3-Point Hitch Ford 6640 3pt hitch problem

[Jackfr]

Anyone have any Ideas my 1991 6640SL won't lift its 3pt hitch it doesn't move at all. Was working fine then when I went to use it nothing. But all my live hydraulics pto power steering front load ect all work fine anyone have any ideas

 

[Soundguy]

Have any selector valves on that thing.. or perhaps draft control that my be on instead of position control?

soundguy

 

[RickB]

Anyone have any Ideas my 1991 6640SL won't lift its 3pt hitch it doesn't move at all. Was working fine then when I went to use it nothing. But all my live hydraulics pto power steering front load ect all work fine anyone have any ideas

You need to flow test the remotes. Your tractor has a dual pump system. The rear pump is the exclusive source for oil to the hitch. The engine driven pump supplies oil to the remotes. If there is no hitch demand, the oil from the rear pump is combined with the flow from the engine driven pump to supply the remotes. If you have no hitch and 8 GPM at the rear remotes at free flow, the rear pump is most likely at fault. There is a whole laundry list of tests and possible faults that should be examined prior to spending dollar one on parts.

 

[Jackfr]

Tried Selector in draft and position no difference unless there is an internal problem with the linkage. The external linkage all looks fine and it feels the same as always.
How could the pump be bad if it was working fine when I shut it down no problems with the hitch just wouldn't work when I started it the next morning?? How do I do a flow test without a flow meter, pump oil into buckets? Is there anything else I can test first? I have pressure guages.

Jack

 

[RickB]

Tried Selector in draft and position no difference unless there is an internal problem with the linkage. The external linkage all looks fine and it feels the same as always.
How could the pump be bad if it was working fine when I shut it down no problems with the hitch just wouldn't work when I started it the next morning?? How do I do a flow test without a flow meter, pump oil into buckets? Is there anything else I can test first? I have pressure guages.

Jack

I didn't say the pump was bad. I said 'most likely'. This hydraulic system is more complex than most. Troubleshooting hitch problems without a factory service manual and proper test equipment is probably not going to be successful. Not having the right stuff doesn't mean you can get by without it.
If the hitch isn't working, the flow from the rear pump isn't reaching the lift cylinder. It's a matter of figuring out why. If the tractor has a trailer brake valve, that is part of the flow chart.
You can use a bucket for a flow meter IF you can control the mess.

 

[Jackfr]

The PTO is working fine thats why I thought the internal pump should be ok doesn't the PTO clutch pack work hydraulically like my F5000? I have complete factory service and parts manual and some pressure guages I started reading section on hydraulics. I'm sure I'll figure it out I was just hoping there was some easy fast fix that someone knew. such as the fix to my hydraulics in my TC45DA when the plug loosened and came out of the return in the loader spool valve. Someone here told me where to look and it was fixed in 20 minutes. If you have any other ideas I would greatly appreciate them as I'm not really looking forward to getting into this. Do you know if Ill have to remove the cab to remove the hitch cover, if I have to rebuild the hitch piston or is there enough room to lift it and slide it out over the internal stuff. I know its heavy but that would save a lot of time.

 

[Soundguy]

The PTO is working fine thats why I thought the internal pump should be ok doesn't the PTO clutch pack work hydraulically like my F5000? .

I think rick said the rear pump was exclusively for the hitch.. while the other pump supplied the other things.. if that is so... then the pto pack is probably getting oil from the other pump.

Rick's a sharp cookie on these big fords and NH's.. he's helped many of us out here.

soundguy

 

[RickB]

The PTO is working fine thats why I thought the internal pump should be ok doesn't the PTO clutch pack work hydraulically like my F5000? I have complete factory service and parts manual and some pressure guages I started reading section on hydraulics. I'm sure I'll figure it out I was just hoping there was some easy fast fix that someone knew. such as the fix to my hydraulics in my TC45DA when the plug loosened and came out of the return in the loader spool valve. Someone here told me where to look and it was fixed in 20 minutes. If you have any other ideas I would greatly appreciate them as I'm not really looking forward to getting into this. Do you know if Ill have to remove the cab to remove the hitch cover, if I have to rebuild the hitch piston or is there enough room to lift it and slide it out over the internal stuff. I know its heavy but that would save a lot of time.

