1939 - 1967: An Experiment by Mack Trucks - Railcar Dept.

The noticeable exterior changes to #4 & #5 after they were both reconstructed into a Gasoline Electric locomotives are as follows;

 1.  A protective grill was installed at each end of the cab to allow air flow axcess for the two  gasoline engines that were installed inside the boxcab at each end.

2.  The locomotives missing head lights that were mounted at each end of the cab were replaced with four auto-truck head lights. Two lights were mounted at each end of the cab.

3.  The fireman side front foot boards were removed and they were then installed onto the engineers rear end of the locomotive.

4.  A auto-truck air horn was mounted a the front of the boxcab to replace the missing brass air-whistle. The locomotives missing bell was never replaced by Mack.

The History of Mack Truck's Inc. 

Railcar & Locomotive Department 1905 - 1960.

Mack Brothers Motor Company, chartered on February 8, 1905, as a manufacture of highway and railway vehicles and commenced full scale production in a large plant in Allentown, PA. The company in 1922 was renamed as the Mack Trucks, Incorporated.

A total of 112 railway units  represent the entire; gasoline mechanical, gas electric, & diesel electric rail motor cars, and gasoline mechanical & gas electric locomotives of the combined Allentown, PA & Plainfield, NJ production between 1905 and 1959. The Mack company only produced a total of 21 locomotives from 1921 until 1939 with #5 and the 'C.J. McHugh #4' being the last built locomotives of Mack Trucks, Inc.

The gas mechanical drive locomotives were introduced in 1921, and were small 4 wheel units units with a weight of 4 to 30 tons. The first Mack locomotive was built in May 1921 , as Allentown plant switcher #1, a four wheel steeple cab, powered by two 4 cylinder 40hp AC gasoline engines, it's actual weight was 33 tons.

The Mack gas electric railway program was introduced in 1927 eventually included and offered for sale twelve locomotive models, 12, 15, 18, 24, 30, 40 ton, four wheel units; 45, 60 ton, six wheel units; 24, 30, 40, & 80 ton eight wheel units.

However actual production was; 2 - four wheel 12 ton units, 8 - auto truck steeple cabs four wheel 12 to 15 ton units, 2 - six wheel 60 ton units, 4 - four wheel 30 ton units, 1 - four wheel 33 ton unit, 2 - six wheel 45 ton units, and #3 & #4 were the only eight wheels units at 35 ton.

The Mack company also produced 70 self propelled 'gas mechanical or gas electric' railcars between 1905 and 1937. Then between 1951 and 1954 produced only 10 diesel powered self-propelled passenger railcars. Then in 1956 the last of those two units sold were purchased back by the Mack company and then rebuilt to another customers specifications. These two units were then resold, one in 1958 and the other in 1959. After a one year period of no sales of railway equipment Mack Truck, Inc. completely exited out of the railroad business in 1960.

Today the 'C.J. McHugh #4' is the only eight wheel and largest Mack locomotive in existance, with 4 small four wheel 12-15 ton and 1 four wheel 30 ton unit also surviving.

The Mack locomotives including #4, along with some other manufactures that produced small industrial locomotives had the name 'critters' applied to them.

An example of the one surviving 30 ton four wheel Mack locomotive is #2. The unit was damaged when an inexperienced contractor transporting it over the highway from New York to Allaire State Park in NJ hit the underneath of a overpass bridge with the top of the locomotive. The #2 has never been repaired by the Pine Creek railroad and it only operated on a short section of dual gauge track a few time since arriving there.