641 3 point bobbing and drifting down.

Experts - know you have addressed this so ofter you are tired of it.
I have attempted to review other postings. But still have a questions.
Call me a slow learner, but would rather ask that do it wrong.

OK tractor has bobbed and drifted down for some time but am
going to address it now. I have removed the fill plug and watched
as I lifted the 3 point. Watch the dog bone cylinder rod bob and
drift down when shut off. But NO oil coming out of the cylinder.
Not even a drop. Can see the PTO shaft and no oil laying on it at all.
Oil looks good - no foam - no bubbles -no movement of oil in
bottom - no rust, and everything look good like you would want to
see inside a housing with oil in it. Have flipped from position to
draft and back to position and still the same. Also one arm loader
running off of same pump and control valve will hold up for a few
hours.

So I am assuming (may be wrong on my part) that it may be the
unload valve. Help me out here if I should be looking at something
other than Unload valve.

Ok to get to it - need to remove top cover. (Does the accessory
plate need to come off first?)

Really do not want to touch any more then I have to - but also want
to do it right. While I am in there what else should I replace/review?
Know that I should look at the control lever pin that wears.

Will replace top cover gaskets, and will replace orings in accessory
plate although those have been replace recently.

In pulling that unload valve it looks like you must force pull the
unload plug. (see picture below) (know that is a 3000 picture, but
can I use washers and a bolt to pull mine?)

My manual does not really tell you HOW to reinstall that plug.
Assuming it has to be pressed or hammered back in but my manual
only says reinstall with threads out. DO I JUST TAP it in till it
bottoms out?

Unloading valve will have nothing to do with lift leaking down after shut off of engine. The green path is what must hold pressure in order that the lift not leak down.

OK, now what could it be, and how do I find it.

Seeing no oil from cylinder - so assuming that o-ring is good.

Ram cylinder safety valve
Check valve
Control valve - but see no o-ring there

Assuming I really need to try to locate leak before I remove top
cover.

Could it be o-ring on access plate?

Should I be looking some place else to see oil leaking from ram
cylinder safety valve, check valve or control valve?

JMOR - Thanks for your reply's - So at this point I think I am going
to remove the Accessory Plate and replace all of those o-rings with
new Ford New Holland o-rings. While I am at the dealer planning
on picking up a safety relief valve, unless price is out of line. (If
price way out - think the safety valve is $35 on line so may go with
that.) From what I am seeing - - the safety valve comes out of the
top (under accessory plate) with a deep well socket. So that seems
to be good simple place to start. And right or wrong it sound like
that valve can cause my symptoms.

I also have a high pressure gage -
and since I have a remote valve.
Think I will try to get the valve plumed to a quick connector and try
to test the pump pressure. Before I go any deeper into the inside of
the unit if the above does not solve my problem.

I have been doing a lot of internet reading - - some place I think I read that pump pressure
or pump pumping air could
cause my symptoms - - don't think that is the problem since the
one arm loader seems to work and stay up - - but once I get the
gage plumbed it should be a easy test and we will at least have that
ruled out.

Guess I just have to work my way through it one step at a time. Was
sure it was just going to be the seal around the lift piston - so now
that it is not showing any leakage guess I go from here. I was really
surprised and happy with how good the inside of the hydraulic
assembly looked while peeking through the fill port.

I would not recommend replacing the safety valve (or the relief valve) with an aftermarket valve.

Bite the bullet for a CNH valve or leave well enough alone.

BTDT

Dean

OK on the CNH - but the way you said "or leave well enough alone" - it sound like you may be think the safety valve is not the solution. Is there something else you would suggest I do first?

I doubt that your problem is caused by the safety valve but you might want to verify that it is tight and that the copper washer beneath it and the lift cover is in good condition.

I did not read all of the earlier posts but you might want to look at the check valve.

Dean

Dean - thanks for your suggestion - that is what I need because this is my first lift cover.

Question or two -

Looks like check valve is way up front. Is there anyway to view it's leakage before I disassemble?

Or do I just have to bit the bullet and disassemble and remove that one to check it's look, function, and replace o-rings in it. What is the most likely issue there gummed-up, wear, broken spring, or just o-ring. Just trying to insure I have a idea of what to really look for there. ((((And yes, I see that little check valve ball which I will try not to lose))))

(quoted from post at 08:28:51 09/25/14) Dean - thanks for your suggestion - that is what I need because this is my first lift cover.

Question or two -

Looks like check valve is way up front. Is there anyway to view it's leakage before I disassemble?

Or do I just have to bit the bullet and disassemble and remove that one to check it's look, function, and replace o-rings in it. What is the most likely issue there gummed-up, wear, broken spring, or just o-ring. Just trying to insure I have a idea of what to really look for there. ((((And yes, I see that little check valve ball which I will try not to lose))))

Click to expand...

ow bad is the situation? How long to leak down , engine off, load on lift? Frequency of bobbing?
IF check valve, it could be trash between ball & seat or a scored ball (some of these were plastic) or seat, broken spring or the o-ring on the seat assy (difficult to view, replace, and metal seat often broken trying to remove).
Picture ('stolen' from unknown person) indicates potential leak paths. One caution is that I would be weary of the left (back-pressure) side of picture, as I think it is not correct & I show that also.

Sorry to be doing this wrong... but I can not figure out how to ask a question here at YT. I saw this thread, and it is related, so best I could do. I have a 600 series, was working fine, mowing, stopped engine to get a drink and move stuff. Got back to it, lift wouldn't lift!! I've had 2 "tractor guys" look at it, neither apparently knew anything about old Fords. I'd order a manual, but will that give me any help as how to trouble shoot? Thank you! And sorry to come in "backdoor" this way. I need to get the old girl working again! Been sitting for months. The one guy did give me another pump to try, but what I've read makes me think it is one of the valves. (safety, unload,etc) something I read said I could get to one thru the inspection plate(dip stick side) but now I can't find that specific blog again. :-(

JMOR - Thanks for the picture much better detail than in my
manual. And yes, sure looks like he has a few too many
components in the picture. Hope he did not put it together that
way. I will kept track of how my components come out and make
sure they go back in the correct order.