Bicycle Mechanics - dark brake fluid

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killerasp
02-23-09, 11:13 AM
so i decided to bleed my avid juicy 3 brakes yesterday because they felt a bit spongy.

when i pushed the new oil from caliper up to the brake lever, i noticed that all the oil coming out was all dark, black even. im pretty sure that the oil should not be dark which is a bad thing.

my question is can i push out ALL the oil and start fresh with new brake fluid? im pretty sure the oil inside the lines are mixed with the new oil i put in and the old oil which is affecting brake power. i was thinking of taking two empty syringes and using one to push all the oil into the other empty syringe. is this the right way to do this? any tips?

Barry in GA
02-23-09, 01:59 PM
I found instructions for bleeding the Avid brake system here:

http://www.sram.com/_media/techdocs/95-5015-019-000.pdf

The instructions refer to "Avid Hi-Performance DOT Fluid" which is probably DOT 3, DOT 4 or DOT 5. In general, the higher the DOT number, the higher the boiling point.

DOT 3-4-5 brake fluids are hygroscopic and readily absorb water which lowers the boiling point and turns the brake fluid dark. IMO, brake fluid should be changed at least yearly and anytime it turns noticeably darker.

Note that DOT 3-4-5 brake fluids are excellent paint removers!