Massey Ferguson 135 hydralic issue

Good evening

Wanted to put a question out and see if anyone can help. I have a 1967 massey ferguson 135. The 3 point hitch will lift a Bush hog or a scrape blade with no issues, but has trouble with a disc. It will come up but is slow and sometimes even has no problem at all. Could this be a dirty hydraulic filter or could the O rings on the stand pipe be the issue ? Any help would be much appreciated thanks

If the cylinder seals are leaking, or the stand pipe orings are blown, it will be slow and weak, but will also rapidly drop with the engine off.

You can open the side covers and look in with a flashlight. Put a heavy implement on, tell it to lift.

Some leakage from the cylinder is acceptable, but should not be streaming oil. The stand pipe should not leak at all. If the lower seal is blown you will see oil boiling up from below.

A bypassing relief valve will cause weak lifting. If there has been a history of water in the gear cases (very common on those) the spring may be rusted and the seat pitted.

With the load lifted, shut off the engine, look for oil boiling up from the side of the pump where the relief valve is located while the load is coming down.

Just be very careful, look but don't touch! Never reach in with it running!!!

If the lift is slow and jerky, there is a pump problem.

The pump is rebuildable, but easier to replace. The repair parts don't always fit, and you are dealing with some precision fits. Unless you have access to the necessary machining equipment to make adjustments, a rebuilt will save much frustration!

There have been many changes to the pump and lift cylinder. Shop carefully, be sure you are ordering the correct parts. Best to open it up and take measurements and compare parts than to depend on serial numbers.

The top cover is heavy! A lift is much better than trying to manhandle it. The control linkage comes all the way down from the cover to the pump. It is fragile and complex, don't want to damage it! The bolt pattern is confusing, some come out, some stay in. Leave the wrong one in, and... Well, it gets real ugly, and expensive!

There is a boot on the draft control plunger. If the cover is off, now would be a good time to replace the boot. Not an easy job but a necessity. Without it water will get inside the case.

A shop manual in hand is a near must before taking on this job. It will more than pay for itself in mistakes not made.

Have fun! Ask questions, keep us posted!