I have a 2005 Mazda B-Series with 30,000 miles. I recently had new front brake pads put on. I can't tell any difference. The pedal is still as spongy as before. What's wrong here?

 

Sounds like air in the lines to me.
2 questions...
1- when did the brake pedal start to feel 'spongy'?
2- isn't your truck still under warantee?

 

It's been spongy for a long while.
It's not under warranty.

 

When was the last time your rear brakes were adjusted? 30,000mi. is too soon for the front brake pads to be replaced unless the rear brakes are out of adjustment.

 

Welcome to FTE. The are lots of folks that can provide good help for you.

I'd pull a rear brake drum to check the lining. If the wear is normal or less, put the drum back on and adjust the rear brakes. The easy way to do it is by backing up and apply the brakes sharply (hard). do this several times and see if your pedal firm up. If no, you should have the brakes bled. You could have gotten air in the lines as the fronts were done.

 

A spongy/soft brake pedal is typically a sign of air in the system, but may also be caused by dryrotted, weak/flexing rubber hoses, or maybe a master or wheel cylinder piston sealing problem.

Did/Do you have any brake fluid leakage/wetness signs, anywhere along the brake system?????

Has the master cylinder fluid level been dopping, such that you've had to regularly add fluid????

 

My bet is a clean and adjust on the rear shoes is needed. Dont count on the self adjusters, remove the drum and adjust them yourself.