M543A2

I had a hard pedal problem like you describe on another truck. If you take the cap off the master cylinder and if necessary to see the bottom of the reservoir, draw the fluid out of it with a suction device. Then you will see a pair of holes in the floor of the reservoir, a larger one to the front and a smaller one behind that one. The smaller one, if plugged by residue, will not let the pressure to the wheels bleed back to the master, resulting in the hard pedal. Use a small torch tip cleaner, wire, or other device to clear the small hole. If I remember right, it is about 1/32 inch or so in diameter. You can check to see if it is plugged by gently pushing down the pedal while watching the fluid in the reservoir. If the small port is open, you should see a momentary upsurge of fluid out of it. No surge, it is plugged. If you push the pedal too quickly, it will put fluid in your eye! Be careful!
Regards Marti

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Warsaw, Indiana
3 M-880 Pickups
2 M-200 Trailers
3 M-105 Trailers
2 M35A2 Deuces
1 M-139 5 Ton Bridge Truck
1 M-543A2 5 Ton Wrecker
2 M-51A2 5 Ton Dump Trucks
1 M-52A2 5 Ton Tractor
3 M-135/ M-211 Deuces
1 IHC T-9 SeaBees Dozer
1 M-313 Shop Van
1 M-689 Shelter Dolly Set
1 M-715 1964 Jeep