MASTER CYLINDER UPGRADE (2011)

swooshdave · Mar 1, 2011

dave M said:
Swooshdave, I agree with what you have said, I also doubt that one would have occasion to rebuild a master cyclinder for a number of years, but my response was to the post by Russ, commenting that he didn't appreciate that the kit he was referring to wasn't owner-serviceable. 20 years down the line the people who did the modification may not be in business any more, however if owners are aware that the internal parts from another machine will probably fit they at least have the chance to keep the bike on the road. I repair classic cars for a living and, as Hobot has said, often an ancient master cylinder can be repaired with a good cleaning, perhaps a light hone and new seals and dust covers. I have a friendly local parts shop who will measure seals or pistons and try to match them up for me, I always chuckle when I find a Daihatsu part that fits a classic Ferrari or something equaly exotic.

Hopefully when we are gone the bikes will still be serviceable and giving the next generation as much fun as we have had so far.

By the time these master cylinders need rebuilding the original converters will not be worried about the warranty. Nor will the the owners and they will be too old to ride. :wink:

If you're so concerned, buy the resleeved unit, take it apart, void the warranty and find out what seal they are using. It's not like they used a custom seal.

Or buy it, use it, forget about it. :mrgreen:

speirmoor · Jan 28, 2017

My resleeved 13mm MC has become spongy. Any tips on how to get it back to the way it was? I know pumping the MC wont help but those instructions with the syringe etc has got me scratching my head

gtsun · Jan 29, 2017

Like many here I found it very hard to bleed but if it is spongy you should change the fluid if it is old. If it's an old rubber line You should replace it with the steel braided one. And as for bleeding the only way to get rid of all of the air that I have found and many here is to tie the handle back and leave it with the zip tie or rubber band overnight. This seems to be the only way to get the pressure back that I have found.

kommando · Jan 29, 2017

To add to Gtsun, have the bike on the side stand and the bars turned so the master cylinder is at its highest position.

Deets55 · Jan 29, 2017

speirmoor said:
My resleeved 13mm MC has become spongy. Any tips on how to get it back to the way it was? I know pumping the MC wont help but those instructions with the syringe etc has got me scratching my head

John,
I have always had success using a syringe. Drain the M/C, fill the syringe making sure there are no air bubbles, attach it to the caliper bleeder and force the fluid up to the M/C. If you have a helper have them tap the caliper, lines and M/C with a rubber mallet or screwdriver handle and try to get the air bubbles to break loose and move. For your system to get spongy all of a sudden makes me think something else is going on. Flexible brake lines, M/C seals or even fluid moving past sleeve in the M/C might be part of the problem. Lack of use might be causing a temporary problem. Tying the brake lever back seems to work sometimes. I am not sure if it causes the M/C seals to stretch out and seal better or maybe it gets the piston seal to sit square in the bore. I think (no proof, just an opinion) that the square piston seal will sometimes roll just a little bit instead of sliding causing the piston to spring back too far when the lever is released. Good luck.

Pete

Pete

JimNH · Jan 29, 2017

I got the best bleed by removing the master cylinder, tipping it so the reservoir is up, and bleeding from the bottom with a pressure bleeder or syringe. I believe those instructions came with my sleeved cylinder. I, of course, ignored them until my usual method didn't work. I found that tying the lever back was only a temporary solution and the lever got soft again. Bleeding per the instructions above and it's never need attention again.

speirmoor · Jan 29, 2017

Lack of use is probably the culprit as the bike was laid up for other mechanical issues for more than 6mo. It has a brand new steel braided line and my mechanic tried the traditional way to bleed it but with minimal success. It worked but only at almost full pull. Of course I couldnt leave it alone and messed around with it and now here we are. I got some syringes and tubing coming so gonna try that next along with your input.

speirmoor · Feb 3, 2017

ok tried the syringe method same result. Tapping with screwdriver handle rubber mallet and I'm not seeing any bubbles. I have brake but only at Full pull. Its not progressive like it used to be. Whats next? Someone suggested leave overnight in the most up position. Is that with Brake lever pulled in or normal position?

madass140 · Feb 3, 2017

pulled in

Deets55 · Feb 3, 2017

speirmoor said:
ok tried the syringe method same result. Tapping with screwdriver handle rubber mallet and I'm not seeing any bubbles. I have brake but only at Full pull. Its not progressive like it used to be. Whats next? Someone suggested leave overnight in the most up position. Is that with Brake lever pulled in or normal position?

