1950s 1956 Hydramatic Trans Flush

[Dave CLC#16900]

Hi, off to visit my long term project/barn find/ "Howard's Eldorado" / or as I like to call her, "Bernadette".  The previous owner bought the car in Chandler, AZ in 1970 from a film company that was shooting a Western in Tucson.  He had the transmission rebuilt in 1978 and said it was never right.  Howard parked her in 1981 when reverse stopped working.  He started some disassembly of trim to repaint the car and stopped.  I bought in 1990 from a local man that bought it to flip it from Howard.

I rebuilt the fuel and brake system immediately and drove it a couple hundred miles.  Seemed to work ok for me except reverse was not good when hot and made grinding noises.

I then took a long break from working on it.  Had to change storage locations 3 years ago and got it running again.  Reverse is not working now, may be low on fluid.

Going to lift the car up for the first time in 20+ years and drop the trans pan.  Was considering putting a quart of lacquer thinner in the fluid to loosen up the crud first, running it on the stands with minimal load. Then draining all the fluid possible from the fluid coupling and pan. Is adding thinner a bad idea?

I have a spare '56 Eldorado transmission but condition unknown from my parts car.  That car was parked in the 70s due to severe rust issues living in Pennsylvania.  One point of getting under the car is to see if Bernadette has her original trans or not.  Howard thought it was original.  If it isn't matching I may just send the parts car's trans for a rebuild.

Thoughts?  Would be great to make some short drives in the car next week....and replace the passenger window, and install the rebuilt antennae, and......

Dave

[Jeff Rosansky CLC #28373]

For what it's worth, we had this same debate when we woke our 55 up. A lot of people here chimed in.
I decided not to change the fluid and just run it. The shifts weren't great, but it shifted. The more I drove it, the better it got. I am happy I didn't change the fluid.
Now with that said, it leaks so it has had a poor man's fluid change over the last few years. But it still shifts ok.

If it is driveable, my advice would be to just drive it a few hundred miles and see if it cleans itself up and gets better.
You can always change it, but you can't unchange it.

Just my thoughts.

[Cadillac Jack 82]

If the 56 is anything like my old 55, just top her off with fresh fluid and drive her.  Mine sat for a while and was clunky from 2nd to 3rd gear.  The more I drove her the better she got to the point where I never noticed shifting as much.

[Big Fins]

If the '56 just has a screen for a filter and a drain plug in the pan, you have it made. I don't know, because I never did any work on a '56.
Why manufacturers can't put in a simple drain plug anymore is beyond me. My pick-up doesn't even have a transmission dipstick. You have to crawl under it, remove the fill plug and there is a little 1" stick on the end of the plug. Modern idiocy!

[Lexi]

The '56 does have a screen inside the transmission and 2 drain plugs; 1) on the pan cover, and 2) one called the "torus drain plug". Shop Manual says to check after running, when refilled partially to start, in N or P for 1-1/2 minutes at 800 RPM, then slow idle, wipe dipstick, and check fluid level. The level should be within 1/4 of an inch on the "Full" mark on the transmission dipstick. Add as required by what the stick says and not rely on what volume of fluid you added. Yes, "modern idiocy" with respect to modern transmission fluid level checking. Clay/Lexi

[Lexi]

For what it's worth, we had this same debate when we woke our 55 up. A lot of people here chimed in.
I decided not to change the fluid and just run it. The shifts weren't great, but it shifted. The more I drove it, the better it got. I am happy I didn't change the fluid.
Now with that said, it leaks so it has had a poor man's fluid change over the last few years. But it still shifts ok.

If it is driveable, my advice would be to just drive it a few hundred miles and see if it cleans itself up and gets better.
You can always change it, but you can't unchange it.

Just my thoughts.

Jeff that is exactly what I did. At first I had some rough shifts and even slippage. All gone after driving it for a few hundred miles, then all negative issues disappeared. Yes, a "poor man's" oil change is what Lexi got-but later a transmission shop did a complete change. Fortunately all went well and has remained so. Clay/Lexi

[Big Fins]

The '56 does have a screen inside the transmission and 2 drain plugs; 1) on the pan cover, and 2) one called the "torus drain plug". Shop Manual says to check after running, when refilled partially to start, in N or P for 1-1/2 minutes at 800 RPM, then slow idle, wipe dipstick, and check fluid level. The level should be within 1/4 of an inch on the "Full" mark on the transmission dipstick. Add as required by what the stick says and not rely on what volume of fluid you added. Yes, "modern idiocy" with respect to modern transmission fluid level checking. Clay/Lexi

I forgot about the torus drain plug. Between that and the pan plug, you can get most of the fluid out.

As far as a 'flush' goes with an additive, NO. It may totally ruin the internal seals and friction plates.

I always disconnect the pressure side of the cooler line, put it into a vessel large enough to hold a couple of gallons of fluid, then pour new fluid down the dipstick tube, run the engine at idle until the fluid runs clean. If you have a paper type filter, that doesn't fix that if it's blocked, but after a fluid swap, drop the pan, change the filter, pan gasket and top it off. It's about a $30 flush at the price of fluid these days.

[Dave CLC#16900]

I appreciate everyone's feedback.  I already have a pan gasket for the trans and really want to drop it and see what is in there.  Will drain the Torus cover too.  From what I learned in the shop manual the pressure is the highest in reverse.  I want to drop the pan to see what has collected there and make sure the pickup is clean.  Heard Walmart is the best place to buy Dex/Merc trans fluid. 

Will skip the additives or lacquer thinner.  Would be awesome if this healed itself, but as the loss of reverse is why it was parked, am very doubtful.

Dave

[Jeff Rosansky CLC #28373]

Heard Walmart is the best place to buy Dex/Merc trans fluid. 

Dave

Funny you say that. I just finished my gallon jug that I've had for years and got another one yesterday.
Walmart had almost the best price but I found it at Menards a couple bucks cheaper.