Originally posted by Steve Blunier on 7-6-01
Frank F.
The centering springs in the trunion arm/cam plate joint allow a small
amount of movement or cushion in the speed control linkage. This is
designed into it to prevent the hydro from bucking you off the seat every
time you move the speed control lever....just like a shock absorber
dampens a suspension.
The hydro WANTS to self accelerate....that's why FRICTION is built into
the speed control lever, to hold it in place. If you loosen the friction
adjustment and barely bump the hydro lever it will automatically move to
wide open...it's the nature of the beast.
The centering spring is designed to only compress during speed changes, at
all other times it should be in the neutral position, holding the hydro at
constant speed. If the springs become weak, or the slot becomes elongated
(effectivly
decreasing the spring force) they will not maintain their "N" compression
when the tractor is moving fwd/rev. Instead, they will compress and allow
the tractor to "free wheel"/self accelerate downhill, or "bog down"/self
decelerate up hill.....just like a worn out shock, it no longer dampens
then holds, it "sort of" dampens then bottoms out. When you compress the
weak springs due to increased/decreased load you change the effective
length of the speed control linkage and the tractor speed changes
accordingly.
Hope that's not confusing, but that's what is happening.
Those same centering springs are also the reason why it's hard to hook 2
hydro linkages together to make a 4wd...different spring rates/hydro
performance/individual pump differences/etc make the hydros fight
eachother. Kelly Birkey (owner of the 1450 4wd and 1450 payloader) and a
few of the forum regulars had a conversation about that at RPRU. made for
some interesting discussions.