The HT-C truck was created in 1970 by Electro-Motive Diesel (EMD) as a component of their range of railway locomotives through to 1994. It was mounted under the experimental EMD SD45X

EMD SD45X

An EMD SD45X is a 6-axle experimental diesel locomotive built by General Motors Electro-Motive Division between June 1970 and February 1971. Power was provided by an EMD 645E3A 20-cylinder engine which generated . 7 examples of this locomotive model were built for American railroads. 6 of these...

, and applied to a majority of EMD Dash 2

EMD Dash 2

On January 1, 1972, General Motors' Electro-Motive Division introduced its new Dash 2 line of diesel-electric locomotives. All designations of these new models were those of the former models with "-2" added...

, 50 and 60 series six axle units built by EMD. It has a total of two brake cylinders on the end axles and a shock absorber on the middle one and has a tail on the fuel tank side to hold the #3 and #4 motors in line with the #2 and #5 motor, unlike the Flexicoil truck which these two face the #2 and #5 motor under the engine

Yawing effect

When Amtrak

Amtrak

The National Railroad Passenger Corporation, doing business as Amtrak , is a government-owned corporation that was organized on May 1, 1971, to provide intercity passenger train service in the United States. "Amtrak" is a portmanteau of the words "America" and "track". It is headquartered at Union...

 bought their EMD SDP40F

EMD SDP40F

The EMD SDP40F was a 6-axle Diesel-electric locomotive built by General Motors Electro-Motive Division from 1973 for Amtrak service. Power was provided by an EMD 645E3 16-cylinder turbocharged Diesel engine, which generated 3000 tractive horsepower .-Origins:The SDP40F was the first locomotive...

's from 1972 to 1974, they specified this truck to be fitted with hollow bolsters to mount the engine on the trucks with a lighter load rating to offset the weight of the secondary water tank that was mounted in front of the steam generators

Steam generator (railroad)

Steam generator is the term used to describe a type of boiler used to produce steam for climate control and potable water heating in railroad passenger cars...

. This contributed to the yawing effect that was characteristic of the second SDP in the consist and the baggage car

Baggage car

A baggage car or luggage van is a type of railway vehicle often forming part of the composition of passenger trains and used to carry passengers' checked baggage, as well as parcels . Being typically coupled at the front of the train behind the locomotive, this type of car is sometimes described...

. The result was that the unit and the car pulled the outside rail out from under the train on high speed curves. Burlington Northern, Chessie System

Chessie System

Chessie System, Inc. was a holding company that owned the Chesapeake and Ohio Railway , the Baltimore and Ohio Railroad , the Western Maryland Railway , and several smaller carriers. It was incorporated in Virginia on February 26, 1973, and it acquired the C&O on June 15...

, and Louisville & Nashville banned the SDP's because of the modified truck. Conrail ordered their EMD SD40-2

EMD SD40-2

The EMD SD40-2 is a C-C locomotive produced by EMD from 1972 to 1989.The SD40-2 was first introduced in January 1972 as the mid-range offering in EMD's six-axle "Dash-2" series, competing against the GE U30C and the MLW M630...

's and their early EMD SD50

EMD SD50

The EMD SD50 was a diesel-electric locomotive built by General Motors Electro-Motive Division. It was introduced in May 1981 as part of EMD's "50 Series", but prototype SD50S locomotives were built from 1980; production ceased in January 1986...

's with the older Flexicoil trucks because of the HT-C issues with BN, Chessie and L&N. The Federal Railroad Administration

Federal Railroad Administration

The Federal Railroad Administration is an agency in the United States Department of Transportation. The agency was created by the Department of Transportation Act of 1966...

 and Electro-Motive determined that the baggage car was to blame.

Usage

This did not doom the truck as it did to the SDP40F. They went under almost every EMD six axle locomotive built from 1972 to 1994 except the Detroit Edison

Detroit Edison

The Detroit Edison Company, founded in 1903, is an investor-owned electric utility which serves most of Southeast Michigan. Its parent company, DTE Energy , provides energy services to a variety of clients beyond Detroit Edison's service area.- History :...

 SD40

EMD SD40

The EMD SD40 is a 6-axle diesel locomotive built by General Motors Electro-Motive Division between January 1966 and August 1972.-Design:Like its predecessor in EMD's catalog, the SD35, the SD40 is a high-horsepower, six-motor freight locomotive....

's, Conrail SD40-2's, Milwaukee Road SDL39

EMD SDL39

An EMD SDL39 is a 6-axle diesel locomotive built by General Motors Electro-Motive Division between March 1969 and November 1972. Power was provided by an EMD 645E3 12-cylinder engine which generated 2300 horsepower . All 10 examples of this locomotive model were built for Milwaukee Road, who wanted...

's, EMD/BN/Siemens AG SD60MAC, and the EMD SD70 series

EMD SD70 series

The EMD SD70 is a series of diesel-electric locomotives produced by the Electro-Motive Division of General Motors beginning in 1992. Over 4000 locomotives in this series have been produced, mostly of the SD70M and SD70MAC models. All locomotives of this series are hood units with C-C trucks...

.