Join Date: Oct 2006
Location: Green Bay, Wisconsin, USA
Make: GL1500 SE
… Or so it seems.
I have both a '85 GL1200A and '97 GL1500 SE (that is a trike), I know they have very near the same rear brake master cylinder. Due to a health issue that I've been dealing with, both have sat.
The Trike did get ridden some in Summer 2017, the 1200 maybe moved in yard but on the road, Sept 2016 was her last ride. I knew back then, likely be a good long spell before I'd get to ride either so I dosed their fresh gas with double dose of Sta-Bil marine fuel saver and ran the carbs dry when last ridden … so not worried there.
Well, I have been checking brake & clutch levers and their pedal feel ever so often, and Trike is all A- OK, but the 1200's rear brake pedal went soft. I ordered a kit, thought I was going to rebuild rear MC. Yesterday I decided time to try the tie down trick, I pumped the rear pedal slowly until it was as best as it was gonna get, and strapped it down with three wraps of a good bungie to lower leg of center stand, checked today, the rear brake is good now.
I did not expect success.
The brakes have been bled before, never had a soft pedal on either, fluid changed, etc., so I see no way for air to get in just sitting in a dehumidified, heated basement as they do. All I can figure is the cup seals of the piston in the rear MC maybe relaxed from lack of regular use, and simply failed to seal the whole stroke. Pumping up to get some pressure likely expands them cups, getting them re - acquainted with cylinder bore wall. That's my theory.
Anyway, tomorrow gonna do same on 1500 just as a preventative measure.
I too have had the same anomaly and I don't know why but I have a theory. (Guess) As the cold weather sets in the seals on the calipers get cold and shrink up as well as less resilient. As it gets colder and colder the brake fluid in the lines and calipers contracts. There is now a slight void and vacuum internal the caliper and lines. The caliper seals are stiff and do not seal real well so the system draws in a very insignificant amount of air. You wouldn't even know it if you rode the next day. Problem is the bike does not get used. The temp goes up and down every day and every week. Eventually all the insignificant amounts of air combine to become significant over months.
I would think that the fluid in the master should run down to replace the void but I wonder if the small hole in the master reservoir and thick viscosity from the bitter cold makes it easier to pull the air past the caliper seal. Just my best guess. What do you think?
Worked on the "big rigs" for 45 years now just riding my Wing whenever I can. Gets cold in Wisconsin.