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Brake Fluid: Flush Or Not?

Q. Mr. Ciulla, Good afternoon, I have a 1997 Nissan 200-SX SE-R, manual transmission, with approximately 58,000 miles. I read your DIY article on changing disc brake pads and had a couple of questions. In the section where you discuss removing the caliper and using a C-clamp to push back the piston, you write that failing to have removed half of the brake fluid from the master cylinder will result in needing to have the vehicle repainted.

Brake Fluid: Flush Or Not?

I'm having difficulty visualizing how the brake fluid would get all over the car's exterior here. Can you explain? Also, when you change the brake pads do you recommend changing the brake fluid? My owner's manual discusses adding brake fluid if the reservoir gets low, but it doesn't state anything about replacing the fluid. I thought I read that you can change the brake fluid using a turkey baster. So basically, would you recommend changing the fluid, and how would you do it?

Have a great day, excellent web site!!

A. Let me regail you with a little story as I am wont to do now and again. I was doing a brake job on, of all cars, a Ford Pinto. I had finished replacing the pads on the passenger side and was working on the drivers side. As I was compressing the caliper piston something started dripping on me. I look up and there was something dripping down the side of the car. It was brake fluid.

I didn't take some out of the master cylinder and with the periodic topping off, as it says in your owners manual, there was not enough room in the master for all the brake fluid. So the fluid squirted out of the sides of the master cylinder cover and onto the fender and windshield cowl.

Brake fluid eats paint. In fact I use it to remove paint from locomotive shells before I paint them. I was lucky that I caught it quickly so I was able to wash it off, brake fluid is water soluble, and a compound and wax fixed up any paint damage. Of course I had to do the whole car, but it was better than paying for a paint job.

Modern master cylinders with a screw on cap have a vent in them. If there is more fluid than the master can hold, it comes out of the vent like a fountain. If it is a push on cap, well, they just pop off like a water balloon exploding. So it is a good idea to take at least half of the fluid out of the master before doing brakes.

A turkey baster is good for taking fluid out of the master cylinder. In fact it is what I use. But, you need to replace the fluid in the lines. So I remove all the fluid from the master, pour in some clean fluid and clean the inside of the master with a brush. Then I take that out, fill it with clean fluid and start bleeding from the master cylinder on back.

I keep bleeding until I get clear fluid out of the bleeders. This should be done every two years because brake fluid absorbs moisture from the air and lowers the boiling point of the brake fluid. If the brake fluid boils it puts air in the system and you lose braking power.

As long as there are no leaks in the brake system, there is no need to add brake fluid between brake fluid flushings.

Additional Information provided courtesy of ALLDATA

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