I am working on a tigercat 630c skidder. Let me first describe the set up. Single rexroth pump driving dual rexroth 160cc motors. Hydrostatic system is electrically controlled with a Parker iqan system. Originally this tractor had a catastrophic drive pump failure. Replaced the pump with a factory reman. Remove and disassemble both motors and reveal. Flush propel hoses and case drain. Open tank and clean and replace all hydraulic filters. Machine worked fine in testing and for two days on the job. It has forward and reverse pedals and a ground speed potentiometer. After two days the min. Displacement screw backed out of one of the motors( left loose more than likely). After replacing the screw the machine started acting up. With the machine in full ground speed it will stop pulling completely for a moment and then start right back if I stay in the pedal. Monitoring charge pressure while doing this, charge pressure is at 400 psi when pulling, it drops to 200 psi and stops pulling, pressure then goes back to 400 psi and it starts pulling again. This only happens when it is in a load. Just driving the machine pulling it own weight I never have the charge pressure fall out. Also with ground speed switch on turtle or half way up it never loses charge pressure and never quits pulling. The ground speed is controlled by proportional solonoids on each motor that controll the displacement of the motors as demanded by the control system. Where could I be loosing this charge pressure? I have already removed and completely went through the motor that the min. Displacement screw backed out of and found no internal damage. Seems to me if I had a leak on any of the three rotating groups it would not matter at what displacement the motors were in to cause a leak to case. Have replaced the charge filter base as it has three hoses and dumps to tank to tank when in bypass mode. Charge pump is internal in drive pump and is a gear pump so it should not be coming and going. Charge pressure is not electronically controlled and has a relief valve in the drive pump. Min. Displacement screws are set to factory specs. Any ideas would be appreciated . I don't which way to go at this point. May a flushing valve on one of the motors. A case drain test is out because I am only getting problem at full load and full speed. Any suggestions may be "another set eyes" for some thing I am not seeing. Thanks
Did I go into to much detail on the first post? Just think general hydrostatic system. Where can I lose charge pressure intermittently ?
Hydrostatics tend to confound even good hydraulics people for the most part. I know a little about them, but some concepts I still don't quite get. I will soon though, I'm sure. Could be a flushing valve issue, but, there should be an orifice in each motor to limit flow. Lots of places in the motors and the pump for internal leakage to occur. Silly question, have you checked the hydraulic tank for oil level, strainer screen obstruction, obstructions or kinks in the suction hose to the charge pump inlet, in fact any place where it could suck air or the oil flow from the tank be impeded? If the charge pump is cavitating and unable to pull oil, it can't push it, or if it's sucking air at random you get the same effect. The charge pump is fixed displacement so it pumps what it pumps, but at maximum pull, the main drive system pressure is highest causing maximum internal bypass within all three components, pump and two motors. At the same time, on a hard pull the engine probably pulls down and reduces the charge flow some. Add in the heat from working hard and you may be just flat running out of charge flow. Or getting air. In any case when you do lose pressure the pump can't stay in stroke and everything slows down till the charge pump catches up with the shortage. Just something to check. Could possibly be a problem in one of the motor control heads, if they're electric proportional they're internally servo'd which doesn't directly steal charge pressure, but if there's an excessive internal leak or one of the solenoid valves is bypassing to tank somehow, again if you're on the edge of not having sufficient charge flow, any abnormal internal leakage could push you into a starvation. Are the motors A6VM or A6VE160's? And the pump, an A4G something? Give us the model code off the pump if you can, might help. Cheers.
hydro I believe you probably answered your own question in your next to the last sentence, "I am only getting problem at full load and full speed". As the other poster replied this is where more internal bypass happens and of course more make-up oil is needed. Not sure with the Rexroth set-up, some of the older Eaton products had a choice of what charge pump displacement you wanted(been several years ago, I think i'm correct on this). One other thing to look at is the viscosity of the oil, thinner the oil the more the bypass, also all oil will have a VI (viscosity index number). VI relates to how much the viscosity changes in relation to temperature change. You might have better results with a different oil. Good luck, Tom
I'm not familiar with Tigercat skidders but I've been running this through my head for a couple of days and am having a bit of a hard time grasping the extent of your problem. Do both motors stop moving when you lose charge pressure? I would tend to think if both motors stop that you have a pump or pump control problem. If just one motor stops turning I would focus on that motor. It there a possibility of something more than the minimum pump screw coming loose. Maybe the maximum stroke is not adjusted correctly and the swash plate is going too far. The control system picks up the overload and throttles back the pump to spare the engine. Just throwing idea out
Hmmm, with two motors, is there a divider manifold of some kind in the plumbing or are they just tee'd in parallel? Is there more to the system than just one pump, two motors and the hoses? If there's a manifold does it have any connections that could if a valve were defective dump oil out of the loop?
The motors are teed together so a leak in one would cause a charge pressure leak across the entire close loop system thus causing both motors to stop. There are two manifolds one on the A port and one on B. Two propel hose hook to each on for a total of four propel hoses. The controller could throttle back the pump but it would not do so by dumping charge pressure. Found another flushing valve and will try that soon. When this machine is turned to full ground speed the malfunction is rhythmic , four seconds on , four sec off ,four seconds off ect. And coincides exactly with charge. 400 psi , 200psi ,400 psi ect. Ground speed control half way ther are no symptoms and no charge lose. I may find out differently but I keep coming back to a motor malfunction. Thanks for helping . Will get model and pump models when back at machine. AAvg160 rings a bell on the motors.
