Gyromatic Won't Shift to 3rd

[Earl Gray]

Joined last week. First post.

 

I own a '51 Dodge Coronet (230cu in, converted to 12v, one-wire alternator) with a Gyromatic. The issue is, when shifting from low to high, it will not shift to 3rd. It only goes from 2nd to 4th, confirmed by coming to a complete stop and it downshifts to 3rd. In fact, when it downshifts to 1st or 3rd at a complete stop, it almost kills the engine. The kickdown doesn't seem to work either. The Service Reference Book for trouble shooting the hydraulically operated transmission says when "the car speed is down, so the governor points are closed and the circuit through the solenoid is completed down to ground. That means that the solenoid plunger is down, holding the ball valve down off its seat."

 

What I've done before creating this topic:

1. Flushed/replaced fluid in GyroMatic according to service manual.
2. Adjusted idle to 450 - 500 rpm range.
3. Adjusted dash pot on carb to meet service manual specifications.
4. Shifted from 2nd to 3rd (low to high) at service manual's recommended speeds.
5. Searched this forum for specifically related issues and read through many.

 

Just for the info, most gyromatic photos show the interrupter switch in the spot towards the vehicle's front and above the governor. My interrupter switch is towards the back of the gyromatic and above the solenoid. Is there some reason for this besides different year/model?

 

Note: If you know of a specifically related thread (shift from 2nd to 4th only), can you please provide a link?

[Dodgeb4ya]

Did it work before for you on 6 volts?

[Earl Gray]

Good question. Unknown. I didn't convert it to 12v.

[keithb7]

Someone way smarter than me informed me:

 

First off: 1st gear and 3rd gear, are the same two gear ratios.  The same two gears are meshed when in either 1st or 3rd.  Additionally 2nd and 4th gears are the same gear set that are  meshed. Same gear ratio when you are in 2nd or 4th.

 

What you are really doing when going from low range to hi range, is changing the final gear ratio of the output shaft of the tranny.  "Drive" on the shift console could also be called "hi range". Ok, so lets you start in 1st (or 3rd gear) in low range. You lift your foot and shift to  2nd gear, in low range. Now lets assume you clutch in and shift the console to drive (high range). The tranny stays in 2nd (which is also 4th) gear. All you did when you shifted into hi range was change the final gear ratio of the output shaft. So you cannot actually go up through all 4 possible gear rations from 1 thru 4. The tranny upshift goes, 1st, 2nd, 4th. It was designed this way. The only way to get into 3rd is either slam the throttle down when in hi range, and it will down shift into 3rd. Or, you are in hi range 4th gear ratio, and you coast to a stop. Then the tranny down shifts into 3rd.

 

This can be confusing. It is weird to understand unless you understand the way this tranny works. Maybe another way to look at it is:

There are only 2 gear sets on the input side of the tranny. Then you have a final drive hi-low gear option on the output end of the tranny.

 

Your down shift problems are not really solved here, however it does explain why 3rd is skipped on the upshift.

 

This is just a 2 speed tranny with hi/low range options. Many a man has scratched his head over it. Many will poke fun at it, however it’s genius. Those who don’t understand may ridicule it. The people who figured this out and designed it were really smart!

Edited March 30, 2020 by keithb7

[Dodgeb4ya]

GyroMatics on Dodges and the other variations don't fare well on 12 modifications.

12 volts will burn up the M-6 solenoid.

The solenoid has to operate as originally designed for the transmission to function properly.

If the solenoid is burnt up or incorrect modified transmission wiring the trans might or  might not upshift or downshift as originally designed.

***With the solenoid still on the car with the key on measure for 12 volts at either of the two solenoid studs...should read close to 12 volts...

***Test it off the car... plunger should pop out and stay out with... 12 volts .

Solenoid still works for time being on 12 volts.

*** Shifting Issue problems can be with wiring, interrupter switch on

trans , resister circuit breaker box on air cleaner bracket and high idle speed.

***Very delicate Silver governor points need to be checked for oil contamination too.

The transmission electrical system won't survive on 12 volts unless dropped down to 6 volts.

