At at loss with front brakes

Emm81 · Post by **Emm81** » Thu Feb 11, 2010 4:18 pm

I'm totally stumped with my brakes.

I rebuilt the front calipers a few months ago - new pistons and seals - nice and clear etc.

Put them back together, filled the system, bled it and got a nice bit of pressure on the lever. Brilliant. But within a few miles of riding, the lever just goes soft again. Comes right back to the bar.

I've tried bleeding them again, tried the lever cable tied to the bar overnight trick... Each time the same problem - firm lever, then spongy within a few pumps.

Any suggestions?

Could it be I've done something wrong when refitting the pistons/seals?

Any advice appreciated! Emm

scooble · Post by **scooble** » Thu Feb 11, 2010 5:02 pm

I oftern found bleeding brakes a right PIA even using a mityvac pump, however, all that changed when I fitted a radial M/C with a bleed nipple on it. Bleeding brakes now is a 5 minute job. If you haven't got a bleed nipple on the M/C, I guess you could try cracking open the banjo bolt whilst squeezing the lever.

Bikemike · Post by **Bikemike** » Thu Feb 11, 2010 5:51 pm

Contaminated fluid?
Sounds like moisture in it could be boiling when they get hot.
Could be worth trying a complete flush and refill with fresh fluid from a different brand new bottle, I've had bad fluid from a sealed bottle before.

Mike

headcoats · Post by **headcoats** » Thu Feb 11, 2010 7:43 pm

scooble wrote:I oftern found bleeding brakes a right PIA even using a mityvac pump, however, all that changed when I fitted a radial M/C with a bleed nipple on it. Bleeding brakes now is a 5 minute job. If you haven't got a bleed nipple on the M/C, I guess you could try cracking open the banjo bolt whilst squeezing the lever.

I had loads of hassle trying to bleed my brakes and did get there eventualy,but i too have invested in a radial master cylinder with a bleed nipple on top and i hope to fit it in the next few weeks.

Tambo · Post by **Tambo** » Thu Feb 11, 2010 8:01 pm

I'd agree, it can be tricky due to little things like angle of master cylinder, pipe routes, and the angles of openings within the caliper. A bike master cylinder only moves a relatively small amount of fluid, and it's trying to push air down, so it doesn't take much for it to trap somewhere, and float up again !!

A trick I've found - get the master cylinder so that the outlet is below the lever end slightly. Remove it from the bars if you have to. Suspend the reservoir, and take the lids off. Now apply the brake lever very slightly (making sure the lever is still higher than the outlet). Keep applying it on and off, and if it's worked you'll see tiny bubbles rising up into the reservoir.

Normally does the trick after you've tried all the conventional ways !!

Good luck.

JanBros · Post by **JanBros** » Thu Feb 11, 2010 11:20 pm

maybe the master brake cylinder needs to be refurbished to

kwackman12 · Post by **kwackman12** » Sat Feb 13, 2010 12:31 am

Never had any problem since I fitted braided hoses, they seem to bleed a lot easier

john-b · Post by **john-b** » Wed Feb 17, 2010 12:04 am

if the lever goes over a period of time its probably the master cylinder seals 9 times out of 10 if that helps

Emm81 · Post by **Emm81** » Sat Apr 24, 2010 7:44 am

Got this sorted the other night (yes I know it's been a while, but the sunshine has prompted me to get my arse back in the workshop).

Took calipers off and pumped pads all the way out with the reservoir cap off - then pushed them back - shoved them back on and BOOM: lever pressure at last - feels like a new bike. Very impressed!

Now, out to create a little smoke on this sunny day