ford 631 piston leak

rgvnaa

Member
Hello. I'm gone through the hydraulic
system 3 times already I have changed
all the orings and the system appears to
have pressure now there is no problem
with the lift it picks up fast and
strong. Although I'm still having a
problem with the leaking down and a
slight bobbing I took off the PTO plat
and put my phone in the belly. There
appears to be a major leak at the front
of the piston housing around the
unloading valve area. Is unloading valve
bad or is there a passage that is
connected to there and is leaking. Could
a bad relief valve be causing the major
leak at the front of the piston assembly
. I have included a picture of the leaks
noticed a large amount of fluid coming
out of the front of the Housing. I
believe this to be the problem as I
cannot see any other leaks or problems.
Any help would be appreciated.
a196079.jpg
 
Thanks for the replies. This picture was taken with the lift going up. Well i was thinking that the bobbing on the three point might be because of theses leaks. I'm only really concerned about the bobbing. If these leaks are considered somewhat normal, then were should I look for the bobbing. Could a faulty relief valve cause bobbing.
 
Another thing, could the fluid be to thin I'm using UTF 134 from TSC. Maby thicker oil will kill the smaller leaks.
 
If the picture is taken while the lift is going up then that is most likely your bobbing problem.
134 is the correct oil; do not try thicker oil to fix the problem
The relief valve works at way higher pressure that we are dealing with here. I do not suspect it.

The unload valve is most likely the problem.
Problem is Ford made 3 of them so you could choose what size you needed to get a very precise fit.
The unload valve needs to move freely with very little pressure but yet hold oil pressure.
There is also a bushing in there that the unload rides in.
If you have been in it several times and it still leaks I would think you would need to replace the bushing and valve as a set to get a good fit.
With that said I do not even think the parts are available anymore to do the job.

I worked on mine several times and never could get all the bobbing out of it.
I just got it as best as I could and live with it now.
 
RGVNAA, one more question.........how well/tight did the unloader valve plug (plug with annular ring cut into it) press into the housing?
 
Well it was not tight at all. It was
kinda lose. I had put a "close" size
oring but it felt to tight. Should it be
tight with the oring or lose. The
original oring just barely is bigger
than the oring groove. The picture is a
replacement oring that was as "close" as
I could get it to the original oring.
This is not the NH part oring. I went to
a hydraulics shop and matched it.
a196131.jpg
 
(quoted from post at 17:46:53 07/16/15) Well it was not tight at all. It was
kinda lose. I had put a "close" size
oring but it felt to tight. Should it be
tight with the oring or lose. The
original oring just barely is bigger
than the oring groove. The picture is a
replacement oring that was as "close" as
I could get it to the original oring.
This is not the NH part oring. I went to
a hydraulics shop and matched it.
a196131.jpg
ommunications problem. I was trying to ask about the plug that goes in after the unloader valve that you pictured. The plug being removed in this picture:

or at extreme right in this picture:

The reason for asking is that the annular ring in that plug carries the pressure of the ram cylinder, whether lifting/holding up a load/ or lowering. Since only metal to metal to seal that hydraulic pressure, a good fit is all important. A leak here would be revealed at "A" in your pictures.
 
That plug was tight. I did use the bolt
and washers method. I tapped it in flush
after I cleaned it.
 
(quoted from post at 20:21:53 07/16/15) That plug was tight. I did use the bolt
and washers method. I tapped it in flush
after I cleaned it.
K, just eliminating possibilities.
 

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