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Case 850B 1990 dozer

S

Sampson

New User
Just bought thi 850D. Not bad shape. One major problem with the blade. It does not want to lift when pushing dirt. Everything else is normal. Blade will lift when not wedged against the dirt. When going down it has plenty of power.
I reversed the hoses on both cylinders. Now to raise the blade I move up in lower position. The up works great now and the down has now power. This makes me think control valve issue. There is an anticavitation valve that is on this valve body. Could this be the issue? Could it be leaking and not allowing pressure to build up? I would appreciate any help and ideas for parts availability. Thanks JS
 
That was a good test,you now know that the cylinders are ok and the trouble is in the control valve lift section,the load check valve may be stuck or have something on it seat,have a look at it,it's under the Allen plug,stop the engine and let the pressure off,take out the Allen plug you will find a spring and valve,a magnet is handy to lift them out.
AJ
 
mvphoto54738.jpg

I took a pic and I think I am posting it with this reply. The photo shows the control valve top. The lift valve is the center of the 3. It has an anti cavitation valve that screws in where the other two bodies have the Allen plug. I took the anti cavitation valve out and disassembled it. When Itook the cap off of it that has the slot I found and Allen head bolt with a round flat plate for the head of the bolt. After removal there is a washer and a spring. This is what holds a plunger that seats on the bottom of the valve. The stem of the valve has a very small hole in it. That is all I see to this valve. I expected more. I will take it back off tomorrow and take some pics for review.
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I was going to say when I replied to make sure the linkage was moving the spool but did not because I thought you would have noticed anything like that seeing you have your hand on it most of the time,it is important the lever is moving the spool valve the right amount,before tearing into anything else fix the lever first.
Good luck
AJ
 
well while waiting on the bushings I decided to put the hoses back to normal. I took a pair of voice grips to actuate the spool controlling blade. It will not raise up while against a load. So the linkage is not the problem however it needs repaired anyway. Back to the control valve.
 
OK so the valve is moving the right amount,have a look at the valve under the Allen plug and see what you find.
AJ
 

Well, I have taken out plugs and looked at springs and poppers. Saw nothing out of the ordinary. I decided to run the dozer with the lines reversed on the blade.
That is a pain remembering that!. After running a while the the system seems weak. The blade and tilt especially. The angle just seems a little stronger.
I bought a pressure guage and I had fittings to hook up on blade lift hoses. I checked all 4. Pressuring up as well as down on both cylinders. While raising and lowering at 2000 rpm pressure read about 700 to 800. When the cylinders maxed out the pressure went to 1000psi.
I know the system pressure is supposed to be 2150.
I did not have fitting to put guage on the control valve as illustrated in the manual but I will have Monday.
I would think pushing a load or raising the cylinder to max lift would at least be 1800psi or more where I installed the guage.
I am thinking it probably is a weak pump. I do not have a flow guage to accurately test flow, temp, and pressures.
What do you think?
 

One thing I left out. I did try to adj. The pressure by adj. The screw on the bottom of the inlet at the control valve. No effect noted on the guage.
 

Well I am back to troubleshooting the dozer. Here is what I have done.
I have removed all the metal lines from the tilt spool valve, the blade spool, and the angle spool. I put JIC caps on the fittings where all lines connect.
I started the engine, ran the RPM up to the govenor
The angle spool valve immediately goes to 2200PSI in both pisitions.
The blade spool valve only goes to 900 PSI in up position and 800 in down position.
The tilt spool valve only goes to 800PSI in both positions.
This has comp,merely eliminated the cylinders. The pump can furnish 2200 PSI in the angle spool valve. So there is pressure from the new pump.
I am not familiar with how these valves operate. Does each spool have it's own relief? The puppets I took out a few days ago looked OK to me. I thought the poppets were to hold the cylinders in place after you p ou position them. Do they act as a relief? I am puzzled as to how this valve works. I would appreciate any input. Thanks JS
 
The basic hydraulic system on a dozer is oil enters the control valve and is diverted by the spool valve say to lift the blade,if the load is too much or the cylinder reaches the end of it's stroke the secondary relief valve commonly called the port valve will open,this valve also acts like a shock absolver when say you drop the blade,it could have an issue but it would only affect one single function,it's unlikely that all four port valves fail at the one time,my feeling is you got an internal leak,the oil is escaping,with the angle pressure normal suggests the pump and main regulator valve is good,I do not know what to suggest but to have the control valve looked at.
AJ
 
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