1948 Chrysler T&C will not shift to overdrive

[Guest carguy00]

I had my Carter ball and ball carb rebuilt by a professional and now the car will not shift to overdrive. The wires on the carb were reconected as original and I have not touched any mechanical linkage to the transmission.Does anyone have a hint as to what I should look for?

[Guest Commodore]

Here is a link to a copy of the Borg Warner Overdrive manual. It has troubleshooting procedures. On Chryslers I think the kickdown switch is in the carb where I suspect where the problem is.

1964 Studebaker- The Old Car Manual Project

[marcapra]

Hey, wait a minute. Unless it was modified, 48 Chryslers don't have overdrive. They have a semi-automatic four speed transmission. Do you mean it won't shift into 4th gear?

[Guest carguy00]

Yesit has four speeds, but the way it shifts is it goes into over drive after you run through first, when you take your foot off the gas. Then you shift to second, the shifter is on the column, at about 30 MPH you take your foot off the gas and over drive kicks in.

Now it only has two speeds, no overdrive.

[marcapra]

Are you aware that they have put many of the Master TEch filmstrips on Youtube. Here is one filmstrip that explains how to fix the semi-automatic transmission on a 49 Chrysler, which is very similar to your 48. Marc

[Guest martylum]

Hi- just finished going through the shifting on a fluid drive 48 Chrysler. I'm wondering if the carburetor warm engine idle speed is too high on your rebuilt carb? The downshift button on the carb affects downshifting but not upshifting. Check you shop manual and your engine for the correct idle speed and you do need to let off the gas so the engine can return to idle speed before it will upshift.

Martin Lum

[Rusty_OToole]

For normal driving you can start with the lever in HI and just shift up at 14mph or faster. LO is for hills, sand, snow, slow driving, heavy loads etc not necessary most of the time.

[Guest carguy00]

Hi Marcarpa,

That link was fantastic! I will let you know if the I can solve the problem after I follow the directions.

[Guest carguy00]

Hi Martin,

Good point I'll check it. Since it shifted before it may be that simple.

Thanks,

Ken

[Guest carguy00]

Problem solved, the idle we too high. I also changed the points after the rebuilt carb was installed. The car ran so much better that the idle was so high the car would not shift to overdrive.

Thank you all for your feed back

[CarlLaFong]

You keep referring to it as overdrive. Your car does not have overdrive. It is shifting into high gear, which is 1 to 1

In 1941, Chrysler offered its “semi-automatic” transmission in combination with the fluid coupling, at considerable (for the time, anyway) extra cost, usually between $100-140 depending on the model on which it was installed. This semi-automatic transmission consists of the fluid coupling, a two-speed manual transmission with integral underdrive, and conventional clutch. The early models (M-4) operate on engine vacuum (“vacamatic”), while the later models (M-5 and M-6) operate on a combination of electric circuitry and hydraulics.

The shift lever is mounted on the steering column, and there is no “shift quadrant” indicating the “gear” the transmission is in, except in later models (1951-53 Chryslers, 1953-1954 DeSotos and Dodges). There are two forward “ranges,” low and high, as well as a reverse gear. The shift pattern is the standard “H” minus 1st gear, as per the illustration on the right from the 1946 Chrysler Owner’s Manual.

There are four forward gear ratios:

1. Underdrive Low: 3.57 to 1.00
   
2. Low: 2.14 to 1.00
   
3. Underdrive High: 1.75 to 1.00
   
4. High (Direct Drive) 1.00 to 1.00