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Regardless of the previous post, everyone has an opinion, I strongly disagree. 1. When considering purchasing any particular piece of equipment that is old, you want to identify the model of it by getting the serial number off it to identify it. On a D-7 of this age, you will find the tag on the back of the tractor, about waste high, on the left side above the final drive case, also a tag on the left side of the engine block ( orientated as if you were in the seat ) You can then I.D. the machine and research if it has any inherent weak areas in its model run etc. for starters, there was a post above about a JD 350-B that described a major wear item on the later model of that run, this is a good example of what I'm talking about. 2. The D-7, 7M, 3T, 4T are practically identical tractors 7M & 4T were built for the military under government purchase orders, the 3T was also bought by the government, but for sale to the general public. The 3T was built from 1944 to 1955, with some 28,000 tractors built, the 7M built 1940 to 1944, 10,000 tractors built, and the 4T 1944 to 1945 10,000 tractors built, so just shy of 50,000 of these tractors built. Oh, another 1000 6T's were built, so really 49,000 were built. 3. Based on the above, they were popular, helped the U.S. win WW-II clearing jungles, building roads, aircraft runways, in both theatres of the war, also built the (Alaska) Al-Can highway and numerous other civil projects in this country. Some may say the D-7 was too big to do small work & not powerful enough for big work, but in that time they were not too far behind the D-8 in HP, & size which was the biggest tractor CAT made then. They were not extremely powerful, but still very capable, by the late 1960's the H.P. had doubled on the D-7 Caterpillar built a reputation on machines like these, they were excellent tractors of their time, the projects that were built with them, the agricultural applications they were used for, and the fact that many of them are still around today supports this fact. Very reliable. The D-7 has the D-8800 4 cyl. non turbo, low r.p.m. diesel engine which was very reliable, and provided long service life when properly maintained. The 2 Cyl. starting engine although low tech. was still very reliable when properly maintained, and it does need some careful looking after, frequent oil changes. You have to drain the gas out of the carburetor to insure that no gasoline leaks into the crankcase, contaminating the oil, thinning it, causing it to lose its properties, could throw a rod or spin a bearing etc, If you buy the CAT, REMEMBER that. It has a magneto that requires solid wire plug wires, and a Zenith carb that can be tempermental on occasion. The advantage with a starting engine, was that you can spin the main engine, let the oil circulate, warm the coolant, really condition the engine to run before you turn the fuel on. This is helpful, prolongs the life of the engine and allows cold starts in low temperatures. The only weak area on these tractors were the dry type main clutch, CAT later went to a wet type oil clutch, around 26,000 in the D7-3T model run, much more durable if properly serviced. You need to get the manuals on a tractor like this, so you can learn how to maintain it. 4. When buying a crawler, the most important thing you need to verify is the condition of the tracks, ( undercariage = U/C ). The only way to do this properly is to measure the U/C components, sprockets, idlers, lower rollers, upper rollers, link(rail), grouser, correctly, and record the measurments. Either get someone to measure it, CAT used to come out and do this for free, or find someone to show you and help you make a good determination. Then compare the measurements against what the dimensions of the components were new,( U/C spec's are available in the manuals for these, including the military technical manauals ) converting the difference to percentages to arrive at an accurate percentage worn on the components, there was another post on this subject above. Eyeballing components does not give you a real number, just a hint as to suspect components that may be worn out. Ex. track pin bosses(pins that conect your track links/rails) hitting bottom roller flanges meaining your rails are worn quite a bit,you can see that, but other components you can't. Bottom line is undercarriage replacement is not cheap, can be more than the machine is worth, but because this was a popular machine, there are options, salvage yards, aftermarket suppliers, track shops, etc. Once you know the condition of an undercarriage, you may discover other options to help get more service life that may not cost a fortune, but will avoid increasing the wear factor by 2 or 3x above the normal wear, and avoid tossing a track every so often, which is not desirable. You also want to make sure the sprockets are not loose on the hubs, good size prybar can be used to check this, no metal pieces or trouble in the final drive compartments, can dip a magnet down into the case, steering clutches function properly, same with brakes, master clutch, pony clutch, etc. Look for obvious stress cracks, poor repairs, suspect welds, and leaks as well. Track adjusters, make sure they work, and make sure the front idler is in line, not loose etc, good oil pressure, clean exhaust, sometimes they wetstack from idling and light use, running them hard usually cures this. Starting engine running ok, the vertical 2 Cyl. ones on these were pretty good actually, engages the main no problem, stays engaged until the main fires & disengages it. Its tough going in blind on a machine this age, but if it's in decent shape, you'll get a lot of hours out of it if you take care of it and operate it properly. 5. Being that this one is a military unit, your cable control unit CCU, is probably a LeTourneau Power Control Unit - PCU with the overhead ridge beam set up. They were reliable, but required tinkering and adjusting, actually based on a simple principal when you look in the manuals. The problem is that the driving & driven cones ( clutch cones ) are way obsolete, I'm not sure if anyone can re-line these, the brake bands are probably much easier to have e-lined. There are bearing adjustments to do occasionally as well. The later Caterpillar CCU's were much better, and I beleive are much easier to get parts for, also will fit on the older D-7, #25 CCU I believe. I kept my LeTourneau ones for originality mostly. They are good machines, as many have survived hard use without proper care. If you are working in real hard soil, a cable operated dozer only uses its own weight for down pressure, so be aware of that. On the price, well it's seemingly high $3000-$4000 unless that tractor is in completely restored condition with a new or excellent undercarriage,in good mechanical condition from top to bottom. I say that in fairness to the seller, as you cannot judge from just a description, or even photographs,( but they do help ! ) you have to really inspect it up close, so my comment on the price is just speculation. On the flip side, spending a little more to get a machine in good shape is usually the better way to go. I've seen people put money into restorations of machines, exceeding their values as well, depends on what its worth to someone. I just saw some west coast auction results, couple of nice D-6's & 7's were bought reasonably & in good shape, sometimes you have to wait it out to find the right machine, so keeping an eye out is a good idea, I bought one 1 1/2 years ago & had it shipped from the midwest to the east coast for $1600.00, overwidth with the blade on, but it was in nice shape, a verifiable low hour machine I could not pass it up, the $$ were right. I hope this helps, I grew up on a 4T, own that one and another 4T, they are decent machines for the farm, weekend projects etc., heavy earthwork contracting and the like, well even if restored in tip top shape, their day has long passed, but you'll be suprised at what you can do with one. Great for clearing & grubbing, and if your not in the woods or in tight areas, even with a cable blade you can push out ponds, hopefully the soil is not too hard & dry, or big boulders etc. Also you have the Antique Caterpillar Machinery Owners Club LINK BELOW, very knowlegable, helpful, problem solving people + very helpful in finding places to get parts, find salvage yards and so on. There's a lot of support on that site for someone with an old CAT. A bit long, but hopefully some help,the old 4T's are a longtime favorite of mine, see if you can get some digital photos and a serial number, I would be highly interested in seeing both. E-mail address is below if you have any questions, be glad to help if I can. E-Mail ElmTree893@aol.com
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