3-point Rapid Leakdown

[Leanier]

Hello!
I recently got an older Cub 154, got it tuned up and it seems to be working pretty good. It needs a clutch and a PTO pulley key and some bits but nothing major.
However, I have one issue that I'm not sure the best path on, the 3 point hitch leaks down quite rapidly, to the tune of full up to full down in ~20 seconds with a back-blade on it.

Assuming the issue had to be in the relief valve or the control valve (older one where they are separate) I got a rebuild kit from Hamilton Bob's with all the O-rings and went through them top to bottom, everything looked good inside.
After re-assembly, same issue at the same speed. There is no external leakage, so it pretty much as to be in the valves.. Hydraulic fluid is topped up and looks good, it lifts and such all without issue.

Based on my analysis of the valve, it looks like there must be fluid leaking by the poppit or plunger (parts 5 and 6 in the diagram), has anyone ever dug this far into one? I have a lathe so maybe will try to turn some new ones, but thats tricky at the needed tolerances.

[Eugene]

Welcome.

Does the mid mounted cylinder leak down?

I think you are on the right track.

One more post and you can access free manuals, Quick links, upper left of this page.

[Leanier]

I haven't been able to assess that yet as I don't have my mower hooked up right now (hopefully soon)
I can hang some weight off of it tonight and see if it also does. I expect it will since they are rigged in parallel (I don't have a selector valve) and there is no external leaking.
Doesn't seem like there is anywhere to buy the control valve or the internal poppits, so I'll be down to trying to make my own. This tractor has a lot of signs of heavy use in its past..

[Leanier]

Hello all, has anyone ever replaced the control valve with something off the shelf (since our unit is obviously not made anymore) Looks like northern tool and some others have options that might work with a bit re-routing of hydraulic lines:
https://www.northerntool.com/products/brand-hydraulics-directional-control-valve-3-000-psi-314366

[outdoors4evr]

One of our forum sponsors may be able to provide a good condition original equipment (or an aftermarket model that fits well)
See the links at the bottom of this page. Hamiltonbobscubs specializes in the numbered series tractors.

[Eugene]

Internet search, parts for the control valve appear to be available. I would disassemble, figure up repair cost. May be less expensive to purchase one from advertisers on this site.

[Gary Dotson]

In leakdown situations, I’m always suspicious of the cylinder,itself. Fluid by-passing the cylinder piston will act like you describe.

[Eugene]

Single action control valve and cylinders.

[Leanier]

Yea the cylinder itself doesn't seem to be the issue for me, both are single sided cylinders with no external leaks (both meaning for the mower deck and the 3 pt) they both leakdown in parallel.
Looking at the circuit, that pretty much leaves either the relief valve or the control valve, both of which I rebuilt with o-ring kits to no effect.

However, the control valve has a spool fit and check valve for the touch control to lower, which appear pretty well worn and would allow a leak past the spool in the control valve from the cylinder back to tank it appears. That would pretty much leave my options being to get a new (or new used) valve or trying to ream out and put a new spool in..

[Gary Dotson]

Right! I was thinking of double acting cylinders, my bad!

[Leanier]

Wanted to update the group here, I was able to solve my leakdown (looks like entirely).
I went through and made a schematic of the valve which made it obvious that the leakdown can only originate from one place, the brass component and poppit in the "to cylinder" end of the valve.

I took that apart, used a poor mans dichem (a sharpie) to see where the valve is hitting, as you can see, its not sealing and there were large areas not contacting. (you don't want the whole surface to contact,but that line on the back edge of the taper should be consistent without breaks)

I then used some valve lapping compound and lapped the brass part into the valve body, and again the poppit into the brass part. Using an air leak check (rubber nozzle on an air gun..) I was able to verify when I got it to seal totally (zero leakage of air past the valve)

I re-assembled, and the 3 point doesn't leak down at all anymore, its been holding this log on the carry-all for hours without any noticeable motion! (previously that would have been on the ground in probably 15-20 seconds)