If the M/C was empty and you forced the fluid up with a syringe till it gets full and you still have a problem I believe either the M/C seals gave up the ghost or fluid is leaking around the reducing sleeve. This is assuming the brake pucks are not retracting a lot off the rotor.
Last resort without rebuilding the M/C is to disconnect the line at the master cylinder and try to bench bleed it. Long shot but it may work. Wish you were closer I'd run up and give you a hand.
Pete

JimC · Feb 3, 2017

I've always had good luck power bleeding brakes. I use a small weed sprayer and a master cylinder cap with a barbed connector fitted to the cap. You do have to drill a hole in the cap to fit the connector, so you need a spare. Works on ABS brakes, as well as non ABS brakes.

B+Bogus · Feb 4, 2017

I've had good results by unbolting the caliper and pushing the pistons back, either by simply twisting the caliper carefully against the disc or with a tyre lever.
In my experience old brake hoses have been the culprit when I've struggled to bleed the brake, and I've wondered if it's due to corrosion within the hose.
New hoses have always bled through without issues, possibly because the air bubbles have nothing to adhere to?

The re-sleeved master cylinders I've used have all been issue-free, but a few folks here have had problems.

Tin Man · Feb 5, 2017

bmwbob said:
I've had a 13mm sleeved master cylinder for years and loved it. Then I hit some diesel fuel and scraped up the right side and had to replace the brake handle. Unknown to me the blade was a little out of specification and brake fluid return wasn't fully opening. I had a hell of a time bleeding brakes, then while riding the brakes started locking up due to fluid heating up and unable to return to brake resivoir efficiently. Finally after going through a quart of brake fluid and warping two rotors the out of spec blade became apparent! Just FYI! :cry:

The RGM website has posted good technical article about this subject. It also has a warning about why it's so difficult for the hobbiest to set up a relsleeved master cylinder properly.

speirmoor · Feb 15, 2017

Last evening I swung by the garage and pulled the lever in to the handlebars and secured with baling wire. Cocked the bars to the right and left the MC cap loose and left overnight. Went back this evening and I have full brake. I mean I can't even get it close to the bar. TBH I didn't think it would work but it has. I went for a quick ride around the neighborhood and all is good again. Thanks guys!

gripper · Feb 16, 2017

In theory that shouldn't work because pulling the lever in has trapped the fluid between the master cylinder piston and the calliper, giving it no route to allow any air to rise to the reservoir. Unless your MC piston has not gone past the port in the bottom of the reservoir. But if it works win win.

madass140 · Feb 16, 2017

my theory is with the lever pulled in overnight the air travels up the hose to the piston but not past it. In the morning when you release the lever
from the bar only then does the air pass back in to the bore and then to the reservoir, I dont know how many times I've recommended this fix.
Don

Craig · Feb 16, 2017

Don is correct 'bout air actually waiting for you to release lever .... this method has worked on all types/makes of bikes since the dawn of hyd. disc brakes for motorcycles ....
Craig

xbacksideslider · Feb 16, 2017

Could be that bubbles are stuck somewhere and when they are squeezed down to a far smaller size by hours of fluid compression, they are easier to dislodge, lose surface tension/attraction, or some similar phenomena. Once dislodged, they float up to the return port.

speirmoor · Feb 17, 2017

madass140 said:
my theory is with the lever pulled in overnight the air travels up the hose to the piston but not past it. In the morning when you release the lever
from the bar only then does the air pass back in to the bore and then to the reservoir, I dont know how many times I've recommended this fix.
Don

Don
If it didnt work I was going to ask you to hurry up and make something for this model. I know your busy so win win

John

Nater_Potater · Feb 17, 2017

gripper said:
In theory that shouldn't work because pulling the lever in has trapped the fluid between the master cylinder piston and the calliper, giving it no route to allow any air to rise to the reservoir. Unless your MC piston has not gone past the port in the bottom of the reservoir. But if it works win win.

I'm questioning if it's truly trapped air in the system. I too have had this happen a number of times in the past on other motorcycles. It wasn't until rebuilding the caliper on the Norton that I really took this phenomenon to heart. I had the caliper off the bike, shoved a thick piece of metal into the disk opening, and rolled the caliper around while bleeding the system until I was confident all air was out of the fluid path. Once the caliper was re-attached to the stanchion tube, the pistons could be seen moving out with a pull on the lever, but then retract back as the lever was released! 'Last time I checked, there were no return springs in the pistons... I assumed that the new caliper seals had a good enough grip on the pistons that they were flexing everything back to battery once pressure was relaxed, rather than sliding along the piston's sides.

Like many others, I strapped the lever to the grip and left for the night. The next day, while closely watching the pistons, the lever was released. Presto! No piston retract! That, and the fluid level in the reservoir dropped noticeably as the M/C piston returned to rest and opened the ports.

Nathan

MASTER CYLINDER UPGRADE (2011)

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