Brake fluid change question

[Trey]

I plan to track my fl5 next month. I’ll be swapping lines, pads and fluid. All things I’ve done before. Usually the old fluid is dark and it’s easy to see when the new fluid is bleeding out the caliper. This time the car has 3500 miles and the fluid is still new.

How do you guys know when the old fluid is fully flushed out the lines when the fluid color is the same? I’ll be using Castrol SRF.

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[chadwicke619]

I just wanted to throw out there that G-four 335 from Project Mu is pretty much equivalent to all the top brake fluids out there, except it starts out green and becomes clearer as it absorbs moisture.

 

[Rhorn]

I just flushed mine the other day. What method are you going to be using?

If using a pressure bleeder like the motive bleeder it will be easier to tell by using the dry method to bleed your brakes.


If you suction out the all of the brake fluid from the master cylinder and pour in the new fluid, the only remaining fluid is the old fluid in the lines which isn't a lot compared to the total fluid in the master cylinder.

I was able to easily tell just how much brake fluid was in the master cylinder and in the lines by looking at how much fluid I suctioned out and put in a bottle. While bleeding the brakes, it was almost half of the fluid from the reservoir that was lost/bled out each time I did bleed a line. My catch bottle is practically full, I thought I messed up the first time I did it and repeated the process correctly and there was ALOT of brake fluid that I got. When done I saw the amount that is in my bottle is way more than the total amount that I suctioned out. So I for sure got out the old fluid, and was actually bleeding out the new fluid.

If you really want to play it safe, there's a total of 6 lines, (2 bleeder valves on the front calipers), the SRF bottle has 1L, so if you want to use the whole bottle each line will need about 0.16L or 160 mL of fluid to be totally flushed out. I didn't measure the amount I suctioned out from the reservoir but that should give you an idea of roughly how much residual fluid is left in the brake lines

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