I have a D37PX-21 and I think it is an AS Valve causing it to stop pulling at times. When this occurs, I have a loss of hydraulics to both the travel motors and work equipment. The only common link I can see is in the HST Brake quick return circuit. However, I cannot determine what valve controls this. Closest think I see for this is the as valve in my manual. And the Komatsu dealers I have been dealing with is little to no help. I have had very bad experience with them when I took my machine into their shop. and have tried to discuss with other service departments but not getting any good information.
Machine serial number, please!
S/N 5116
Your thinking is correct. Valve AS was the cause of the problem. As you can see in the hydraulic circuit attached below. When the AS valve moves to the right side, it causes a loss of pressure to control the travel motor and work equipment. Then AS van works like in preventing overrun mode. Note that the AS valve has a orifice, if that orifice is stuck, it will cause the above phenomenon.
LACHAU, Thanks for the information. Going to look into this as soon as I can. I am talking to my friend who is working on this for me while I am offshore. So maybe he gets it going if not I can do it when I get home in about 3 weeks. So I might follow up with you for more advise. Again thank you for your response on this issue.
LACHAU, Can you point me to the exact location of the AS Valve sorry but my manual is not so clear regarding location. It looks like to me is on the left-hand side of the pump setting in the operators seat? Attached is pages from my manual.
You are welcome. Yes. It's on the left-hand side of the pump set in the operator's seat. Please see attached images.
Outstanding thank you so much for the information.
Hello All, Have pulled the AS Valve and inspected it nothing found wrong with this, and the orifice looks good and clean. No noticeable issues with the AS Valve. Next, we tested the pressure at both side of the HST filter and it starts out cold at 690psi then as the oil pressure rises drops to around 350psi. Then when the hydralics fail or falls out and stops pulling then the pressure drops down even more to around 100psi. Considering this I am leaning to it being a charge pump issue. Would that be a correct direction to look are does anyone know what this pressure should be at the HST filter? And is there another valve to be checked are should I go straight to the charge pump. Komatsu have told me they do not sell a charge pump but only the entire HST Pump assembly. I do not see why I cannot have the charge pump section rebuilt. LACHAU, Any suggestions
Have you checked the charging safety valve? The drop in pilot pressure can come from a lot of places in the pilot line!! In my opinion, you should localize and lock each component on its entire path to check before thinking about the charging pump. After checking all and the correct case is the fault in the charge pump. In Vietnam, we will rebuild the charging pump or modify by using another external pump, not necessarily using the pump attached to the HST pump.
I not sure if this is the pump you need , if it is its available HYDRAULIC PUMP D37EX-21 S/N 5001-5499 Komatsu Part catalog k-part.777parts.org PUMP ASS'Y 705-12-32110 - KOMATSU Part catalog k-part.777parts.org
If you want to buy the charging pump from Komatsu, its part number is in the attached image.
Is it possible to buy just the charge pump section of this? Komatsu and others I have spoken with only want to sell the complete HST pump with charge pump. And not the charge pump alone. If I could find charge pump or rebuild kit.
Have you tried giving the above part numbers to the Komatsu dealer? I assume it was Komatsu who gave the part codes, they will supply them according to the given codes OK, let me check with Komatsu in Vietnam.
Please go to the conversation to see the quotation from Komatsu Vietnam for the charge pump.
Finally found a Komatsu dealer to provide the internal parts for the charge pump. Seems the other only want to sell a complete HST pump. Parts on ordered will see what the final out come is when put back together. Thanks to you Gentlemen for the support and advise. This is a great forum for advise.
May I ask what price of the parts . May be better to buy a new pump You bet they want to sell a complete HST pump .
