135 -- weak 3 point hydraulics

S854 · Feb 8, 2018

This past autumn I purchased my first ever tractor, a MF 135 Deluxe. It came with a snow plow mounted on the front.

My issue is with the 3 point lift. The arms drop "immediately" upon shut down of the engine (about 3-5 seconds)... When the engine is running I can push down on the arms and cause them to lower... they come right back up when I stop pushing down.

The front plow is hydraulically raised via a cylinder connected to the hydraulic lift cover (#3 in the photo has been replaced by the previous owner and has two lines running to a control valve for the plow). The front hydraulic works just dandy... (I can literally raise the front of the tractor with down pressure on the plow) ...which leads me to believe the hydraulic pump is working as it should.

I'm wondering what part of the hydraulic system I should begin my search for the gremlin that's causing the 3 point to have very little pressure.

Any ideas?

old · Feb 8, 2018

I don't know that tractor as such but to me it sounds like the 3 point lift cylinder has bad rings or a bad cylinder it self so you have a bad leak by in the lift cylinder

Brendon Warren · Feb 8, 2018

I'd start with the 0rings on the tube to the sump. #2 in
your picture. A few dollars for parts and only two external
bolts. It's worth a shot.

Dieseltech · Feb 8, 2018

Something is not plumbed right, there should be a way to EITHER use the three point OR the front blade, not both at the same time. Most use a two spool valve in place of the two bolt lift cover cap, the left spool is used to switch between three point use or turn on the right spool for cylinder use. The left spool handle is locked back for three point use, and centered for the right spool to operate the cylinder, WITH the DRAFT lever fully up to keep the three point pump on. Otherwise the draft lever is kept lower on the quadrant. Remember when the three point is fully raised the internal linkage turns the pump back off. That's why for cylinder use the draft lever is used to override the linkage to keep the pump on.

S854 · Feb 8, 2018

One thing I didn't mention...

When I first start the engine, the 3 point begins to rise... but until the 3 point is all the way up the front cylinder doesn't respond...

It's like the hydraulic fluid needs to fill the 3 point cylinder first [b:da67afd89f][i:da67afd89f]then[/i:da67afd89f][/b:da67afd89f] flow on to the front cylinder...

I'll check the draft position when I get back outside... I have toyed with it a bit but I really don't know what I'm doing...

My position control has a "constant pumping" position for use with auxillary items... is that possibly in place of the spool valve you refer to?

Dieseltech · Feb 8, 2018

Yes, use the constant pumping for the cylinder valve use. One way to fix it correctly is to place a shut off valve in the supply line to the blade lift valve. Turn the shut off valve ON for blade use, and OFF for three point use. Neighbor had his 165 set up like that years ago to operate his cylinder valve, using the three point pump. When using three point only DO NOT place the lever in constant pumping, or pump may be damaged..

S854 · Feb 9, 2018

(quoted from post at 18:18:49 02/08/18) One way to fix it correctly is to place a shut off valve in the supply line to the blade lift valve. Turn the shut off valve ON for blade use, and OFF for three point use.

If I'm understanding this correctly... the spool valve I'm using for the front cylinder may have a return line which is "open" when the lever is in the neutral position... the return line prevents full pressure from building in the 3 point cylinder... causing the weak 3 point performance?

A shut off valve inline before the front spool valve would divert pressure to the rear...

I hadn't approached my issue from this angle...

Dieseltech · Feb 9, 2018

Yup, now you got it..

S854 · Feb 9, 2018

(quoted from post at 10:31:44 02/09/18) Yup, now you got it..

I guess the $60,000 question is...

Which line is the pressure line and which is the return? I could just remove both, start the engine and look for which one fountains out... :shock:

Or...

Maybe it doesn't matter which I plug... put the shut-off valve in the most convenient spot?

Dieseltech · Feb 9, 2018

The oil shut off valve needs to be in the oil SUPPLY line to the blade valve, not the return. A photo of what you have now would really help. Most MF lift covers have a 3/8 inch pipe plug on each front side for supply, and a return plug in the left side just ahead of the left lift arm. The two bolt transfer cap is seldom used for hose connections, though it is possible.

S854 · Feb 12, 2018

Just tried a brief experiment after plowing the snow this morning...

I raised the front cylinder to maximum lift which caused a squeal from the relief valve inside the tractor then returned the actuator valve to it's neutral position... I pushed down on the 3 pt arm (which caused it to start down) then pulled up on the actuator valve as if to raise the front cylinder.... the 3 pt immediately began to raise rapidly and forcefully...

Dieseltech... you're a cyber-genius!

Here's a photo or three showing the current set-up...
The top two pics are the same except for the colored arrows added for clarity...

My guess is the line from the red arrow to the white is the supply line.. the yellow to green is return and the blue are work ports... the top blue port runs to the top of the front cylinder (lower blue to lower front)...

So... what's next?

S854 · Feb 12, 2018

...another thing just occurred to me...

My OEM transfer plate has been replaced with something... a "diverter plate" for lack of a better term? It was installed to divert the flow of oil to an outside accessory rather than keeping the oil flowing inside the confines of the tractor rear end.

If I install a shut off valve in the supply line where will the oil flow from the pump go? It could be there's no connection between the two ports of the diverter plate ... any oil flowing through the diverter [b:04b5785ece][i:04b5785ece]must[/i:04b5785ece][/b:04b5785ece] exit the tractor in this case...

I found a 3 way valve on Amazon that could solve this issue... if it is an issue... the 3 way valve hooked between the two ports of the diverter with the third leg heading over to the spool valve... I'd need to install a check valve in the return line from the spool valve...

Dang... I'm probably making this way more complicated than it needs to be...

Dieseltech · Feb 12, 2018

You have it backwards, the GREEN arrow is the supply line TO the valve, THAT'S the line where the on-off valve should be. Red line is the return from the valve. With a shutoff valve you can choose to shut off the blade lift cylinder valve for three point use. With the valve on, place the position in constant pumping, block the lift arms up so they won't settle. When the arms DO settle they must lift full up BEFORE the blade will lift, killing time..

135 -- weak 3 point hydraulics

S854

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old

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Dieseltech

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