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Locomotive Phases - GE B23-7, B30-7, B30-7A, B36-7

In the mid 1970s, GE made a large number of changes to their locomotives aimed at improving reliability and ease of maintenance. A first batch of changes were incorporated into the last Universal series locomotives in 1975 and 1976. A second set of changes led to the introduction of the "1977 Series" or (as it was later known) Dash 7 series of locomotives at the end of 1976. The series continued GE's logical use of model names, with the first letter (B or C) denoting four or six axles, and the second two digits indicating horsepower. While the new series was characterized by several major design changes related to the air compressor location, lube oil and cooling systems, and electrical system, there were also a number of other smaller changes made to the prime mover and cab. Notably, the trouble-prone aluminum wiring used on a portion of Universal series locomotives was replaced with copper.

While four-axle Dash 7 units shared the same overall appearance as their Universal series predecessors, there was hardly a single body panel in common between the two series other than the cab and central hood doors. One of the most obvious changes was the elimination of the equipment air intake immediately behind the cab, as the equipment blower was moved to the radiator compartment at the rear of the hood. Additionally, unlike six-axle models, four-axle Dash 7 units extended the underframe by 2 feet compared to Universal units, resulting in noticeable "porches" at each end, and there were two more frame length/wheelbase changes made later in production.

The wide radiator "wings" of the U36B were lowered and adopted for all Dash-7 models, and changes to the oil filter/cooler and air compressor were reflected in modified doors and intakes under the radiators. The break in the hood width previously near the radiators was moved to just behind the engine room doors, which themselves were moved closer to the cab. The cab sub-base doors on the conductor's side were also modified.

Four-axle Dash 7 production began with the B23-7 and B30-7, followed soon after by the B36-7. As with the U23B, the 12-cylinder B23-7 proved the most popular. The B18-7 (a replacement for the U18B) along with two intermediate models, the 12-cylinder B28-7 and 16-cylinder B33-7, were cataloged but never built. With the pending elimination of cabooses from freight trains, a unique variant (the BQ23-7 - "Q" for "Quarters" cab) was built for SCL with the cab extended to take up the entire space of what would normally be the short hood. In 1981, the 12-cylinder engine was uprated to 3,000 hp, resulting in the B30-7A, which was visually nearly identical to the B23-7. Two variants - the slightly longer B30-7A1 and cabless B30-7AB - were built for SOU and BN respectively. All 12-cylinder models were distinguished by six (rather than eight) engine room doors per side, but shared the same carbody and frame dimensions as 16-cylinder versions.

The improvements made by the Dash 7 series paid off. While some late model Universal series units saw service lives of as little as ten years, many Dash 7 locomotives remained in service with their original owners for more than 20 years. Many continued in service on smaller railroads into the 2010's.


These phases are of my own making. Six-axle versions followed a similar evolution; see GE C30-7, C30-7A, C36-7 Phases.

In some cases (such as with Phases 2a/2b and 2c/2d) two variations were offered concurrently before being standardized in later phases.

Phase 1a 1b 2a 2b 2c 2d 3a 3b
Dates 1977-09 -
1978-01 -
1978-04 -
1979-03 -
1980-01 -
1979-11 -
1980-10 -
1982-04 -
Left side sill access hatches 5 2 3
Truck centers 36' 2"
(equal distance from pilots)
37' 2"
(rear truck moved 1' rearward)
36' 8"
(rear truck 6" closer
to pilot than front)
Jacking pads plain flat metal plate on underside
Hinged panels under radiators 3 bolts, straight bottom edge central latch, notched bottom edge
Exhaust small stack, no silencer, narrow base large stack/silencer, wide base
Rear numberboards flush raised
Rear class lights high low
Cab side windows 4 2
Phase 1a 1b 2a 2b 2c 2d 3a 3b
Overall length 62' 2" 61' 2"
Left-side hatches under cab 2 narrow, 3 wide;
small latches; bolted panel at front
1 wide, 1 narrow, 3 wide;
large latches; no bolted panel
Cab vent circular, on roof rectangular, behind cab
(inconsistent in Phase 3a)
Hinged panels on hood ends No Yes
Long hood grabirons Closer spacing
Short hood left-side louvres Yes No
Short hood headlight housing present on all units (blanked off when lights not installed) present only with
headlight installed
Hood doors behind cab no bolted strip behind hood door closest to cab bolted strip added, first
2 hood doors narrowed
Phase 1a 1b 2a 2b 2c 2d 3a 3b

Model variations

Other details


Davis, W. (2014). General Electric's 1977 Series Locomotives. Retrieved December 2019 from

Foster, Gerald. (1996). A Field Guide to Trains. New York, NY: Houghton Mifflin.

General Electric. Locomotive Service Manual for Series-7 Road Locomotives. GEK-30150, 1978-08.

The Diesel Shop. (2011). General Electric B23-7 & BQ23-7. Retrieved December 2014 from

The Diesel Shop. (2011). General Electric B30-7 & B30-7A. Retrieved December 2014 from

The Diesel Shop. (2011). General Electric B36-7. Retrieved December 2014 from