J D301a brakes

all sudden brake pedal goes clear to floor and needs pumped . what do i check or adjust

1st thing I suggest is to bleed both sides of brakes. Engine needs to be running at idle so trans pump can replenish brake valve reservoir with hyd oil. Be sure pedals are fully returning to home position when released. If bleeding doesn't solve the problem then I'll guess faulty valve or valves in brake valve housing.

(quoted from post at 06:10:59 02/24/21) all sudden brake pedal goes clear to floor and needs pumped . what do i check or adjust

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Do you have the John Deere technical manual for this tractor? From your question, I am guessing you don't. You really should have the technical manual (TM1088) for the 301A to go through the diagnostics and make repairs.

Your brakes work off the tractor hydraulic system. The pedals are connected to valves that send hydraulic fluid through lines to apply pistons which apply wet brake discs inside the axle trumpets. There are no adjustments other than a few related to the pedals to be done when the brake valves are overhauled. What do you run for transmission hydraulic fluid? It should meet the current J20C spec, like Hy-Gard. (J20A (older Hy-Gard) might be ok at the 301A vintage, 303 or any UTHF only saying they are equal to or meet 303 specs are not ok.) Wrong oil can ruin the brake discs, which break up and can plug the transmission screen and plug the filter.

You may have problems in the brake valve(s). You can try bleeding the brakes, but that likely won't cure it. Isolate the brake valves from the brakes (disconnect and plug the ports where the lines go to the brakes). If the leak down stops (pedal stays solid), the problem is in the brake assemblies in the axle, if it doesn't it is in the brake valve(s). There are several possible things it could be in the valve(s).

Your brake bleeders are on the top of the rear axle,one on each side of the seat.The brakes get there fluid from the trans. with a port on the side that goes into the housing,problem is it's a dead end so if you get water in your system it can freeze and you could have a crack in the housing,happened to me and I had to replace the out side or right brake cylinder.

Check your hy trans fluid make sure it's not milky looking your brake linings might have disintergrated.