Stupid hydraulic machines!

CJONE · Oct 8, 2013

wdchyd said:
Your rotating groups (pistons, shoes, valve plates and barrels) are going into catastrophic failure

+1 1 pump runs 1 side of the machine the other runs the other side. The pump and both drive motors need to be inspected and repaired as required per side. The hoses on the high pressure side need to be cleaned at a minimum or replaced. You either do it right or you will never fix it. Both pumps and all 4 motors do not need to be repaired [unless everthing is shot] just the side that is giving you fits. The creeping is either a adjustment or zero is not set correct on the hystat. Your other functions run off of a gear pump and control valves in another location in the machine. Almost every hydrostatic system either has a suction filter or a medium pressure filter on the discharge side of the charge pump to keep crap from the reservior out of the high pressure loop. CJ

Cord · Oct 9, 2013

CJONE said:
+1 1 pump runs 1 side of the machine the other runs the other side. The pump and both drive motors need to be inspected and repaired as required per side. The hoses on the high pressure side need to be cleaned at a minimum or replaced. You either do it right or you will never fix it. Both pumps and all 4 motors do not need to be repaired [unless everthing is shot] just the side that is giving you fits. The creeping is either a adjustment or zero is not set correct on the hystat. Your other functions run off of a gear pump and control valves in another location in the machine. Almost every hydrostatic system either has a suction filter or a medium pressure filter on the discharge side of the charge pump to keep crap from the reservior out of the high pressure loop. CJ

That machine has a common reservoir. The debris will not stop at just a loop between the pump and motor but would be found throughout the entire system. Only one central filter. Looks like the return from the drive pump/motors is not filtered. That would explain why the filter is not catching the flakes. The charge pump is inside the drive pump. I don't see where the reservoir supply is connected to the drive pump, but the hard line connecting the two pumps is shown.

View attachment SL5635 & SL6635 Series II Parts Manual.pdf View attachment SL5635 & SL6635 Series II Parts Manual1.pdf

CJONE · Oct 9, 2013

Cord said:
That machine has a common reservoir. The debris will not stop at just a loop between the pump and motor but would be found throughout the entire system. Only one central filter. View attachment 340736

Really? According to your print and every correctly designed hydrostatic system the suction for the charge pump is filtered, so this means that the only dirt that can enter the system has to be generated by the HP side of the system or by the charge pump itself. Some systems have a filter on the discharge side of the charge pump but that allows the charge pump to be unprotected [read dumb] I have only seen 1 charge pump failure to where it blew particles into the system and that is because someone adjusted the chargepump relief to high not knowing what they were doing. So yes the debris will not cross contaminate 2 high pressure loops. The dirt, metal will find it's way into the low pressure system for the gear pump side. But hey what do I know! CJ

Cord · Oct 21, 2013

Well, heard from the dealer this morning; both lift cylinders have gone bad. Severely galled cylinders are the diagnosis. $900 to rebuild the pair of them. It's so expensive because they are replacing one rod, two pistons, two glands and both cylinders. Frankly, I don't know they are saving with that parts list! However, he says this is way cheaper than buying a replacement cylinder. Ironically, I just had a bucket cylinder rebuilt and they said that one was just as bad. I asked him if this was a sympathetic failure and he wasn't sure. At the end of the conversation, we agreed that he would continue with the diagnosis and see what else he can find...

aczlan · Oct 21, 2013

Cord said:
Well, heard from the dealer this morning; both lift cylinders have gone bad. Severely galled cylinders are the diagnosis. $900 to rebuild the pair of them. It's so expensive because they are replacing one rod, two pistons, two glands and both cylinders. Frankly, I don't know they are saving with that parts list! However, he says this is way cheaper than buying a replacement cylinder. Ironically, I just had a bucket cylinder rebuilt and they said that one was just as bad. I asked him if this was a sympathetic failure and he wasn't sure. At the end of the conversation, we agreed that he would continue with the diagnosis and see what else he can find...

Ouch, I might look at Surplus Center and see if you could find a set on there for less...

Aaron Z