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(Sorry for the orientation, can’t figure out how to rotate it)

Looks like the cap seam is leaking and a new seal would fix it. However, I have read elsewhere that in some cases a new cap was required to stop the leak. Further, whether I replace just the seal or the cap, can it be done with the pump installed on the mower? Any tips, tricks or advice is greatly appreciated.

That cap should been sealed with an O ring, so replacing the O ring should fix the issue. May have to top off the oil after replacement due to there may be a fair amount of oil loss unless you are really fast.

Highly recommend ordering the charge relief ball and spring since the 1/4 ball is plastic. HG 70403. It wears heavily. You need to pull charge pump anyways.

Two o-rings will need to be at least replaced.

HG 51232
HG 9004101-1340

Though other seals needs to checked while you are at it.

Also this a job might be better done with pump off as pistons and springs will tend fall out of the cylinder. However it can be done with it still in place if you can keep the cylinder, pistons and springs in place.

Thanks for the replies.
Should I do a system drain even if I leave the pump mounted on the frame?
Is the drive shaft pulley difficult to remove?

Threejack said:

Thanks for the replies.
Should I do a system drain even if I leave the pump mounted on the frame?
Is the drive shaft pulley difficult to remove?

Click to expand...

I left the pumps mounted to the frame i.e., did not pull the pump. In order to do this job, you need to drain all the hydraulic fluid. Even then, there is a lot of extra oil running around the engine compartment after you disconnect the lines. Have a full roll of paper towels standing by.

StarTech said:

Highly recommend ordering the charge relief ball and spring since the 1/4 ball is plastic. HG 70403. It wears heavily. You need to pull charge pump anyways.

Two o-rings will need to be at least replaced.

HG 51232
HG 9004101-1340

Though other seals needs to checked while you are at it.

Also this a job might be better done with pump off as pistons and springs will tend fall out of the cylinder. However it can be done with it still in place if you can keep the cylinder, pistons and springs in place.

Click to expand...

As StarTech says this can be done in place, which is what I did. The key to keeping the master cylinder in place is to not get in a hurry as you lift the cap off the body after the retaining bolts have been removed. The piston springs will push the cap up off the body after the bolts are removed (push the cap down and feel it spring back up to get a feel for that) With a free hand, feel under the cap for the cylinder block as you retract the cap with your other hand. If it continues to come out, stop and push everything back in place. The 20w50 oil is very sticky/tacky and the the entire cylinder (and valve plate) will come out as one piece if you aren’t careful here. Which is exactly what happened to me, and only by sheer luck did I get the master cylinder back in place without pulling the pump off the mower.

Lastly, the valve plate(which is between cylinder and cap) is stenciled “up” to make sure it goes on correctly. IOW, I think it can be installed upside down if you don’t pay attention.

I still have a hydraulic leak after replacing the o-rings. Very disappointing.