By the end of the 1950s, International’s “jack of all trades” TD-18 was getting beyond further economical development. The TD-20 was the result. By Richard Campbell
The International TD-18 had been first introduced in 1939 after a couple of years of development and was itself a logical progression of International’s previous TD40 track type tractor which first saw the light of day in 1932.
At just over 11 tons bare with 111 horsepower at its disposal, the TD-18 was an ideal mid-sized tractor, suitable for all kinds of work.
During WWII, the TD-18 was supplied in quantity to the US Armed Forces and acquitted itself well from the hedgerows of Normandy to the various island hopping campaigns in the Pacific where it built up a good reputation as a tough tractor.
However, all was not well as the TD-18 had an inherent flaw in the engine cylinder heads which were prone to cracking due to inadequate cooling. This was partially a result of the engine starting method adopted by International which was one of gasoline to diesel conversion.
Each cylinder head contained two sets of valves – one for gasoline combustion and the other for diesel. This compromised the surface area available for adequate cooling and despite several attempts by International to correct the issue (including adding a water header tank on the hood of later models), the issue was to plague the machine until its discontinuation in 1958.
International’s designers had been working on a heavily reworked replacement for the TD-18 which was initially to be called the TD-18B. However the end product was so radically different from the former machine that International gave it a new designation, calling it the TD-20.
First introduced in 1958, the TD-20 200 series was powered by the same International D-691 engine that had powered the TD-18 only this time with redesigned cylinder heads and a completely new cooling system, the increased size of the TD-20 chassis allowing a lot more room to fit a larger radiator.
Meanwhile, engine output was increased to 134 horsepower.
A redesign of the exhaust manifold to allow better engine “breathing” reduced exhaust back pressure considerably compared to the TD-18 which had two exhaust pipes. The TD-20 just needed one.
A six-speed manual transmission delivered power from the engine to the final drives and featured a forward/reverse lever to allow easier shifting.
Changes to the track roller frame also meant a stronger, more stable tractor. With all the above alterations, a new TD-20 tipped the scales at just over 15 tons without attachments.
Speaking of attachments, Bucyrus-Erie supplied the bulk of attachments to equip the TD-20. Either hydraulic or cable-controlled bulldozers and angle dozers could be installed depending on customer preference.
The cable control units were supplied by Superior, one of International’s trusted outside suppliers which also offered a sideboom attachment for pipe laying. For logging operations the most common towing winch fitted came from Carco.
International’s Drott division could completely outfit the machine as a track type loader complete with one of its legendary “4-in-1” skid shovels.
Where the TD-18 had been a very popular tractor, the TD-20 suffered sluggish initial sales – why is not known, but only just over 1500 TD-20 200 series machines were built between 1958 and end of production in 1961.
In 1961 the first TD-20 upgrade took place.
Improvements included the addition of a turbocharger to the engine giving an extra 10 horsepower, a pressurised transmission lubrication and filtering system plus additional improvements to the track rollers and frame.
This version of the machine was known as the TD-20 201 series. Sales of this machine were also low with fewer than 500 being built. The increase in engine output was also leading to problems with the machine’s final drives.
International’s engineering and design team took steps to address the problem and in 1963 introduced the TD-20B.
This was a giant leap in the right direction as the TD-20B now featured a new engine, the 150 horsepower International model DT-429, a powershift transmission and planetary final drives.
Coupled with all these improvements were an isolated track frame with pinned equaliser bar, lifetime lubricated track rollers and improved operator’s environment.
To the credit of the IH design team, the new tractor (for that’s what it was) weighed no more than the former TD-20 201!
International, which now owned the construction division of Bucyrus-Erie, supplied all the attachments other than cable controls and logging winches.
This version of the TD-20 was quite well regarded by the industry and sales of the TD-20B exceeded 4700 machines during the period it was manufactured.
The TD-20B had a reputation as a well balanced and reliable tractor. During research for this article, the only gripes about the machine that I have come across concern the short life of the undercarriage track rollers, a fault not unique to International Harvester.
Optional attachments included a cab with heater, optional size track shoes, relieved sprockets, track guards, engine hood doors and an ether starting aid for cold weather. Mention should also be made of the dedicated track type loader that International produced, using the TD20B as a basis.
This was the 250B, a dedicated loader from the ground up incorporating all of the Drott goodies that International could muster (International having done a deal with Drott in the early 1960s). The 250B was popular with contractors in housing developments and especially in demolition where the machine had few equals.
The TD-20B was finally replaced in 1970 by the further improved TD-20C which falls outside the scope of this story and will be covered in a later article.
The New Zealand connection
All models of the earlier versions of the International TD-20 were imported into New Zealand but records of how many and where they went are regrettably long gone with the demise of International Harvester. As can be seen from the overall production figures the total that came into New Zealand cannot have been very high and the most likely example you are likely to come across will be a TD-20B.
For the diecast model collector
Ertl make a diecast model of the International TD-20C to 1:64 scale.
Although not the exact subject of this article, it is the only model of a TD-20 that has been produced to date.
The model is somewhat crude and has a straight hydraulic blade ROPS canopy and rubber tracks.
It should not be too hard to find an example if you want one as they regularly crop up at swap meets and on Ebay.
Be aware that the model has been released several times over the years, most recently in Desser markings.
Brief Specifications – International TD-20B
Engine: International DT-429, 6-cylinder, turbocharged, inline diesel rated at 150 horsepower @ 2300 rpm
Transmission: International 2-speed full powershift with hi-lo shift lever giving 4 forward and reverse speeds
Top speed: 5.2mph
Steering: Hydraulically boosted planetary type giving full power to the tracks at all times during turns
Brakes: Contracting band
Track frame: Isolated, pivot shaft type with pinned equalizer
Roller: 6 bottom rollers, 2 carrier rollers per side
Track shoe: 20″ standard
Operating weight: 15 tons (bare)