640 hyd. problem

I've had the cover off the hyd. and taken out the bypass valve polished and cleaned inside and out hyd. work great for a while let it set for a month or so and the system won't work I've done this 5 times am I missing something or what. Please help

(quoted from post at 11:48:01 03/27/15) I've had the cover off the hyd. and taken out the bypass valve polished and cleaned inside and out hyd. work great for a while let it set for a month or so and the system won't work I've done this 5 times am I missing something or what. Please help

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here is no valve called a 'bypass valve' on a 640, so let me take the liberty of assuming that you mean 'unloader valve'. If correct on that, then if you have an unloader with a rubber like o-ring (not the steel ring), then be sure it is the correct ring. Safest to get that one from CNH unless you are an o-ring expert. Otherwise, what is condition of fluid? Any water contamination?

Are you checking the pump prime every time it won't work? Make sure you don't have a blown seal in that pump. Do you have a piston pump or a vane pump?

I'm sorry it is the unloading valve and the fluid is new [synthetic] no water and pump has good flow no air the o-ring is original no damage thanks for the advice I'll have to check with NH dealer I think one is about an hour away.

I have had a few off of various Fords the un-loader must work free... The o-ring fit is just enough the valve should not fall out and takes very little pressure to move it...

The one I fixed last week was the first hundred series I had been into I noticed one end of the un-loader is open... I am going to post a few pix of this from a assy I had in my parts stash... On this one the valve was stuck all the way to the open end I took a tool and tapped on it, it freed up and worked as it should. I took it apart all looked good... I told JMOR I used a -113 o-ring but my notes showed otherwise so I needed to back what I told him up anyways...

un-loader tip painted yollow extended out... as I found it and as I found the other I worked on





I put my elcheapo pocket magnet on it




It takes little pressure/pull to push it in and pull it back out the valve moves 7/8" BTW I replaced the o-ring that did not need replacing I used a -114. Having worked on a few and had a few that worked no new o-ring needed I have developed the feel for it... I did have to try a 3/4 -114 orings to get it like I wanted... The valve O.D. is .802 with the o-ring installed the O-ring installed OD. is .803 that's 1 thousands over the valve O.D. and were you should be I would say 1 to 2 tho thats it...

All the way in


I don't have the angle of the dangle just right in this pix I think one could remove the PTO cover and move the un-loader for diagnostics I am not sure were it should be at a given command..
I did not load the pix

I did tell JMOR I have never seen it posted if it was I missed it you can manually move the position control valve thru the oil fill hole to eliminate a bunch of chit...





I am learning as I go I need my hands on it to figger it out... Y'all know the hard way :x
I am not recommending you use a -114 altho that's what a 10 cent CNH o-ring is but only $5 what a deal... Its not about the price I want there employees to enjoy a good life its about my learning the hard way... I get to deal with allot of o-rings I need to know a little about them BUT a un'loader is a different animal pay up...

I'll be in NJ Saturday before Easter till Tuesday my son lives about 5 miles south of Great Adventure theme part at Cream Ridge if you are not far from there I would like to visit your shop..Thanks for the info.

(quoted from post at 17:45:01 03/28/15) I'll be in NJ Saturday before Easter till Tuesday my son lives about 5 miles south of Great Adventure theme part at Cream Ridge if you are not far from there I would like to visit your shop..Thanks for the info.

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You are welcome to stop buy bring plenty of cash

Its probably a bit out of you way I am in Sanford, NC

I was in Sanford when I was in the Marines back in the mid 60's flat country sorry about the mix up on states I'm in northern WV