MF-85 Hyd help needed.

[Torpex]

Hi,
So I started by splitting the tractor, Rebuilding the PTO clutch, cleaning and rebuilding the the PTO HYD control Valve. Reassembled the Tractor But still had Low Pressure. I removed the switch and Installed a Gage. Its Only reading 145 without PTO Engaged, and with PTO engaged its reading 140.

I removed the Steer Pump, cleaned the screen (it wasnt clogged) and did an "air pressure" test of the system to check the lines. No leaks at the lines, but where the PTO Pressure relief dumps, there was air leaks out the PTO dump-Relief valve end.

Split the tractor, and removed the dump valve but didnt find anything. I used air again and it leaks out that "dump port" inside the cavity where the PWR Steer Pump is.

This little spool like valve confuses me though, it looks like they machined a flat spot on the small spool. This is where the air is leaking by I figure?? Why???

So I reassembled and checked the adjustment of the dump valve forks.

Next I removed the Relief valve, as I found posts stating that a .15 shim would boost pressure. I added a .60 shim and it did boost a tiny bit but not much. 3-4psi Id Like toi see pressure up around 200-245 so the clutch doesnt slip.

I worked on some of the most Complex Submarine Hydraulic systems while in the Navy and this system makes no sense to me. LOL

Any experts out there that can lend some insight? Is the steering control valve leaking by??

I apreciate any wisdom anyone could bless me with ))
Frank

 

[John Deere D]

Info from Archives:

Info posted by Dieseltech some time ago...

The PTO is fed by the power steering return and has a pressurizing valve in the front trans cover maintains just under
200 PSI if I recall. That pressure can be checked where the red dash light pressure switch is in the PTO supply/power
steering return line. The power steering relief valve is in the front of the trans cover, and a split is needed to
access it.

I WOULD have found this useful info 40 years ago as I my parents owned a MF 88...

Bob..

 

[Torpex]

Hi,
Thank You. I saw that post, been searching for a couple weeks now. LOL

That "pressurizing valve" is in the service manual ID as a Relief Valve. Thats the Valve I added the shim to and No significant Pressure change took place.

I did as the Manual suggests, and checked the output Pressure of the Pump and its at 1300PSI @ 1000 rpm. The Manual says run the engine at 2000rPM but I couldnt do everything myself so that pressure at that RPM tells me the Pump, filter, and suction screen are Good.

Im gonna split the tractor again (4th time) and explore that PTO Dump/relief valve. If it is a two purpose valve then maybe the relief spring is weak and its relieving at too low a pressure, or maybe the spool is not traveling in the valve body as far as it should.

I really dont understand whay that Dump valve has a Relief valve attached..If they are worried about overpressurization, they should have piped it into the return line, or installed a proper relief valve in the system.

 

[Dieseltech]

What JD D said, plus a question, how well does the power steering work? The left over return oil from the power steering is pressurized by the valve placed in the trans
front cover. If the pump is weak and there's little or no power steering that can explain your pressure loss. There's also a chance if steering is OK that the oil line
from the trans front cover that feeds to the trans/diff case joint has come out of the rear of the front cover. I've seen that happen before, line can be seen inside with
the power steering pump removed from the trans side. There's no O rings on it, just a given length it has to be so it's under slight tension when the trans input cover is
bolted in place.

 

[Dieseltech]

The dump valve was used so the PTO could be stopped with the clutch pedal pushed all the way down, similar to a two stage clutch like the smaller MF tractors have. I'd
eliminate it if it were mine. The LARGE relief valve IS the Power steering relief valve, NOT the PTO pressure controlling valve, that is in the front cover. Either that
valve is stuck, or that line I mentioned before has popped out of place. If I recall the trans front cover needs removed, and the PTO presurizing valve is NOT shown apart in the parts list photos.

 

[Torpex]

For lack of anything else Im using the MF terminology from the service manual.

All the Valves that see that "150-250Psi Oil Pressure are:

PTO Clutch Control Valve
PTO Dump Valve (Serves 2 purposesTO relief valve and control valve) from the book pg61 pgh 132
Power steering system relief valve
Steering Control Valve

That Dump Valve Isnt a simple spool valve, or Id remove it. There are two spools, and the smaller one is spring loaded. When you press the pedal all the way down, the larger spool is pulling against the snap ring that retains the smaller spool, and the small spool then dups all return pressure.