 

[Dodgeb4ya]

And as Keith is saying....be sure you know and fully understand how this transmission shifts both manually...and automatically.

**1st and 2nd gears are the power range..shifter up position

**3rd and 4th gears are the driving  range gears..shifter pulled down for all normal driving

[Earl Gray]

17 hours ago, keithb7 said:

Someone way smarter than me informed me:

 

First off: 1st gear and 3rd gear, are the same two gear ratios.  The same two gears are meshed when in either 1st or 3rd.  Additionally 2nd and 4th gears are the same gear set that are  meshed. Same gear ratio when you are in 2nd or 4th.

 

What you are really doing when going from low range to hi range, is changing the final gear ratio of the output shaft of the tranny.  "Drive" on the shift console could also be called "hi range". Ok, so lets you start in 1st (or 3rd gear) in low range. You lift your foot and shift to  2nd gear, in low range. Now lets assume you clutch in and shift the console to drive (high range). The tranny stays in 2nd (which is also 4th) gear. All you did when you shifted into hi range was change the final gear ratio of the output shaft. So you cannot actually go up through all 4 possible gear rations from 1 thru 4. The tranny upshift goes, 1st, 2nd, 4th. It was designed this way. The only way to get into 3rd is either slam the throttle down when in hi range, and it will down shift into 3rd. Or, you are in hi range 4th gear ratio, and you coast to a stop. Then the tranny down shifts into 3rd.

 

This can be confusing. It is weird to understand unless you understand the way this tranny works. Maybe another way to look at it is:

There are only 2 gear sets on the input side of the tranny. Then you have a final drive hi-low gear option on the output end of the tranny.

 

Your down shift problems are not really solved here, however it does explain why 3rd is skipped on the upshift.

 

This is just a 2 speed tranny with hi/low range options. Many a man has scratched his head over it. Many will poke fun at it, however it’s genius. Those who don’t understand may ridicule it. The people who figured this out and designed it were really smart!

Great points here! Thank you.

[Earl Gray]

17 hours ago, Dodgeb4ya said:

And as Keith is saying....be sure you know and fully understand how this transmission shifts both manually...and automatically.

**1st and 2nd gears are the power range..shifter up position

**3rd and 4th gears are the driving  range gears..shifter pulled down for all normal driving

Great points here too! Thank you both!

[greg g]

http://www.imperialclub.com/Repair/Lit/Master/024/index.htm

 

https://www.allpar.com/mopar/m6.html

Edited March 31, 2020 by greg g

[Tom Skinner]

Earl Gray,

Start out in 1st Gear low Range, (Shifter Up and Forward) take your foot off the gas at 8mph (It should Shift up to 2nd) Drive it up to 18-20mph

Clutch it at about 18-20mph and move Shifter to Lower Position (3rd and 4th) Now because you are in 4th range no 3rd is needed.

Start over from a full stop. (Shifter in Lower Position 3rd Gear) Drive to 16mph take you foot off the Gas it should Up-Shift to 4th. Drive away at anay speed.

You shouldn't need to clutch at full stops until you clutch to neutral to park it. This is how to drive the m6 Hydraulic Transmissions operate.

I might have missed the bus here but I think you are just over thinking this.

Tom

Edited March 31, 2020 by Tom Skinner

[greg g]

The car was designed to utilize the upper range of the transmission in 90% percent of normal on road driving. Low range was for starting in slippery conditions, using engine compression braking on long slow down grades, pulling a trailer up steep hills, or when remodeling, pulling your house off its foundation.  It was never envisioned to be used on a daily transporting yourself or the family around town or across country. With a top speed of 20 mph or so using it is kind of an exercise in redundancy.  Just use reverse and high range and enjoy the clunks.  You are not going to win any stoplight drag races no matter how you shift it.

[Dodgeb4ya]

Drive it like a 4 speed and that trans comes to life...using the after market shifter downshift button.

Then learning again how to shift it with the button....a good working item that's kinda hard to find.