Blade will go down lifts tracks Off ground but won't lift blade up off ground any ideas
Is the control valve moving the full distance? If there's not oil gushing out somewhere, it sounds like dirt or something is stopping the control valve or linkage from moving far enough to lift the blade. Worn linkage maybe?
If the valve is operating the spool correctly, and the spool is moving the same distance up and down as it should, then it could be a piston came off the rod, or a seal even. When it's cold, hold the valve to lift the blade for 20 seconds, hop off and check the cylinders for heat where the piston is, if one is warm, that's your problem. If you do it on a dewy or frosty morning, you might even see the problem.
Had guy come out to start with told cylinders needed redone so that has been done. Holt is wast of time, said most machines this old have been scraped, dad bought in 73. I pulled tank apart found one four valves stuck I thought that was it. Didn't take spool apart. Linkage appears to be good. Gonna try spool I guess. 36A4099
I just had that happen a couple of months ago after a complete lift cylinder rebuild (D8H)- it would lift blade WOT but drop down unless lever held back, down would hold up fine. Back to hydraulic shop- some QD valve/hole in cylinder [piston] messed up they did something (I think welded up?) and worked fine.
Had lift cylinders redone does same thing. It goes down will pull up to ground level then looks like it's slacks off, no lift, tilt cylinder works. Not sure at this point.
Hydraulic shop was positive it wasn't their work and it was something else. We lifted the blade, held it up with the 980, capped the cylinders and let down with the loader- psssssshhhhh right to the ground.
Did anyone check the quick drop valve mounted on the top of the cylinder?
Is the spool linkage adjusted correctly?
There is a Quick Drop check valve in the cylinder that will do that. I had it happen on a D7E. You could lift the blade up but it would drop back down. The hydraulic shop found that the plunger had a wear ridge on it and would not seal against the seat. He just ground the wear ridges off so that it would seat again. It's there to unload the oil quickly. I was there when he did it, and I think it was on the piston and not in the Quick Drop valve itself. It's been over 20 years ago. The hydraulic shop actually missed it the first time we tore it down to reseal. Then I tore down every valve in the hydraulic tank without finding anything and finally took the lift cylinders back to the shop when we found it. Sounds like similar to what happened to Crummy. I do not have a parts book handy to post a picture. Edit: Come to think of it, I think that it was on the head that bolts on and not the piston.
I also went through the valves in tank! Had one that appeared to be stuck, had to tap it out, polished it, all four moved free, Took lines off heads of barrels two valves per side, all move in out smooth. So does anyone have break down of lift cylinders? What I am understanding correct me if wrong it's either the spool or drop mechanism but most likely the drop. Thanks bunch all!
I also remember that there were poppet pistons mounted in the cylinder piston. Basically they would hit the bottom of the cylinder and open oil to the other side. It was basically to soften the blow of bottoming out the cylinder. All this stuff shows on the parts diagrams. I'd give that to you if I had one.
There is not much to the drop valves. You have a spring, plunger, valve and valve seat/sleeve. Same operating parts for raise and lower. The only difference is in raise there is a small orifice passage that adds hydraulic pressure to assist the plunger spring so that the plunger seats the valve against the seat.
Need Hydraulic system s/n (on tank) and lift cylinder part number if possible as there is more than one style of lift cylinder and drop valves. or pictures would help.
The guys who have spoken about the quick drop valve, or valves needing checking, are right on the mark.
I ran two different 8N's on different jobs. Both of them would lift the blade, but it would drift down. It was the quick-drop valve causing the problem.
You know a little history of what lead up to this dilemma would most helpful, and what has been done since. Otherwise you will get a bunch of WAGs. Bad Bob
Was clearing brush less than hour push forward went to back up, pulled blade to come up nothing just dragging on ground backwards, going forward just diggs in, but will push blade down and hold in place. While trying to lift won't come up, looks like won't hold up either. Tilt works but is on different circuit. Done/checked Real sealed both cylinders, pull hyd tank apart found one valves of the 4 appeared to be stuck, had to tap out, polished all four, slide good , thought that was it. Checked all four valves on top of cylinders all, moved fine. Put all new o-rings were taken apart. Checked linkage on from seat to tank. Beat my head couple times! At this point I didn't open spool up, should I have done that? Any suggestions much appreciated!
No s/n = no answers!!!
Kinda sounds like the relief valves in one of the cylinders pistons got broke, if you were dead ending the cylinder. If the hyd shop is not familiar with Cat cylinders they might not catch that. Call and ask if they pressure checked your cylinders both ways? Bad Bob
The guy came out just took the rams back with him the put them back in.
