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 the clutch pack. And yeah, maybe even bevel gear shaft bearings going out but the dozer sure doesn't look like it has those kind of hours. Either way it doesn't sound like a fun way to start off buying a dozer... If it wasn't for the steering issue, I'd say it was a clean dozer and worthwhile to purchase but I'm not too familiar with these beasts. Need to use it a couple years as a ranch dozer for clearing and leveling then I'd sell it. Could this be a simple fix or should I run from it?
To me it really depends on a few things, What are your mechanical skills? Can you tackle this problem. What kind of condition is the rest of the machine. If its really nice than its probably worth fixing. What does it sell for? cost plus repairs still a good deal? I tend to fix stuff that is in good condition mostly because it is made to last, also no stupid electronic problems. Plus the value is most likely bottomed out. fix, use, sell could work out for you.
What’s the Serial Number.? It might also help if you can get an engine Serial Number. Have you checked that it has all the upgrades to the issues that plagued the early D7F tractors.? Edit: The military D7F is 61G prefix. According to the service documentation that is equivalent to a civilian D7F from first built to 94N5191. 94N5192 was the first D7F built with the "new style" (physically smaller) transmission, so are you sure that the auction machine has an upgraded transmission.? I'm not even sure if the upgraded style tranny could be retrofitted into earlier machines.
@farmerlund Mechanical skills are pretty good but I definitely rely on this forum for help. I own a couple other pieces of yellow iron that are 40+ years old so I understand a little bit...probably just enough to get me in trouble...about working on heavy equipment. Being this is a Cat, I know parts are readily available but I also know it's a PITA to repair heavy stuff like in the field by yourself. @Nige I tried logging into SIS to find info on the serial number but SIS is down for me at this min. And I don't know if SIS captures the service life extension program (SLEP) upgrades but I assume this dozer has the 'better' transmission. Of course you know what happens when I start assuming... PM sent too
Got your email but will reply here. The transmission upgrade also involves a transfer gear change. I can not speak to the (SLEP) upgrades and would have to actually see the transmission to verify the upgrade. Here is some of the info I have on the subject..... Forgot to add there is nothing in the 94Nxxxx parts books that indicates early units can be upgraded.
Thanks, Old Magnet- the info is much appreciated. Because I can't see the dozer in person to verify part numbers, I'll have to accept the SLEP dozers kept the old "large" low rpm transmissions that were troublesome even though engines and random other items were upgraded. Darn. For my original question, does anyone know how much of a PITA it would to replace the clutch seals in the field? Reading the forum, that seems to be the most common issue of a non-working steering lever if the linkages are okay but again I just tossing **** at the wall to see what sticks.
See if you can get the transmission arrangement number, it's on an aluminium tag on top of the transmission housing - that will identify the transmission precisely. If the steering clutch piston piston seal is blown, it generally means the bevel gear bearings have collapsed on that side. Not always, but a lot of the time. These seals are a large square-profile piston ring made from a synthetic teflon/nylon type material, and when the cross shaft drops due to a failed bearing, the seal gets chewed out rapidly. Regardless of what is wrong in the steering clutch housing - seals or bearings - there is no choice but to pull the steering clutches. This involves removal of the fuel tank (you'll need a crane or several pairs of strong hands and an empty fuel tank), removal of the brake pedal support shaft, the brake actuation mechanisms, the steering clutch hydraulics spool valve and a number of hoses and pipes, to access the top of the steering clutch housing. From there, the steering clutch covers have to be unbolted and removed, then the steering clutch assemblies unbolted from their drive and driven flanges. This process involves having to jack the track with a bottle jack to turn the steering clutches so you can unscrew all the retaining bolts. Before all the steering clutch retaining bolts are undone, you place a small wire rope sling around the top of the (one piece) brake band, take the weight on that sling, unscrew the remaining steering clutch bolts, then using the brake band as a sling for the steering clutches, you lift the steering clutch assemblies and brake band out as a unit. It's important to ensure that the wire rope sling is tightening the brake band as you lift the assembly, so the clutch assembly doesn't slip out of the brake band. You still exercise great care and hold the steering clutch assembly in position when lifting, anyway, as the clutch assembly can still slide apart as well. Once the steering clutches are out of the way, the drive flanges on the cross shaft have to be pulled. This involves Cat hydraulic pullers - and they also have to be pressed back on. As you can see, this is major tractor surgery. You can't do it on your own, it requires 2 people at least. The important thing is, before presuming the steering clutch piston seal is blown, is to ensure: A. That the steering clutch linkage is all connected and actuating the steering clutch hydraulic valve. B. That the steering clutch lever linkages are properly adjusted to provide the specified free travel at the levers. C. That the steering clutch valve body is clean and functioning correctly. The steering clutch valve spools contain little pistons and tiny orifices - which orifices can become blocked with trash - and the pistons can become sticky with trash and debris in the transmission oil. The transmission oil is shared with the steering clutch hydraulics and the transmission oil filter is a bypass type, which will dump dirty oil back in the system if the filter becomes overloaded. This then allows fine trash to enter the steering clutch valve spools and affect the spools correct operation, and may cause erratic steering clutch behaviour. I hope this helps. I owned 3 x D7F's for around 20 years, both early model and late model tractors. The later 2P arrangement transmission is the same as fitted to the D6C and D6D, it's a far more reliable transmission than the early D7F 9S arrangement transmission. It would be an enormously expensive exercise to try and change over from an early type transmission to the later type transmission, there were just too many engineering changes to the whole setup to make it a viable exercise.
Thanks, Oz. Your write-up is amazing and gives me a complete picture of what type of gamble I'll be jumping into for a steering issue. It could be a simple as adjusting the linkage/cleaning out a sticky spool or as major as taking it to a heavy repair facility for some surgery. I wont' be able to look at the transmission tags to determine which tranny is in there but it's kind of a moot point with the steering issue right now anyway. But I sincerely appreciate the healthy dose of reality you just provided me.
That is an understatement! Now you know just how much "fun" this could be.
If the Tractor is not steering in any direction, try when engine is stopped pressing the brake peddle down on 1 side at a time, if you have no solid peddle after about 3 to 4" of travel you need a brake adjustment,this should return things to a correct working stance.
Thanks, TCT. The problem I'm facing is I can't inspect the tractor in person and I can only go on the seller's provided info. I know, I know... this is a horrible way to purchase an older, used tractor. But if I do buy it, I'll be coming back here for advice