Serial number (provided by customer. No tag on machine). 94N02917. As the title says, the complaint was that the blade would lower but not raise. I tend to shy away from this older stuff because I prefer to only work on machines that people actually use to make money, you know... Production machines. I also shy away from customers trying to use 50 year old machines to make money. So, I am a bit ignorant about these hydraulic systems. But a friend asked me to look at it so I did. My friend has a g series d7. So he already knows more about this than I do. When I finally shoehorned a bit of time to look at it, it turns out that they were able to lift the blade and turn the machine around... So it seems to be an intermittent problem or a cold vs hot oil problem. His theory was oil bypassing the piston seals so he had the actual owner buy seal kits for me to change. Personally, I never rely on someone else's diagnostics. And rely even less on customers providing parts. So, anyway, rolled up and met my friend on the job site the other day and decided to do a few checks on the machine before starting to tear things apart. (Please remember that I am pretty ignorant when it comes to this vintage of machine) Since everything was working when I got there, had him do a few cycle times on the blade lift circuit. A few raise and stop and lower and stop cycles on the circuit to see if there was drift or failure in the lift function. Also had him blade down to raise the front of the machine off the ground to try to determine if the cylinders were actually bypassing. This is maybe about fifteen minutes in operation, so I assume we are close enough to operation temperature. There is no drift, machine is rock steady with weight on blade. This is where things go a little side ways. I have him lift the blade and hold it against relief. Then lower the blade a little. Now I have drift. Lower it more; no drift. Lower it more; drift.. So, tracks are back on the ground now. I tell him to raise the blade again. Blade will not raise. Just a tiny jerk and that is only the slop in the pins. This is where my ignorance is blinding me. In my mind a low power circuit on a cat is either a resolver issue or a pump not stroking issue. So I ask him to raise the ripper and hold it against relief to stroke the pump and the try the blade raise. This is where things get confusing. He holds the ripper up against relief. He tries to raise the blade. The blade goes down and lifts the front of the machine off the ground until this hydraulic line blows.
Did not mean to put that in 4 times
I may be wrong, but looking at the piping, the configuration of the head of the cylinder and (after draining the tank and removing the access door for the valve body in the tank) looking at the control valve. I think this is the hose for the blade raise circuit.
I would be looking at the rams first. They have quick drop valves in the head and the piston probably has an internal bypass valve so when the rod hits the ends of the cylinder oil bypasses through the piston.
The implement pump is a gear-type and there are no resolvers in the system. Attached a copy of the SysOp for the Implement hydraulic system.
Thanks for the replies Nige and rc. I just realized that the second part of my post didn't actually post. The original thought was that there was a problem in the cylinders. But when I couldn't get it to drift down with the blade weight or up with the machine weight I started to doubt it. And when the ripper held against relief test with the blade control in the raise position made the blade raise the machine until a hose blew, I thought it had to be a control valve problem. Drained the tank to open up the access door on the tank and had a peak inside. Found that it had two very simple valves that seemed to have nothing in common that could make that happen. Also pulled the floor panel to look at the pump and realized that it was just a gear pump. Like I said, I don't deal with very many machines of this vintage. So at least I am learning something. By the way, my local cat dealer can barely find any parts for this machine. As far as I can tell most of the parts info on this machine is only available on microfiche. Which I think my dealership threw away a few years ago. So I cannot really get my hands on parts breakdowns to help me along. (thanks, Nige, for the pdf). If it is possible, can someone id the part number for the gasket for the hydraulic tank access cover? It looks like the one in the PDF, but there is nothing attached to the outside of it. So I did disassemble the blade cylinder that the hose blew on thinking that maybe the piston had come off the rod and pushed to the end of the cylinder blocking the oil out port. I am not sure if that makes sense, somehow I thought it did. I had to do ripper cylinders on this machine a couple of months ago and the rods were stuck in so hard, I had to use an excavator to remove them from the bore. The piston seal looked perfect. Nice protrusion 360 degrees. But I had a bag of (ahem... Customer supplied parts) so I went to repack it and found that I only had parts for one cylinder, not two. And actually did not have enough parts for one. The spacer for the u-cup seal was missing (this cylinder still had chevron seals) So everything got bagged until I could get more parts.
RC, yes, the piston does have bypass valves. The one I disassembled had two, one on each side of the rod. They seem to move freely. But, my ignorance comes into play here. I know nothing of quick drop valves. So, I don't understand what can go bad in one to make this problem.
