Looking at D7. Guy says it’s an E series, the logo says 7E. However it has a 6cyl and from the pictures it looks like an F he also says it’s a ‘72 which my understanding is they only made the Es until ‘69? Now the part some of you have been waiting for S/N 61G1121 so what am looking at? I’m pretty certain it’s not an E
61G1121 is an ex-military D7F, equivalent to an early "civilian" D7F of Serial Number 94N1-5191. This is the D7F model prior to the introduction of the high-speed "D6C-style" transmission from 94N5192-Up. Production of 61G machines started in 1970. If it's original the engine should have the same Serial Number as the tractor. The engine will be a 6-cylinder D333C producting 2000 BHP @ 1800 RPM. EDIT: If it was a D7E then it would be fitted with a 4-cylinder D339 engine that produced its power at a maximum of 1200 RPM.
If it has the old style trans mission stay away unless you like changing transmissions
Gee the military really screwed the rack up to get that HP out of them.
Thank you. That’s the I for I was looking for.
I do not. I have read that it you’re “easy” on them keep them out of 3rd they will hold up okay. Can you sawp the hi speed Trans into them from the late Fs/G
No, too many engineering/design changes to try and convert the transmissions, it would cost a fortune. The early transmissions are O.K. on light-duty work, they just don't like constant heavy-duty work. "Keeping them out of 3rd" is a dubious recommendation, all the damage is caused by low-speed heavy duty operation and high transmission loads, not high speed. The early transmission is a low-speed, high torque transmission - whereas the later transmission is a high-speed, low-torque transmission. The later transmission had the reduction gears on the rear of the transmission changed to allow the later transmission to operate at a much higher rotational speed. The later transmission is only 2/3rds the size of the early transmission, but it lasts much longer and gives much less trouble. The military D7F's underwent a huge rebuild program in the early 2000's to extend their lifespan. Virtually every wear component in the tractors was replaced, and all the engines were upgraded from 180HP early model engine to the later 200HP D7G engine. The military had an acronym for the D7F rebuild program, it was called the SLEP program (Service Life Extension Program) - the program ran from the mid-1990's to the late 1990's.
In addition, the very earliest D7F transmissions did not have a transmission modulation valve installed. A transmission modulation valve drops the transmission oil pressure momentarily to reduce the impact of clutch engagement, which without the valve, is a more vicious clutch engagement. The transmission modulation valve smoothes out directional and speed changes and improves transmission life due to reduced shock loading. There were quite a number of design changes to the valving in the earlier transmissions as Cat sought to address their problems.
So if it is a later model like a ‘72 with the updates you’re talking about. would it be better/more reliable than the earlier ones? It sounds like you have owned a couple, would you own one again or are they really just more trouble than they’re worth? I’m looking to use it for pushing trees and brush that I take down with the excavator. Not planing on using it for hogging a ton of dirt. It’s much bigger than what I really want or need but the price is pretty good I think.
Anything above 94N5192 would have the updated transmission, above 94N5660 it would have a 3306 engine.
Right, by update I ment the modulation valve and updates to the earlier trans that OzDozer mentioned
Hopefully someone has a serial number guide for military versions or a cross reference to civilian serial numbers. Failing that maybe there's physical clues or certain components that are visibly added or deleted depending on which transmission it has?
Knuck, yes, I owned 3 x D7F's, 2 with the early model transmission and 1 with the later model transmission. I bought 2 new, and 1 near new with only 2000hrs on the clock. The 2000hr tractor had been purchased new by a local farmer who farmed 8000 acres, and he traded it to the local Cat dealer on a new D8K when he needed another big tax break. They're a good tractor, nothing seriously wrong with them. The brother and myself were full-time agricultural earthmoving contractors, we ran our tractors hard on contract virtually all the time. Constant heavy dozing, pushing out dams (ponds), averaging probably 8,000-10,000 cu yds shifted a week, full throttle at all times, ripping rock, clearing, flood drains construction, ripping and stockpiling gravel roadbase. A lot of work in muddy dams, extending them to double their size, very hard on the tractors (and operators!). Bogged aplenty, and then when you weren't digging out mud, you ran into hard rock! We put around 20,000 hours on those tractors over about 10 yrs, before we left agricultural earthmoving and went into open-pit mining and gold recovery treatment, using heap leaching with earth-formed, plastic-lined leach vats. Didn't need the dozers so much then on that kind of work, they went into low-hour use, and we moved onto big front-end loaders. Sold all the D7F's in the early 90's after around 10 years of hard use, and 10 years of lighter use, they were becoming "old technology" by then - but it's technology that's simple to run and fix, and I'm sure that tractor will suit your needs just fine, if you acquire it at the right price.
Thank you. I appreciate it
I suspect it would have had lubrication issues. At higher RPM's it needs more lubrication as bearings and such are running faster then their original design speed. Combine that with the no modulation valve, clutches slamming together at higher rotational speed causing greater stress on cast iron parts. But it is all theoretical these days, although it is amazing the number of D7F threads in these forums for a model only produced for but a few years.