The PTO, Dual Power (if equipped), MFD clutch and difflock are supplied by a second section of the rear pump. If you have PTO, all that verifies is that the rear pump shafts are turning; no proof that the main section is pumping oil. Quick and easy fixes for these two pump systems are few and far between. You may need to isolate the flow from the rear pump. Unless the hitch lifts and settles under load, your piston seal is OK, although you may have to pull the hitch cover for other reasons. You should ber able to get the hitch cover out without pulling the cab.

It may have been me posting about the TC loader valve; I have mentioned that fix here a couple times. I don't have any magic cures this time, though.

 

[Jackfr]

Thanks Rick

Do you know if the plug on top of the pump for the trailer brake option is a pipe thread or oring type? The service book says if I use Fords adapters I can test pressure of main High pressure pump at this location with a 6000 psi pressure guage which I have. If pressure stays between 2550-2650 psi at 2100 rpm and then 1200 rpm then main pump is ok. Then next place to look probably is the Priority valve pack on top of the cover. My other option is to invest in a flow meter and try your original suggestion. Any other thoughts would be greatly appreciated.

Jack

This tractor has no Trailer brake option and no ASC Valve option (that I can find).

 

[RickB]

Thanks Rick

Do you know if the plug on top of the pump for the trailer brake option is a pipe thread or oring type? The service book says if I use Fords adapters I can test pressure of main High pressure pump at this location with a 6000 psi pressure guage which I have. If pressure stays between 2550-2650 psi at 2100 rpm and then 1200 rpm then main pump is ok. Then next place to look probably is the Priority valve pack on top of the cover. My other option is to invest in a flow meter and try your original suggestion. Any other thoughts would be greatly appreciated.

Jack

This tractor has no Trailer brake option and no ASC Valve option (that I can find).

NH's online parts deal indicates that all the external plugs on the pump cover are metric straight thread. Tapered pipe threads are pretty much non-existant on this tractor except for some of the housing drains. Good luck.

 

[Jackfr]

Thanks again Rick

I was able to get fittings at local Hydraulic hose repair you were right metric straight thread with an oring. Checked pressure of main pump at Test port (Trailer brake Port) it was only approx 50 psi couldn't really tell exactly on 5000psi guage, but when I operated the loader it jumped to 650 psi and when I dead headed the loader or any of the remotes it jumped to 2600 psi. I pulled the main relief valve to the right of the filter on the pump to check it but it is all one piece. Iit seems to be closed I tried forcing air thru it and it doesn't open. I seems that the Auxilary pump is working fine and the problem is with the main pump or a relief valve for the main pump. Could the priority valve pack be causing this problem? The other thing that puzzles me is why won't the hitch lift if I dead head a remote this is giving me 2600 at the test port on the pump?? Shouldn't it flow through to the hitch? That was one of the tests in the book that I tried and it doesn't lift the hitch. Any other ideas??

Jack

While Cleaning up I realized the approx 2 gals of hydraulic oil I lost while pulling the pressure relief valve appeared to be possibly burnt or extremely dirty and dark in color with some type of silvery film running through it.

 

[RickB]

Thanks again Rick

I was able to get fittings at local Hydraulic hose repair you were right metric straight thread with an oring. Checked pressure of main pump at Test port (Trailer brake Port) it was only approx 50 psi couldn't really tell exactly on 5000psi guage, but when I operated the loader it jumped to 650 psi and when I dead headed the loader or any of the remotes it jumped to 2600 psi. I pulled the main relief valve to the right of the filter on the pump to check it but it is all one piece. Iit seems to be closed I tried forcing air thru it and it doesn't open. I seems that the Auxilary pump is working fine and the problem is with the main pump or a relief valve for the main pump. Could the priority valve pack be causing this problem? The other thing that puzzles me is why won't the hitch lift if I dead head a remote this is giving me 2600 at the test port on the pump?? Shouldn't it flow through to the hitch? That was one of the tests in the book that I tried and it doesn't lift the hitch. Any other ideas??

