Remove fluid during brake job

I will be replacing brake pads (and either machining the rotors or replacing them) on my wife’s 2007 Dodge Grand Caravan and my 2008 Pontiac G6. I purchased the Haynes repair manuals for each vehicle. In both cases, the Haynes manual tells me to remove two-thirds of the brake fluid before beginning the job. In the past, I performed pad replacements on my old car (1998 Pontiac Grand Prix) and did not remove brake fluid from the reservoir. I never opened the cap of the reservoir. I compressed the caliper piston with a ‘c clamp,’ replaced the pads, bolted the calipers back on, and pumped the brake pedal afterward to re-set the piston.

My question: Do I need to remove brake fluid as described in the Haynes manual? If so, why? If the reservoir needs to be topped off after the brake job is complete, do I use the fluid that I removed?

Thank you for your assistance.

Craig Deno, Darien, IL

Where does the displaced fluid go when you crank down the C clamp, do you open up the bleeder and drain it through a hose that way into a container?

If the brake fluid hasn’t been flushed for a couple years, this might be a good time to do this.

Yes, you MUST remove the brake fluid from the master cylinder, or have the brake bleeder valve open when you are compressing the pistons back into the caliper body.

The reason for this is to remove the brake fluid that has been contaminated with dirt, road grime, oils, and most importantly, water, from the brake system.

Brake fluid is clear when it is poured out of the bottle, and should be clear in your brake system. If it isn’t, then it needs to be flushed.

If you were to just compress the pistons back into the caliper body, all those contaminates can get into the ABS components, and possibly cause expensive damage over the long term, if not decrease braking performance during an emergency.

You only ever put in new brake fluid to replace brake fluid removed from the system. Never put used brake fluid back in.


I never opened any “bleeder” for the fluid. I never considered where the fluid goes when compressing the caliper piston with a c clamp. I guess I assumed that it goes into the brake fluid reservoir. As I said, I completed a brake job in the past without removing any fluid from the reservoir.

It went back in to the master, if you haven’t added any fluid, then there is room, since it was full when the pads were new and the piston out.

This is what I used to do, too. Since new brakes are a good time for new fluid, open the bleeder, then when it comes to pump time, pump through new fluid (pump, add, pump, add - do’t let it suck air) or ask a friend to slowly add while you pump until it runs clear. close bleeder, top off and pump a few more times.


Thanks for your info. So water, dirt, and road grime can get into the brake fluid? I assumed that this part of the brake system is a “closed” system. How do contaminants get into the fluid?

The darker your brake fluid coming out the bleeder, the more contaminated it is. Keep bleeding it until it looks like the new clear stuff coming out of the bottle.

Brake fluid sucks water in from the air anytime you open the cap on the reservoir, plus most reservoir caps do not make an air tight seal.
Rust, bits of metal, and bits of seals from the brake system itself also wind up in the fluid over time.

Its not a completely closed system. Just very well sealed.

Most of the stuff that gets into the brake system is actually transferred from the brake caliper piston into the caliper. Usually done when the pistons are squeezed back into the caliper.

As the pads wear, more of the piston is exposed to the elements.
Road grime, dust from the brake pad material, water, and all other stuff can get onto, and harden on the brake piston.

When you squeeze the piston back in without fully washing it clean with brake cleaner, all this stuff gets pushed into the caliper, past the dust seal, and the actual piston seal. Some of it builds up around the piston seal, and over time can wear out the seal, or score the piston itself.

So, that’s how the dirt and grime gets into your brake system, even though its a mostly closed system.


When replacing brake pads, you should ALWAYS open the bleeder on the caliper when retracting the piston. You do NOT want to force old brake fluid back into the master or ABS system. Discard the old fluid that drains out the bleeders and refill the master with FRESH fluid which will then refill the calipers after you pump them up. Recheck the master and top off as necessary…

Thanks to all for your information!

I’ll add to the suggestions one more. Hang a small vessel 1/2 full of brake fluid as ner the bleeder as possible, with a clear plastic tube between the bleeder and the fluid in the bottle. When you push the caliper in, the air in the tube will burp out the fluid in the bottle, and any drawback will pull back only fresh fluid. This is the best way to prevent air from getting into the system.