A 1961 Clark Utilitruc lpg 6 cyl continental engine.

I came across this thread and thought I might be of some assistance. I see it as my responsibility to shift the trans selector lever to neutral if I'm going to be idling against the brake for awhile or want to raise the mast high up in one place and feel like I need to rev the engine to reduce cycle time. I got a new master cylinder, new wheel cylinders and piped the MC direct.eliminated the left-side functionality all together. So there is a shuttle valve - same thing as an 'OR' element in fluid logic - that was apparently sticking or leaking. The function puts the trans in neutral and applies the brakes. I eliminated the functionality of the left pedal on mine.

Parts were not true OEM but were like generic 'auto parts' where they are built by a 3rd party supplier 'to fit your make and model'.no complaints about the parts - I think I used Nash Lift somewhere in Kentucky as I found them easy to deal with. A lot of messing around with gearwrenches and box ends to get all the fasteners loose, then a super heavy 'final drive' assembly on each side which is spline-driven by the transmission. I changed the brakes on my avatar Clark - not that bad to do but a *lot* of bolts and I twisted off a 1/2' square drive breaker bar before I realized that 3/4' drive tools were necessary at least on the lug nuts. I would also look at the rod looks to me like a single stage mast, so right up at the top - if all is good you can rebuild the mast cylinder with a seal kit and some work - if the chroming is rusted badly at the top it could be eating the rod wiper which in turn eats the u-cup which in turn creates a leak.

Clark c500 ys80 service manual