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how to clean points in M6 transmission
I changed the transmission oil in my 48 custom club coupe. I checked the screen. It was clean and had no metal or other debris in it. No metal in the drain plug. I wanted to clean the governor points, but could not get the cover off. I detached the wire and took out the 4 screws. I expected the cover to slip off but it was still firmly attached. How do I remove the cover so I can clean the points? I replaced the screws and wire and went for a 10 mile drive. It downshifts fine, but often I have to keep trying to get the upshift. Once I pressed down and released the gas pedal 4 times before it shifted. When I pulled away from the last stop sign of my drive, it shifted fine. I thought I even heard a "clunk".
Turn your idle speed down and see if that helps it shift better.
I am thinking like Steve that it is probably something simple like rpm's not coming down or not enough speed. When mine doesn't shift when I think it should I depress the clutch about 1/4 of the way down and it shifts right away even if speed wasn't high enough or rpm's aren't down.
Your 1948 car uses a relay to control down shifts, unlike the 1949 and later cars. While the later cars control the downshift solenoid directly with switches, the S11 models control a relay with the switches, and the relay controls the solenoid. Those relays will sometimes stick or malfunction in creative ways. Do you have a shop manual? Reprints of those are available for a reasonable price on the internet. The transmission section has a pretty good description of a procedure using a test light to determine if an electrical problem could be the root cause. It also explains how to get the top off and clean and set the contacts of the governor. Your slow shifting problem sounds like something is intermittently holding the downshift solenoid open and bleeding oil pressure. An electrical malfunction seems the most likely culprit. I hope this helps to guide you.
Owner of a 1952 Desoto Firedome
Thanks for the advice. I checked the idle and set it at 450. It would shift perfectly at the first shift, but would not the shift the next time and would require as many as 4 attempts to shift. When I parked the car I put it in neutral and rechecked the idle. The linkage is sticking and it was idling close to 550. I sprayed all the joints with carb cleaner and ( I know I am not supposed to oil) I sprayed some WD-40. I worked linkage several times and drove it again. It was better, but still sometimes would not shift the first time I raised my foot. I found that I could bump the gas pedal and jar it loose and then it would shift. I am optimistic the linkage will free up and it will shift perfectly.
I found some very old Chrysler tech videos on youtube that explain how the transmission works, how to trouble shoot, and how to service the transmission. They are actually slide shows and half way through a slide tells the operator to flip the record. They have a lot of good info and show more about the governor points than the shop manual.
Many thanks to all who offered advice and especially to Les Fairbanks. It appears that the problem has been the throttle hanging and not letting the engine rpm drop to idle. I have been working on the throttle linkage and now it shifts almost every time. When it does seem slow to shift I bump or tap the gas pedal and it shifts every time. I think the throttle linkage will eventually loosen and it will go to idle every time.
Those videos were pretty neat. Now find me one that explains the Simplimatic transmission operation!
1937 4 door Touring Sedan
1941 DeSoto Deluxe 2 Door Sedan
It's Delightful, It's DeLovely, It's DeSoto!