Classic Machines

Equipment Controls – the cable era

caption: Another very popular LeTourneau PCU was the front mounted Model AN8, seen here fitted to a reasonably new Caterpillar D8-1H series. The tractor also has a LeTourneau WCK8 angle blade fitted, and is scrub clearing prior to crop planting.

Ever since the invention of the track type tractor, people have been hanging all manner of attachments off them, or towing behind them and they need cables. By Richard Campbell.

In order to make machine attachments work required a method of control was necessary and, these days, we take for granted the precise and effortless control offered by hydraulics, and electro-hydraulics as offered by laser technology.

But, and it’s a big but, everything had to start somewhere, and in the case of bulldozer blades, rippers and towed scrapers, there was only one answer, cable.

The very earliest rudimentary dozer blades were fitted to small track type tractors and raised and lowered by means of a hand operated winch.

This was a slow, laborious but an effective method of obtaining control over the machine’s attachment. Most of these hand operated winches were ‘shop-built’ one-offs, fabricated in order to do a local job.

However, it was not too long before some of the tractor manufacturers (and their suppliers of attachments), to realise that there was a huge untapped market for an effective cable control unit that could operate a variety of attachments and was easy to use.

Through the ‘cable control era’ (1930s through early 1960s), there were several notable manufacturers of cable control units (also known as PCUs), and most of these manufacturers also designed and built attachments. Frequently encountered types included LeTourneau, Caterpillar, Garwood, Bucyrus-Erie, Isaacson and Buckeye.

These six manufacturers represented the bulk of PCU builders and suppliers, and all of them (excepting Buckeye), made other attachments including blades, rippers and scrapers.

There were, of course, other minor players, and Slusser-McLean, Wooldridge and Kay-Brunner were three further examples. In the UK, both Blaw-Knox and Vickers also manufactured cable control units for use on track type tractors.


By far the most successful manufacturer of cable control units up until 1945 was RG LeTourneau, which designed and manufactured a complete range of PCUs including the Model N, Model T, AN7, AN8 and others to suit Caterpillar track type tractors from D4 through to D8. They included a four-drum model for tandem scraper operation called the N4.

They were very successful for several reasons, including being easy to adjust, reliable, and plenty of spare parts supply, plus everyone knew how to fix them due to their simplicity!

LeTourneau PCUs involved designs that could be fitted to the front as well as the rear of a track type tractor

LeTourneau was a preferred supplier to Caterpillar up until the end of WW2 when Caterpillar introduced its own line of attachments and PCUs and cancelled the ‘co-prosperity’ agreement.

LeTourneau’s PCUs were not restricted to Caterpillar machines, being available for Allis-Chalmers, Cletrac and International-Harvester, although fitting to the latter brand tractor was rarer.


Just prior to WW2, Caterpillar attempted to market its own range of cable control units designed for its D6, D7 and D8 tractors.

These were introduced in early 1941, but very, very few were actually manufactured and delivered due to the USA’s entry into the war, and the fact that LeTourneau was already building suitable cable controls en-masse that fitted Caterpillar tractors.

It was deemed by the US War Production Board that Cat was better off building tractors and leaving the attachments to LeTourneau!

Caterpillar once again entered the PCU market in late 1945 with a whole new range of cable controls specifically designed for its entire range of equipment; basically keeping everything ‘in-house’ so to speak.

Caterpillar’s new cable controls bore no resemblance to its previous units, and were a huge success being easy to operate and repair, and with a model to suit every tractor that it manufactured.

The new PCU’s included front and rear mounted types as well as some specifically designed to fit Caterpillars new range of motor scraper, the DW10, DW15, DW20 and DW21.

Cable control production at Caterpillar finally ceased in the early 1970s as most tractors by that stage were all-hydraulic in operation.


Garwood was located in Findlay, Ohio, and was a major supplier to Allis-Chalmers, producing cable controls, bulldozer blades and towed scrapers (including cable and hydraulically operated types).

Garwood’s biggest selling PCU followed a basic LeTourneau design, having two air-cooled and ventilated drums and was known as the model CU-2. It followed up this design with the model 241 PCU, which was not in production for very long.

It is rare to see Garwood PCUs on other manufacturers tractors other than Allis-Chalmers, and Allis-Chalmers bought Garwood’s earthmoving division in the late 1950s.


Bucyrus-Erie has always been very closely allied with the International Harvester Company and for many years provided a wide range of attachments for I-H including cable control units.

The manufacturer’s most numerous PCU was the model P-28; a rear mounted unit often seen (and very popular) on International TD-24 and TD-18 tractors.

Bucyrus-Erie sold its attachments operation (including towed scrapers, dozer blades and cable controls) to International-Harvester in 1954, after which time, all former Bucyrus attachments were marketed as International-Harvester.


The Isaacson Iron Works was located in Seattle, Washington and manufactured a small range of twin and single drum PCUs that were popular on International-Harvester and Oliver-Cletrac tractors, especially those engaged in forestry, as the company offered a high-lift option for its blades.

Principal models included the HHL, HL and H, and these could be installed on the front or rear of track type tractors down to D6 size.

Due to intense competition in the track type tractor attachments market following WW2, Isaacson exited the industry around 1950, making its products rare today.


Buckeye was a very interesting company, with no real close affiliations to any of the major equipment manufacturers of the day.

Its manufacturing facilities were located in Findlay, Ohio, not too far from Garwood, producing a narrow range of single and double drum cable control units, most notably the models HD and MD that were frequently seen fitted to Cletrac and Allis-Chalmers track type tractors.

These PCUs were well liked by operators and it is quite surprising that they were not more widely used.

Buckeye also manufactured a range of popular trenching machinery and proved a big competitor to the Cleveland Trencher Company.

Garwood purchased the attachments division of Buckeye in 1947 and absorbed its PCU production line into its own, eventually hybridising several of the Buckeye designs before Garwood became part of Allis-Chalmers.

Buckeye’s trencher operation eventually closed for good in 1972.


Hydraulic improvements

During the early 1960s, the development of reliable hydraulic systems and better methods of high pressure sealing took off, and more and more manufacturers began to use this form of control in preference to cable control.

Where previously hydraulic systems were mid to low pressure, significant advances were made in the field of high pressure hydraulics, especially in Europe by Poclain and Liebherr.

This signaled the end of cable control as a method of dozer blade and scraper operation, and by the mid-1970s even Caterpillar, one of the last hold-outs to this form of control, had discontinued its extensive line of PCUs.

However, due to their simplicity and unarguable reliability, you can still see PCUs in use to this day.

For the model collector

Models of tractors with rear or front mounted cable controls are relatively rare, and seem to be restricted to the “limited edition” market or scratch built enthusiast.

I have quite a few 1:25 scale models with cable controls fitted and a smaller number of 1:50 scale models, so they do exist, but some research will probably be necessary to track an example down.


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