Jack

While Cleaning up I realized the approx 2 gals of hydraulic oil I lost while pulling the pressure relief valve appeared to be possibly burnt or extremely dirty and dark in color with some type of silvery film running through it.

I am not a whiz on these systems; I deal with them when I have to, but it's not enough to get really good at it. From all you tell me now, I would shift the focus from the rear pump to the priority pack. Pull it off, disassemble it checking for stuck valving, scoring, and plugged screens. You MAY also be able to identify the port feeding the hitch valve and air test that with the priority pack off the tractor.

 

[Jackfr]

Thanks for the help Rick.

I have to work next two days so I won't get to that until Monday unless I get real ambitious Sat or Sunday Night

Jack

 

[Jackfr]

Hi Rick

I took out the Priority Pack as you advised and found the check valve spring in the remote valve feed line broken. I ordered a new spring and all orings to put it back together. I checked all the spool valves and they appear to be ok. I found no bad grooves or scratches on any of the spools or sockets. I'm planning on draining the oil and replacing the filters also. Is there anything else I should look at while I'm in this far? It took a while as it seemed everything was frozen. Parts should be here Thursday.

Thanks again

Jack

 

[RickB]

It may well be that you have found the problem. Let's hope so! The silverish residue in the oil makes me think you are loosing a hydraulic pump (aluminum), but until you have noticeable pressure or flow problems. I'd not be too concerned.

 

[Jackfr]

Should I see if I can get my hands on a flow meter (Probably have to buy one) to check the pump flow out or just wait until I put it back together to see what happens with pressure and whether hitch works?

 

[Soundguy]

I think I would at least button it up and see what happened.

Glad you found the problem in the PP. I had a similar hyd problem at a remote that was a casting defect and was not fixable.. .. err.. it was fixable by replacing parts!

soundugy

 

[RickB]

Should I see if I can get my hands on a flow meter (Probably have to buy one) to check the pump flow out or just wait until I put it back together to see what happens with pressure and whether hitch works?

At this point, I'd put it back together and see how it works. If you can get hitch function and some remote flow to either the rear remotes or the loader valve (if you have a separate loader valve) simultaneously, then you are getting flow from both pumps. Loader speed, for instance, should be about 1/2 as fast with the hitch moving as when it is not.

 

[redneckford]

Be sure you have not moved the ASC lever that is at the front right hand corner under the seat----just a little movement will cause the oil to be diverted to the remotes and cut off the oil to the hydraulic cylinder--- just like on the 5000--that black round knob on the right hand side of the lift top----there is a ball and spring that holds that valve in the selected place---when you start to shell a pump----particles get hung up in the valve and slowly cause the priority valve pack to stick one valve at the time!!! The long end of the lever should be pointing at about 3 o'clock--find the picture in Part 8 Chapter 2 page 47 of the 6640 service book---if it got move a little bit the lift will not lift!!!!!

 

[Jackfr]

No luck. I replaced the broken check valve spring in the remote valve feed line and all the orings on the priority valve. I checked all the spools and they all move freely and there appears to be no grooves or scratches in any of them. I was carefull to put everything back as the book instructed. The pressure came up to about 50 psi and the hitch still doesn't work. The draft control lever seems to work easier though. Deadheading the remotes or loader gives me about 2600 psi on the guage and still doesn't move the hitch. The guage is still connected to the test plug on the main pump (Trailer brake Port). I double checked for an ASC Valve and there is none only a plastic plug on the floor and a pressed in plug on the side of the case. Any other Ideas Rick?? I got prices for a pump that range from online $600 to $1800 from NH. Is there a way to isolate the pump and just check it?? Or do you think I need to get into the rear case? Do I need to order a flow meter or should the pressure guages be enough?