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Dear Jim,

I have a 1965 Chevrolet Impala, and I'm having some trouble with the brakes. The brake pedal feels very spongy when I step on it. I'm a retired mechanic, so I tried to fix this myself by turning the brake drums and installing new brake shoes, front and rear. That didn't work, and the brakes still feel soft. Obviously, the problem is somewhere else, so what should I be looking at now?

-- Clint Wells

I like to hear from old-school mechanics like yourself, bro, and it sounds like what you've done so far makes sense. This spongy effect you're talking about shows up when fluid leaks out of the brake system and air gets in. Normally, there's only fluid in there, and brake fluid is noncompressible.

That's why it works so well: You step on the pedal, which pushes on the fluid, which pushes on pistons in the brake cylinders that ultimately stop the wheels from turning -- all in one tight motion. Air bubbles in the brake line are very compressible -- spongy -- and that's why your brakes feel as they do.

You're going to have to get that air out by "bleeding" the brake system. Take all four drums off, pull back the rubber cups on those brake cylinders and look for leaks. If you find one, you can rebuild the cylinder with a proper hone tool, or else just replace that cylinder.

No leaks there? Then check all the brake lines for leaks and replace any of those that need it. Still no leaks? There's only one possibility left, brother, and that's the master cylinder -- the one that controls all the others. Replace the master. That spongy feeling should vanish and your braking should get a whole lot tighter.

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Buffalo Jim, owner of Allstate Auto & Marine Repair in Las Vegas, writes a weekly column. Send your automotive questions to him at buffalojim@lasvegasniftynickel.com. If Jim picks your question to answer in Nuts & Bolts, you'll also be the proud recipient of a deck of official Buffalo Jim playing cards, presented in a classy, tin box bearing his hairy image.