No problem see attached one of the quotes I received from one of the Komatsu dealers that actually looked for the parts and did not try to sell me a complete pump. Also note I have been told by some dealers this pump was non serviceable and they wanted to sell me a complete HST pump including the charge pump for $17,000. I have ordered the few parts I think will get me back operational. From this list I only ordered the following: Coupling 2 x O-rings guide The only obvious problem with my pump appears to be the coupling. I will update this once we have it put back together. Thanks
Still Having problems, Hope I can get some more help with this issue. Thanks to Lachau for the part numbers that you sent. None of the Komatsu dealers would give me any information for these parts. Only after suppling them with the part numbers, you provided they then magically was able to match and provide these parts. The charge pump has been rebuilt and is pumping as it should. Maybe pumping at higher pressure then needed. Since rebuilding the pump, the machine preforms as it should temporarily. When it operates actually maneuvers and pushes much better than it has for quite some time. However, it will seem to lose all hydraulic pressure and dumps back to the hydraulic tank. Testing the fluid pressure at the HST filter (This is straight out of the Charge pump) I am getting a steady 600 PSI then when the failure occurs will drop to 100 PSI. This is back to the original problem where I have a full loss of hydraulics. However, when it is operating before it fall out the machine is performing flawlessly. So, there was certainly a problem with the Charge pump I did not realize how weak the machine was until we fixed the charge pump. Now it appears the only issue is that when something occurs and lets the fluid bypass to the tank. Looking at the return line in the tank I can see a good stream of fluid returning to the tank. Then when it fails, and the loss of hydraulic power occurs it is obvious that the fluid returning to the tank is tremendously increase as if it is just completely dumping all fluid back to the tank. Please advise where to check.
We found a fault in the Charge Pump. The coupler was nearly stripped we replace it and some other components. See attached. Since repairing the charging pump, the machine will operate as it should very strong and responsive. However, it will fall out loss of all hydraulic function now more than before. Before I could normally decelerate and if would recover and get hydraulics back. Now it appears that it does not want to recover. When the and it is obvious the fluid is dumping back to the tank. I am thinking the Charge safety valve is stinking and dumping fluid to the tank? Could it be this charge safety valve? And were is its location? Looking at page 56 I am thinking on the left side of the pump while sitting in the operator's seat?
I have not confirmed the location of the charge safety valve. Can you point me to its location? I have checked 2 valves. one on the left side of the pump I beleive to be the AS Valve and one in the center of the bottom of the pump I assume to be the safety valve but I am uncertain. since the location and discription is so vague.
Its shown on post # 7
I see the drawing on Post 7, But I must be missing something. If I am looking at this correctly from sitting in the operators, I see it as follows. Item 4 AS Valve on left side mid-forward section of pump? Item 6 Charge Safety Valve is that on the bottom side of Pump? (I cannot locate this.) this location appears to be a plug in this location If I am looking correctly. 1/2" drive square for removal no adjustments that I see. Item 5 Safety-Suction Valve I have tried adjusting this but have not removed it. I must confess the locations do not seem to be correct on my machine are somewhat different. So looking at the HST PUMP on post#7 Top picture looking at left side of pump? Next picture down looking at bottom of pump? Picture to the right indicating item 4 looking at back side of pump left side up? Also not mentioned previously The foot brake has been bypassed since before I purchased this machine. Although it was working as it should when I purchased. Nothing has changed on how it is bypassed. I would like to reconnect it once I get it back operational. Is there something in this bypass that could be cutting it off and sending fluid back to the tank? Again, thanks for the advice. and any help is greatly appreciated.
I drew a black line between the two illustrations showing the safety valve , it should be on the left side and appears to be a square drive , one of several on the main pump
Thanks I am printing this now to go trace these on the machine. Thanks so much for the help. As you guys have probably noticed. I am not a mechanic by trade just an ole Red-Neck Country boy trying to keep my old equipment running. This forum and you guys has proven to be the best information source I have found so far Thanks for that.
What oil pressure is the system supposed to operate at when its at work temperature , the pressures you have given have a wide gap between them .
Those pressures are taken at the Charge filter and the wide range if from in neutral position to traveling i think is the wide variation of pressure. Pressure is holding steady in a neutral position. However varies quite a bit once traveling depending on the demand, I think. See attached scan of standard values for pressure specs. Looks like this pressure should be from 455psi to 370psi I will test this again from the test points in the manual. I am testing at the charge filter now and not the specified test point.
I changed the charge pressure safety valve today and they problem of loss of hydraulics and fluid being dumped to the tank still continues. Still asking for suggestions of what to try next. I have removed and inspected AS valve and attempted to order a replacement however. Komatsu said this valve is not avalible. Although I do not see anything obvious wrong with this one. any other suggestions on a valve that would divert fluid back to the tank? Also it seems that the pressure is lost any time traveling over a mound or hill and once the maching crest over and the weight of the machine is going downhill it will cause fluid pressure to drop and send all fluid to the tank. have to shut the engine off and start it several times before pressure comes back up. occasionally will come back after first restart. but the problem appears to be more frequent now.
