Merry Christmas all. I have a 580B w/ diesel & Twin Disc. I had a super soft reverse (fwd worked fine), did all the standard issue stuff - changed fluid, filter, drilled & tapped for pickup screen, flushed, etc. Pressures at A and C ports we within spec, the B port plug was sheared off flush w/ top of shift housing so I never tested it. Figuring the shuttle was clapped out, I split the tractor and put in new fiber discs, new steel discs, new piston rings & o-rings, and input shaft rings. Both fwd & reverse sections. Found a lot of not right things with teardown but not an "ah-ha" that was root cause, so I figured I'd just replace everything I could since it was split. Took my time and hit all the clearances/specs as described in the manual (I've assembled north of 100 engines, transmissions, rear ends, etc and have a small machine shop at home, so I'm not completely stupid - only partially). Now - reverse spins the tires but fwd is super soft & acts like reverse used to. Barely can get up a minor grade without the hoe attached. Once it gets rolling, I can feel the shuttle grab as if it finally quits slipping & locks up. I think my game plan is to pull the shift cover off the shuttle, EZ out the B port plug, re-check pressures and look for any obvious issues with that valve itself. Anything else you guys would look for at this point?
Pressure test is what you need to do
Back to life. Unknown shuttle temp - Ambient was 80F & sunny yesterday afternoon, fast idled it for 10 minutes or so to warm up. Had 150psi at port C at idle in neutral, fwd or rev. Added rpm (tach is broke) and it didn't move past 150psi -> relief has to be opening, yes? When I had the shift cover off the shuttle to drill out the sheared B port plug, the relief had two shims stacked in it, can't remember thickness but I recall them being what was listed in the manual. Game plan is to whittle another shim on the lathe this afternoon, add to stack and see what happens.
Pulled the shuttle relief valve back out of it. Spring free length measured within spec, and it had the 0.021" + the 0.042"shim in it. So with the note in the manual that the .021 shim raises pressure 5psi and the .042 shim 10psi, I turned bar stock into a .230" shim (should have added 40 psi to the 150 I was seeing) and put it back together. Had 200-210ish psi while moving, and the slippage appears to be resolved. I'm calling it close enough with the manual spec, should thin out & drop some pressure once it warms up running.