Been awhile since I’ve been on here but I’m having an issues I just can’t wrap my around. Hoping someone here can give me some insight on this issue. 95 model 310D backhoe. was doing some pushing and the brake just Suddenly lost all pedal pressure. No brakes but parking brake does work. Both spools stuck in the actuated position in the brake housing. Took brake valve apart and got the spools unstuck and moving freely. Here is the main issue I just can’t understand. This brake valve is apparently feed from the hyd cooler. There are 4 hoses total on this valve. One hose returns to tank about half way down. Two hoses go to brakes and The other hose goes into a tee on the bottom side of hyd tank and there is no Oil coming out of this hose when removed from the valve. Also removed the hose from the tee and no oil comes out of bottom of tank. NOW on the end of this tee is a hose that runs to the hyd cooler. When we remove this hose from the tee oil comes out. We took compressed air blew back through the hose that goes from brake valve to the tee and air flows into the tank. Attached is pic of tee smaller hose goes to brake valve and larger hose goes to cooler
The brake valve is kept full of oil from the hydraulic return circuit. There is no power assist or hydraulic input into the brake valve other than to keep it filled. When you step on the brake pedal, your leg strength is all the power assist that system gets.
Oil should flow out of the Tee fitting towards the brake valve. Depending on your serial number, I think that Tee might have an orifice on the threaded side entering the tank to ensure that oil is pushed to the brake valve. If you do not have oil flowing out of that Tee then I would remove and inspect it.