Your oil pressure is going to have to be corrected at the first test point , pressure of 690 cold then dropping to 350 as in your earlier post looks like the a valve is opening rather than just hot oil . If its the safety valve can it be reset to never let the pressure above 455 , hot or cold if that is the pressure for that port . Post # 4 looks to me to be referring to overrun , as in going down slope where your pressure is lost . Are you able to access a parts book , the web one I posted is not detailed enough but is free compared to the $200 dollars for the model specific I wanted and good enough for what I need . Why I ask if there are parts numbers you can quote to a dealership they will most likely supply even though reluctant . If your pump has been working harder than it should may explain why the drive to the pump was worn
The oil pressure is steady when the brake valve is closed and in test mode. It only varies when traveling. Maybe I didnt define it correctly. When traveling then the gauge fluctuates from 600 to about 350 PSI. I now have the charge pressure adjusted to the spec of 455 PSI and the same is happening. Pump falling out and sending all fluid back to the tank. Now worse than before with the pressure reduced closer to the specs for charge pressure. Machine still runs very well when pressure is up but if falls out more often now that I reduced the charge pressure. Pressure holds steady when in test mode with brake valve closed or parked in neutral position. Pressure fluctuates when traveling as I would expect due to demand? Attached is the specs for standard values of pressure. my cheat sheet converted to PSI.
I have one doing the same thing
What was the problem with yours was you able to fix it
Still trouble shooting have not isolated the fault yet
Have you checked the suction screen inside of the hydraulic tank
Your work equipment pump must not be getting oil for it not to be working , its on the same supply line as your charge pump . Check the tank suction valve setting followed by the line back from the join (including the joint ) back to the tank . Yeah the screen in the tank needs to be checked to . The by-pass setting by the filter will need setting why we are at it . All sort of marked in red
Thanks, Can you help me find the tank suction valve where to set it and the test point? I cannot find in my manual. However, I must admit I find it very difficult to find location within this manual. Maybe it's just my limited knowledge. I have cleaned the strainer in tank, but I have not removed the lines from the block of where suction split to the Charge and work equipment. I will open this today since I currently have the tank drained. Since I have just pulled both safety suction valves from the bottom of the pump. nothing looks wrong there.
It doesn't show the exact position of the tank suction valve in the parts online book . It will be either on the tank , off a short line breather , it could be in the cap . One way or another both the charge pump and the work pump are starving at the same time . There is a second line running off the supply line that will need to be checked that it not sucking air . If you have it running again try with the cap loose enough to suck air , I'm assuming the oil is the correct grade . I wonder about the charge pump relief valve being set so high , did it look like it had been changed , broken paint or spanner marks ? It could have been set high to get the dozer running to be sold rather than find the actual fault . Too heavy an oil grade would affect settings and flow down the supply line . Don't worry about the pumps at this point as the issue of supply has to be sorted first . Although finding the drive issue on the charge pump a good catch . Note the settings on the tank suction valve on the attachment , if there is not one there it should be .
I don't think it is starving for oil I think it is a valve opening and dumping back to the tank. If starving for oil the pumps would be crying for oil. I would think. There is no abnormal sound of the pumps sounds the same as when it is running. Once it loses pressure there is a noticeable increase of fluid volume returning to the tank. I have checked the solenoid bank and I was expecting to find a fault there in the braking or inching system. However, I have not found a fault yet. But it seems like a sensor that has opened a releif valve to protect the system and returning all fluid back to the tank. Is how it is appearing. But I cannot find anything in the electrical drawing for such a sensor. But if someone was explaining this problem to me on the phone my first guess would be a faulty sensor but there are not on this machine that I am aware of. Thanks
Still Seeking advice on this machine. It has now begun to become more often that the fluid dumps back to the tank and losing all operational hydraulics. And when this happens take more time before it recovers and gains functions back. I still believe the pumps are good since the power if very good when operational. but when it falls out, I see the return fluid to the tank dramatically increased pressure is only about 200PSI at full RPMs at the filter when this happens. since it is being dumped back to the tank. When the machine is operational it is about 600PSI. this happens regardless of temperature. It is like a pop off or relief valve has opened and dumps all fluid back to the reservoir tank.
There are two pumps that could be dumping the oil , has the relief valve for the work equipment been checked for the correct pressure . Why is the pressure back at 600 lb after you reset it at 455 lb . The inching valve also sends oil back to the tank , that opening on its own will stop your drive but not the work equipment . The common thing between the work equipment pump and the charge pump is still the supply line .
