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Ford TW25 low hydraulic pressure
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b_central_ks
Posted 9/7/2016 21:41 (#5515997)
Subject: Ford TW25 low hydraulic pressure


We have a Ford TW25 that won't build up full hydraulic pressure, looking for ideas. We think the problem came on suddenly, a baler was functioning properly late in the week, then Monday morning the tractor couldn't lift the tail gate more than 1/4 open. A gage on the remotes shows we are only getting around 1300 psi. Dead headed, no flow.

Tractor: TW25, later hydraulic system, has the auxiliary engine mounted pump.
No trailer brake. Normal relief valve setting is 2500 to 2600 psi.

Here are some tests we've done, some tests are per the service manual.
1. pressure tested on lh and rh remotes and is the same on both the raise and lower side.
2. pressure stays at 1300 psi when two remote levers are activated simultaneously.
3. pressure stays at 1300 psi when the 3pt arms are raised.
4. Lifted a 15' 3pt drill half full of seed, acted normal although we don't have a pressure reading on this portion of the circuit.

We removed several of the components from the tractor looking for missing or damaged orings, binding spools or worn surfaces. We did find a couple of damaged orings and one missing oring. New orings were installed in these locations.
Here are the items we have torn down, inspected and repaired:
a. filters changed, old filters cut open and inspected.
b. main relief valve
c. in the valve bank above the pump: Unload check valve, Unload valve, Flow control valve.
d. main hydraulic pump in the rear axle cavity. (torn down and inspected for excess wear or blown orings in the end caps ect...)

Have not inspected:
e. auxiliary pump on the lh side of the engine.
f. the valves in the rear axle cavity situated near the 3pt lift cylinder. (the cab
would need to be pulled)

A couple of tests that are good clues:
g. The main relief valve was removed and shims were added under the spring per the service manual. Pulled 0.050" shims and replaced with 0.080" shims (maximum allowable per the service manual) Service manual says each 0.010" shim added will increase the pressure by 100 psi.
Result: no change, pressure at the remotes still 1300 psi.

f. The system can develop 1300 psi at the remotes at an extremely low idle (and) it does not change when the engine is sped up. This to me indicates that the problem is not a worn gear pump)

Has anyone seen this? Any ideas?
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Bern
Posted 9/8/2016 02:15 (#5516348 - in reply to #5515997)
Subject: RE: Ford TW25 low hydraulic pressure


Mount Vernon, WA
From what you say, I would agree that it's not the pump(s). My bet is you have contamination in the auxiliary pump relief valve, causing it to stick open and bypass prematurely. This valve is located internally in a spool known as the combining valve. This combining valve is located in an assembly known as the priority valve pack, which sits on the top of the main hydraulic pump mounting cover, where the remote valves used to sit on the older TWs.

Remove the combining valve from the priority pack. Carefully grab the spool with a vice grips on an unmachined area of the spool, and then use an allen wrench to remove the plug from inside of the combining valve. Be careful to note the depth of this plug before you remove it, so you can put it back where it was on reassembly. Once the plug is removed, there should be a ball, retainer, and a spring. Clean all parts thoroughly, reassemble, and give it another try. It should do the trick. BTDT more than once.

Also, make sure the combining valve moves freely in its bore.

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