1955 Automatic Transmission Low Gear Shifting

[Selfrich]

My 1955 automatic transmission seems to be shifting funny.

First - I know that the "L" shift position is 1st gear instead of the "D" gear that starts out in a higher first gear. - Is this true? The "L" gear seems to be a lower gear than the "D" gear.

Second - My "L" and "D" seem to both have 3 gears. I would have thought that "L" would be first and second gears and then you could shift to "D" for third. If I use "D" I still get 3 gears but first is not as low as the "L" first.

I have no issues with the transmission, performs great - just this doesn't seem right. I have had a lot of Chevy's and MOPARs and none of them acted like this.

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[Dick Rupp]

L is low gear/ 1st gear. D is 2nd gear and 3rd gear. When the selector is in D the car starts in 2nd, then shifts to 3rd / high gear. The transmission has 3 speeds.

 

[Selfrich]

L is low gear/ 1st gear. D is 2nd gear and 3rd gear. When the selector is in D the car starts in 2nd, then shifts to 3rd / high gear. The transmission has 3 speeds.

I know all of that. I am asking for any ideas why my trans is shifting like that?

 

[Tom Alpers]

I know all of that. I am asking for any ideas why my trans is shifting like that?

Here's what goes on. In D, as you know, it starts out in 2nd and shift to 3rd. The reason it does not start in 1st is because of design choices, specifically, they chose to omit a sprag (overrunning) clutch. It is not entirely clear to me why that prevents doing the usual automatic 1-2-3 shifting but it does... I think it creates a freewheeling condition for some situations. They needed a way for people to downshift to lower gears when going down a steep hill so that is why it has the L position. If you are driving normally and you put it in L it will downshift to whichever lower gear does not cause it to exceed about 4000 rpm. So if you are going 60 in third gear and you put it in L it will downshift to 2nd. If you are on a steep hill and you keep slowing down in 2nd you will eventually get to a speed where it automatically downshifts into 1st. For the situation when you are stopped... if you put it in L it will shift the transmission into 1st while you are stopped. Then when you take off my understanding is it will never shift out of 1st gear so you could blow up the motor if you weren't careful. I have not verified that as I don't want to blow up my engine. It may be it will automatically shift to 2nd but I doubt it. Some people like to "race" by putting it in L to take off, then after they are going whatever speed they want it to upshift to 2nd at they shift it to drive and back to L quickly so that it shifts into 2nd but not up into 3rd. It's not really necessary to do that if you just want to be doing a stop light grand prix. If, when you take off, you smoothly and quickly push the gas pedal to the floor it will shift itself into 1st gear as you are taking off. As long as you hold your foot down it will stay in 1st till it hits "redline", about 4200 rpm, and then it will shift to 2nd.... if you keep your foot down it will stay in 2nd till it hits redline again and will shift to 3rd. I don't like to do the thing where you manually put it in 1st and then quickly shift to D and then right back to L because it's pretty easy to be too slow and the trans shifts to 2nd and then right back to 1st and I'm not a fan of shock loading these things. If you want to be in first from the get go for the best takeoff launch I recommend putting it in L when you are stopped. Then put the gas pedal to the floor as you take off. While the pedal is on the floor you can shift it to D anytime before redline and leave it there. With the pedal on the floor its not going to upshift till it hits redline (4200) and then it will upshift. In researching this and comparing 0 - 60 times it looks like starting in 2nd adds about 1 second to the 0 - 60 time. Unless you are drag racing or just want to get the jump on the 55 Chevy next to you, there isn't really any need to bother with a 1st gear start other then the fun factor. Unlike modern cars, these cars have so much low rpm torque that 1st gear is not really needed in everyday driving. My guess is the designers felt only having one upshift seemed more classy than having two and since it wasn't needed for normal driving they just said "lets go for the smoothest feeling operation". Keep in mind that GM had the hydramatic for a decade earlier and up thru the 60's and one of the big complaints about it was it's clunky and hard low gear shifts. It was often called the Hydra-jerk. What better way to show that the ford's had a better transmission then to have only one smooth upshift.

 

[doug7740]

My 1955 automatic transmission seems to be shifting funny.

First - I know that the "L" shift position is 1st gear instead of the "D" gear that starts out in a higher first gear. - Is this true? The "L" gear seems to be a lower gear than the "D" gear.

The 1955 – 1957 Thunderbird Ford-O-Matic transmission is a two speed. In reality, it is a three-speed automatic. This impression comes from either listening to sources unfamiliar with the facts or in believing that that the shift quadrant on the floor, showing only “Lo” and “Dr”, must indicate a two-speed transmission.

