450B Loader Check Valve

[KMTKMT]

I have a ’73 450B loader and I have the May-87 edition of TM-1033.
My machine has the same fault as described at the bottom of page 70 5-7: when I slowly move the lever back to the raise position, the loader boom settles before it raises (it also settles a bit when I release the lever, both in raise and lower). The manual states that this is probably the result of the ‘check valve’ leaking.
In Fig. 7 on page 70 20-5, two check valves are shown: the ‘Check Poppet’ (4) and the Anti-Cavitation Check’ (18), (which, based on the ‘2500’ stamped into the cover, is actually the boom raise circuit relief). There are also various relief valves (1, 11, 15).
On the original boom valve, the seat for the poppet valve had worn in an oval shape. I took the valve body to my local machine shop and he reground the seat, re-bored the valve guide in the plug (7) and fab’d a new poppet valve with a larger diameter shaft and head.
When I installed this back in the machine, it didn’t offer much, if any, improvement. I then bought a used unit from Wenger’s. Before installation, I checked the poppet valve, the valve seat and the valve guide in the plug and none had appreciable wear. I installed this unit and same results: the loader boom settles before it raises.
My question is: what is the manual referring to when it mentions a ‘check valve’ on page 70 5-7? In the text beneath Fig. 7 on page 70 20-5, there is the ‘Check Poppet’ and the ‘Anti-Cavitation Check’ but no ‘check valve’.

[LeonardL]

This sounds more like you have a spool leaking past more than any of your check valves. Have you pulled the valve apart and inspected the spools and bore of the valve itself? I've only seen this a couple of times and both times the control valve was worn out and leaking past the spools when you try to raise or lower.

[KMTKMT]

This sounds more like you have a spool leaking past more than any of your check valves. Have you pulled the valve apart and inspected the spools and bore of the valve itself? I've only seen this a couple of times and both times the control valve was worn out and leaking past the spools when you try to raise or lower.

Thank you for reply.

I should also note that, when I'm not working the control lever, with the original control valve, the loader arm barely settles (with the engine off, it takes 20 or 30 minutes to settle from horizontal to the ground). Wouldn't this indicate that the spool isn't leaking/bypassing? I also note that, with the used valve that I bought from Wenger's, the loader arm does settle at a fairly rapid rate, which I presume to be from a worn spool.

I've inspected the spool in the original unit, however the Wenger's unit is presently installed so I can't remove the spool to inspect.

[LeonardL]

If your hydraulics are settling then it is either the spool in the control valve or the cylinders are leaking past the pistons. When you say it is several minutes before it settles, I would bet on the seals and packing inside the cylinders are old and worn from age. The spool in the valve should be more instantaneous if it is leaking past. In other words when you raise it and stop then it should settle are start to settle more rapidly. Cylinder bypass is more subtle and takes longer. Sometimes you can even hear it pop or creak or make some sort of noise as it settles.