4-8-8-2 Cab Forward Locomotives

The Sacramento division of the Southern Pacific had close to 150 miles of grades of up to 2.5%. On this Roseville - Sparks line over the Sierra Nevada there were also almost 30 miles of snow sheds and tunnels. Over the years, as trains grew in length, more powerful locomotives were required.

Stack splitter In 1908 the Southern Pacific ordered two 2-8-8-2 conventional mallets classified MC-1 (Mallet - Consolidation) numbered 4000 and 4001. On a trial run up the "Hill" two problems became immediately evident.

  1. The great volume of exhaust gasses almost asphyxiated the crew.
  2. The stack exhaust velocity was so great that it blew the roof boards off of the snow sheds.
The second problem was easily handled by installing "stack splitters" (a deflector located above the smoke stack which directed the exhaust to the sides), as shown at the top of the image on the right. The first problem required more consideration.

Shortly after delivery of the MC-1s, an enterprising engineer decided not put up with nearly being asphyxiated or exposing himself to the tremendous heat and noise. He had the engine turned, hooked the engine pilot to the front of the train, and backed his locomotive over the hill pulling the train behind. This alleviated the above problems but created others such as pushing the tender ahead of the engine and the engineer being on wrong side for the signals. Despite these problems, other engineers began following this example.

A team of Southern Pacific design engineers came up with a plan and designs for a mallet with the cab in front, classified MC-2. Southern Pacific had Baldwin build 15 without testing one! Numbered 4002-4016, they were delivered in February and March of 1910. The engineer's and fireman's controls were shifted to opposite sides of the cab so that when run "backwards" the crew was on the usual side of the track.

Since the firebox on these locomotive was located in the front (far from the tender), they were designed to burn oil. Oil was piped from the tender along the locomotive to the firebox. The oil bunker in the tender on these locomotives was made air-tight and was structurally braced. They were slightly pressurized with air from the main air reservoir to insure a constant oil flow to the burner in the fire box when to the locomotive when traveling upgrade.

Cab After the MC-2s had proven themselves, 32 more, classified MC-4 and MC-6 (MC-3 and MC-5 were skipped) were ordered. Before it was all over, Southern Pacific ended up with a total of 256 Cab Forwards (all classes). these Cab Forwards came in several wheel arrangements including 2-8-8-2, 4-6-6-2, and 4-8-8-2.

Although the crews initially complained about concerns that if they hit a gasoline truck at a grade crossing they would be right on top of it when it exploded. Fortunately, in 46 years of running Cab Forwards, this never happened. This was partially because of the unobstructed view from the cab. The advantage in visibility was tremendous.

Cab Forwards were a distinct trademark of the Southern Pacific. They were sometimes also called "Cab-in-fronts" or "Backup Mallies" (even though, technically, only some of the first classes were true mallets). According to the definitive book on Cab Forwards (Those Amazing Cab Forwards by George Harlan), no other railroad in the world had locomotives like them. However, a few other unique examples did exist.


Cab Forward Facts and Trivia

Cab Markings

What did those Cab Forward cab markings mean?

24 24
AC-4 AC63 475 SF
32
AC-4 Class designation
AC63 Articulated Consolidation, 63 inch drivers
24 24 Cylinder diameter (front and rear) in inches
32 Piston stroke in inches
475 Weight on drivers in thousands of pounds
SF Superheated, Feedwater heater

Southern Pacific Yellowstones

Not all Southern Pacific articulateds were Cab Forwards. Class AC-9 was made up of 12 Lima built Superpower , coal burning Yellowstones (2-8-8-4). They had the same tractive effort of the Cab Forwards. They were numbered 3800 - 3811 and were used in the Southwest.

Cab Forward Classes

Class Locomotive
Number
Wheel
Arrangement
Driver
Diameter
Cylinders Steam
Pressure
Tractive
Effort
Horse
Power
MC-1 4000-4001 2-8-8-2 57 26x40x30 200 85,040 4000
MC-2 4002-4016 2-8-8-2 57 26x40x30 200 85,040 4000
AC-1 4000-4016 2-8-8-2 57 22x22x30 210 90,940 4350
MC-4 4017-4028 2-8-8-2 57 26x40x30 200 85,040 4000
AC-2 4017-4028 2-8-8-2 57 22x22x30 210 90,940 4350
MC-6 4029-4048 2-8-8-2 57 26x40x30 200 85,040 4000
AC-3 4029-4048 2-8-8-2 57 22x22x30 210 90,940 4350
MM-2 4200-4211 4-6-6-2 63 25x38x28 200 65,900 3000
AM-2 3900-3911 4-6-6-2 63 22x22x28 210 76,800 3450
AC-4 4100-4109 4-8-8-2 63 24x24x32 235 116,900 5640
AC-5 4110-4125 4-8-8-2 63 24x24x32 235 116,900 5640
AC-6 4126-4150 4-8-8-2 63 24x24x32 250 124,300 6000
AC-7 4151-4176 4-8-8-2 63 24x24x32 250 124,300 6000
AC-8 4177-4204 4-8-8-2 63 24x24x32 250 124,300 6000
AC-9* 3800-3811 2-8-8-4 63 24x24x32 250 124,300 6000
AC-10 4205-4244 4-8-8-2 63 24x24x32 250 124,300 6000
AC-11 4245-4274 4-8-8-2 63 24x24x32 250 124,300 6000
AC-12 4275-4294 4-8-8-2 63 24x24x32 250 124,300 6000
NOTE: Class AC-9 were Yellowstones (not Cab Forwards)

The Monkey Deck

Monkey Deck The Southern Pacific Cab Forwards had a platform immediately following the smokebox of the locomotive (as shown in the figure on the right). This platform was called the " monkey deck . Smoke boxes were often stained with rust from boiler water and boiler water treatment chemicals. Because of its proximity to the stacks, the monkey deck was often stained with rust from boiler water too. Occasionally articulateds would spew hot water and mud from their stacks. Most railroad employees were aware of this fact. However, many hoboes thought the monkey deck was a good place to ride. After passing through tunnels or snow sheds, hoboes riding the deck were either scalded or asphyxiated depending upon how the locomotive was performing. The monkey deck was not a good place to ride on Cab Forward locomotives.

The Last Cab Forwards

  • The last Cab Forward in revenue service was 4-8-8-2 4211 which hauled freight from Oakland to Davis and then to Roseville with only a caboose on November 30th, 1956.
  • In November, 1957 4274 was brought out of retirement to make the last run of a Cab Forward over Donner Pass from Sacramento to Sparks and back.
  • In 1960 the last Cab Forward to be scrapped was AC-10 4243.
  • On May 7, 1981 AC-12 4294 was designated a National Historic Mechanical Engineering Landmark.

USA and Canadian Railroads that used 4-8-8-2 Cab Forward Locomotives

Surviving Examples of 4-8-8-2 Cab Forward Locomotives

No. Class F.M. Whyte Gauge Railroad Line Location Status Builder Information Notes
4294 AC-12 4-8-8-2 4'-8½" SP California State Railroad Museum, Sacramento, CA display Baldwin #70101, 1944
4219 AC-10 4-8-8-2 4'-8½" SP Oregon Rail Heritage Center, Portland, OR operational Baldwin #64310, 1942 Tender only. Used as aux tender behind 4449.

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