JIMMY MACK IS BACK!

1949 Mack Model 75 with Jimmy Power

While this Vintage Smoke column usually centers around period original diesels, this Mack drew our attention. While it’s technically a “resto-mod” it’s a resto mod done in a vintage way. Have a look at this 1949 Mack Model 75. It started life as a fire truck but fell into disuse and was rescued from the back of a used car lot in 1982 and given a new life with a historic powerplant. Sit back and we’ll tell you that story.

Special thanks to paul androvich, christopher kouttron, mike martinelli, the bigmacktrucks fire appliance forum and the detroit diesel forum at smokstak

Mack Fire Trucks

Mack started building fully fitted out fire appliances in-house in 1935. They built a wide variety of units based on the Mack trucks of the eras in which they were sold. Sometimes they had different model designations than the equivalent standard trucks they were built upon and sometimes had slightly different styling. From the info from the Mack Museum, it appears that only 5,222 fire trucks of all types and models were built from 1937 to 1969. The majority of those were built between 1937 and 1955.

Only the most Mack-knowledgeable would know this truck was not built as a tractor. Some of the fire truck details would include the bumper style and the lack of horizontal cross bars in the grill, plus a “75” on the radiator shell, under the bulldog. There was a real dog that was the company mascot and his name was “Mack” … and now you know the rest of that story. The spotlights on the A-pillars are original to the fire truck and a common fire truck item.

This Old Mack

This truck is a Model 75, which was built on the bones of the ‘37-50 Mack E-Series. In fact, this one is the last E-Series truck shipped for 1949. The only available engine for the 75 lines was the Mack “Thermodyne” ENF-510A, 510 cubic inch,150 horsepower gasser. Though there were several diesels in the Mack lineup at this time, including the END-510 Mack-Lanova diesel variant of the gas 510, it wasn’t on the options list for the fire trucks. The Thermodyne had dual ignition systems and two spark plugs per cylinder for maximum starting reliability. Gas engines were generally preferred for fire trucks in that era due to the lack of cold starting issues versus diesels. See a Vintage Smoke article on the Mack-Lanova diesel at https://www.dieselworldmag.com/diesel-engines/vintage-smoke-2/.

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Power comes from a turbocharged 1977 Detroit 4-71N that was originally naturally aspirated. It’s an engine Lowell went through, adding a factory style turbo setup. In stock form, the NA engine was rated at about 160 horsepower at 2100 rpm and 400 lbs-ft at 1600 rpm. If he fully configured it as a later model turbo engine, internally and externally, output could be up to 200 horsepower and 525 lbs-ft. Just adding a turbo to an NA engine, won’t gain much. That’s a typical situation with Uniflow two-strokes… they don’t benefit much from more air because most of it blows out the exhaust valves during the scavenging part of the stroke. The intake posts are covered before the exhaust valves close. If he incorporated all the turbo mods, slowing down the blower, a blower bypass (the blower impedes airflow from the turbo), the liners (specifically the inlet ports in the sleeve), exhaust valve timing and injector sizes, he’d get all the bennies of the turbo. Reportedly, performance is adequate, even with a 40,000 pound load behind the truck. Part of that’s obviously due to the gearing flexibility the 13-speed gearbox adds.

Thanks to Mike Martinelli and the Mack Museum, we know this Model 75 truck was built in 1949 as a pumper for the Schwenksville, Pennsylvania, fire department and shipped December 30, 1949. We don’t know much about the truck from that point but it acquired 18,641 miles in service of the Schwenksville community. By the early ‘80s, it was long out of service and pretty much living the life of a giant paperweight.

If you are in the enthusiast world of GM two-strokes, you may know the name Lowell Baker. He has the reputation of being one of the best two-stroke techs in the Midwest and one of the best Great Lakes Diesel in Vermillion, Ohio, ever had on staff. He also worked for Greyhound, helping keep their vast fleet of Jimmy-powered busses on the road. Lowell was a noted collector of vintage diesels, particularly Jimmies, tractors, trucks and many other things that have an engine. Sadly, Lowell passed on in 2017 but this old Mack is one of his many legacies.

The interior is mostly original and very utilitarian. An underdash air conditioner was added for those warm hauling days. The AC compressor runs from the rear accessory drive on the engine, along with the alternator.

The truck was acquired in 1982 from the back lot of a used car dealer in Allentown, Pennsylvania. It was stored at the Baker shop until a resto mod began in the early ‘90s and it was completed in 1996. Why wasn’t it restored back as a fire truck? Well, Baker needed a 5th wheel truck to haul his various tractors, trucks and equipment to shows more than he needed a restored, essentially useless fire truck so the stylish Mack was converted to a 5th wheel tractor. Fire appliance collectors may be foaming at the mouth by now but there aren’t many uses for vintage fire trucks other than to be restored and shown, or converted for other forms of useful employment. Baker chose the latter and used the truck extensively.

The rear axle is a modern unit (make unknown to us) with air brakes. The front end still has the original Mack hydraulic brakes. Lowell set up an air over hydraulic setup to make the dissimilar types of brakes work in concert. The big Tulsa winch is hydraulically operated, driven from a pump powered by a PTO outlet on the transmission.

Reportedly, the original Thermodyne engine was seized up but no self respecting Jimmy fanatic would drive a gasser anyway. Lowell shortened the wheelbase and added a stouter, more modern rear axle. He wanted to install a 6-71 but it was too big. Instead, he built a ‘77 4-valve 4-71N (“N” indicating a four-valve engine). It was originally built as an automotive engine and had been removed from an International stakebed truck. Lowell added a turbo but we don’t know much more than that. He may have done the other mods needed to take full benefit of the turbo but apparently he took that knowledge with him to Detroit Diesel heaven. The current owner doesn’t know and isn’t likely to do a teardown to find out anytime soon. The Jimmy is backed up by a 13-speed road Ranger gearbox. Also installed was a fifth wheel from another truck and a big Tulsa winch behind the cab for hauling derelict equipment onboard the flatbed trailer.

Lowell’s Legacy

John Androvich is the current owner of the Mack. He was a friend and neighbor of Lowell’s and spent considerable time working with him on the initial build and subsequent maintenance of the truck. In fact, around 2005, Lowell sold him the truck under an agreement where he retained what John describes as a “life lease.” Both men used the truck when needed and when Lowell passed, full unfettered ownership went to John. John uses it the same way he and Lowell always did, hauling equipment to shows and sometimes showing the truck on it’s own.