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1956 Powerflite shifts fantastic at cold start up - once operating temp is reached downshifting doesn't really occur. When at operating temp - tranny wants to start in 2nd gear.
 

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Welcome to Allpar. As ATF warms, it thins out. If there are internal leaks at seals, etc., it will show up more (leak worse) when warm than when cold.
Test the line pressure between cold and warm to see if it drops significantly. A heavier bodied fluid, like synthetic ATF+4 may hold higher pressures when warm, despite the internal leakage.
It may also be time for a transmission rebuild?
 

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It could also be caused by a stuck governor. I had a Ford C6 do that to me. Pressure testing as IC mentioned is an excellent diagnostic tool. Chrysler transmissions have pretty good pressure test points if you have the manual with them called out, and from what I recall governor and throttle pressure test points are both there.
 

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Welcome to Allpar. As ATF warms, it thins out. If there are internal leaks at seals, etc., it will show up more (leak worse) when warm than when cold.
Test the line pressure between cold and warm to see if it drops significantly. A heavier bodied fluid, like synthetic ATF+4 may hold higher pressures when warm, despite the internal leakage.
It may also be time for a transmission rebuild?
200-300 miles on recent rebuild.....I did see the tranny apart so I believe the rebuild kit was used & tranny was air/bench tested.
Thank you for pointing me in a direction. I was going to try the fluid "upgrade".
"POWERFLITE OVERHAUL MASTER TRANSMISSION KIT - 2 SPEED AUTOMATIC
Includes all clutches, steels, gaskets, seals and O-rings."
 

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It could also be caused by a stuck governor. I had a Ford C6 do that to me. Pressure testing as IC mentioned is an excellent diagnostic tool. Chrysler transmissions have pretty good pressure test points if you have the manual with them called out, and from what I recall governor and throttle pressure test points are both there.
In discussing with my Mopar buddy's this also came up - nice call! How to unstuck it?
Thank you
 

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Unfortunately you may have to pull the extension housing to get at the actual governor. I would do a pressure test first and if the governor pressure stays up then go after it. If the governor pressure falls off as you coast down, it may be sticking valves in the control valve body. Possible fresh fluid (all of it, that transmission is old enough the have a torque converter drain) may clear things up. If you floor it when it sticks in high, does it then kickdown to low? Chrysler did not have part throttle downshift on any Powerflite and only later Torqueflites.
 

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I hope to have the car in the air tomorrow to flush fluid - going to try ATF+4 and cross my fingers......
Tranny will kickdown most of the time but I try not to drive it all that much when displaying this symptom. Forgot to mention when this is happening reverse is almost non existent!
Can thank you enough & stay well!
 

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Ok, I would definitely try to get some pressure tests. I have a copy of the 1957 Dodge service manual which covers PowerFlite and TorqueFlite transmissions. Chrysler had plenty of pressure test points on both and the manual covers the value ranges for all the test points. On a PowerFlite, it is much like a PowerGlide as far as function, you have a Kickdown (low) band, a direct (high) clutch and a reverse band, at no time is more than one applied at a time, as the direct clutch engages, the kickdown band is released by the same oil passages that supply the direct clutch. Reverse is a servo applied band just like the kickdown band.

Low oil pressure in reverse will cause problems, it is way higher than any of the other gears on the order of 250 psi vs 90 in forward gears.
 

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The Walmart Supertech ATF+4 says that it meets Chrysler MS-9602 on the label and smells like the real (Mopar) thing. The Transmax fluid calls itself ATF+4, but says nothing about meeting MS-9602, is thinner-bodied and does not have that distinct ATF+4 odor.
Using the Transmax has caused lockup shudder issues after a fluid change for me. Avoid it.
The line and governor pressure test taps and adjustments are accessible on the outside of the case. See attached:
 

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IC, I was trying to figure a good way to attach a picture from the 1957 Dodge manual, thanks for that!
 

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Make sure you drain that torque converter too. As mentioned by 85lebaront2, it's old enough to have the drain plug. Replace ALL of the fluid, not just part of it.
 

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Update - I messaged my buddy with the lift and told him the plan. Well...... he had already drained and filled the tranny with synthetic ATF+4 and did NOT drain the converter. Cant be upset as he was only trying to help. So I decided to put some miles on - I would say a 80% improvement. The only issue I noticed was after all the miles - reverse still was a little "sluggish". But I'll take that over no reverse at all!
My buddy felt so bad that he offered to pay for the next fluid swap. The saga continues. ALSO I stomped in it several times and every time it dropped right down to "Low".
 
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