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Need rear brake help

cruisincruzan

cruisincruzan

Ute's Chauffeur
Just awakened my ‘14 9T from winter sleep and decided after 5 years to put in a new battery. No issues put everything back together ride away and no rear brake. Front works fine no other problems I can detect. I didn’t do anything else to the bike and when I put it away everything worked. I flushed the fluid, no improvement. Before I bring it to the dealer a logistical PITA thought I would check if anyone had any suggestions. Thanks
 
1) Is there brake fluid in the rear reservoir?

2) With the bike off and on the center stand, spin the rear wheel and apply the rear brake with your hand. Does it stop? Does the pedal go all the way to the bottom stop? Does it feel mushy (a dea giveaway that there's still air in the system.

3) Are you familiar enough with flushing brake fluid to know, for sure, that there air isn't still trapped in the system?

4) Do you have a GS-911 (or know someone who might, say, in your local BMWMOA club) to check for codes and try running the ABS pump and flushing the brakes again? Does the ABS system warning light come on (I have a '13 Camhead, same engine but a year younger so a '14 9T might be different in this regard)?

5) Did you compress the rear brake pads when flushing? Air could get trapped in the caliper pistons. Even a tiny bubble would be enough to severely affect braking.

These are just some ideas.
 
Assuming it's like my RT, the rear brake fluid lines start at the reservoir, through the rear master, then it goes forward to the ABS actuator then back to the rear caliper. It a long run and a lot of tubing. It take a long time to work new the fluid through all that tubing. You should bleed it again and be EXTREMELY careful not to accidentally draw air into the system. It happens to me all the time. Bleeding brakes can be tedious and I sometimes lose the open-pump-close-release rhythm and next thing you know there's a huge air bubble in there.
 
Also, check if the brake line is not twisted under the reservoir.
The rear reservoir is only held by a clip and tends to twist when you screw the cap back on it.
 
Thanks for the advice I will look at it again. To clear up my initial post, this happened before I bled the brakes. I bled the brakes hoping this would fix the issue. The fluid was in the middle of the lines. If I jack up the bike and spin the wheel by hand, press on the rear brake the pads contact the disc but I can still turn the wheel by hand. When I rode the bike there was no noticeable slowing of the bike. Brake line not twisted. I will see about the 911.
 
Hmmm...remove the rear caliper and see if you can determine if the pistons are frozen (corroded)?

I'm speaking generally here because I don't specifically know how these calipers go together exactly (I've done something like this with my car's calipers in the past):

Push the piston(s) all the way back into the caliper and then, using the pedal, see if they move. Be careful not to over extend the pistons as they might pop out causing more headaches. Maybe find something that's just a tiny bit thinner than the disk for the pads to land on but enough that you will move the pistons beyond where they are now. Does that make sense?

If there's no air in the system and it was present before you bled them but after a long cold winter (New York State right?) in storage I could see corrosion being a possibility.
 
Line is not twisted, removed the caliper, press on the brake piston moves slightly, press a few more times and it did not move enough to clamp on to the large screwdriver blade I had between the pads. The area that the piston is in has no discernible corrosion, and the part of the piston that protruded looked clean. Should I try getting a rebuilt caliper or is this caliper fixable? I have replaced calipers, but have never rebuilt one.
 
Put everything back together and took a ride. The rear brake barely slows the bike, although there were a few times that it actually worked. I have to press on the brake very hard and to the limit of travel to get any activity. Most of the time it does not feel as if there is any resistance throughout the brake pedal travel. How about some penetrating oil where the pistons slide out? I will also try bleeding again.
 
I just finished flushing/ bleeding the brakes on my RS. I rig up a device that allows the rear brake to be held full on maximum travel and leave it that way overnight to push any residual air out of the system.
I use one of those cheap fan belt tighteners that two pads expand as you adjust it. but you may just use a short stick cut to the correct length and add wedges to get the final full travel on your brake pedal.

I burp the front and rear brakes overnight , always have great brakes afterward.
 
Did some penetrating oil, kept working the pistons and did repeat bleedings using the “traditional” method rather than my ez bleed. I now have brakes. My theory there was some corrosion that prevented the pistons from extending normally and my initial bleeding did not do the trick. At least that makes sense to me. My question is how to prevent that from happening next season. The bike is kept in an unheated, well insulated garage on a battery tender.
 
I know it can be rough in central NYS but probably the best solution is to take it out out for a short run every now and then. This, in addition to just exercising them, gets some heat added to the equation.
 
Glad your up and running, sounds like you had and air bubble in the system, bloody things will give you fits.

I have found caliper pistons will get a ring of crud (brake dust, mud, salt, etc) caked up on them that can slow or prevent the pistons from moving well, my old Triumph was notorious for this. Part of my annual maintenance is to remove the brake pads, shoot some cleaner on the pistons and give them a quick scrub with an old tooth brush, then recoat pins and sliding points with anti seize and reassemble.
 
Sliding calipers (pistons on only one side, like most rear brakes and a few front ones) need to slide well in order to work properly. If they don't, then once the non-piston pad wears the braking force just flexes the disk away from the piston and you have reduced effect. At least once per year I have to free up a caliper that doesn't slide any more.
 
cruisincruzan said:
Did some penetrating oil, kept working the pistons and did repeat bleedings using the “traditional” method rather than my ez bleed. I now have brakes. My theory there was some corrosion that prevented the pistons from extending normally and my initial bleeding did not do the trick. At least that makes sense to me. My question is how to prevent that from happening next season. The bike is kept in an unheated, well insulated garage on a battery tender.
Click to expand...

I have a grave concern with the use of penetrating oil. Typically seals designed for brake fluid don't tolerate petroleum well. There is much discussion about this concerning the hydraulic clutch circuits when BMW switched from DOT 4 to Mineral Oil and what happens when the wrong fluid is used. Monitor things carefully.
 
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