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Front brakes!!! ARRRRGH!

3K views 13 replies 9 participants last post by  BobS761 
#1 ·
I have been riding my 2004 750 Aero all summer with a brake handle that I can pull to the grip. I changed my brake fluid last year. I never got the pressure back. I have bled traditionally, I bought a reverse bleeder, I bought a speed bleeder, I have tried a vacuum bleeder, I have bled the banjo bolt at the MC, I bought a kit and rebuilt the MC. What am I missing here? Never in my 38 years of riding have I ever not been able to bleed a brake line. Is there a secret to the Aeros that I don't know?


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#4 ·
are the slides and piston moving freely on the brake caliper?

what state is the hose in, time for a braided line?
 
#5 ·
Is there more than one banjo bolt connection than at the mc and caliper? If there is, you may want to bleed from there as well. It may go without saying, but double check you put the right fluid in. I have accidentally grabbed the wrong bottle before, thankfully realized it before pouring.

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#6 ·
I`m still thinking on this...
;)


Pads?Are they in good shape?
Pistons moving freely in the caliper?
Are they clean and lubricated?
Operating correctly?
What about the rotor?


Point??
There are other parts to the brakes system to check too...
I might suspect hoses next..
Are they in good shape?
You mention you rebuilt the master cylinder, is it functioning correctly?


Dunno what the deal is here?
Bring it over, you & I will figure it out,
D
 
#8 ·
Pads?Are they in good shape?
Pistons moving freely in the caliper?
Are they clean and lubricated?

Pads are good. Bike is never ridden in the rain, and obviously not in the winter, so no road salt to eat things up like a car. I never thought to check the pistons, but because I had all kinds of brakes prior to the fluid change,I would have to say they're fine.

Someone else mentioned the proper fluid. I used DOT 4 Synthetic.



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#9 ·
Many times with cars I've seen perfectly functional calipers have the pistons get stuck when bleeding, as the process brought all the skunky fluid and contamination through the system where a chunk of crud lodged between the piston and the caliper bore. Happened a couple times on my own car which has six piston dual bleeder fronts which drive me insane.
 
#7 ·
Sounds like you've covered all the likely spots where air could be trapped.

Your problem is likely with the master cylinder. Likely will have to be rebuilt again. Don't know if the bore is bad but if so you might have to hone it.

Three things tend to happen with master cylinders on older bikes. The small hole in the bottom of the master cylinder gets plugged, the piston in the MC gets overtravelled and damages the rubber seal at the front of the piston, and the piston in the caliper sticks.

My gues is that you've overtravelled the MC piston. So get another kit, tape a 1/2" socket on the handlebar, between the throtle grip and the brake lever ( this prevents the lever from going right to the grip which damages the seal on the piston ). Install the kit, fill the reservoir with proper brake fluid, install new crush washers at all banjo bolts ( if they've been disturbed ). Don't touch the front brake lever. Bleed at bleed valve at caliper, using a vacuum bleeder ( sounds like you have one ). Once you get all the air out of the system, then go to the front brake lever and see if you have pressure. Hold a rag over the master cylinder, and look for a squirt of brake fluid when you pull the lever, that tells you that the small bleed hole in the MC is working properly. Or just go ahead and put a known good MC on the bike. Sometimes that ends up being the onkly thing that works. That's what I ended doing in one case that I couldn't get the old MC to work properly.
 
#11 ·
I would look at the master cylinder again or keep bleeding to see if that fixes it. One bubble will make you crazy. The pistons , pads and calipers won't cause a soft lever if the hydraulic system is tight and properly bled. If the pistons were sticking the lever would be tight but it wouldn't stop well because of a lack of force at the pads. If the pistons leak that will be seen as fluid on the outside of the calipers. Sometimes it is possible to put the master piston cups on backward and have no pressure build up.
 
#12 ·
Ok so I sucked the MC dry and removed it. Seals are good and over travel of the piston isn't possible in this bike. What I DID discover is that there are no copper crush washers on the banjo bolt at the MC. I don't know if there are any on the caliper, as I have never had that apart. Could this prevent me from being able to build pressure?? I know it sounds stupid to ask, but I only ask because there is no leaking around it. I would think brake fluid would seep out of there if there wasn't a good seal


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#13 ·
That would be a good reason to not build pressure. No crush washer or reused crush washers could definitely be preventing pressure build. Usually, you can visually verify installation of the washers without removal. Installing new washers, do not tighten the banjo bolt all the way, bleed it some, once you've gotten all the bubbles out, then completely torque and seat the washers in. That's the way I've done it and had plenty of success. Hopefully your mc is not a culprit in itself and you can get this fixed! Good luck.

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