This came from Cat while looking for o-rings
OK, based on the picture of your Hydraulic Control and 36A4099 s/n you have a model 36Exxxx front mounted Hydraulic Control. Single valve in the tank and a remote control valve for the tilt cylinder. Attached are parts diagrams for the Quick Drop Valves. There are three valves in the QD housing that need to be checked out (movement and sealing). Also a parts diagram for the typical lift cylinder. Not likely there is a problem with the main control valve if you are able to make down pressure although spool and bore wear could be a factor. End of travel (cushion valves) in the piston could be a source of problems and leakage in one direction. Others please comment.....
When we were fighting with the hydraulic shop we swapped the lines- if it was the control valve it should have done the same thing but opposite directions, but same result, pull back down & hold push forward up and then drop, so cylinders.
The quick-drop valves will likely be the easiest to check first
The problem I had was the end of travel valves in the piston as shown in the drawing. My blade would lift but would immediately drift down like it had air in the system. His problem sounds more like a problem in the QD valves. I think I'd first suspect a broken spring in the check valve allowing a bypass.
It's a little tricky. In the raise position the check valve is cut out of the circuit by a "working" flow control valve.
If I were troubleshooting, I'd make sure I had pressure oil to the lift cylinders in the "raise" position first. Looks to me like if the flow control valve spring broke or if the valve was stuck open by a piece of debris, pressure oil would just flow in a circle without lifting the blade. I question if only one "open" flow control valve in one lift cylinder (no chance in hell both cylinders have trouble) would bypass all the pressure oil that the pump could put out. Should be a quick check to find out. If all is good there, I'd look at those end of travel valves on the pistons.
Yes, it would have to be a good sized leak, it uses a 100 gpm pump.
Many years ago, I had a tiny chip of stray metal, about 1/16" wide and thick, and about 1/8" long, become tightly jammed under the main hydraulic relief valve of one of my D6C's. Despite the relief valve being barely propped open, that little chip lodged in there ensured that the total output from the main hydraulic pump was dumped, and I could not get a single hydraulic cylinder to operate, either on the blade or the ripper. Can't recall the exact output of the D6C hydraulic pump, but it was fairly substantial. It just blew me away that so much oil could go through such a small orifice, and totally prevent the operation of any cylinder.
OK, I believe pressure is the key. If the pressure is low in the raise position the flow control valves in both lift cylinder quick drop valves can bypass fluid (big leak). As this supposedly came on rather sudden these "old timers" are somewhat famous for a fatigued/broken pressure relief valve spring (in the tank).
Yes, I could see that happening. That would eliminate my scenario of an open flow control valve in only one cylinder since the low pressure would allow both to stay open due to lack of pressure.
Hello, sorry for not responding, was feeling bad. So does anyone have pic of pressure valve in the tank or just explain we're it's at. Thanks again for support! Harold
You need to run a pressure test on the system before going into the tank.
Just wanted to update. In the top of cylinder is 4 values one was stuck in place would not move had to drive out to unfreeze and polish it. Had to polish spool also, it lifts blade now. Thanks for helping, Harold.
When working the clutch assist will not engage no matter how hard you pull. You have to idle down rpms then it will engage. Next it may work couple times, then it will get hard and not engage. Sometimes it not so hard but will pull in, but hard. This of course is the manual transmission. Clutch is not slipping, will spin tracks. Harold
The clutch in a direct drive machine has oil and a boost pump in the compartment along with a dipstick. The older direct drives that I worked on had a dipstick under a removable piece of deck plate over by the right side brake pedal as I recall. Most of the direct drive machines leaked oil around the case but you couldn't see it because of the dirt packed in the belly pan underneath.
I checked oil already thinking it was low, it wasn't. What don't understand is it works one or two shifts then doesn't. I have to idle down then it will pull in. Sometimes it little hard but pulls in, other times you can't get in. Any ideas?
All the the dozer clutches I worked on had a cover you could remove on top that would allow you to look at the internal linkages. You can open that up and look at the movements inside with the engine shut down maybe to see if there are problems.
This is a new one on me - but as it is an erratic problem, I'd suggest a fastener of some type has come loose in the linkage, allowing enough movement of what it is supposed to be clamping to create interference with other components. The erratic style indicates something is moving out of whack on an irregular basis. It could also be a failing bearing, with the shaft support provided by the bearing altering as it collapses.