a suggestion I would drain it properly including the torque converter, remove the pan and clean everything you could and then refill it by the manual, so all the fluid will be correct. My 56 Fordomatic takes "typeA " which is not available but I found it was. Try to use the exact fluid from 56 for a hydromatics and not "this should be compa***able fluid" from a parts house. Good Luck.
The hydromatic will run just fine on dextronII. I don't remember what the manual says (and I don't have one damnit) but I have chatted with a hydro guy and he says that dextron II is what you want. '56 was a transition year from the slant pan hydro to a more modern transmission. But they still had a rear pump and as I recall the parking pawl fell into place when you killed the motor like the earlier motor. Pump pressure kept the pawl from engaging. If you are dropping your idle off to slide into reverse it could be that you are loosing enough pressure to let the pawl try and drop. proper fluid level and fresh fluid may cure that, the fluid does not last forever. I would try that first and if that doesn't cure it I would then consider cracking it open.
Dextron II, like Pork'n'****** said. He has a good idea with the pump operated pawl. Buy the 1956 Cadillac shop manual. It will tell you how to completely dis***emble, rebuild and re-***emble the entire car, including the ****** It will also describe any "easy fixes" that I can tell you are hoping someone here will provide. There are lots of charts that describe symptoms and possible causes. Bottom line is that there will only be 5 or 6 things that you can try without dropping and rebuilding the entire ******. Any of them could be causing this problem, but it's a slim chance. You can remove and clean the governor. You can drop the pan, remove the valve body, check it then clean it. Same with ac***ulator and servo. You can try to adjust the band. You can replace the filter. You can adjust the levers. You can see if the parking pawl is damaged. The whole thing is an intertwined rotating ***embly, any number of things can be going wrong deep inside the ****** to cause things to collide in reverse, there are bands that are meant to grab things and bakelight cones and wave springs that need to engage to get reverse gear to activate properly. Anything beyond the governor, the valve body or what's accessible under the pan, basically you are looking at a rebuild. If the ****** hasn't been rebuilt in a long time, chances are all the rubber seals and O-rings inside are hardened and no longer controlling the fluid. There are a lot of aluminum and steel parts inside that may be damaged. When you dis***emble it, you have to replace the seals you disturb. It is difficult to drop the ******, so you don't want to do it over and over, it's better to rebuild the whole thing. The reason it works differently before it warms up is that the fluid gets less viscous when it's temperature rises, and the "gaps" in the worn seals/broken parts that are able to control the fluid when it's thicker cannot control it when it's thinner. Good news is that with that manual, some cheap specialized tools, a phone call to Fatsco Transmission parts, a few hundred dollars, some time and patience, you can drop the transmission and rebuild it yourself. I am an untrained part time mental patient with non-opposable thumbs, and I was able to do it. You can try to kick it like the Fonze, maybe it will just start working like that jukebox did.
Check out the social group Hydro Tech. You'll have to join to see the threads, but there is a lot of information there. You can find it by clicking the icon below my avatar to the left. Also, I have the 1954 Pontiac manual uploaded. Find it starting here: https://www.jalopyjournal.com/forum/media/1956-pontiac-hydra-matic-manual-1.403206/#media 54-56 Slant Pan Hydro's are essentially all the same. The diagnosis info will help you regardless of Old, Pontiac, Cadillac, etc.
The changes made to the Hydromatic trans for '56 were intended to smooth out the shifts from what had been a trans with positive shifts hat you could feel in the seat of your pants to something that felt smoother for the old folks that Caddy and Olds were targeting with their marketing efforts. And for these people they were successful. But for those who wanted to use the power in those engines for spirited driving, and those who wanted to drive, even fairly conservatively, for high mileage use, they failed and were criticized in all performance oriented publications. Today there are very few in use outside of cars just pulled on and off trailers at old car shows. As a result people who repair them and the parts to do so are expensive and scarce.
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