OK Gents, I have gone full circle back to the beginning of this thread I originally thought I had a problem with the AS Valve. after inspecting this I did not see any problem with it. So, it has not been changed. However now I wish I had changed it. since it still appears to be the main common link. So I tried to buy an AS Valve now and Komatsu tells me it is not available and if they can get it would be around $800. Can anyone give ne a part number for this so I can search online for an available and cheaper price. Since I still am not certain this is the problem, but I think worth swapping. I also had previouly ordered this valve from Komatsu and they sent me the wrong valve. It was the Charge pump safety valve so I kept it and changed it without any help. Since then I have tried to get the correct valve from Komatsu and they are telling me it is not available and the part # they gave me is 720-2M-03641, However since I had previously order an AS valve and they sent me a charge safety valve. I just want to confirm the part number before trying to order one online.
Is this it ? VALVE ASS'Y 720-2M-03641 - KOMATSU Part catalog k-part.777parts.org
This sounds similar to a suction line leak. Have you checked the fluids when this fails to see if it is foamy looking? The fact that you lose everything including the implement hydraulics is a huge hint at the problem. Have you connected a gauge to charge pressure and watched it during the normal run and failed run?
That does look like it. I have sent them a message for confirmation but have not confirmed yet. And want to confirm its the correct one before ordering. Also still not 100% this is the problem. Just willing to take a chance at this point. I have pulled it and looked at it but do not see any obvious problem with it.
I am convinced it is not sucking air on suction. no foam in tank. Machine will operate as expected with good pressure at the filter and normal return to the tank. Then when problem occurs pressure drops and a noticeable increase in fluid volume returning to tank. it's like a relief valve opens and all fluid returning to tank. So once the charge pressure drops I have no control pressure to operate the PPC valve. I beleive there is fluid to the working equipment (Blade) however I am not able to operate the joystick without control pressure from the charge pump once it relieves back to the tank. (This is how it appears to me)
This fault has not taken a turn to a hard failure. The pressure no longer comes up as it previously did. Previously it would regain pressure after shutting the machine down then would go again before dropping out and dumping fluid back to the tank. Regardless of what I try now it does not gain pressure and drives or work equipment will not function. I still believe the pumps are outputting volume and pressure of fluid and dumping it to the tank. So now that the failure has become hard and will not reset. Have draining the fluid again and connected air to the solenoid block to back feed to the pump to see if it bypasses and it does. Putting air into the hose from the solenoid block that goes to the HST pump it freely flows through the pump and goes straif to the hydraulic tank. Can anyone help me with a detail drawing of the HST pump I believe the problem is within the pump or one of the many valves. However, I have been unable to find a exploded view of the HST pump assembly.
There are 6 separate views listed under service kit and component parts , click on each one to get what you want . HST PUMP (5/13) D37EX-21 S/N 5001-5499 (For North America) Komatsu Part catalog k-part.777parts.org
Found the problem in the pump see the attached pictures changed the bearing and Cam Rocker plate on both front and back sections of pump were broken. Items 5 & 7 on the PDF file. Although some other parts and Orings were changed to get to these. these 2 items were the failed components. Silly design those needle bearing are in a type of plastic carrier.
Looks cheap enough , would have cost badly having someone look for it , this your doing ?
LACHAU, Can you give me any suggestions on how you in are installing external modify by using another external pump, not necessarily using the pump attached to the HST pump.
LACHAU, Can you give me any suggestions on how you in are installing external modify by using another external pump, not necessarily using the pump attached to the HST pump. Just an ole Country Boy.
So I’m currently looking at purchasing an 06 37 that is doing something similar . Looking for some more advice. Engine runs fine dozer starts up , blade works fine but the dozer will not move in forward or reverse . Going through and reading this thread looks like it could potentially be the inching valve or potentially clogged suction screen ? The dozer is 3 hrs from me and I’ve yet to go and put eyes on it to see myself what it’s doing . Just looking for ideas on where to start. Obviously I know to check filters and oil level.
Sorry for the delay on getting back to you have not been on this forum for a while. One issue that I found on my machine was the charge pump coupler had some damage. When the work equipment was working good and no travel that would be my first test. to check pressure at the HST filter test point. That pressure should be about 450psi