Best of Deals Car Reviews Repair Shops Cars A-Z Radio Show

Brake system flush!

Hello car-gurus,
My name is Joe, I live in Atlanta. I am the owner of a 2008 Volkswagen Jetta with manual transmission. I bought the car at 52000 miles and have been meticulous about maintenance, etc, etc,. My last maintenance attempt seems to have been a blunder. My last trip to the dealer alerted me that I need to have my brake system flushed. I didn’t agree with the dealers pricing and so I decided to go to a well-known VW-Audi specialist to have to job done. Now mind you, in lieu of all this my brakes and clutch (they share the same fluid reservoir) have functioned reliably since I’ve had the car. But before I left this shop after having “repairs” I was warned I may need a brake master cylinder although the mechanic said he was uncertain and second guessed his opinion as I walked out. The first few days my brakes seemed normal and functioned as they had for months. Then, along with a sudden drop in temperature, I noticed a dramatic difference. From the time I started in the morning till the end of the day I noticed my pedal would sink almost completely to the floor before any noticeable changes in speed. I’m worried now. Did these guys just scam me, hoping I would come back and have the MC replaced? Were they simply unprofessional and perhaps forget some procedure during the repair? Im a bit skeptical about an MC failing after 30K miles of driving with attentive preventative maintenance?HELP!?!

It’s always possible, but I haver only ever replaced one master cylinder in my long life; that was on a 1948 Chevrolet!!

They normally last nearly the life of the car, or at least 10 years. This defintely call for a second opinion, and I suspect the guys who “flushed” the brakes did not do a proper job! You normally just bleed them extensively and make sure all the old fluid is out and no air is trapped in the lines.

Flushing the brake system means you use a power brake bleeder instead of pumping the brake pedal. But it does the same thing only with one person instead of two.

The sudden drop in temperature might indicate that there’s a problem with the brake master cylinder. Now, would this have still have happened if you didn’t have the brake fluid serviced? We’ll never know.


I had the same problem years ago and would strongly recommend you bring the car back to the dealer, let them know they need to fix this, and subtly let them know you are documenting their responses. I’d also let your insurance company know, too, and if the repairs don’t work out consider a consumer complaint and a visit to another repair shop. Anyone can make a misteak, but this is a potentially dangerous situation.

You might want to have your brake system bled once again at all four wheel cylinders. If it still works as you describe, a new master cylinder seems to be indicated. I am of the view that brakes are flushed more effectively if one person pushes strongly on the brake pedal while another works the wheel cylinder valves to generate the necessary turbulence at each wheel cylinder to more effectively flush out debris as well as old brake fluid.

If it was mine, I would install a new master cylinder myself for little money and get that worry out of the situation.

The robber said to Jack Benny: Your money (optimum brake performance) or your life. Jack said in reply: I’m thinking, I’m thinking!

Master cylinders do go bad from time to time. I dont know what a tech could do to sabotage your m/c so it would fail in a few days to get work. Maybe he saw a little residual moisture and was not fully convinced you had a problem. What would you have said if he told you that you needed a m/c and was not sure you needed it? Maybe he felt the pedal fall just a touch and was not sure what he felt.

Don’t assume someone scammed you after a car part fails.

Here’s the thing about brakes. Whenever they are worked on, pretty much no matter how careful you are, there’s a chance it will damage the MC, especially it has been in use for several years.

The pistons inside the brake MC normally reside stay bounded in a certain location in the cylinder. They are where they are normally when driving, then when you push on the brake pedal, they move a few mm. But the pistons, they stay in that area all the time. So that area is kept clean and smooth by the piston’s daily movement to and fro from normal braking.

The problem is when the brake system is depressurized and bled, when you step on the brake pedal when it isn’t holding pressure, as is commonly done during the bleeding process or in testing it afterward, the pedal will push the piston much further down the cylinder than it is normally. And when this happens, burrs on the walls of the cylinder wall (from debris accumulated, rust, etc.) which normally are not hit, are hit, which damages the neoprene seals of the piston, causing an internal leak.

And everything I just said applies to the wheel cylinder (for drums) and the calipers (for discs) too. There’s always a chance these were damaged during the fluid change out. This problem is not uncommon, and is easily fixed. Take the car back to the shop and have it addressed.


When you do a brake flush with a power bleeder, you don’t touch the brake pedal.


@Tester; Are we sure the shop did a flush with a power bleeder.

I think they probably used the two man technique, floored the pedal and that is how they knew to warn the OP about potential failure.

When I see the word “FLUSH”, It means they didn’t use the conventional method. Or in other words, “They Used one of those new fangled machines to to service my vehicle”.

And that’s not a bad thing.


George took the words right out of my mouth.
And I tip my hat to the mechanic for giving you a “heads up”. If it were me, I’d go back to the same guy.

I’ve seen George’s explanation in a factory service manual (I forget which).