One of the last GM-powered track type tractors offered by Allis-Chalmers, the HD-15 was also a top performer and paved the way for the subsequent model HD-16. By Richard Campbell.
Introduced in 1950, the Allis-Chalmers HD-15 replaced that company’s former model HD-14 in the Allis-Chalmers track type tractor product range.
The HD-15 was one of the ‘new generation’ of Allis-Chalmers track type tractors which had been in development since 1947, and in the interests of parts commonality, shared a lot of components with its smaller stablemate, the model HD-9, most notably the transmission.
Allis-Chalmers had established a well-deserved reputation for quality track type tractors and the new HD-15 was expected to further bolster the company’s reputation.
The introduction of the new HD-15 was not before time either, as the previous model HD-14 had ceased production in 1947, leaving a hole in the Allis-Chalmers tractor product line which its competitors were not slow in filling.
As Allis-Chalmers did not, at this point in the company’s history, manufacture an engine of its own design, the powerplant chosen for the new tractor came from an outside supplier in the form of a General Motors 6-71 two cycle diesel, rated at 130-flywheel horsepower.
This was actually quite a conservative rating for this engine as the same powerplant, fitted to the HD-15s predecessor had a 140-flywheel horsepower rating.
Allis-Chalmers had entered into an agreement with GM just prior to WW2 to be its prime engine supplier, an agreement that stood until November 1953 when Allis-Chalmers bought out the Buda Engine Co., and began rebranding the Buda diesel engines as “Allis-Chalmers”.
This did not affect production of the HD-15 however, all units manufactured having the GM 6-71 powerplant.
Twin oil bath air cleaners were fitted to provide an ample supply of fresh air for combustion. These are also a spotting feature of both the HD-15 and HD-19 track type tractors and are mounted on the engines right hand side (the larger HD-20 has them on the left).
The HD-15 was manufactured at Allis-Chalmers’ Springfield, Illinois, USA facility and followed conventional track type tractor layout for the period with a massive welded box-section main case, and box section channel frame rails which were bolted to the main case to form the machines chassis.
The HD-15 had a 74” track gauge and featured a 6-roller track frame with 38-section sealed track chain and 20” single grouser track shoes.
Optional sized track shoes and grouser types were optional to equip the HD-15 for specific job requirements.
A floating multi-leaf equalizer spring permitted a generous amount of track frame oscillation allowing the HD-15 to cross uneven terrain whilst maintaining good ground contact.
Allis-Chalmers used a constant mesh transmission of their own design and manufacture in the HD-15 which featured 6 forward and 3 reverse speed ranges.
A hydraulic torque converter drive transmission was also available as an option which had 3 forward and 3 reverse ranges.
In either configuration the HD-15 had a top speed of approximately 7 miles per hour, making it a very useful scraper tow tractor.
The torque converter allowed the machine to lug right down before the operator had to change to a lower transmission ratio, thereby saving on the amount of gear shifting that was required, a real labour saver if ever there was.
Allis-Chalmers had been a pioneer in torque converter drive transmissions introducing its (and the industry’s) first production machine, the HD-14C, with this type of transmission in 1946.
Double reduction final drives transmitted power to the machine’s sprockets.
The machine was steered in the conventional fashion using multiple disc steering clutches which were hydraulically boosted to reduce operator effort.
These steering clutches were bi-metallic faced and could be removed for maintenance without major disassembly of the final drives.
Braking was also conventional, via contracting band brakes which could be easily adjusted for wear in the field.
The operator was provided with a very generously padded seat which spanned the width of the machines fuel tank.
Good visibility was a feature of Allis-Chalmers tractors and the HD-15 was no exception.
A great deal of thought had been given to lever, pedal and instrument placement making the HD-15 a real operators machine.
All this in a time before the term ‘ergonomics’ had even been thought of!
Allis-Chalmers manufactured 3,909 examples of the HD-15 between 1951 and 1955 when the model was eventually discontinued.
Its replacement was the model HD-16, a machine which was to carve a long and illustrious career for itself, especially in the New Zealand timber industry.
As with diesel engines, Allis-Chalmers did not begin to manufacture its own attachments until the mid-1950s, instead, relying on outside manufacturers to produce what the customer specified in the way of bulldozer blades, rippers and scrapers for its machines.
Allis-Chalmers had several preferred subcontractors for this type of equipment, notably LaPlant-Choate (acquired by Allis-Chalmers in 1952), Baker Manufacturing Co (acquired by Allis-Chalmers in 1955) and the Garwood Company, all of whom manufactured good quality equipment.
Both Baker and Garwood dozer blades were popular, interestingly, Garwood for the cable operated and Baker for the hydraulically operated variety.
The Garwood cable blades came with their own radiator guard and were somewhat heavier, and of a more rugged construction than Bakers blades.
Once Allis-Chalmers had formalized the takeover of both Baker and LaPlant-Choate, a whole new range of attachments were made available.
This left Garwood out in the cold so to speak, and it finally exited the construction attachment business in 1966.
The Allis-Chalmers HD-15 weighed approximately 14 tons ready to go to work and shared this size category with the International Harvester TD-18, Caterpillar D7, Oliver OC-18 and Vickers VR180/Vigor.
Although the exact number is not known, over 30 Allis-Chalmers HD-15s were imported into New Zealand by the New Zealand distributor, Cable-Price..
For the model collector
Unfortunately, nobody has produced a model of the Allis-Chalmers HD-15 in any scale to date to the best of the authors knowledge, so if you really must have one it will have to be a scratch build.
In general, models of Allis-Chalmers track type tractors are reasonably scarce and those that are available (HD-20, HD-21, HD-41) command high prices at auction.
Engine: General Motors 6-71, 6-cylinder, 2-cycle diesel engine rated at 130 flywheel horsepower at 1600 rpm
Transmission: Allis-Chalmers built, 6 speed forward, 3 reverse, constant mesh manual transmission. Optional torque converter drive transmission with 3 forward and 3 reverse speeds.
Clutch: 17”, single disc (either transmission).
Top Speed: 7 mph (either transmission).
Steering: Multiple disc bi-metallic steering clutches
Brakes: Contracting band brakes
Track Gauge: 74”
Bottom Rollers: 6
Carrier Rollers: 4 (2 per side)
Track Chain: 38-section, sealed
Standard Shoe: 20”
Length: 15’ 5” (bare)
Width: 8’ 1” (bare)
Height: 7’ 10”
Operating Weight: 13.5 tons (bare)