Sorry but they only get a 2/10 for effort.. The info is right there on SIS under the Serial Number. Where do you think I got the SysOp document from.? What other specific parts info do you need.? See my comment below about the S/N of the Hydraulic Control if you want anything cylinder-related. See below. There will be a S/N tag on the hydraulic tank for the hydraulic control part of the machine. It's not included in the tractor. Can you get that tag info.? The explanation of how the QD valve works is on the last page of the SysOp. It's pretty clear. Look for stuck spools, scoring, broken springs, etc. If there is anything wrong it ought to be fairly obvious.
If you want a picture of the hyd. cylinder or the quick drop valve you need to find the serial number on the back right side of the blade. They won't be in the hyd. control section. The Cat store should be able to find this info for you. Bob
Bob's right. The blade cylinders are part of the Blade Gp as far as parts are concerned, not the Hyd Control. My bad. If you can't find a tag on the blade get a part number off the tag on the blade cylinder barrel if there is one, or from the head of the blade cylinder where the wiper seal.chevron packing sits.
Sounds like a sticky or bad relief valve inside the tank
Thanks guys! Got someone heading over there to search for numbers now.
Near as I can tell there is only one relief for both circuits and it is under the tank.
Perhaps it wasn't my best idea to send a 75 year old man with only one eye to look for serial numbers. He got me numbers for the hydraulic filter cover and the cast numbers on the quick drop valve. I finally got back to this machine today. There is no tag on the blade, but I didn't expect there to be. I did find the tag on the hydraulic tank. Pretty beat up and heavily painted over. Some paint remover, some Emory cloth and a little rubbing ("This isn't mechanicing, its archeology.). I think I have an actual number 35H4912, maybe, the bottom half is pretty beat up. Finally had the seals to put the cylinder I had apart together. So buttoned it together and pulled the quick drop valve off to inspect it. Didn't really find anything. Everything seems to move freely but not so freely that I would assume bypass. Cylinder on the other side is exactly the same. I did get a little excited when I looked at the other side and saw what looked like brand new piping to the quick drop valve. I thought, "A-ha! Someone changed this piece and lost the spring from behind the plunger.). But it was all there and all in the right orientation. So I think I have ruled out the issue being in the cylinders.
Sorry, Nige. I completely forgot to check the head for numbers. There are no decipherable numbers on the barrel. I doubt it helps, but the quick drop cast number is 5J3851.
That should be a 173B hyd control 3 valves. Bob
It doesn't have a tilt function. Just blade up/down and ripper up/down.
Still don't get why holding the ripper in raise against relief made the blade go down.
Can anyone confirm if this is actually a good number for the hydraulic tank group? I need to identify the gasket for the access plate that I removed to look at the valve.
Your the one reading it ,again a 35H is a 173B 3 valve hyd group. That number is all Cat needs for parts. Bob
By my parts book 35Hxxxx is a two valve unit. Correct for 94N with dozer and ripper and uses a 60 gpm vane pump.
Cover plate gasket is a 5J3140 Causes for excessive lift cylinder drift: 1. Worn piston seal rings 2. Worn spool valve 3. Lift circuit make-up valves not seating 4. 0-ring seal failure in circuit 5. Worn bypass valves in lift cylinder pistons The fact that the problem is intermittent would lead me to check the make-up valve seating and the operation of check valves in the control valve. Also the main relief valve (pilot operated) protects both the lift and ripper circuits which may explain the influence on both circuits although that seems like a long shot.
Hey, thanks. I am sorry for the delay. Somehow the forum didn't let me know about the new reply.
Piston seals had nice protrusion. So 1 is off the table. Worn spool valve makes sense. But it doesn't seem to explain the reverse operation of the lift function when the ripper is held in relief. Actually, nothing does. I have gone through the schematics and theories of operation a bunch of times and can't get my head around how there could be any crossover between the two valves. I am starting to question whether the guy I had operating the machine actually had the levers in the right directions. I agree that the relief valve is a long shot. One relief, two circuits. One circuit has a problem. I was starting to toy with the idea of the make up valves. I don't know how to test them. Same for the bypass valves. I am just not sure what to do next. It seems like any further testing means that I need to reseal the hydraulic tank. And it looks like I need to pull the tank apart to look at the rest of the likely problem.
Honestly, guys. I am thinking about eating the time that I have spent on this and having the client find someone else.