D7F

1. #1Dave Neubert2023-07-17 17:03

   early ones had the 4 cylinder trans and did not do well with the higher RPMs of the 6 cylinder

2. #2OzDozer2023-07-17 22:30

   This recent thread (link below) may help you some. Yes, the tractor has the early-type large diameter, low-speed powershift transmission that first appeared in the new D7E in 1961. These transmissions can be troublesome and costly to overhaul if they're worked really hard. Many of them seem to give satisfactory service under moderate operating conditions - but Cat finally decided to replace this transmission in the D7F with the smaller transmission from the D6C/D6D, around 1973. The later transmission operates at a much higher speed, and is a "high speed/low torque" transmission, as compared to the earlier transmission, which is "low speed/high torque" transmission. The transmission operating speed was changed via altering the reduction gears on the rear of the transmission, before the drive speed got to the bevel gear. The later transmission is much more reliable and robust and longer lasting - however, it's not practical or a feasibly economic exercise to change the transmission from the early to later type, because there were other extensive engineering changes carried out when the transmission was altered. D7F at auction not steering left. Should I run? Coming up for auction is a D7F military dozer with upgraded tranny that appears in good shape overall. It's just not steering left. Steers right okay but pulling on the left steering lever does nothing. From reading up on the forums, this sounds like a blown clutch seal that requires pulling... HeavyEquipmentForums The tractor you're looking at went through a major Defense rebuild program called SLEP (Service Life Extension Program) in 1996 and was rebuilt totally from front to rear, and this program saw all new, later model engines fitted to these D7F's. Other upgrades were likely to have been carried out at the same time. All bearings were replaced under SLEP. The condition of the tractor would be governed by the number of hours it has done since the SLEP rebuild, the type of work it has done, how it was stored, and how well it was maintained during storage. Most Defense equipment dies from neglect, not from serious amounts of use.

3. #3StumpSlinger2023-07-17 23:23

   Thanks, we plan on clearing with it from time tot time, push scrapers, and general dirt work. Not a full time use machine.

4. #4OzDozer2023-07-18 00:32

   I'd have to opine heavy ripping and constant heavy dozing is the hardest work that shortens the life of the transmission. Plus, oils have improved substantially, even in the last 25 years. They find new additives all the time that improve oil performance, and which additives lengthen component life. The other factor is that during the SLEP program, the tractor would have received all the transmission upgrades necessary for improved life. The earliest D7F and the D7E transmissions didn't have a modulating valve, which lowers transmission oil pressure temporarily during shift changes. The modulating valve eased the harshness of shift changes by allowing more gradual clutch engagement. The modulating valve improvement was installed a couple of years after the D7F was released, around 1971. The earlier transmissions had harsh directional transmission changes, not helped by the fact that Cat advised you could run the tractor at full RPM during directional changes. A lot of operators like to drop the engine RPM during directional changes, but this becomes a chore, and it also uses more fuel. The early transmission used to wear out the bearing surfaces in the planetary gears and shafts, as these areas contain caged needle rollers that have no races, they use the inner surface of the gear and the planetary shafts as the bearing race surfaces. Under the low speeds and heavy torque these planetaries had to endure, they wore out too rapidly, and it's an expensive exercise having to replace all the planetary shafts and gears, simply because the bearing race areas are badly worn.