What really happens is as follows: When you start off in “Dr” or Drive, the transmission is in intermediate range. As you reach about 25mph, the transmission shifts to High (Drive). This misleads people into thinking the transmission must be a two-speed as it only shifts once. However, if you start off in “Lo” or Low range, the transmission will be in a gear lower than intermediate, i.e., Low gear. As you are driving, if you move the shift lever to “Dr” at any speed under 25mph, the transmission will then shift to Intermediate and then automatically to drive as road speed increases.

Second - My "L" and "D" seem to both have 3 gears. I would have thought that "L" would be first and second gears and then you could shift to "D" for third. If I use "D" I still get 3 gears but first is not as low as the "L" first.

I have no issues with the transmission, performs great - just this doesn't seem right. I have had a lot of Chevy's and MOPARs and none of them acted like this.

If you feel that the transmission isn't shifting quite right, you should perform a throttle and control rod linkage adjustment.

Holes for the throttle linkage adjustment are provided in the accelerator assembly mounting bracket.

Disconnect the throttle control rod from the transmission control to the accelerator assembly at the attaching pin. Insert a 1/4-inch drill bit through the holes at point “A”. Adjust the length of the carburetor connecting link to close the carburetor against its stop.

Adjust the accelerator assembly connecting link to obtain a pedal height of 4¼ inches. Remove the drill bit and check the alignment at point “A”. The drill bit must re-enter the holes freely.

Remove the drill bit and then adjust the throttle control rod. Pull upward on the throttle control rod to hold the transmission lever against its internal stop. Rotate the clevis until the attaching pin freely fits in the transmission control to the accelerator shaft assembly. Lengthen the throttle control rod by rotating the clevis 2½ turns counterclockwise. Assemble the throttle control rod to the accelerator shaft assembly. Hold the clevis to prevent binding and tighten the lock nut.

doug7740
1955 Thunderbird Blue

 

[Selfrich]

Well I must not have the original transmission in my Tbird.

It is a nice day here in Ohio, so I went for a drive. The "D" drive does start out in second and shifts to third around 2500 RPMs and the engine runs at 1500 RPMs. Did not go 60 MPH to see if it shifts again.

I then came to a stop and placed the shifter in "L". As I slowly started, the RPMs got to 2500 and it shifted into a second gear. I continued in the "L" gear and it shifted for a third time at around 2500 RPMs. RPMs went down to 1500 and I was traveling at 35-40 MPH.

I could shift back and forth to "D" and "L" and the RPMs stayed at 1500.

It does not act like the original description.

It runs great so I am not going to try to understand it. I don't have a lift so I am not crawling under it to see the transmission numbers.

One weird Ford transmission!

Thanks for providing the information.

 

[Tom Alpers]

Well I must not have the original transmission in my Tbird.

It is a nice day here in Ohio, so I went for a drive. The "D" drive does start out in second and shifts to third around 2500 RPMs and the engine runs at 1500 RPMs. Did not go 60 MPH to see if it shifts again.

I then came to a stop and placed the shifter in "L". As I slowly started, the RPMs got to 2500 and it shifted into a second gear. I continued in the "L" gear and it shifted for a third time at around 2500 RPMs. RPMs went down to 1500 and I was traveling at 35-40 MPH.

I could shift back and forth to "D" and "L" and the RPMs stayed at 1500.

It does not act like the original description.

It runs great so I am not going to try to understand it. I don't have a lift so I am not crawling under it to see the transmission numbers.

One weird Ford transmission!

Thanks for providing the information.

It sounds like someone may have swapped a 3 speed cruiseomatic into it. For some years they had the two different "DRIVE" positions. Typical quadrant was Park, Reverse, Neutral, Drive 2 (white dot), Drive 1 (green dot), Low. In Drive 2 it would start in second gear like the Fordomatic. In Drive 1 it would start in 1st gear. And in Low it would do what you would expect in Low.
The fordmatic has 5 shift lever positions, P, R, N, D, L whereas the Cruisomatic has 6 positions, P, R, N, D2, D1, L. When these conversions (replacing a fordomatic with a cruiseomatic) are done what can happen is that the original 5 position shifter is used and it has no position for LOW. What was low with the fordomatic is Drive1 with the cruiseomatic. Most people almost never use L anyway so it's rarely missed.
They look pretty similar but as I understand it, the fordomatic has an integral cast iron bell housing whereas the cruisomatic has a separate aluminum bell housing.

 

[hotrodbuilder]

Back in the day, when I raced the early Fords, I used to start out in low gear with the gas to the floor until I felt the need to shift to second gear. I then would shift the lever up into drive position and immediately pull the lever back into Low position, while keeping the gas pedal to the floor. That kept the transmission locked into second gear. When I wanted to go to third, I again moved the lever into drive position and it would shift into third. I did this with all of the early Ford automatics, including Mustangs and Thunderbirds. I believe Ford actually used some 2 speed automatics in the lower horsepower models and 6 cylinder cars beginning in 1959.