Before Dropping a Bundle on a Master Cylinder, Loosen That Booster

Dear Car Talk

Dear Car Talk | Sep 01, 2016

Dear Car Talk:

I have a 2003 Kia Sedona. The front brakes hang up on both sides. They don't lock up, but they stay engaged, as if my foot is still on the brake. If the car sits for five or 10 minutes, they go back to normal. I had the calipers and hoses replaced. What think ye?

-- Claude

I think ye didn't need the calipers or the hoses, Claude. I think you probably need a power-brake booster, or a brake master cylinder.

The way we diagnose these is we take the car on a drive and use the brakes a lot to get them to hang up. Then, once they misbehave for us, we hop out of the car and unbolt the master cylinder from the power-brake booster.

It's just two bolts, and you don't even have to remove them completely. You just want to create some separation between the master cylinder and the booster. A half-inch will do it. That removes the booster from the braking equation.

So if removing the booster causes the brakes to free up, we know that the booster is bad. And if the brakes don't release, then we know it's the master cylinder. Nine times out of 10, it's the booster.

It sounds like you like to gamble on auto parts, Claude, so if you want to take a chance on wasting a few hundred more dollars, just throw a new booster in there.

But if you'd rather approach it scientifically, take a wrench with you and do that test first.

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