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Old 02-28-2010, 09:18 PM
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gyromatic three speed trans question

What does the governor and solenoid and interruptor switch do on the gyromatic trans do. Had the 1950 dodge on the road over the weekend. Driving in third gear seems like the engine RPMs are high

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Old 03-01-2010, 10:55 AM
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Off the top of my head- and not specific to the "gyro", but the solenoid actuates the OD, the governor prevents OD from engaging until the engine's up to a certain RPM and the interrupter , well, interrupts the OD when the brakes are hit, tranny down shifted, etc.
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Old 03-01-2010, 05:32 PM
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Hey that's not bad for being off the top of your head.

I am no expert on these transmissions, but here is some info I found in a dusty old book that might help:

Quote:
Dodge Gyromatic, Chrysler Prestomatic & Fluid-Matic, and DeSoto Tip-Toe Shift.

Description:

Semi-automatic 4-speed transmission with hydraulic actuation and electrical (governor switch and throttle "kick-down" switch) control. Transmission has "Low Range" and "High Range" controlled by shift lever on steering column and two speeds within each range (first and second in Low Range and third and fourth or direct in High Range) engaged automatically by the hydraulic shift mechanism. Automatic shifting is dependent on car speed and throttle position.

Operation:
Manual control (Shift Lever on steering column) operates in the usual manner by shifting the "Manual Clutch Sleeve" on the transmission main shaft. The automatic (hydraulically operated) control operates as follows:

Automatic Upshift - Governor switch contacts open at car speed of 6-7 MPH (Shift Lever in "Low Range"), 12-14 MPH (Shift Lever in "High Range"), de-energizing the pilot valve solenoid. The pilot valve actuates the main valve which admits oil under pressure from the transmission oil pump to the hydraulic cylinder causing the piston in the cylinder to move forward which compresses the return spring and the engaging spring on the shift rail. When the throttle is released momentarily, the engaging spring causes the Direct Speed Clutch to engage the higher gear. (Second in "Low Range," Fourth in "High Range").
Note - Hydraulic piston actuates Interrupter Switch in moving forward but ignition is not interrupted because circuit is open at the Governor Switch. (no interruption required for shifting since transmission "free-wheels" before shift occurs).

Automatic Downshift - When car speed drops to 6-7 MPH (Shift Lever in "Low Range"), 12-14 MPH (Shift Lever in "High Range"), Governor switch contacts close, energizing the pilot valve solenoid. The pilot valve causes the main valve to close, shutting off oil pressure (oil is by-passed into transmission case through pump pressure relief valve) and opening a passage to case for oil drainage from hydraulic cylinder. The return spring in the cylinder moves the piston backward and when the piston strikes the shoulder on the shift rail, the rail and Direct Speed Clutch are moved back into the lower gear position (First in "Low Range," Third in "High Range).
Note - During the initial movement of the piston, a shoulder on the piston causes the Interrupter Switch to close momentarily, grounding the ignition coil, and interrupting the ignition to relieve the engine torque and allow the shift to occur. Further movement of the piston opens the Interrupter Switch and restores the ignition.

Accelerator Pedal "Kick-down" Downshift - At car speeds under approximately 27 MPH (Low Range), 53 Mph (High Range), the transmission can be shifted down from Second to Low (Low Range), Fourth to Third (High Range) by fully depressing the accelerator pedal which causes the kick-down switch contacts on the carburetor to close and provides an alternative ground than the governor which energizes the pilot valve solenoid and enables the Interrupter Switch. The downshift then occurs in exactly the same manner as for the Automatic Downshift (above).
Note - The transmission cannot be "kicked-down" at higher speeds since the kick-down contact plunger is held up out of engagement by manifold vacuum.

So there you go, more info than you ever wanted to know about your transmission.

Mostly, this is the same thing Cobalt said, except that in this case, the Interrupt Switch interrupts the engine ignition system to allow a downshift to occur.

Quote:
Originally Posted by chuckyishere
Driving in third gear seems like the engine RPMs are high
Did you let off the gas pedal to let the transmission shift into fourth?


Hope this helps...
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Old 03-01-2010, 06:06 PM
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Quote:
Originally Posted by Joe G
Hey that's not bad for being off the top of your head.
That's kind of you, but I admit I was off base pretty good. But this info is great!!

When you mentioned letting off so it would shift, I was reminded of the OD in my old '52 Willys, I would shift into high (3rd.) and then let off the gas and it would engage the OD. Almost like shifting gears...
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Old 03-01-2010, 09:39 PM
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The reason im asking is that i had to disconnect the governor cause it blows the circuit breaker and drops the amp meter down to discharge not sure if it went bad and shorted out
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Old 03-01-2010, 11:18 PM
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If the system is mis-wired and there is a wire going directly from the circuit breaker to the governor, then it would be a short circuit and would definitely trip the circuit breaker.

If the wiring is correct as shown in the diagram above, a short in the governor would only cause the transmission to stay in low gear (first or third, depending on the position of the shift lever). It wouldn't be a short circuit and shouldn't trip the breaker.

You said in a previous thread that your carb doesn't have the kick-down switch or anti-stall device, and that the wires that would have connected to these devices have been removed. So the only thing the circuit breaker should be powering is the solenoid via the red wire. The yellow wire from the solenoid is it's ground wire. It finds a path to ground through the governor when conditions are right (low speed) and thereby activates the solenoid.

At this point, it seems more likely that the solenoid is shorted to ground, which would trip the breaker and cause the transmission to malfunction.

But also in your previous thread, you stated that the circuit breaker still clicks when the wire to the solenoid is removed. This indicates that the circuit breaker itself is shorted to ground. If that's the case, you'll need to find a better original style breaker/resistor unit, or you could abandon the original circuit breaker and wire a modern auto-reset circuit breaker in it's place...like one of these:


(click for link)


These are available from any auto parts store for less than $10.

Good luck....
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Old 03-02-2010, 06:41 PM
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I forgot to mention that i did replace the circuit breaker and that one was a 30 amp and that it still popped.
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Old 03-03-2010, 08:40 AM
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OK, so it's got a new circuit breaker and everything is wired as shown in the diagram, but the circuit breaker still pops unless you remove the wire from the solenoid to the governor.....Right?

That being the case, the most logical cause is a shorted coil in the solenoid - not shorted to ground, but shorted to itself so it draws way too much current.

Hope this helps...
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