Main Detroit Transmission Page
Detroit Transmission (Hydra-Matic) Division of General Motors Corporation in World War Two / WWII

The Detroit Transmission Torqmatic Model 900-T
- as used in the M18 Hellcat Tank Destroyer and M26 Pershing

This page added 12-27-2016.
The circa 1944 Detroit Transmission sales brochure on the Torqmatic 900-T Transmission reproduced below provides the most information that can be found on the transmission used in the Buick M18 Hellcat tank destroyer.  Publications on the M18 have had very little information, if any, on the transmission in the Hellcat.  If the publications say anything, they indicate the vehicle had a Torqmatic, Torquematic, or fluid coupled transmission.  That is all.

While the engine, armor and armament are all discussed in detail in various books on the vehicle, only one or two words are used to describe the transmission.  The reader is then left wondering what the Torqmatic or fluid coupled transmission was.  And who built the transmission?  That key piece of information was missing until in March 2016 when I posted the1944 Detroit Transmission booklet "Teamwork in Peace and War."  For the first time in print, the Torqmatic is described in detail.

The information provided in "Teamwork in Peace and War" is a huge step forward in understanding the WWII Torqmatic.  The Torqmatic 900-T sales brochure now opens up the transmission and gives the details on how it works internally.  While now, 70 years later, automatic transmissions are standard equipment and their operation understood, that was not the case in 1944.  This concept was all new at the time, especially to military leaders who by nature are conservative in their thinking, think they know it all, and do not want to change, even though there is a better way of doing something.

The "Torqmatic 900-T" brochure is filled with detail on how it worked.  It is a treasure trove of information for the military hardware historian and enthusiast.

While not explicit,  the document indicates that the 900-T was the transmission used in the M18 Hellcat.  On page 4, the graph shows tractive effort vs. speed for the T70 tank destroyer, which later was redesigned as the M18.  Other implicit details in the brochure are that the top speed which matches with the top speed of the M18, along with the torque and horsepower rating of the Continental R-975 400 hp radial engine used in the M18.

It would appear from the brochure that Detroit Transmission was attempting to have the 900-T fitted in an M4 tank, as there are several pictures of it. 

Technically there is the general description, performance characteristic, operation, construction, torque converter, cooling circuit, hydraulic systems, and applications along with multiple engineering drawings of the Torqmatic 900-T.  This is as complete a description as one can hope to find on this rare WWII tank destroyer transmission. 

  
 This M18 Hellcat is at Ropkey Armor Museum in Crawfordsville, IN.  Author's photo added 12-27-2016.

  
Looking through the driver's hatch the Detroit Transmission Division of GM Torqmatic automatic transmission is viewable.  The Buick M18 was the only tank destroyer to have an automatic transmission.  Author's photo added 12-27-2016.


Here the gearshift handle is viewable along with the gear indication on top of the transmission.  On the floor there are only the accelerator and brake pedals.  A clutch pedal is not needed with the automatic transmission.  Author's photo added 12-27-2016.

Author's photo added 12-27-2016.

"The Torqmatic Transmission Model 900-T"
General description, performance characteristic, operation, construction, torque converter, cooling circuit, and hydraulic systems

For the WWII tank enthusiast, there is a treasure trove of information on the transmission used in the M-18 Hellcat.  Much of the information is also generic to the Torqmatic transmission used in the T26/M26 Pershing.

General Description of the Detroit Transmission Torqmatic 900-T

The Torqmatic 900-T weighs 1,200 lbs.  The only operation the driver had to do with the 900-T was set the range.  There was no clutch pedal to operate.

Performance of the Detroit Transmission Torqmatic 900-T

This graph is of tractive effort of the Torqmatic 900-T with the T-70 Tank Destroyer, which became the M-18 Hellcat.  This graph therefore ties the 900-T to the M-18 and is the only evidence of what model Torqmatic was installed in the vehicle.  With this key piece of information, the rest of the data in the booklet provides more detail on the M-18's transmission.

Once the speed range was set, the M-18 could be driven at any speed from 0 mph to the top speed of the range without the changing gears or use of a clutch by the driver. 
Low Range:  0 to 16 mph
Intermediate Range:  0 to 34 mph
High Range:  0 to 60 mph

Operation of the Detroit Transmission Torqmatic 900-T

While the performance section indicated that the M-18 could be operated from 0 to the maximum range of the any of the three forward ranges under light loads, this page indicates that under full load there are restrictions.  For the intermediate range the M-18 should be operated at 11 to 34 mph and in the high range at the speed of 30 to 60 mph.

General Construction of the Detroit Transmission Torqmatic 900-T

The key point on this page is that when shifting ranges there is no loss of power flow.  This means the tank would not slow down or stop as would tanks with clutches.  This was very important on the battlefield.

The Torque Converter of the Detroit Transmission Torqmatic 900-T

The Cooling Circuit of the Detroit Transmission Torqmatic 900-T

The Hydraulic System of the Detroit Transmission Torqmatic 900-T

Applications for the Detroit Transmission Torqmatic 900-T

Only the M-18 and the M-26 utilized Torqmatic Transmissions during WWII.  But the technical advantages outlined in this brochure have been used on every American tank built after WWII.  General Motors transferred the technology to the Allison Division in Indianapolis in 1946 as the CD-850 series.  Today Torqmatic is a trade name for transmission built by Allison Transmission.