When Conrail took over operations in 1976, they retired many of the first generation diesels that had been in hump yard duty, leading to a major shortage of those engines. In a Railroad Model Craftsman article, Ken Goslett mentions how the hump yard at Allentown, PA, went from using Central Railroad of New Jersey RSD-4's to leased Bangor & Aroostook Geeps and Pittsburg and Shawmut Railroad switchers. By 1978, however, Conrail's "real" hump engines had become their former Penn Central SD38's. Still, a pair of painted-out Penn Central SD9's worked the Allentown hump for years after the leased power left. Over at the former Reading Company hump in Rutherford, PA, a pair of GP30's did duty on one end until the hump closed.

In 1978 and 1979, Conrail decided to construct a fleet of slugs using worn-out Alco RS-11, RSD12, and RSD-15 units. Conrail removed the diesel engine, generator, and cab from the original units. The underframe, trucks, traction motors, and blowers remained. The hoods were chopped down and patched up. Details of individual slugs varied depending on the original unit and what the shops had on hand. As a result, the former-RSD15 MT-6's are slightly longer than other units due to the longer RSD-15 frame. Those slugs that came from six-axle Alcos became classed as MT-6's (Motor Trailer 6-axle). Conrail began rebuilding their MT-6 slugs around 1988. The original 3-axle Alco trucks were replaced with EMD trucks from retired SD7's and SD9's.

In 1975, Penn Central in their DeWitt shops did create one six-axle slug from an RSD-5 carbody (former Penn Central #9949, prior Pennsylvania Railroad #8450) with portions of an RS-1 hood. In 1976, Conrail renumbered this as Conrail #6849 and paired it with an "AEH12" also numbered Conrail #6849, which was an RSD-15 that had been repowered with a 12-cylinder EMD 567 prime mover, producing only 1,200hp spread across 12 traction motors. In 1979, this mother and slug were set aside. Around December 1979, they renumbered as Conrail #6899. Both the mother and slug were retired on January 30, 1980, and then sold to NI&M scrappers.

By May 31, 1999, all 29 MT-6's remained in active duty. These units were transferred to CSX and Norfolk Southern on June 1, 1999.

Comprehensive MT-6 Roster

The roster below covers those units operated by Conrail from the creation of the first unit in 1978 to their retirement from Conrail, along with first disposition. The roster includes each unit's first disposition. A special thanks to the Diesel Shop, X2200 South, the Conrail Historical Society, and the many Conrail enthusiasts who helped put this roster together.

CR #      Reblt   Former    Prior     Previous   Previous   Removed   Disposition  Notes
========================================================================================
CR 1100   06/78   CR 6874   PC 6874   PRR 6874   PRR 8674   05/31/99  NS 1100         1
CR 1101   08/78   CR 6873   PC 6873   PRR 6873   PRR 8673   05/31/99  NS 1101
CR 1102   08/78   CR 6872   PC 6872   PRR 6872   PRR 8672   05/31/99  CSX 1006
CR 1103   09/78   CR 6864   PC 6864   PRR 6864   PRR 8664   05/31/99  NS 1102
CR 1104   09/78   CR 6865   PC 6865   PRR 6865   PRR 8665   05/31/99  CSX 1007
CR 1105   10/78   CR 6878   PC 6878   PRR 6878   PRR 8678   05/31/99  NS 1103
CR 1106   10/78   CR 6868   PC 6868   PRR 6868   PRR 8668   05/31/99  CSX 1008
CR 1107   11/78   CR 6869   PC 6869   PRR 6869   PRR 8669   05/31/99  NS 1104
CR 1108   11/78   CR 6863   PC 6863   PRR 6863   PRR 8663   05/31/99  NS 1105
CR 1109   11/78   CR 6866   PC 6866   PRR 6866   PRR 8666   05/31/99  CSX 1009
CR 1110   12/78   CR 6867   PC 6867   PRR 6867   PRR 8667   05/31/99  NS 1106
CR 1111   12/78   CR 6875   PC 6875   PRR 6875   PRR 8675   05/31/99  NS 1107
CR 1112   12/78   CR 6876   PC 6876   PRR 6876   PRR 8676   05/31/99  CSX 1010
CR 1113   01/79   CR 6870   PC 6870   PRR 6870   PRR 8670   05/31/99  CSX 1011
CR 1114   01/79   CR 6871   PC 6871   PRR 6871   PRR 8671   05/31/99  CSX 1012
CR 1115   01/79   CR 6860   PC 6860   PRR 6860   PRR 8660   05/31/99  CSX 1013
CR 1116   02/79   CR 6862   PC 6862   PRR 6862   PRR 8662   05/31/99  CSX 1014
CR 1117   02/79   CR 6859   PC 6859   PRR 6859   PRR 8659   05/31/99  NS 1108
CR 1118   02/79   CR 6858   PC 6858   PRR 6858   PRR 8658   05/31/99  CSX 1015
CR 1119   05/79   CR 6857   PC 6857   PRR 6857   PRR 8657   05/31/99  NS 1109
CR 1120   09/79   CR 6879   PC 6879   PRR 6879   PRR 8679   05/31/99  NS 1110
CR 1121   08/79   CR 6861   PC 6861   PRR 6861   PRR 8661   05/31/99  CSX 1016
CR 1122   07/79   CR 6877   PC 6877   PRR 6877   PRR 8677   05/31/99  NS 1111
CR 1123   06/79   CR 6855   PC 6855   PRR 6855   PRR 8655   05/31/99  NS 1112
CR 1124   04/79   CR 6856   PC 6856   PRR 6856   PRR 8656   05/31/99  NS 1113
CR 1125   12/79   CR 6812   PC 6812   PRR 6812   PRR 8612   05/31/99  NS 1114
CR 1126   10/79   CR 6816   PC 6816   PRR 6816   PRR 8616   05/31/99  NS 1115
CR 1127   12/79   CR 6814   PC 6814   PRR 6814   PRR 8614   05/31/99  CSX 1017
CR 1128   10/79   CR 6813   PC 6813   PRR 6813   PRR 8613   05/31/99  CSX 1018

Roster Notes:

1. For a brief time, Conrail #1100 originally was numbered Conrail #6820.