When you release the pedal to the "non dump" position/pedal up, that small spool is only held back/shut by a spring inside the larger spool. Im thinking MF calls it a relief valve because an over pressure in that return line could move the spool against that smaller spring, moving it forward-opening it to the dump position.

I did check those lines, I attached an airline at 145psi and no leaks from the lines in the transmission or the transaxel case
.
In my other post I mentioned ! checked the pump and even at Half the recommended engine RPM the pump put out over 1250PSI

The steering was ok, not super powerful. The PTO control valve was stuck in the open position and the PTO was separated inside as the collar that holds the spring against the PTO internal Piston had come off. This cause that pressure to drop to 50 when HOT, but even then the steering worked. I fixed all that and gained almost 100 psi.

What about the steering control valve? Can it cause a Low pressure? Its NOT mentioned in the MF service manual as a source of low pressure problems.

I attached a pressure gage to the HP line at the control valve, and when its attached to the control valve the pressure is only about 450psi. That Line when dead headed puts out over 1250psi or more so that drop tells me the fluid is blowing through that valve at a rate high enough to lower the Pumps head pressure from 1250 down to 400. That cant be right or is it?

Thanks foir your patience. ))

Frank

This post was edited by Torpex on 04/06/2022 at 07:57 pm.

 

[Dieseltech]

I don't think you have any steering valve trouble, but in the trans front cover area. I'd try adding some shims to the small spring in the dump valve assembly, and
DISABLE that assembly so the fork does not ever pull it out as you don't need it. If I recall on my Super 90 8 speed there is another 200 PSI valve in the front cover
that can only be seen with the cover removed from the trans case, but my memory is foggy and the parts list does not show the valve I'm thinking of that was only held in
place by a snap ring. The steering relief pressure won't blow unless the cylinder pistons are bottomed out at full left/right turn, and you should see that pressure OK
WITH the gage TEED in the line and full left/right turn is done. The steering pump has a relief valve built in it too, and you checked that with that line dead headed
with the gage. The steering relief valve in the clutch housing should be holding until about 1100 PSI before it blows open.

 

[Torpex]

(quoted from post at 04:12:25 04/07/22) I don't think you have any steering valve trouble, but in the trans front cover area. I'd try adding some shims to the small spring in the dump valve assembly, and
DISABLE that assembly so the fork does not ever pull it out as you don't need it. If I recall on my Super 90 8 speed there is another 200 PSI valve in the front cover
that can only be seen with the cover removed from the trans case, but my memory is foggy and the parts list does not show the valve I'm thinking of that was only held in
place by a snap ring. The steering relief pressure won't blow unless the cylinder pistons are bottomed out at full left/right turn, and you should see that pressure OK
WITH the gage TEED in the line and full left/right turn is done. The steering pump has a relief valve built in it too, and you checked that with that line dead headed
with the gage. The steering relief valve in the clutch housing should be holding until about 1100 PSI before it blows open.

Ok! Thank You,. You've Given me some more wood to chop here!

Ill split the tractor and work that relief/dump valve after checking the steering full right and full left. and see what pressure is at the steering control valve.

Inside the Bell Housing My 85 only has that large HEXagonal relief valve. that connects to the same steering pump output through a "T". One output of the T goes through the filter to the steering control valve (full pump pressure)and the other to that relief valve which the output is connected to the 150-250 line. I did add a shim to this relief valve but with the static pressure only around 400, I dont think adding a shim helps.

Thank You again!!

Frank

 

[Torpex]

I think I made some headway today. There was a weak spot from rubbing on the line from the Filter to the Steer control valve, the HP Line. After fixing that I put my gage setup inline again to observe what the pressure is when the steering is all the way left or right, also monitor the 150-250 line gage and see what it does.

When steer all the way left or right, both sides gave over 1100 PSI and The low pressure side dropped below 100.

So Dieseltech, what do you think the chances are that there's a problem in the steering control valve? The plungers and gaskets are no longer available, springs, shims and thrust bearings are though.

I also discovered using air pressure that that Relief valve thats part of the dump valve is dumping around 100psi, and after I shimmed it around 125psi. its a metal to metal spool no software, so air may be giving me a lower relief pressure. Still working this valve. Gonna try filling with oil and put air over oil to see what pressure I can get it to hold..trying for 200.

