How To Inspect a Hydro Brake Booster

Garage Guru John Dixon shows you how to properly inspect a Hydro Brake Booster.

Hi, I’m John Dixon with Garage Gurus. Today we’re discussing hydro brake boosters. If you have a customer that brings in a vehicle like this late model Chevy Express Van, and some of their pickups that use this system as well, you may want to go ahead and try some of these tests to inspect and make sure that the hydro booster is working. We’re going to go under the hood a little bit later and look at some of the components and also some of the common problems. But for right now, we’ll discuss what happens if a customer complains of low brake power or a hard pedal.

So the first test we’re going to do is, we’re just going to sit here with the engine off after it’s been running, and we’re going to pump the pedal several times to count how many pumps it takes to deplete the pressure stored in the accumulator. And there we go, the pedal’s getting nice and hard after six or seven pumps there. So we know that we have plenty of reserve power. In case the engine dies, we can get the truck stopped.

The next test we’re going to do is to see how fast the system builds pressure with the engine running. So I’m going to start the engine in a second with my foot on the brake pedal, and what you’ll see is going to happen is, my foot will sink towards the floor and then it’ll get kicked back a little bit as soon as the system builds pressure. It happens pretty quick. Here we go. All right, you saw that little kick that happened right after it started, that was as soon as it made pressure, I pushed my foot back. So we know that this one has a functioning hydro booster.

All right, so now we’re under the hood. We want to do a visual inspection. Here’s our master cylinder. We want to make sure that it’s full of clean brake fluid. And then, next door over here, here’s the power steering reservoir. Take the cap off of that. It’s got a small dipstick inside, make sure that it’s full of clean power steering fluid. What you can’t see because we’re working on a van today, and it’s got this big filter housing in the way, is that there is a power steering pump monitor at the front of the engine. And then, through a pressure line, it provides pressurized power steering fluid to the hydro boost unit located back here behind the master cylinder. Also, it uses a pressure accumulator right here. And then, when the engine is on, and the power steering pump makes power steering pressure, that pressure is routed to the hydro boost unit first, allowing us to have break assist.

One common problem that you’ll see on these Chevy Express Vans and some of their trucks is, if you look at the mating service back here between the master cylinder and the hydro boost unit, there is a small gap. It’s got a weep hole there. Now, I know a lot of times when we see brake fluid leaking out of the back of the master, when we see any fluid back there, we assume it’s brake fluid. On this system, you’ll want to take a look and see if it’s not power steering fluid. If you have power steering fluid back there, that means that the pressure piston in the booster unit is leaking. The hydro boost unit will have to be removed, and then we’ll either have to service the seals inside there, or we’ll have to replace the unit.

All right. Thanks for watching our video today on hydro boost brake system inspection. For more information on Garage Gurus, please go to And don’t forget, for more tech tips, subscribe to our YouTube channel.