Bicycle Mechanics - Tricks for bleeding brakes?
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I just attempted to bleed a set of Hayes 9 hfx brakes. The front came out great with a nice solid lever. After two attempts at the rear (no air bubbles came out on the second time) it's still mush and doesn't grab till close to the bar. Yes I have read the postings on adjusting the lever. I don't think thats the issue. Do you guys have/know any tricks to get all the air out? About how much fluid do you use for the rear brake? Yes, I know it will be different for me, but it will give me an idea. Thanks...
I know what you're going through. I spent hours trying to bleed the Nines. One "trick" I learned late was to make sure the bleed port is at the highest point on the system - in other words, rotate the master cylinder so it is pointing up. As I recall, the instructions that came with the bleed kit said one thing, but the photo showed something different, with respect to the orientation of the master cylinder. I eventually got mine to bleed properly after much frustration. Did you split open the caliper? I did (for kicks) and I think lots of air gets trapped in the corner recesses of the caliper (just guessing).
When I bled mine last summer, I posted a query like yours. Many came back and confirmed these Nines are a pain in the butt to bleed.
By the way, you can use regular DOT 3 or 4 brake fluid from the local auto store for the system- much cheaper than the Hayes fluid.
12-12-05, 09:33 AM
Try reverse bleeding. Get the largest syringe you can find at a pharmacy or surgical supply store (not the little tiny needle injection syringes, these are huge in comparison). Put a piece of bleed tube on the end and suck up some brake fluid, then hold the tube upwards and get all the air out of it. Open the bleeder valve and inject the fluid. Watch the reservoir in the master so it doesn't overflow.
Works really well because air tends to rise, so you are pushing air up in the direction it wants to go as opposed to pushing it down.
The Great Stonk
12-12-05, 10:20 AM
are you making sure the pistons in the caliper are fully pushed back ? (remove pads and insert aprpriatly sized wooden/metal/plastic block)
is the reserviour/master cylinder rotated to be the highest point of the brake ?
are you using braided hose ? if not, is your hose twisted/rotated ?
and finally, are the pads relativly new ? somtimes rebleeding a brake but putting old worn pads in results in a poor feel and low bite point.
Well... I took the idea of placing the master cylinder at the high point farther. It was the advice of my roommate (an automotive mechanic for 40 years) to remove the master cylinder from the bars and position it in the air vertical to the caliper. Not too sure how you do this by yourself but it worked really well. The only flaw was that getting fluid into the line from the caliper was a pain. I think a syringe like San Rensho recomended would work better.
the syringe is bottom line crap, if you work the bottle right you could have the brake bled in like 3 min with perfection. Just remeber that air travels up, it like to hide so tap everything while bleeding, cycle the lever(this empties the MC of trapped air on the spring. The syringe will not allow you to extract the air in the caliper correctly, the bottle is designed to be released to suck air from the caliper. IF the brake still dont work after a couple of bleeds then call the cool guys at hayes. They helped me out tons:) I am now a pro at bleeding and no longer screw around with them for hours of frustrating anger.
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