MF 35 lift arms loosing pressure

[john in the highlands]

A number of years ago, my hydraulic pump ground-up some metal "object" and it got pushed thru the hydraulic system and scored the lift cylinder and pistons along with most of the parts in the pump. I replaced the pump, lift cylinder and piston along with the piston rings. Cleaned out the hydraulic cavity and installed new fluid. I had taken off my front loader to replace it's seals so I started using the tractor without the loader and replaced the Ferguson double spool hydraulic control valve with a hydraulic cover cap. I was only cutting my fields with it at that time while I worked on rebuilding the MF 32 loader. Years passed by before the loader was reinstalled. The loader works fine and maintains it's position weather the tractor is running or not. The lift cylinder for the 3 point hitch however does not. It falls slowing weather the tractor is running or not. I removed the hydraulic cover a found the lift cylinder and it's corresponding piston and rings in excellent condition! Except for the fact to and the gaps in the piston rings were lined up. Correcting this problem only made a little difference. I did notice more dirt inside the hydraulic reservoir than I would have expected since I change the fluid yearly and the boots over the transmission shifters are also new and intact. The pump hasn't been running smoothly. I'm thinking the hydraulic valve seat might have some dirt on them, causing a rough movement of the hydraulics. Restoring the hydraulic control to the hydra-lever and the draft control lever by locking the external control lever in the intake position, both levers work as they should. The corresponding springs are set to 3 pounds pressure. However the lift arms still slowly loose pressure weather the tractor is running or not! All the seals in the double spool control valves have also been replaced! Standpipe o-rings and back-up washers are also new. So what am I missing, that's causing the loss in the lift arm pressure? Could the new looking rockshaft cylinder and piston not be snug enough? I still haven't addressed the rough pump flow issue. I'm getting tired taking off the hydraulic cover. I'm not getting any younger!

 

[DavidP,South Wales]

Hello John, what a posting!!!! I drank a cup of tea whilst reading it! Ok, if your adjustments are correct and let’s assume that you Han a significant internal leak the 3-point would fall but the change in ‘balance’ between the quadrant lever, the control valve and the 3-point linkage position would send a message to the control valve to open up and return the 3-point to it’s selected position. You do not have this. I believe that your problem is due to the control valve being adjusted so that it is slightly in the discharge position when it should be squarely in the ‘neutral’ position. This would account for the loss of lift pressure and the linkage falling.
I would suggest that you tighten the 1/4unf nut on the rear of the pump 1/4 turn at a time and see if this improves the problem. Doing this will move the control valve more into the ‘neutral’ position. Let us know how you get on.
DavidP,South Wales

 

[DavidP, South Wales]

Hello again, delete the instruction about tightening the nut. I've just drawn a sketch to check the adjustment direction and you have to SLACKEN the nut 1/4 turn at a time. It is confusing because the 35/65 work in the opposite direction to the 100 series. DavidP

 

[john in the highlands]

Thanks David, for getting back so soon to me! You gave me hope to get back at it. So I did try making the 1/4 at a time adjustment like you suggested. There was no noticeable change. However, while waiting for the time to pass so I could determine if there was any change with my last adjustment, I detected fluid dripping, at a rate of 8 drops per 30 seconds, with not much weight on the lift arms. Even with a mirror it wasn't possible to see where. Naturally, with the engine off I put my hand in and found the open end of the rockshaft cylinder, having some space below it and being good a diverting drips from their source using thick plastic. I discover that indeed the rockshaft cylinder was allowing fluid to pass by it's piston. Should the inside of the rockshaft cylinder be perfectly polished? As I recall, mine showed machining markings in a overlapping pattern. Looks like I'll have to haul off my hydraulic cover again.

 

[DavidP,South Wales]

Hi, sorry for the confusing answer. Your leaking cylinder may be contributory to the problem but I don’t think it’s the sole cause. With any load on the 3-point linkage is there ever any sign of it going back up once it has gone down a little? Have you checked to make sure that there is no cross-over leakage between the internal and external settings on the divertor valve, and that the selector is moving fully?
DavidP

 

[john in the highlands]

Thanks again David! I caught on to what you were saying after I sent my last email. That the system, if working properly should try to make up the lost fluid. I got distracted by the leak and didn't carry on with the 1/4 turn adjustments with the tractor running. My understanding is that the position control lever and the draft control levers in their respective neutral positions externally, should be just touching the pump control valve internally. This amount of touching is adjusted by the locknut on the rear of the pump, where you want me to make the 1/4 turn adjustments. As for the external double spool hydraulic control valve ("the diverter" valve that you refer to), I believe it can only have cross-over leakage where it attaches to the hydraulic cover, if the three o-rings are not doing their job. I have managed to stop any leaking out from underneath the external double spool valve, but am not sure about between the o-ring "sealed passages". One passage leads to the rockshaft cylinder, and gets it's fluid when the left lever of the double spool valve is pulled back (intake position), two of them are returns to the hydraulic reservoir. The loader gets its fluid from the external back port of the right side of the double spool control valve. I know that when the standpipe comes up into the double spool valve with fluid and both the double spool valve levers are in their neutral position (center), that the fluid leaves thru the bottom of the double spool valve thru the most forward return passage to the hydraulic reservoir. One can only use one lever at a time. Can this location be the source of cross-over leakage? I don't think the double spool valve splits in half to see what happens at that intersection. I'm not sure what the selector moving fully means. There is no divertor "switch" in this external double spool hydraulic control valve. To restore the use of the draft control lever (and the position control lever), the left lever of the external double spool hydraulic control valve has to be locked in it's rear (intake) position. The front loader can only stay where it is when this happens. Sorry for the length of my reply. I'm trying to give you and whoever reads this the best picture of the situation that I'm facing.

 

[john in the highlands]

Some good news today. However, only with the restoring the hydraulic control to the hydra-lever and the draft control lever by locking the left sidelever of the external double spool control valve, in the intake position (back) and while the engine is running, that the 3 point hitch arms, with moderate weight attached, maintain their position. Looks like, I have that locknut, at the back end of the pump, finally, adjusted properly, to compensate for my "leaking" lift cylinder. Thanks for that David! The bad news is that I'll have to take apart my external double spool control valve to see if it can be fixed. It looks like two screws on the top, keep a top and bottom half together. I'll have to remove the springs on the levers first, to avoid an explosion of parts! Then the other bad news is replacing the rockshaft cylinder, piston and piston rings with ones that are machined to better standards than the ones I have...Then of course, whether or not, I take my hydraulic pump apart, to see why it's not running smoothly. Winter is approaching and I don't have a heated workspace!

 

[john in the highlands]

Locking the external double spool control valve (directing hydraulic control to the position control and draft control levers), in the FULLY open position, allowed the 3 point hitch arms to maintain it's position when the tractor was running. Changing the lift cylinder and it's piston allowed the arms to stay up when the tractor wasn't running. The new lift cylinder was 2.85" inside diameter, the less newer one was exactly 3" inside diameter ! Both pistons were the same outside diameter ! My hydraulic pump wasn't producing a even flow because it's pistons were scored. The filter wasn't snugged-up to the seal enough to block stuff from being sucked in, it still had it's lock wire, with it's lead seal on, as it came from the manufacturer ! I never had to clean it, so it was never touched!!! An expensive lesson learned. Always check someone else's work!!!