I'd like to change the transmission fluid on my car. Since the transmission has a "P" position for park, I have been told that it is unfortunately the less desirable Jetaway transmission as opposed to the Hydra-Matic. I have never changed the transmission fluid of anything...ever. I have done countless oil changes, but never a transmission fluid change. Is this something that I should have a shop do, or should I try to tackle it myself? If I can do it myself, what would I need to get the job done? Thanks so much in advance.

 

A 1956 shop manual or even a Motor's or Chilton's Prefessional Trades Edition manual will help you here. I think the 56 trans had a drain plug on the pan but I'm admittedly not that familiar with them. d2willys and coldwar are good with these years HydraMatics.

The old slant pan HMT was a tough bird. The reason a lot of folks slam the Jetaway HydraMatic is because it was new for 56 and had some teething problems, not unlike most automatic transmissions back then. Its teething problems didn't compare to Buick's Triple Turbine Dynaflow though.

 

Thank you so much! I will check the shop manual. What are teething problems?

 

Changing out the tranny fluid isn't difficult ... just messy, if you want to do it right. You want to drop the pan and it's load of fluid (usually right onto your tshirt) and change out the filter. Put the pan back on and add as much fluid as you took out back in down the dipstick tube. That drains about a gallon of the 3-4 gallons in the system. The rest is in the valve body, torque convertor and radiator. A shop will cut the return line from the rad and install their swap machine there, allowing the transmission pump to push all the old fluid out and injecting replacement fluid in via the return line. They'll then patch the low pressure line with either a rubber sleeve, or a compression fitting. You can do the same by removing the return line and adding a length of clear hose to the end, leading to a bucket with carefully marked graduation lines .. by the pint preferable. Have someone start the engine and pay attention to how much is draining out and add back down the dip stick to keep the level as even as possible ... you don't want to go more than a pint low, even at idle. Cut the engine if it's pumping out too quick, but be careful to not overload it. This will get everything that's in the cooler and TC .. the little bit that's left in the valve body will dilute quickly into the rest as you drive. I like to add half a dozen nuts threaded onto the bottom of the clear hose to weigh it down. If it firehoses itself outta that bucket ... you're gonna have a bad day.

 

Holy crap...I think I'll leave this to the shop then and see if my mechanic will let me hang out and watch while he works on it. Thanks so much for the tips, though! I will pass them along to my mechanic.

 

Some people can make a simple job seem like only a NASA engineer can do it

 

Hadn't considered being able to machine flush an older HydraMatic, but I suppose it's possible to do it using the cooler lines. I'd be wary of disturbing any sediment in the trans doing that though. Make sure shop uses Dexron fluid.

Teething problems are minor problems and modifications they had to make after initial design to get the thing working reliably. After 1956 Jetaway HydraMatic became a VERY reliable and tough transmission.

I often wish they'd stuck with it instead of switching to the new "more efficient" Slim Jim in 1961. It's telling that Cadillac kept their version of Jetaway and Pontiac kept it for their long wheelbase cars thru 1964. They didn't have near as much trouble with it as Olds had with the Slim Jim.

 

Well I'll simply do my best to keep it up to snuff, and I'll run it until she can't go any further. The car has very low mileage for it's age (31k original miles verified as accurately as possible), so hopefully I can get some longevity out of my Jetaway transmission.

 

It's obvious to me that some of the posters of "advice" on this thread have never really worked on these cars and are going "off the top of their hat".
There is a plug on the rear of the trans pan where the trans itself can be drained. There is also a plug on the on the torus cover (torque converter). You must turn the engine so the plug is at the bottom. There really is no need to pull the trans pan if it is not leaking or unless there is a problem with the trans. There is no filter inside, only a screen.

 

true enough, I've not worked on this one ... but somehow I doubt many tranny shops today have either. Feel free to correct me any time.