Hydraulic overpressure???? HELP

[jcriddl]

I have a NH L785 and it began leaking from the rear pump but everything moves fine. The rear pump runs the left side and when the left side is move forward or backward the pump blows oil past the seals. I have replaced the seals and it still blows past the seals. Do i have an overpressure? I am getting frustrated and need the machine badly. Any suggestions? Maybe the pressure valves are bad?

 

[Tazza]

Did you replace this seal with a genuine one? or did you just get one from a seal shop that assured you it was the same? For the charge pressure that these have against them, seals are not seals, they MUST be exact.
When you replaced it, was the shaft worn? if there is a grove worn in the shaf, it could be the cause of oil leaking past, you may need a speedy sleeve for a nice surface for the seal to seal against.
Just a thought.

 

[jcriddl]

Did you replace this seal with a genuine one? or did you just get one from a seal shop that assured you it was the same? For the charge pressure that these have against them, seals are not seals, they MUST be exact.
When you replaced it, was the shaft worn? if there is a grove worn in the shaf, it could be the cause of oil leaking past, you may need a speedy sleeve for a nice surface for the seal to seal against.
Just a thought.

there was no wear and i did use a factory New Holland Seal. I just got done rebuilddig the pressure relief valves and they both had grooves in the seats. Would this cause them to stick? The more I investigate the more I become confused about why the pressure builds in the pump instead of blowing by the relief valves.

 

[Tazza]

there was no wear and i did use a factory New Holland Seal. I just got done rebuilddig the pressure relief valves and they both had grooves in the seats. Would this cause them to stick? The more I investigate the more I become confused about why the pressure builds in the pump instead of blowing by the relief valves.

It shouldn't have that much pressure on the shaft, they are designed to have at most, 200PSI on the seal, this is regulated with the charge relief, which is genearlly 120PSI or around that mark. With an OWM seal, it should be spot on, could the housing be worn or cracked around the seal? or it it leaking out along the shaft? I know some housings can be worn and prevent the outside of the seal from sealing against it.
Has it only just started doing this? or did you buy the machine with the leak already?
Marks on the seats for the relief shouldn't matter, it may let oil by-pass a little, but shouldn't stick. You could always check your charge pressure by putting a gauge in the line. There should be a pressure sender somewhere around the filter, not too sure on a NH though. If you remove it and add the gauge, see what you are getting.
Ken knows his NH machines, i'm sure he will throw his 2c in.

 

[Earthwerks Unlimited]

It shouldn't have that much pressure on the shaft, they are designed to have at most, 200PSI on the seal, this is regulated with the charge relief, which is genearlly 120PSI or around that mark. With an OWM seal, it should be spot on, could the housing be worn or cracked around the seal? or it it leaking out along the shaft? I know some housings can be worn and prevent the outside of the seal from sealing against it.
Has it only just started doing this? or did you buy the machine with the leak already?
Marks on the seats for the relief shouldn't matter, it may let oil by-pass a little, but shouldn't stick. You could always check your charge pressure by putting a gauge in the line. There should be a pressure sender somewhere around the filter, not too sure on a NH though. If you remove it and add the gauge, see what you are getting.
Ken knows his NH machines, i'm sure he will throw his 2c in.

It happened to me once but for two differnet reasons:
my backhoe: after rebuilding the entire system I switched two hoses which blew the seal.
big trencher: hit a big chunk of concrete under full power and the relief didn't react quick enough.
In either case the $15 seal was the cheap part--$90 for hydraulic fluid is what hurt.

 

[robbp]

Go to page 2 of the posts and look at the post "L785 Hyd Pump Seal Leak" I had the same problem and received some good information on making the repair. robb