Brake Fluid Replacement


Old 03-19-05, 04:11 AM
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Join Date: Oct 2002
Location: USA
Posts: 57
Brake Fluid Replacement

I am an adherent of fluid changes as part of my preventive maintenance program on my vehicles. When I get any brakes replaced I have the mechanic also flush and replace all of my brake fluid. Since I have not tackled brake flushing yet and pending having this done with a brake job, will replacing the brake fluid in the bowl be usefull as an interim measure. I have read that the moisture in the brake fluid goes to the lowest point in the braking system so I am wondering if the replacing the brake fluid in only the bowl will have the effect of removing any of this moisture?

A secondary question is this. Can I replace the existing bowl fluid with synthertic fluid or is a complete flush and replacement necessary in this instance? Thanks.
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Old 03-19-05, 04:36 AM
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Join Date: Jan 2001
Location: Kansas City, Missouri.
Posts: 1,172
Interesting. I am guilty of having used a suction bulb to extract bowl fluid and topped it off with new fluid. There may not be an argument in favor of it, but it gave me peace of mind.

Mixing synthetics with non-synthetics? I really don't know the answer, but my thoughts are to not mix unlike products together.
Old 03-19-05, 05:28 AM
Join Date: Nov 2001
Location: North Texas
Posts: 2,345
do it right

First off do not mix fluids use what the book says.Second brake fluid does not move much in the system like power steering fluid.
You need to open the bleeder and get all that old fluid out if you replace only fluid in the master cyl with clean stuff it will never get to the wheels.
Old 03-19-05, 05:47 PM
Join Date: Oct 2000
Location: Livonia, Michigan
Posts: 923
Vetisme, it's not clear from your post, but I'd like to state that for most DIYers it is common accepted practise to exchange the fluid every two years for good brake system maintenance.

I see nothing wrong or wasteful with exchanging the brake fluid in the bowl. It may even help prolong the life of the master cylinder. Keep in mind it's less important to exchange the bowl fluid nowadays since you don't have to open the new see-through bowls to inspect the fluid level. I doubt that exchanging the bowl fluid has much affect in removing any moisture that finds its way at the calipers. Only a complete fluid exchange every two years is acceptable.

I don't believe there is such a thing as 'synthetic' brake fluid. I haven't heard of such a thing, nor anybody using that term for brake fluid.

The brake fluids I know are DOT 3, DOT 4, and DOT 5.1. All are ethylene glycol, compatible with each other, with 5.1 being the best.

This is not to be confused with DOT 5, which is silicone. This fluid is not commonly used, and it is not compatible with the previously mentioned three grades.
Old 03-20-05, 02:59 PM
Thread Starter
Join Date: Oct 2002
Location: USA
Posts: 57
Sometime ago I purchased Valvoline high performance synthetic brake fluid compatible with all dot 3 and dot 4 fluids. That's what's on the container. The nomenclature on the container also speaks of a higher boiling point etc. I might call valvoline to check if I can mix them but I am assuming they will verify what already is written on the container. The more I consider it, I do not think they would chance selling this stuff if it was not compatible with the non synthetic brake fluids. Needless to say, a complete flush will negate the mixing issue. Thanks

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