Like I said, if you haven't already, check the charge pump suction line and the strainer if there is one, for possible starvation or air suckage. Change the charge filter if you haven't done that. I would lean toward a motor controller malfunction, but without more clues it still could be an internal leak anywhere in the system, even on the high pressure side of the loop since charge pressure makes up the leakage. Here's a question: when you re-installed that screw that vibrated out, was it set on a test bench? If not, have you tried just turning it in a turn at a time and see if the symptoms change?
I have checked the suction hose for tightness, I have not removed to tell if there is an internal collapse. Have changed the charge filter as well as the charge filter head . In the tigercat service Manuel it gives a spec for how much protrusion from the top of screw to top of nut, which is 17 mm for 90 mm screw. Could not find the screw that fell out and all I had was a 100 mm, so I set it to 27 mm. Also checked screw in other motor and it was dead on spec. Since this problem started I have only removed the motor that screw backed out on. After flushing valve does not fix it I will remove other motor, the pump last as it will require considerably more labor to remove and draining the tank. It might be time to acquire a flow meter and isolate case drains to see which component has the leakage at full load full speed. The old hose in bucket and stop watch for case drain test is not going to be possible while operating this machine at full speed. And yes, I have tried positioning the displacement screws at different depths. The pump was purchased from tigercat and is a reman, so since I installed and not one of the dealers " certified" techs there is no warranty . So will have to fix it if it is in the pump. The reason for purchasing the tigercat pump was some parts needed to fix original pump were eight weeks out. They had pump in stock in state.
Got the flow meter today to check individual components for case leakage at time of malfunction. Will post results.
Just for giggles, start at the inlet to the charge filter. Then the outlet. Probably easier to get at than the motors and will verify that you have good flow from the charge pump even when the pressure drops, and that it's not going to tank from the filter head. Just a thought. Good luck!
I brought this problem here for ideas on getting to the bottom of this problem by diagnosing before changing parts, so I will certainly check that. Thanks.
Did flow test on all components as well as charge pump inlet outlet and found no problems. Got a tip that my motor controls are out of adjustment ( lantraxco ). Since the motors are electrically controlled it has to do with mili amps to motor proportional solonoids. By Adjusting mili amp in regards to reductions in motor speeds I will be setting begin of stroke electronically. Will get back to it on Saturday . Will post results.
What kind of reading are you getting, total charge flow through the filter? How much from each motor case? Did you check pump case drain flow, if it's isolated? Where is the charge relief valve, in the pump case? Are they using an integral charge pump, or separate external charge pump?
I did the case drain test my self. Case drain on one motor is teed at other then line returns to tank. Tap into line going to tank and case flow off both motors combined was about 1 1/2 gals per minute. About because it was hard to tell exactly that low on the scale. Same on pump. Could not see any fluctuations when charge fell out. I had long hoses made and had flow gauge and charge pressure gauge in the cab. I thought I saw some fluctuation from pump when charge went down but could not be sure. Had my shop man check the charge inlet and outlet, he said he saw no variance in the flow on either side, but I failed to ask him what the flow rate was. Will ask him tomorrow . Yes, the charge pressure relief valve is located in the head of the pump, and it has an internal charge pump. This machine uses a pressure reducing valve for ness. Pilot control functions ,so there is no parasitic draw on the charge oil. Shop man doesn't like electrical and I am on a field job that I should finish tomorrow .
Wow, so total case drain flow, motors and pumps is about 3 gpm, is that what you're saying? Hmmm. If that's true it seems very low. Any chance you can get the model codes off the pump especially and a motor if possible? Cheers.
I will have those for you Saturday evening. I was only giving you what read on flow gauge and it is the cheapest one it could find. I don't think that it is actually that low, just that the gauge is inaccurate at the low point of its scale. However I feel that it is low enough to tell me I do not have excessive leakage. Flow meter is a Hedland and I paid about 225.00 for it. The man I talked with experience with machine claims to have run in to this before and says my motors a shifting at the wrong time. The set up procedure is as follows: milli amp adjustment pump: drive motor speed to 4000 rpm ( 3800 min), set ma to max allowed around 700, reduce ma by increments of 5 until motor rpm is reduced to by 10 rpm. Next reduce ma to motors until rpm drops another 40 ( 50 rpm total). Reset ma to pump to spec of 600 ma. This can be done for no money so I am going to give it a whirl. This type of begin of stroke set up I am familiar with on a hydraulically controlled set up.
I have worked on one of these tigercats once. At about 1600 hrs drive pump was wore out! Not catastrophic. Same as you found had to install dealer part because hydraulic shop was to far out on parts for rebuild. I Installed new pump skidder worked great left shop worked for one day next morning started up but wouldn't move! I found a tiny piece if shaving of steel in a 3/16 th in spool in the pump controller. Can't remember the procedure I used to decide where the failure was? Probably no charge pressure. Any way my suggestion would be to remove each motor one at a time and test that way! I don't exactly remember how these motors are plumbed but I am sure it is possible to only run one at a time, however you would need to remove the other motor so it isn't running dry! .....theironoracle
Pump AA4VG140, Motors AA6VM160. Did not have success with setting, motor rpm never got high enough . Contemplating the next move, have to find problem with motor speed now. Frustrated !
Is there a whole string of letters and numbers after those models? I'm looking for the pump code that shows charge pump size and charge relief setting and on the motors, the code for the flushing orifice. One 140cc pump pushing two 160cc motors, the motors must have a wide displacement shift to get up to speed. Did your man tell you what kind of flow you're getting before and after the charge filter?
A little late but I never did put my finger on the problem exactly but replacing both the motors with new fixed the problem. I did however find micro cracks on the barrels of the old motors after replacement with new.