MF 35 lift arms won't lower

[Farmer Scott]

1959 MF 35 with 2 spool valve with levers in front of the seat.

As soon as I start the tractor the lift arms go all the way up and the pump continues to try and lift further.

I bought this tractor a month ago and the previous owner used the left lever on the 2 spool control valve in front of the seat to lift and lower the 3 point hitch. The quadrant position and draft levers did not work. I thought it might just be the linkage for the quadrant levers being to the rear of the roller on the vertical control valve lever. But as the top link spring had much play and the boot was dried out and cracked we decided to remove the lift cover and replace the spring, and rubber boot along with a new nut as the entire spring assembly needed be serviced and adjusted as per the Service Manual. We manufactured a wrench for the nut.

We set the position and draft levers on the underside of the cover to the correct 3 pound setting and also set the eccentric roller against the position lever as per the Service Manual. We drained all the old fluid and replaced the filter and bottom O-ring under the strainer. We also decided to remove the 2 spool valve control in front of the seat and replace it with a brand new cover plate since that 2 spool valve was leaking fluid when used. We replaced the O-rings on the stand pipe and put a new one on the new cover plate.

We lowered the lift cover with a chain hoist making sure the Position and Draft levers were in front of the roller of the vertical control valve lever. The standpipe was put in the correctly and the we bolted the cover down without a gasket or sealer just to make sure everything worked correctly. We added new hydraulic fluid to just below the bottom bolt hole on the dip stick cover.

With the dipstick cover off we started the tractor. I made sure the position control quadrant lever was at the lower end of the control range. Right at where the draft response range starts. I made sure the draft was set at the sector position between the little dots on the quadrant.

The lift arms immediately lifted upon starting the engine and the pump continued to try and lift further. It doesn't matter where we move the quadrant levers. Nothing happens. Evidently the hydraulic fluid is being pumped into the standpipe as the lift piston is working.


One thing I recall when we tried the 2 spool valve levers prior to all this lift cover removal was that when we locked the left lever in front of the seat all the way back the pump continued to try and lift the arms further. The pressure caused fluid to leak out by the valve levers in front of the seat. This was one of the reasons we wanted to replace this 2 spool valve with just a cover plate. This was not suppose to happen as we were told that if locking the left lever back that we could use the quadrant levers to raise the lift. But the quadrant levers were not working.

I'm guessing there was a problem with the control valve or something at that time when locking the left lever back did not allow the quadrant levers to work.

What should I do next to troubleshoot this issue? Control valve replacement? I read something about an oscillator but have no idea where to look or how to check this.

Thanks

Scott

 

[Farmer Scott]

Found the problem after checking the rod coming from the control valve that pushes against the valve lever assembly. The rod was not moving freely. The control valve was stuck in the lift position. Makes sense now.

So after removing the entire pump and taking it apart it was clear that everything needed to be cleaned and some new parts ordered. The pin attaching the oscillator to the cam follower was missing. Without that part the oscillator was useless and the reason the control valve wasn't working.

It appears that whoever had it apart previous either left out the pin or forgot to put it in as we could not find anything in the bottom of the casing. Thinking it may have broken off from a weak cotter pin as the cam follower had some apparent damage.

Waiting on some O-rings and a new control valve with sealing washers and a new cam follower pin. I'm not taking any chances on the old control valve as there is a bit of corrosion and I don't want it to stick again. The new one should do the trick.

Scott

 

[shaeff]

Glad you got it figured out, Scott. I was going to suggest you check the control valve, or the control valve nut (if it's too tight the lift arms will go up immediately when the tractor is started and stay up- often times popping the relief valve)

I just got done rebuilding my hydraulic pump, it's a pretty easy design. I put new pistons, rings, cylinders, etc.. all in it. If you go that far, it's easiest to assemble the pump upside down. Don't make the same mistake I did! I assembled the pump upside down, but put the cylinders "right side up"- which of course when I put the pump right side up the cylinders were upside down! OOPS! I ended up replacing all the o-rings again and swapping it around, it's been good since then and everything works great.

Definitely replace the control valve and the washers/o-rings that go inside. It's cheap insurance that everything will work better.

Lastly, if I remember correctly, you need to install the right side dowel pin (that holds the pump in the bottom of the case) first. I just snugged it up a touch, then put the left one in. I had it snug enough that hydraulic oil would hardly seep out. I started the tractor like this, then loosened them both just a touch and engaged the PTO (of course with the PTO shaft/seal in place to keep your oil in!). With the PTO spinning, it'll center the pump perfectly, snug up the right side, then the left.

If the pump is off center it'll knock when running (anytime tractor is running). That's the best way I found to prevent the knocking.

PS- check the control valve spring too. Mine was sitting in the bottom of the case in two pieces. My dealer couldn't get the flat washer like end piece that goes against the spring, then against the circlip, so I just filed down a small washer and put it in there. Without that, the spring pushes directly on the circlip.