Bleeding woes on new master cylinder.

[Jaymichael]

Hey guys, I am hesitant to make this post, I know there are quite a few threads related to this issue. I was going to give it another go on my own tomorrow but I'm feeling pretty deflated at the moment. Turning wrenches on cars for 15 years I must have bled a couple hundred master cylinders but this things got me licked.

My parts, Hughs Handbuilt slimline master cylinder. Stock rebuilt single piston caliper. 1 piece stainless line from master to caliper.

Attempts made. Caliper and line filled with fluid prior to install. After install used vacuum type bleeder on system, ran about 6 to 8 master cylinder fills though the system, zero lever feel achieved. Performed typical pump, hold, open bleeder screw, tighten bleeder screw rinse repeat about 30 to 40 times. Noticed very slight resistance in lever just before touches bar. performed gravity bleed to system various times, bleed master by cracking line on exit of master cylinder at banjo bolt many times. Went back over system using all these methods over and over, threw wrenches various time

I feel like I tried every variation I can think of, my master is perfectly level, Im just not getting anywhere. I would say I feel brake resistance start at about 70% lever pull and it will not touch the bar now. I gently rode around my parking lot at school and the front brake does function, but the travel is way too far for my liking and there is no way I could lock the front brake up even if I tried. I left the master open for the night, hoping any air trapped may migrate up top.

So, any thoughts guys? Something I'm missing here? Any help appreciated.

 

[weaselbeak]

I bleed the master by itself with the line taken off. This saves a butt load of pumping for nothing. Block the hole with my finger and in only a few pumps it's shoving plenty of fluid. Then put the line on and bleed traditionally. If I don't get quite the lever I want I pump it as good as it gets, tie the lever to the hand grip fully depressed with a zip tie and leave it set overnight.

 

[Brassneck]

Sounds like you have literally tried it all. Not sure I have any other insights other than to follow-up with Weaselbeak's comment...are you getting good pressure from the master cylinder itself? (Remove brake line, and hold finger over it to see if it's pumping well?)

Are you getting any bubbles out of the bleeder valve? (I use a clear hose pressure fit on that nipple and then hang it over the caliper before coming down to a cup. So as I open the bleeder valve, the brake fluid rises up, forcing the air bubbles up to the top and away from the bleeder valve and so can't really return into the caliper as I close it off...

I also am a fan of just smaller pumps at the lever...then hold for 30-60 seconds, before I repeat...for some reason, this seems to work best for me.

Sorry I couldn't be any help...sucks when the concept is so simple...and yet nothing works. I bet leaving the lever squeezed open over night will help.

Good luck.

 

[weekendrider]

Was pushing fluid back with a syringe or turkey baster trisd?

 

[kevski]

I always found air gets in around the bleed nipple on the caliper when opening and closing, so for many years now i take that right out and put a little plumbers tape on the thread put it back in and bleed using a syringe to draw through while bleeding it takes me about half an hour tops to do one brake. Maybe the master cylinder is not functioning as it should.

 

[TwoManyXS1Bs]

If it has that spongy "trapped air pocket" feel, remove the caliper, pump the piston out about 1/4", dangle the caliper so the hose fitting is topmost, tap it a little to dislodge any bubbles, do the 'C' clamp trick on the piston, look for bubbles in the reservoir, repeat...

 

[ThatXS650Guy]

I have that same MC from Hughs. You are going to like the improvement.

I always perform a "bench bleed" on the bike. Open the lid to the MC so you can observe the fluid. Now perform several slow partial squeezes to the brake lever. You should be able to observe bubbles coming from the inside ports. You have to coax them out with short and long squeezes to the lever. It can take a dozen or more but just keep going until you can't see any more bubbles and the lever firms up. Be careful you don't splash brake fluid everywhere. The key is slooooooow and gentle.
Good luck,
Jim

 

[gggGary]

Are both ports on the MC open? if that tiny second port is plugged or (sometimes happens) not drilled through to the piston you will never get it bled. is the line 100% up hill the entire route? any "downhill" area will leave an air bubble that won't escape. Better luck I have done the wrench whip thing a time or two....

 

[member3480]

I don't know if this will help but I did have some problems with some aftermarket masters with the wrong handle and it was not allowing the piston to close all the way. What I did to get it to bleed correct was remove handle and just use a small socket on a extension and bleed with out the handle. It worked and then I just filed down the handle to allow the plunger to close all the way.

 

[Punkskalar]

For whatever reason, no matter what brand the bike is, or how many times I've done it - Bleeding front brakes with a new master cylinder has either gone one of 2 ways.

1. Smooth as silk, with no extra effort

2. Cuss, kick, moan and groan, finally remove the master cylinder, bench bleed it, remove the handlebar grips to make sure I have full throw of the cylinder, get some brake fluid in an old cut to remind me of how much that burns, and then after 2 hours it works....

I also responded to your email, but for a new install, typically a bench bleed is in order.

Hugh

 

[Jaymichael]

Frick, you guys are awesome, thanks for the information and tips! For Gary, yes both ports are open, and yes when I bleed it right at the master cylinder I seem to get good flow and pressure coming from the banjo bolt. Tonight I will remove the master towards the end of the bars to ensure I have maximum travel of the lever and Ill try the slower strokes method. Keep you posted. Thanks again