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Spongy front brake

5K views 15 replies 7 participants last post by  MrZappo 
#1 ·
Okay, I'm about at my wits end: 2008, high mileage blah blah blah.
*I've replace the pads, lubed the calipers real nice and slick,
*New master cylinder rebuild kit including a new diaphragm.
*Stainless brake line.
*I've bled the system about a thousand times, both manual and with my Mighty-vac pump according to all the instructions.
*Clamped the lever overnight to 'burp' the system.

Brake lever still comes down to almost touching the grip.
It will stop me, but was much firmer before doing all this.

What have I missed?
Why won't they firm up????????
 
#2 ·
Sounds to me as if there is an air bubble up high in the system.

With the reservoir about half full & the cap installed and the front wheel turned Left, compress the caliper piston back into the caliper bore.
This will many times purge an air bubble out of the upper banjo bolt & master cylinder bore back into the reservoir. Slowly, smoothly pump up the handlever and repeat.
 
#4 ·
So...

-get a bunch of wet towels to place on painted body parts beneath, to the side, to the front... wherever you figure brake fluid might spray or drip in the area of the banjo bolt on the master cyl. Wear safety glasses and crappy clothes,

-have a spray bottle full of water close by,

-crack the banjo bolt slightly,

-loosen the banjo bolt slowly while squeezing the brake lever,

-watch for fluid and hopefully a burp of air.

Do this a couple of times. Tighten the banjo bolt properly, spray water on any areas you even think have brake fluid on them.

Make sure your reservoir is full, and good luck.
 
#7 ·
Did you replace all the washers in your banjos, they are one use only. Are all of your banjo bolts correctly torqued, and your bleed screw in good condition? O2 molecules are sneaky!

So, now it's time to disconnect the brake line from the m/c (master cylinder) and the caliper. Drain it first!

-Push the brake pistons back as far as you can. I use a "C" clamp and the pads.

***DO NOT LET THE M/C BECOME LOW ANYTIME DURING THIS PROCEDURE***

-Bench prime the m/c.

-Attach the top of the brake line, with new washers, torqued properly, to the m/c.

-Place the caliper end of the hose in a catch can for the brake fluid you're going to lose.

-Pour brake fluid into the m/c until you have a continuous stream.

-Finger and thumb over banjo holes, top off the m/c.

-Pull in the brake lever slowly. If you feel fluid pressure on your finger/thumb, and you should...great. If not buy another gallon of brake fluid and repeat.

-Attach your brake line to the caliper, with new washers!

-Snug the banjo bolt very lightly.

-Wet rags and H20 spray bottle on hand, pull in the brake lever slowly. You should have bubbles and brake fluid leaking around the banjo bolt and "new washers". If not loosen a smidge.

-Hold brake lever tightly to the handle and tighten the banjo bolt.

-Let go of the brake lever.

-Open the caliper bleed screw totally.

-Start putting brake fluid into the m/c until it flows out of the caliper bleed screw.

-When you have a nice flow of fluid from the bleed screw, close it.

-Now..you may start "bleeding" the brakes.

Hoping this will get you going...and stopping!
 
#6 ·
Are you sure that there is much fluid in the system at all? If you open the bleed screw and push the lever do you get a stream of fluid free of any bubbles out?

If you do, and you are bleeding the system, can you empty the reservoir with a dozen pumps or so?

Sound like you have air in the actual pressure cylinder inside the reservoir housing.
 
#8 ·
Use a vacuum pump

I am a mechanic and have had his issue with many bikes often resorting to bleeding the banjo bolt at master cylinder but best results come from using a vacuum pump to bleed the brakes. If you have not used a vacuum pump, they are relatively cheap and easy to use.
 
#12 ·
I am a mechanic and have had his issue with many bikes often resorting to bleeding the banjo bolt at master cylinder but best results come from using a vacuum pump to bleed the brakes. If you have not used a vacuum pump, they are relatively cheap and easy to use.
In his first post he indicated that he had used a vacuum pump.
 
#13 ·
I am starting to suspect the M/C myself. Followed everyone's great advice to the letter. I am quite mechanically minded and do have a vacuum pump. When I rebuilt the M/C it was not readily apparent which washer went where as they looked identical. (even though it was an OEM kit) Could have maybe got them switched.
I'll pull it all apart again and double-check my work.
Sigh...
: /

Thanks to everyone again for their input.
 
#14 ·
Eureka!!
Pulled the master cylinder apart to check my work and all seemed just fine. Proceeded to disassemble the calipers and make sure everything there was as it should be. It was.
Put it all back together and pumped about a liter (pint for you guys south of the 49th) of brake fluid through it for a proper bleed.
There must have been some air bubble hiding in there somewhere, cause everything is hunky-dory now.
Good, firm lever = happy rider!!
 
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