No Pedal on R100RT

jim in the north · Post by **jim in the north** » Sun Apr 29, 2012 8:43 pm

Istalled new flex rear brake line ( nicked) and rear wheel after a doing a tire replacement. I have bled the system but can't get back to original amount of free play on the brake pedal. Pedal now goes down about 2 to 3 inches before it firms. It will stop the bike but not well. Doesn't feel spongy and doesn't creep further down when I hold pressure on it. I got steady stream of fluid on the bleed stroke so I don't think it's air in the line. Reservoir is topped up. This is a disc brake. Does anybody know what could cause this change in free pedal just by doing the little bit of maintenance that I did?

schrader7032 · Post by **schrader7032** » Mon Apr 30, 2012 6:52 am

I don't have a rear disk brake on my bikes, but I've heard that you need to remove the caliper and rotate it so that the bleed nipple is at the very top. Put something between the pads and bleed like normal.

jim in the north · Post by **jim in the north** » Mon Apr 30, 2012 10:50 am

Thanks Schrader 7032,

I'll try it. Sounds like somebody discovered that air can get trapped if the bleeder plug isn't at the top. Hard to imagine but I'll give it a try.

jim in the north · Post by **jim in the north** » Mon May 07, 2012 8:15 am

I tried rotating the caliper assembly like Schrader suggested so that bleed valve was at the top when doing the bleeding. Maybe helped a little but still too much motion on the pedal until she starts to bite.
Unsafe really. I am now going to try siphoning the brake fluid with a syringe tool.
By the way, I only have about 3/16-inch pad thickness left. Could this be part (or all) of my problem?
Manual talks about pads being OK down to the color line. I don't see a color line.

jim.mcmahon44 · Post by **jim.mcmahon44** » Mon May 07, 2012 9:24 pm

This might sound a bit crazy, but I have seen master cylinders build up corrosion in the "non-active" part of the bore,to the point where a weak return spring can't overcome it and prevents the piston from returning all the way back to where it was before you started bleeding the system. When bleeding, the piston is going over bore surface it never sees in normal operation. A possible change in effective fluid volume downstream (larger ID, CLEAN new lines...) coupled with this could cause the symptoms you describe. Highly recommend a master cylinder clean and hone, and a rebuild kit, then re-bleed, because it sounds like your piston is not going back to its normal "rest" position. I am a big believer in Mity-vacs, and they usually move sufficient fluid volume so you don"t have to worry about bleed nipple orientation. There are some articles out there that talk about how cautious you need to be if you are NOT rebuilding the master cylinder, because if the the piston gets into the corroded part of the bore (in front OR in back), it will damage the seal and set you up for a true failure.
Just a thought....
Jim

jim in the north · Post by **jim in the north** » Thu May 10, 2012 10:24 am

The problem is solved. Took the bike to a friend who has a syphon pump and he gave her a good sucking. That coupled with a little more old fashioned "pump the pedal and open the bleed nipple" cured the problem I now have pedal and it's safe to ride. Thanks for the input guys.

jim in the north · Post by **jim in the north** » Tue Jun 02, 2020 9:00 am

Does anyone have a suggestion on how to re-label this worn-off lettering on my R100rt?
I have thought about lettraset with a coat of varathane but I don't think it would survive the first good rainstorm.
Jim

Vintage BMW Motorcycle Owners