Thirty-five years later, Caterpillar celebrated the unrivaled success of the elevated sprocket design in the medium dozer class by producing three commemorative 175,000 units in May 2020. For the first time, variable pitch angle tilt (VPAT) blades were made available to high drive dozers with the D4H and D5H models for finishing jobs faster by grading at higher speeds. This helped to fine-tune machine balance and ground pressure for specific applications more easily than oval track machines. In addition to bringing many of the same large dozer advantages to the medium line, the elevated drive sprocket allowed movement of the front and rear track idlers. The Cat ® D4H, D5H, D6H and D7H dozer models were the first to feature the high drive design, and in 1987, the D8L model was added to the family. Still unique to this day for the 130 to 350 hp (100 to 250 kW) dozer class, the high drive design conformed to the ground better, improving durability, serviceability and performance compared to low-drive and oval track designs. Tracks for the U series were 6-3/4” pitch and are replaced by the D5 (6.91” pitch I think ) tracks and sprockets these days.In 1985, Caterpillar expanded its revolutionary elevated sprocket undercarriage concept to its medium track-type tractor (MTTT) line with the launch of the H-Series models. Sometime around there the tractor became the D6D. When the D6C came out in the mid 1960’s it was a larger more capable machine still with the D333 and ultimately the 4-3/4” bore D333C which was basically the 3306 until around 1973 when the engine was designated the 3306. If the old horizontally opposed 2 cylinder ponies on the U series tractors were troublesome, the vertical two cylinder inline design used after 1960 was doubly so! Just as a comparison, the older engines were governed at about 3500 rpm while the later ones revved to 6000! They quickly earned the “buzz bomb” nickname and probably hastened the end of pony motor start as an option on Caterpillar equipment. Hydraulic system was a little more integrated into the engine compartment instead of being a self contained unit hung on the front of the hard nose like the earlier ones.Ī pony motor was still an option on the D333. Grease type track tensioners became standard but the rest of the tractor wasn’t much changed. Engine was a different 4-1/2” bore 6 cylinder called a D333. The flywheel housing has the boss cast in and the hole can be cut with a hole saw and the holes drilled and tapped without removing the engine from the tractor.Īround 1960 the 8/9U were replaced by the D6b 36/37a I think it was. The problem is the older ones aren’t machined to bolt the starter on. It’s far cheaper to buy a 12 volt DELCO 40MT and the special drive for the bevel cut flywheel gear than to overhaul a blown up pony motor. The factory direct electric start system was 24 volt but most folks use 12 volt starters these days when replacing the pony motor. The plain Jane model had no pony electric starter, you used a pull rope wound around the flywheel. Lots of them are jump started using a 12 volt vehicle and jumper cables. Pony USUALLY had 6 volt starter and the diesel had a generator to charge the battery if it had one in a box on the fender. Oil clutch is practically indestructible compared to the dry clutches.ĭirect electric start was an option but pony start was most common by far. Look for a dipstick and a breather on the right side of the clutch housing of the oil clutch. You may find some that were retrofitted to earlier machines as there was a kit offered at that time. That can bite you if you forget when you’re trying to get out of a cloud of bees in a hurry!Īll CAT tractors in those days had hand clutches.Īt serial number 13263-up, the oil clutch was introduced. No reverse in 5th no matter where you shift the reverser lever. All have a 4-1/2” bore 6 cylinder D318 engine and a 5 speed manual transmission with a reverser lever next to the gearshift. The U series D6 was introduced in 1948 and produced until 1959.
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