Rebuilt 580B shuttle, new problem

[bkj110]

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?

 

[Dave Neubert]

Pressure test is what you need to do

 

[bkj110]

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.

 

[bkj110]

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.