Lazy Power Shift engagement


New User
I have a fairly new-to-me YM226D. I bought it in the winter and it had no drivability problems. Now with warmer temperatures here, the engagement of 1st and reverse is delayed significantly, and when good and hot, it won't engage at all. It is more noticeable at low engine RPMS and after working the tractor for a while (1 hour brush hogging, for example). Once the Power Shift clutches engage the gear, it has good solid connection. I suspect 2nd and 3rd has the same problem, but I never start out in those gears.

I pulled the Delay Relief Valve, inner and outer springs and the Main Relief Valve in the Power Shift Relief Valve Module. Both springs were intact, but did measure shorter than information in the YM276 Service Manual. The inner spring measured 2.117 in. (Specification is 2.13 to 2.16 in.) and the outer spring measured 2.511 in. (Specification is 2.54 to 2.57 in.).

I bought a hydraulic gauge and fitting and measured the Power Shift hydraulic pressure per the manual. At 1500 RPM, the pressure was only 70psi. At 2000 RPM, it rose to 100psi and at 2500 RPM it reached 130psi. The manual states the pressure should be 213 to 227psi, but it does not state the RPM at which to measure. Obviously, my pressure will never reach 200+ regardless of RPM.

Do you think replacing both inner and outer relief valve springs will restore the pressure to normal or do you suspect the problem is internal leakage somewhere else in the system?

Other relevant information:
1. I changed the transmission/hydraulic fluid (twice). First to Travellers from TSC, then John Deere Hy-Gard J20C
2. I cleaned the suction screen
3. I replaced the spin-on hydraulic filter
4. The transmission internals are very clean.

Thanks in advance for any guiding information. It's a great tractor otherwise, so I'd like to fix it if possible.

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