jd dozer losing transmission pressure

First off... What model dozer are we talking about ?? Different machines adjust differently and act differently ....You're not going to eliminate bypass valves to check pressures. It's best to check things in order to eliminate problems with the gear pump.. Usually the pump isn't the culprit.. Please let us know exactly what the machine is doing and we can figure it out from there..
 
It is an early seventies jd 450 or 450b. The tractor just gradually got to the point where after about an hour of operation it was very slow to engage in reverse and back up. I decided to check the pressures and adjust everything as described in the manual. I only had about 70 psi on the gauge but adjusted the clutch linkage rod to the pump and it would rise in pressure about 10 lbs before dropping of as it is supposed to as the pedal is depressed farther. I then took off the plug for the pressure regulating valve and added two more dimes as shims to the one already installed and was able to raise the pressure to 120 psi. (still not near the 170 to 180 required and added more than two dimes did not increase pressure anymore.) I tried out the machine again and shortly it got worse. I then pulled off the top cover looking for something obvious and I decided to remove the clutch accumulator valve. I found that the line from the pump to this valve would slide back and forth even when the tubing nuts were tight. After removing this pump feed tube which originally had some kind of rubber o ring seal built into it with the ends brazed on I thought this was the problem. I bought some adapters and replaced these fittings with hydraulic compression fittings. I did not go any farther with the valve and put the tractor back together but this did not fix the problem and I could now get about 25 lbs on the gauge. The tractor will move itself and thats about it.

Today I decided to remove the top cover again and remove the clutch accumulator valve again and disassemble it this time and also look to see that the clutch rod is not adjusted wrong and just dumping all of the oil back into the reservoir. I pulled off the valve and in one port there was a cylindrical piece of brass tubing wedged sideways in the hole blocking off most of the passage. I could not pry it up and after taping gently on it it fell down to the bottom. I tried to lift it out with a wire and grease but it disappeared down deeper. I pulled out the clutch bypass spool and was able to blow it into the bottom of this larger port with compressed air. I then used the wire and grease to lift it out but after it just came up it fell off back the clutch dump spool bore and on into the reservoir. I then disassembled the valve, everything looks good, but the screen behind the o ring on the accumulator cover is not there. I believe this is what was stuck in the hole.
Tomorrow I will put this back together and try it again without a screen. I am hoping that this was blocking the hole enough to have caused the problem. I will find out tomorrow and report back. Thanks for asking.
 
By chance, is the transmission lazy when cold ?? Try opening the needle valve on the side of the transmission case. [ Under your right foot when sitting in seat ] Square headed pipe plug in the way of the brake rod.. Remove plug and stick a deep 11/16 socket in the hole. I have a short screwdriver with the handle ground short that I stick thru the socket.. Once the locknut is loose, back out the screw 1/2 turn and snug the locknut down again.. Then try your HLR pressure adjustment again.. You might get lucky, who knows ?? Also the 2 lines that go from the front wall of the trans case and go to the HLR control valve are crossed on machines that have the lines sealed with O-rings and held in place with oblong washer and 3/8" bolt.. Are yours supposed to be crossed too ?? On later machines if the lines are installed straight top to top and bottom to bottom you are trying to operate the transmission on lube oil and force pressure oil to the lube circuit.. I've seen this done several times before..
 
Oh... One more thing.. Is the roll pin at the rear of the clutch valve operating shaft where it attaches to a small lever that operates the clutch valve.. Seen many of these break before..
 
Yes, the roll pin is in and I have adjusted the needle valve in and out and it did not affect the pressure. It did affect the speed of the shift though as it is supposed to. However, when I disassembled the clutch control valve I found that the small orfice behind the check ball located at the back of the bore of the pilot control valve was plugged solid. I think that this may have stopped oil from opening the bypass valve and letting full pressure to the clutches and check plug, yet I believe that it should have worked anyway in the neutral position. I decided since this was plugged that I better get a new screen and some new o rings for the clutch control valve before installing it back on the tractor and trying it out. I will also check out the line routing.

Do you know if pressurizing the clutch control valve with air will activate the clutches? I had put 100 psi on the port that feeds the clutch valve from the pump and I heard air leaking around the clutch dump spool in all positions. I would think in neutral there should be no leaks and should have been able to read pressure on the gauge at the test port. Thanks again for your input.
 
At this point , I'll tell you where I would go next.. I'd start the disassembly process and actually see where the leak is at..
 
I think at this point I am going to put the cover back on with the new parts and see if the three things I found bad actually fix the problem, i.e the plugged bypass orifice, the barrel off the end of the screen that was lodged in the supply port, and the leaking supply line to the clutch valve.

I am not really sure I have an interior valve body leak and was asking if you have any knowledge of what happens when you pressurize the system with compressed air. I think that the tolerances in the spools are such that they are probably not air tight anyway. It was the air leaking by these that I had mentioned was leaking.

I will post the results when I get it back together and see what happens. Thanks again for your input.
 
BACK IN BUSINESS:
I got it back together today and everything seems to be normal again. The transmission oil pressure is 80 psi at idle and 175 at 1800 rpm. I am hoping what I have done fixed the problem. I did not put any hours on it but I will know for sure after a few hours of operation. Thanks again for the input.
 
Most of HLR leaks are at either the 5 sealing rings at the rear of the clutchpack shaft or piston sealing rings
 

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