855 john deere, when I push the peddle to go forward it move slow and has a high pitch wine. Whwen I pus thge peddle for reverse is runs fine, no noise and moves fast. Is this possibly a releaf valve

Visit the on-line store, known as reliable-store, they have the repair manuals. I'm sure you will get the solution of your problem -

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The drive belt may be broken, or it may have slipped off a pulley.

(Simple answer)Hydrostatic drive machines have a setting that allows you to push them. machine won`t move if this is engaged.
Also If park brake is on. Otherwise check drive belt has not snapped is loose or broken. Jack machine up and see if wheels will drive without weight of machine.

Parking brake not released?

this hydrostat drive tractor is designed to max at 5.5 mph forward, 2.5 in reverse, check linkage at pedal if you dont think your achieving those speeds

Go to youtube . Type in your make and model/ forward and reverse will not engage. Should be helpful.

I have a lx277 john deere mower it move good forward reverse move real slow can you help me

there is a release usually behind the seat that has to be pulled in order to push it physically. make sure that the release is pushed in for the forward/reverse to work.

Try jacking the unit up. Start it up and try moving pushing the forward and reverse back and forth and see if it does it then. It sounds like an oil way in the hydrostatic unit has a check valve stuck. Of course make sure that the fluid lever is up. Hope this will help you. donnyb60