I recently got a 94 GMC Sonoma that has been setting for 4 years. The brake pedal went to about 1 inch from the floor with marginal stopping power. I bled the brakes with no change. I then changed the master cylinder and now the pedal goes down about 2 inches with so-so brakes then slowing drifts to about 1 inch from the floor. There are no visible leaks in the system. Any idea what I should do next?
I would look for the rear wheel cylinders to be leaking. If the pedal drifts downward, there is a leak… either internal in the master cylinder or external. If you are certain there are no external leaks you may need to try yet another master cylinder.
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