hello all to whom reads, been fighting this dozer for awhile now and i could really use some advice. first inital symtom/problem - dozer was grading steep incline (jump face on dirtbike track) as dozer was climbing the hill it lost all pressure and free wheeled backwards down the hill till it got to flat ground and stopped rolling. there was no external leaks, engine was running fine, working equiptment still functioned normally but there was no drive and no pressure to the powertrain system. drive train and all mechanically linakge was still connected. hooked pressure gauges up to testing ports for power train control system found minimal pressure there way below specification. tested pressure out of pump and that was also below specification. first thing we had repaired was our hydraulic tandum pump. powertrain side of pump tested bad and working equiptment pump tested okay. we had pump fully rebuilt anyway, re installed pump and re checked pressures. still pressures were below specification and we were not getting the pressure to drive the machine. next was the transmission modulation/pressure valve removed and inspected then rebuilt the unit and reinstalled same symtoms low pressure not enough to move machine. we started going through the entire powertrain system and rebuilt and resealed every valve on the transmission (prioty valve, shift control valve, all brake and clutch valves, steering ppc valve and replaced any cracked or damaged hydraulic lines) we also removed the transmission and gone through and found foraward clutch assembly was burnt up so we replaced all clutches and piston ring seals for each pack and rebuilt and resealed transmission. while we had everything out before moving onto installation we had a look in steering case and found worn out clutch and brake steering pads so we replaced those as well. as well as making sure trasnmission oil cooler was clear and cleaned of any sludge after doing all this work and reinstalling and adjusting of all components and mechanical linkages as neccessary the machine is now moving and functioning but the pressure is still below specification and the fluid is aerated and the pump hums like its cavitating. causing heat at powertrain pump and filter. new fluid. new hose on suction side and triple checked suction screen + seals multiple times. when running the pump outlet line feels like its pulsating and my pressure gauge needle bounces. all my transmission vents are clear and venting correctly. my vaccum pressure should not be between -3 to -5 psi, i have -5 psi vacucum on suction side of pump currently. i need advice on where to go with this, any opinons is apprectiated!
What kind of oil are using in the bevel case. Did you make sure there was nothing on the way to the pump that could cause it to cavitate. Are the pumps OEM or aftermarket? Does the bottom of your torque convertor have the suction screen in it behind a plate? Was it cleaned out. Not sure if you have the tiny pump in the bottom of the torque that larger units have. Your rebuilt pump could be no good, have seen before. Maybe your charge pump is no good or is it part of the other pump. Do you have a hydraulic schematic of what is in there.? Simon C
hi simon thank you reply would love to bounce ideas off you. im using cheveron sae 30 w oil in transmission case and cheveron sae 10w oil in steering case. the power train pump is a suction style (sucks from bottom of transmission into main pump, gravity is not on my side in this situation) suction screen has been checked and cleaned multiple times finding little to nothing in screen and have replaced the orings on suction screen housing. this model does not have a charge pump/secondary pump in bottom of case to help feed the main pump unforuntly. this model does not have a torque converter. i agree with you the rebuilt pump could be no good but we have sent it out three times, first time we sent it out came back okay, still did same thing so we sent it out again to a different shop and it was bad so they rebuilt it and we got it again and did same thing. we sent it out once more and they said pump was good and actually walked me through proccess of bench testing and showed me all the specifications. it came out 95% efficent. but transmission oil is still aerated and something is cavitating the pump which will cause it to wear out prematurly. i do have the shop manual from komatsu and can read the hydraulic schematics. im at loss at what else could be causing this symtom. i know if it is cavitating it has to be caused by something in suction side of pump. which is pretty simple, transmission sump, transmission suction screen and transmission suction line, is there anything else you can see in schematic that i am missing ?
In my dozers operating manual it says to add 20% ( I'll have to recheck %) more oil to the transmission if operated on steep ground . Something that may have failed at any time took that time to fail but the aerated oil and the steep ground point to low oil level . I don't know about your dozer but mine have one pump of the brakes after a motor stall or a dry pump . It has to be held and held hard while the brake lock is applied .
Agree about on steep ground having more oil in sump. Simon C
So straight 30 oil is extremely hard to suck in colder weather, will cause a pump to cavitate. So you live close to Maple Ridge and warmer than here but still very cold for that grade of oil. Wonder how it would work with 10 weight in it. I know 10 weight does not like heat like 30 weight. Put machine under tarp and frost fighter for 2 hours before use and maybe different machine if you want to stay at 30 weight. Have not worked on that vintage of that machine. Simon C