The Stovebolt Site Forums The Shop Area Driveline Hydra-matic Transmission

I have a 1954 Chevy 3100 with the Hydra-Matic Transmission. Is the GMC 1/2 ton Hydra-Matic the same Transmission? Also, is there an official name for this transmission? I have heard "dual range" but I have 3 ranges. Just trying to track down some manuals to service the transmission.

Thanks

MFW

Hy MFW, Dual Range Four Speed Hydra-Matic, there were other transmissions referred to as "Hydra-matic" but they were different. The GM cars stopped using this design transmission in the mid fifties, but Chevy and I presume GMC continued to use this transmission until 1962 in trucks. Rolls Royce used this transmission (with some Rolls Royce modifications) until GM started marketing the Turbo 400, hope that helps.

There were at least 3 versions of the Hydramatic. The original one came out in Olds and a very few Buicks 1938 or 39, with a manual clutch. In 1940 Oldsmobile added a fluid coupling (not a torque converter) that allowed the engine to idle in gear. GMC used the transmission in military 6X6 trucks during WW II, and it was used behind Cadillac flathead V8 engines (2 of them) in a light tank.

After the war, Cadillac, Olds, Pontiac, Nash and GMC truck used the transmission in its second generation model which did not have the Dual Range capability. In 1954, Dual Range added a selector position to lock the transmission in 3rd. gear up to about 65 MPH depending on rear end ratio, and them made a forced shift to prevent engine damage. In 1956-57 the Controlled Coupling Hydramatic was introduced in cars, not trucks. It was sometimes called the "Jetaway" which was actually incorrect. The Controlled Coupling Hydramatic continued until 1964 in Olds, Pontiac and Cadillac, along with a really crappy version called the "Roto Hydramatic" (AKA "Slim Jim"). In 1965 the 3-speed Turbo 350 replaced all the previous models, and the Turbo 400 was the heavy duty option, also a direct drive 3 speed.

Chevy and GMC continued to use the original Dual range transmission in trucks long after cars went to the Controlled Coupling and Roto models. I believe 1962 was the last year of production, as they were not used behind the 230/250/292 engines.
Jerry

MFW,

There were, of course, many types/models of H-M transmissions. Talking about what you do not have will not help you much (even if you wanted to know the useless information that there was even a mid-50s 21-speed H-M transmission used in very large GMC trucks).

The 1954 1/2 ton GMC H-M transmission (1954) was most likely the same as the 1954 Chevrolet 3100 H-M transmission.

There were minor differences between the 1953 GMC 1/2 ton H-M transmission and the 1954 1/2 ton H-M transmission.

Note that your 1954 transmission was a 1-year Chevrolet truck transmission. Your 3100 transmission is set up for the enclosed drive-shaft. The 3/4 ton and 1-ton H-M transmissions in 1954 were open drive-shaft.

I have a web-site that shows the complexities of the 1954 3100 H-M transmission, if you are interesting in seeing the steps in a complete rebuild (let me know). You might also be interested in seeing these 1954 Chevrolet Truck Hydra-Matic service manuals.

Q1. Is the GMC and the Chevrolet 1/2 ton Hydra-Matic the same Transmission?
A1. Yes, Internal component should be the same.
The GMC & Chevrolet transmission linkage and control linkage are different.

Q2. Is there an official name for this transmission?
Detroit Transmission Hydra-Matic
Fluid coupler, no torque convertor

It has 4 forward speeds and 1 reverse speed.
1-4, All 4 speeds
1-3, 3 speeds used
1-2, 2 speeds used
R, Reverse, Park when engine Off

Hydra-Matic Transmission
1940-1956 ID Plate info
1954 Chevrolet Hydra-Matic ID Plate

1954 GMC Truck Hydra-Matic Transmission Maintenance Manual
1954 Chevrolet Truck Shop Manual
Chevrolet Truck Hydramatic Transmission-Linkage Mechanism
Chevrolet Truck Hydramatic Transmission-Control Mechanism
Chevrolet 1954 Chevrolet Passenger Car & Truck Specifications

Hydra-Matic Transmissions have 3 main housings.
Front Chevrolet Truck Hydramatic Transmission -Flywheel and Fluid Coupling
Center Chevrolet Truck Hydramatic Transmission Assembly-Exploded
Tail Chevrolet Truck Hydramatic Transmission (Reverse Unit)

The front housings were matched to the engine at the factory.
Text casted in the front housing.
Front housing engine ID plate number, should match engine number located on engine boss to the left of the distributor.
Housing Engine ID plate

I have seen Cadillac Hydra-Matic transmission center housings Picture C-54 used on some trucks.

Model 180 in the half tons. Orange tag means model 180.

greg and jorb both know there stuff
about hydramatic trans
you both do a good job
thanks keith

Thanks guys, I just want to make sure I am ready to roll after a long rest (39 years). I am sure I will have some leaks I will have to address.

MFW

Here is something to chew on.

The 1954 Cadillac Hydra-Matic trans. gear ratios are the same as the
1954 Chevrolet 3100 1/2 ton Hydra-Matic gear ratios. (upper RH column on page link)

1954 Cadillac Hydramatic trans. gear ratios
Transmission ratio, first...... 3.8195:1
Transmission ratio, second... 2.6341:1
Transmission ratio, third...... 1.45:1
Transmission ratio, fourth..... 1:1
Transmission ratio, reverse... 4.3045:1

1954 Cadillac Rear Axle Ratio Options:
3.07:1
3.36:1
3.77:1

What's interesting is, if you do the 3.90 to 3.55 ring & pinion swap.
On your 1954 Chevrolet 3100 1/2 ton with Hydra-Matic.
And wondered if the 235 engine would bog with the 3.55 ring & pinion.
The answer is no, because Cadillac used lower gear ratios than the 3.55
Granted the 1954 Cadillac used a V8 331 cu.in. engine with 230 hp.
Source PDF Page 126

Below is a 1954 US Army video on how "Fluid Coupling" works.
Auto Mechanics: Transmissions: &quo...s of Operation" 1954 US Army 13min

One important note about towing a vehicle with Hydra-Matic trans.
For Transmission Not Functioning Properly—The propeller
shaft must be disconnected at the rear universal joint and removed,
or the rear wheels raised off the ground, to prevent further damage
to the transmission when towing.
The reason is that the rear main output shaft bearings are lubricated by the transmission.
If the engine is not running the transmission is not lubricating the bearings.
When towing, the rear axle is still spinning the transmission rear main output shaft.

can i put a chevy trans into a gmc pickup
both are hydramatics
thanks keith

Yes,
I believe there are some differences in the flywheel, bell housing and shifting linkage & trans control levers.
To find out what the differences are for sure. Call http://nwtparts.com/ ask for John

If both truck are the same tonnage & year helps.
For example, 1/2 ton Hydra-Matic trannies are different than 3/4 ton Hydra-Matic trannies.

John would know the details.