'48 Crown Imperial Limousine Fluid Drive shifting

[thomasrc]

I am verifying all of this has been attempted - the mechanic did get it to shift on the road last week, once he turned around to come back, it no longer shifted.

ANY HELP is greatly, greatly appreciated!

The following was posted on BaT:


Using a Firefox Duck Duck Go query “1948 chrysler m6 will not shift from 3rd to 4th after letting up on gas“, I found the following site “https://forums.aaca.org/topic/383942-c38-chrysler-1948-windsor-transmission-issue/“.

I am copying from this site a relevant section for you written by Rusty_OToole (I want Mr. O’Toole to get full credit for the following list of things to look at on your 48 Windsor)

1. It could be low on oil. The transmission is filled separate from the Fluid Drive unit. The transmission will not shift if it is low on oil.


2. Could also be a loose or frayed wire somewhere. Check the wires from the transmission to the carburetor, and from the carburetor to the ignition coil.

3. It is possible the contact points in the governor are dirty. If that happens the trans will not shift down when you stop the car. You can take the top off the governor and clean the points. Be careful, they are made of silver and are not as hard as ignition points or relay points. Use contact cleaner spray, or brake cleaner spray to remove grease and drag a strip of white typing paper between the points until it comes out clean.

4. If the idle speed is too high the trans will not shift. Idle speed should be very low, 400 RPM, about half the speed of a modern car.

Those are the most common causes of not shifting.

 

[SIPLOWGUY]

I'll ask around in my circle.... unfortunately, all the guys who worked on them are no longer with us.

 

[Ross Wooldridge]

@thomasrc - have you talked to anybody in the WPC Club? There are a number of Fluid Drive owners there who might be able to help. One that comes to mind is Greg Biskey - Greg Biskey

If you need help, PM me.

 

[sprice]

Might be something here that is helpful.

Fluid drive/ Tip Toe transmission info.

 

[moparstan]

I am verifying all of this has been attempted - the mechanic did get it to shift on the road last week, once he turned around to come back, it no longer shifted.

ANY HELP is greatly, greatly appreciated!

The following was posted on BaT:


Using a Firefox Duck Duck Go query “1948 chrysler m6 will not shift from 3rd to 4th after letting up on gas“, I found the following site “https://forums.aaca.org/topic/383942-c38-chrysler-1948-windsor-transmission-issue/“.

I am copying from this site a relevant section for you written by Rusty_OToole (I want Mr. O’Toole to get full credit for the following list of things to look at on your 48 Windsor)

1. It could be low on oil. The transmission is filled separate from the Fluid Drive unit. The transmission will not shift if it is low on oil.


2. Could also be a loose or frayed wire somewhere. Check the wires from the transmission to the carburetor, and from the carburetor to the ignition coil.

3. It is possible the contact points in the governor are dirty. If that happens the trans will not shift down when you stop the car. You can take the top off the governor and clean the points. Be careful, they are made of silver and are not as hard as ignition points or relay points. Use contact cleaner spray, or brake cleaner spray to remove grease and drag a strip of white typing paper between the points until it comes out clean.

4. If the idle speed is too high the trans will not shift. Idle speed should be very low, 400 RPM, about half the speed of a modern car.

Those are the most common causes of not shifting.

I have a ‘48 Chrysler Royal with Fluid Drive. I recently dealt with a similar problem, wouldn’t upshift. I’m assuming your Imperial has an 8 which has a slightly different carb than my 6 but otherwise they are the same.
It took me awhile to understand that these systems shift hydraulically. The electrical components can control the operation but they don’t actuate anything. So proper oil level in the trans is the first thing to verify. (Mine was quite low, I hadn’t checked it in several years and it leaks a little at the driveshaft)
The second thing to check is the kickdown circuit. This involves the transmission control relay and two switches in the carb: one mechanical push button and a vacuum operated one that is partly internal. Make sure there is not something in that circuit that is preventing the trans from upshifting. In my case, I had installed the choke rod upside down, and that let it short against the kickdown contact on the carb. The purpose of the kickdown circuit is to force the transmission to downshift when you floor the accelerator, but with safeguards to prevent this if you’re going too fast. A short in this circuit will keep the transmission from upshifting.
Proper idle is also needed for a proper upshift.
If you do not have a wiring diagram, here is one.

 

[fullsized]

Drove a 50 Chrysler for over 30 years. The M6 transmission is a tough old bird. A 6 volt trouble light is your friend. On the drivers side fender well there is a relay with a fuse check it out.