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Vacum Pull Cable on Chrysler fluid drive

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I have a 1941 Chrysler Royal with a fluid drive transmission, I have had the diaphram replaced and now I am being told that the vacum pull cable is broken and the transmission won't shift on its own, because the vacum pull cable is broken. I thought that this cable was for freewheeling when pulled out, and I wanted to know if anybody can tell me what this cable does, before I continue to troublshoot the transmission. Any info would be of a great help

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I have an old Motor Repair Manual in front of me. It has a diagram of the control system for your transmission. It does not show a control cable of any kind. It shows electrical wiring and a vacuum piston unit which seems to push directly on a lever in the transmission.

The vacuum piston unit is controlled by a vacuum valve connected to the intake manifold. The vacuum valve, piston unit, governor, carburetor, relay and ignition coil are all wired together.

I would inspect the wiring first and make sure it is all according to the factory wiring diagram.

What you describe sounds more like the setup on the straight eight cars not the six cylinder Royal. Sixes and eights had completely different transmissions that year. The Eight was more like a manual trans plus overdrive.

But the diagram for the eight cylinder trans does not show a cable either.

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The under dash cable is only used (pulled out) to prevent free wheeling of gears when push starting the car. The 6 sided rubber diaphrams are used on the 41's with the "Vacamatic" 2 range transmissions. Not he OD cars. I have installed NOS diaphrams on these transmissions only to have them fail after a couple weeks of use. The rubber is old and dry and sometimes cracks and won't push the plunger to shift trans into high gear. As mentioned alread, The control unit and wiring/ vacuum hoses and pipes need to all be checked to for proper operation/condition. There is also a vacuum control valve up on the intake manifold that needs to be checked. You or your mechanic really need a shop manual to do these repairs with understanding and confidence.

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Some Pictures of a 1941-2 VacaMatic and DeSoto Simplimatic transmission.

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Does anyone have experience actually activating the Vacuum Pull Cable? The first time mine was used, a car club friend activated it one evening and we had trouble getting it to disengage. It clearly worked, because until we were able to, the engine really braked the car with no freewheeling. The second time was last Fall, when my present problem arose and I assumed that it was the diaphragm that had failed. At the moment of failure, the transmission had shifted and there was a loud 'bang' and it jumped back into third gear. At that point, the pull cable was very difficult to pull and when it finally came up. it was difficult to push back down. Any ideas?

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I think your problem may be a little deeper than the diaphragm. What you are calling the Vacuum Pull Cable is actually the freewheeling lock-out cable. The purpose of this pull out knob is to allow push starting of a car with Vacamatic transmissions. When the car is stopped, the transmission is either in first or third gear, depending on the shift lever position. Both of these gears are freewheeling gears, which allows for the gear speed differences for the shift to occur. Second and fourth speed are non-freewheeling gears. The only way to get the transmission into a non-freewheeling gear is for the tranmission to shift on its own, via getting the car up to speed, lifting your foot off the gas and letting the vacuum valve do the shift. This can't happen if the car is not running.

Chrysler provided the freewheeling lock-out so you could push start the car and have the rear wheels turn the engine. Pulling out the spring loaded lock-out knob, manually moves the transmission from freewheeling first or third to non-freewheeling second or fourth allowing the car to be push started. The recommended procedure from the Chrysler shop manual is:

"Shift the manual shift lever in the "Low Speed Position", depress the clutch pedal, pull out lock-out cable, and turn on ignition switch. When towed car reaches approximately 5 to 10 miles per hour, engage the clutch, when the engine starts, release the lock out cable, which is spring loaded and will return to its normal position. THIS IS AN EMERGENCY CONTROL, AND THE CABLE MUST NEVER BE PULLED OUT EXCEPT WHEN IT IS DESIRED TO START THE ENGINE BY TOWING THE CAR."

With this said, the lever may be stuck in the lock-out position, meaning you are already in second or fourth gear. Get under the car and make sure the lever on the transmission has moved back to to released position. If it has moved back, I suspect you have damaged something internal in the transmission. Good luck. Let us know what you find.

Edited by 61polara (see edit history)

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61polara is on the money. That lockout round shift cable knob should be left alone (pushed in) unless push starting the car. Possibly the vacuum shift unit and lockout cable have becomed jammed with the kickdown lever on the passenger side of the transmission. There is a 3/8" pushrod that pokes out of the vacuum shifter unit and that rod needs to be pushing straight on the kickdown transmission shift lever located directly in front of the power shift unit. When you pull the lockout cable out it pivots the power shift unit and that causes the push rod coming out of the shifter unit to pop off the kickdown lever. Then the spring on the KD lever pulls the lever into direct gear lockup. You will have to look at the trans to figure what has happened. I think all that has to be done is syncronize pushing in the lockout cable and at the same time someone underneath the car who understands that the power shift unit and push rod needs to be pivoted back into alignment with the KD lever- so the pushrod is dead on pushing against the Lower tab on the kick down lever. This will also require pushing the KD lever forward carefully so the vacuum shift unit rod can pivot back into place.

I'm sure this sounds complicated. :eek: You really need the shop book if you keep this car.

I've attached a couple more pictures.

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