Frank

 

[Dieseltech]

Problem is not the steering control valve, but further down the line. I still suspect the trans front cover..

 

[Torpex]

(quoted from post at 16:01:27 04/07/22) Problem is not the steering control valve, but further down the line. I still suspect the trans front cover..

If you mean the HYD relief valve thats connected to a Hose, that valve got a 1,05 shim added with no improvement. It had a .60 shim and a ,21 shim. I tried it with all the shims added and with just the 1,05 and the ,21 shim and the pressure remained @ 145psi.

Theres no other valves in that cover. The Dump/relief valve is assessable there but that's it.

 

[Dieseltech]

The hose relief valve is the high pressure relief for the power steering only, and if the steering works it's OK. On this open center system the return oil from the power
steering system does not just go back to the sump, but is FIRST raised to 200 PSI for the PTO circuit, and oil ONLY goes to sump after the 200 PSI is maintained. Since
pressure is caused by resistance to flow, there's a leak somewhere to the PTO circuit. If I recall on my Super 90 trans front cover with the eight speed trans which is
the same as 85/88 models the 200 PSI valve was in the cover on the back side held in place by a snap ring and NOT shown in the parts list break down. There could still be
pressure loss at the dump valve, and/or that S bent line that has popped out of the front cover bore. I have some 85/Super 90 parts tractors, but none are split to remove the front trans cover for parts inspection.

 

[Torpex]

(quoted from post at 04:14:18 04/08/22) The hose relief valve is the high pressure relief for the power steering only, and if the steering works it's OK. On this open center system the return oil from the power
steering system does not just go back to the sump, but is FIRST raised to 200 PSI for the PTO circuit, and oil ONLY goes to sump after the 200 PSI is maintained. Since
pressure is caused by resistance to flow, there's a leak somewhere to the PTO circuit. If I recall on my Super 90 trans front cover with the eight speed trans which is
the same as 85/88 models the 200 PSI valve was in the cover on the back side held in place by a snap ring and NOT shown in the parts list break down. There could still be
pressure loss at the dump valve, and/or that S bent line that has popped out of the front cover bore. I have some 85/Super 90 parts tractors, but none are split to remove the front trans cover for parts inspection.

Hmmm....the lines are tight, checked by 145psi air. Air compresses easier and therefore would find a leak easier than HYD fluid. So the lines are Good.
The HYD pump is removed, and the tractor is split so I can see both sides of that transmission cover, theres absolutely no other valve in the system anywhere.

I'll be removing the shim I put in that relief valve!

I definately understand what your saying now so the only valve that meets that criteria is the relief valve attached to the dump valve. Without any shimming, its dumping @ 120 PSI and thats without moving the pedal. With the dump valve locked in position, the relief end moves when pressure exceeds 120psi. So Id say thats the culprit, the leak in the system. I need to shim it so that it stays shut until 200psi...

The Dump Relief are in the PIC #52 is the relief/dump valve. If it was just a dump valve it wouldnt need that spring #55

 

[Torpex]

Under spring #55 I added 6 .37 shims progressively using air over hyd fluid test rig in the tractor itself since the outer body of this valve is pressed inside the casting.

The Pic is with the tractor halvs back together for an operational test of the system.

Hopefully with that pressure the PTO clutch wont slip!

 

[Dieseltech]

Thanks for the update, if the PTO clutch pack did not have that heavy spring inside for the brake a lower pressure would lock the clutch fine. I may have to do the same
thing on the MF 85 diesel I sold my brother awhile back, he has said the PTO was acting up last time he used it.

 

[Torpex]

Ya know, I kick myself now...I think I would have cut that spring some as I agree 100% that its way too Stiff.

I rather deal with a functional PTO that has a weak brake than a PTO with a Good Brake and No clutches.

Time will tell if the clutch mod I did will pay off. The Kit I got from AGCO came with 7 clutch discs. The Book only shows 6. I checked and double checked and they all fit and still allow the Piston top have over 3/8" travel, so there shouldnt be any drag. Also having a clutch on each end actually makes sense when you look how the clutch is made. Maybe its an upgrage?? LOL

Time will tell. .