Nissan Repair: calibers and brakes, brake light switch, competent mechanic

Question
I have a 2001 Nissan Frontier 4x4 off road 6 cylinder. I just had both calibers and brake pads replaced due to locking up. After having the truck serviced the same problem with calibers locking up reoccurred. Vehicle was driven 100 miles with calibers locking and unlocking. Returned the vehicle to garage and the master cylinder was replaced. I haven't driven the truck for any considerable distance since but the brakes still feel tight and when applied there is a squishy air release sound. I would also like to know what is your opinion on driving the vehicle that many miles(100) while locking up. Do you think there has been damage enough to the new calibers that they need to be replaced again?

Answer
Hi Shirley -

Usually an air sound while pressing the brakes is a defective brake booster. If the pedal is also hard to press down while the engine is running, that is probably what is wrong. This is the large round device behind the master cylinder.

However a defective booster does not necessarily cause brake to lock up.

If the barkes are still locking up check the brake light switch. I ran into some vehicles where the switch is not adjusted correctly, and that causes the pedal to partially apply the brakes. The other thing you might want to check is the proportioning valve, but that rarely goes out.

100 miles is a good distance. I would have a competent mechanic check the calipers

Hope this helps -
aloha
calvin