front Brake losing pressure : Yamaha R1 Forum

Leftinthedust · 10-10-2009, 11:20 AM

Ok so heres the dealio, I bought a 06 636, the guy installed ss front brake lines, and it has always been spongy, and just kept getting worse. Las weekend I rebled the brake lines, and it was perfect for a day or two, then it got spongy fast, and lost nearly all its pressure in a few days. I thought maybe I didnt tighten the top bleeder nipple very tight because it looked like it was leaking ever so slowly out the top. I rebled them, and this time cranked the top bleeder nipple down (I now know after reading this was a mistake) and I can feel them starting to loose pressure.

How do I correct this? I imagine the previous owner tightened it down too much previously and now I need a new master cyl?

Leftinthedust · 10-10-2009, 11:24 AM

oh and when I rebleed them air came out the top bleeder screw/nipple, nothing out of the bottom ones.

Dark_ · 10-10-2009, 11:29 AM

If the bleeders are sealing properly then you may need to rebuild the master.

sl33pyriceboi · 10-10-2009, 11:53 AM

try buying "speed bleeder" nipples. they really make bleeding great because you don't get rid of ALL the bubbles.

try taking apart your brake pads + calipers and giving them a good clean with degreaser.

also clean n degrease your rotors and wipe them down.

i did this to my rear brake yesterday because it has seriously been SUCKING lately. and now my rear brake feels almost amazing as my front.

Sharksawyer · 10-10-2009, 02:35 PM

+1 on the speed bleeders. Install clear tubing to drain fluid, crack nipple and pump. I've gotten a couple of sets from this guy:

ebay@sevensaturdays.com

Mark
99 R1

MrQuickR1 · 10-10-2009, 04:52 PM

You basically answered your question with the air coming out of the top bleeder.
You cannot crank them too tight as you just found that out.
Quick and easy try first is to replace the bleeder with a new one and see if air comes out of that one, if it does, then I would start looking for a master on ebay or somewhere.

r1phil · 10-10-2009, 05:27 PM

if air is getting in ....then should be signs of fluid leak...maybe even residual sweating ...sometimes road debris covers...clean areas and recheck..

87CR250R · 10-10-2009, 11:58 PM

Are you bleeding the calipers and the master cylinder? You only made mention of the master cylinder.

Also, about brake systems, they don't maintain pressure and don't lose it over time. When you bleed them, you're trying to remove compressible gasses from the system so that the brakes can build pressure faster as you squeeze the lever. Pressure is only created as you squeeze the lever. Air isn't the only thing that will make brakes spongy. Anything which causes the pads to get pushed back into the caliper will, like a bent rotor. Anything that hangs the pad up as it sqeezes the caliper also will, this includes worn pad retaining pins and anti-rattle springs.

It would take a supprisingly noticeable leak for you to really feel it in the lever.