Brakes Not Pressurizing After Reassembly

[b_h_dowell]

I'VE GOT A PROBLEM WITH MY BRAKES. I HAD MY 79 R100RT TOTALLY APART OVER THE WINTER TO DO SOME WELDING AND POWDERCOAT THE FRAME. THE BRAKE SYSTEMS WERE APART FOR 31/2 MONTHS AS I WAS IN CHILE WORKING. EVERYTHING IS TOGETHER BUT I CAN'T GET THE BRAKE ACTUATOR PISTONS TO PUT OUT ANY PRESSURE. THE ONLY FEEL IN THE BRAKE LEVERS COMES FROM THE RETURN SPRING PRESSURES. I HAVE A HAND OPERATED SUCTION BLEED SYSTEM AND HAVE BLED MUCH FLUID THROUGH THE SYSTEMS, TAPPING ALL OF THE LINES, BOTTOM TO TOP, AND WORKING THE BRAKE LEVERS TO NO AVAIL. I HAVE TILTED THE MC FORWARD WITH THE WHEEL REMOVED TO GET THE FRONT SYSTEM ALWAYS RUNNING UP, WITH NO POSSIBLE SPOTS FOR AIR BUBBLES TO COLLECT, STILL WITH NO LUCK. I TRIED TO MAKE UP A PRESSURE FEED SYSTEM FOR THE REAR BRAKE SINCE THAT RESERVOIR CAP HAS A NIPPLE ON IT BUT FLUID LEAKED FROM THE NIPPLE HOUSING. I HAVE LOOKED FOR NEW PLAIN CAPS TO ALLOW ME TO FIT NIPPLES AND PRESSURIZE BOTH RESERVOIRS BUT HAVEN'T BEEN ABLE TO FIND CAPS. THE CAPS ARE OF 2 DIFFERENT SIZES. HANDY! I HAD HAD THE BRAKES APART 2 YEARS AGO WITH NO PROBLEMS WITH THE FRONT SYSTEM BUT THE REAR PISTON HAD SEIZED AND WAS IMPOSSIBLE TO FREE UP SO I HAD TO BUY A NEW ACTUATOR PISTON ASSEMBLY. IS THERE ANY THING ELSE I COULD TRY. THIS HAS DELAYED MY RETURN TO OPERATIONS FOR 2 WEEKS. THANKS

[Rbike]

If the line was off of the master cylinder, and it was open to air then it will need to be 'bench bled' seperatly to regain operation. Bench bleeding means to remove it from the system and recirculated the fluid from the output port back to the resevoir. You can do this by attaching the brake line and putting the other end in the resevoir. Pump the master cylinder with both long slow strokes ans short little vibrational types until no air comes out of the hose or the small port in the bottom of the resevoir. without doing this it is nearly impossible to get all the air out while bleeding it installed in the system.

If it wasn't opened, I have also bled brakes with vacumm and with a pressure method, to the point that I don't see any more air and have had your problem. It always has turned out to be a line that isn't sealing properly. So if it isn't bleeding, you have a sealing problem, otherwise it's possible the master cylinder is bypassing and will need to be replaced.

Good Luck

[R100RS]

Hey Dwight! Welcome aboard.

[Rbike]

Mike...Funny that I'll probably see more of you on this board than in town...NOW GET BACK TO WORK:)

[Rbike]

I just remembered another trick to use when you bleed your brakes...

After finishing the bleeding process I use a zip-tie wrapped around the brake lever and hand grip. I squeeze the lever firmly and hold it in that position with the zip-tie. Leave it that way overnight and the brakes always feel firmer than before.:idea

[coyotebmw]

Hey RBike, What do you think using the zip tie on the brakes does? I changed my brake fluid yesterday and am still not totally happy with the feel of the brakes. Any secret to bleeding the brakes, other than the zip tie trick?

[Rbike]

I think that no matter how well you bleed them that a very tiny amount of air is always stuck in the rubber cups of the master cylinder. So when the lever is pulled in, the air is allowed to rise into the resevoir. Without agitation it probably takes a long time...yet I haven't tried agitating the cylinder for any period of time to see if it works better or faster than securing the lever overnight.:dunno

[Rbike]

Oh yeah...bleeding tricks? I always hear from others that the speed bleeders work really well for doing a one man brake bleed process. I don't seem to have a proble reaching the master and the bleeder valve at the same time.

I attach a piece of clear tubing to the bleed screw to run the excess fluid off neatly. Then when I am about finished, I hold the tube straight up in the air for the last couple of pumps. As the fluid fills the clear tube you can see if any bubbles are comming out. If the bubbles never cease, try removing the bleeder screw and applying a bit of thick grease to the threads to help seal it when it's open. Sometimes the air you are seeing is comming from the threads and not from inside of the caliper.

[kbasa]

I use teflon tape on the bleeder threads if I'm having trouble. Probably works about the same.

FWIW, I have SpeedBleeders on the RS and will be bleeding the brakes this weekend. The advantage is that you don't have to play the wrench game on the caliper. You put the tube on, stick it in a jar and start squeezing the lever until the fluid comes out clear. Since you're standing up near the reservoir, you just pour fluid in as needed. Makes it really easy, especially for the left caliper.

dave

[b_h_dowell]

Thanks a lot for the suggestions. I have managed to get the front brake working by removing the actuator assembly , immersing it in brake fluid and working the brake lever until it was obvious that it was pumping. I then reinstalled it and finally had some brake lever feedback. With a bit more bleeding the rubbery feel disappeared and it works fine now. I tried something similar for the rear brake; I removed the piston outlet fitting and attached a source of brake fluid there. Working the foot brake I started to get some obvious brake fluid movement but when I reatteched everything it still wasn't getting any pressure. I will try some of the other suggestions later today. Thanks a lot!

[amiles]

Originally posted by b_h_dowell
I tried something similar for the rear brake; I removed the piston outlet fitting and attached a source of brake fluid there. Working the foot brake I started to get some obvious brake fluid movement but when I reatteched everything it still wasn't getting any pressure. I will try some of the other suggestions later today. Thanks a lot!

I believe that some ingenious airheads have found that the rear wheel cylinder must be removed from it's mounting (not the hydraulic line) to bleed. Reportedly the bleeder is not at the highest point of the caliper which due to the law of physics is where it must be to bleed.

A spacer mimicking the rotor placed in the caliper so as to prevent over extension of the piston (wooden shim works here) is next.

The caliper is then oriented so that the bleeder is at the highest point & then bleeding is done in a usual manner pumping & refilling & repeat.

when done re attach the caliper.