no rear brakes in high altitude - Harley Forum

#1 10-03-2009, 10:45 AM

here's the problem i got i go for a ride up into the mountains elevation ranges from 5000 to 8000 feet and then i go to hit the rear brakes and there's nothing therethen I get home which is around 100 to 200 elevation and then they are back I've rebuilt the master cylinder and caliper and the brake pads are new and to no prevail it still has no brakes in high elevation any help would be much apreciated and there is no problem with the front what so ever

unclepsycho · #2 10-03-2009, 11:23 AM

Welcome to the forum jdog,
I gotta wait for some of the other experts to log on and check out this one. What kind of bike do you have? Has anyone else done anything to the brakes ?
Hmmmmmm

milindh · #3 10-03-2009, 12:05 PM

Seems like, even though you've rebuilt the brakes, you still have some air in the lines. As you go up in altitude the air expands and you'd have to move the pedal further to get any stopping power. That's my guess anyhow.

Good Luck Dude

#4 10-03-2009, 05:49 PM

the bike is a 2005 fatboy for the second reply when I get back down to lower elevation all you got to do is barely touch it and the tire is skidding I've asked other riders and mechanics and it doesn't seem possible it goes from 1" to stop in lower elev to 5" in high elev and it don't want to stop

unclepsycho · #5 10-03-2009, 06:18 PM

Good idea, milindh, Air in the system does make sence. As the altitude increases, so does the air volumne in the system the air will then in turn force the brake fluid back up into the reservoir making it need to travel farther to do it's job when you apply the brake.

Try this: take off the master cover, and tap lightly on the brake lever....... watch for bubbles. Tap lightly for approx 1-minute, if nothing comes out, leave that cover off and then open up the bleader valve on the caliper and tap lightly with a plastic hammer or something that wont damage the finish of your caliper. the vibration should make the air move, if it is close to either end. I did this on my BMC and it worked fine, but then.... I didnt have the altitude problem, just the air in the line.

good luck

unclepsycho · #6 10-03-2009, 06:22 PM

Adding to what I posted above..... watch the fluid level in the master when you open the bleeder, keep it topped off as it runs out the bleeder... but you already knew that....

jimkelley · #7 10-03-2009, 07:56 PM

What Unk and milindh said. I haven't had to do any serious caliper rebuilding lately, but what he said regarding atmospheric pressure makes perfect sense. Since the brake line is sealed off from the outside air, it acts like a balloon (the air bubble) expands as the outside air pressure becomes lower at altitude. Go for another bleed. By the way I live at 7,000'. Unclepsycho rocks!!

unclepsycho · #8 10-03-2009, 08:17 PM

Thanks for the compliment....

What would happen if you went up to the highest elevation, and took off the master cylinder cover??? would that "burp" the system easier???

#9 10-03-2009, 10:54 PM

thanks guys I gonna give it a try and let you guys know what happens

Bigincher · #10 10-04-2009, 02:21 AM

I guess air in the system would be the only logical diagnosis, but to me it sounds kinda hokey. I mean, it's not like you're going to 35,000 feet, or anything, but .... from 200 feet to 8000 feet is a substantial gain in elevation. I knew there was a reason I should've taken physics in High School, because I really have no idea of the 'numbers' involved here. Can the difference in atmospheric pressure be so much as to cause this condition?
I live around 200 feet also, and routinely ride in elevations above 4000, and often up to 7000 or higher, and the worst I've ever experienced is some stumbling caused by the jets in the S&S on my shovel. (The Mikuni on my Evo has less sensitivity to elevation changes.)

I might comment that I have a Fatboy, too, but it's an old one ---1994. But I've never had this happen to me at upper elevations, not even going over Independance Pass at 11,000 feet!

I keep thinking it has something to do with the brake fluid expanding------ but what do I know, I'm just a poor black farm boy with limited intelligence. Let's wait for the master guru of all things motorcycle...!!!