Rear brake pedal gone soft - fixed ... - Steve Saunders Goldwing Forums

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post #1 of 5 (permalink) Old 04-06-2019, 11:19 PM Thread Starter
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Join Date: Mar 2011
Location: Fairfield, Virginia, USA
Year: 1997
Make: Honda
Model: '97 GL1500SE/ '98 Lehman GTL Trike
Posts: 3,288
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Rear brake pedal gone soft - fixed ...

… 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.

.
.
.
1997 GL-1500 SE / 1998 Lehman GTL Trike
...(Candy Spectra Red )
GWRRA, NRA, & VSPA Life Member

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post #2 of 5 (permalink) Old 04-07-2019, 05:16 PM
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Join Date: Oct 2006
Location: Green Bay, Wisconsin, USA
Year: 1999
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Quote:
Originally Posted by CrystalPistol View Post
… 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?
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Mike

Worked on the "big rigs" for 45 years now just riding my Wing whenever I can. Gets cold in Wisconsin.
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post #3 of 5 (permalink) Old 04-07-2019, 06:09 PM
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Join Date: Oct 2018
Location: Toledo ohio
Year: 84
Make: Aspencade
Model: GL 1200A
Posts: 38
interesting??? I never thought that far thru it. got the same problem with 84 GL. rebuilt stuck piston rear caliper, bleed back well with 1" bore plastic syringe and clear plastic hose, no bubbles. then I read in book.... "bleed front R brake first" ok will try that as have over 1" of pedal travel and that cant be right.


read in popular mechanics that when bleeding brakes and PUMPING the pedal ALL THE WAY, to the floor, in the stroke the piston in the master cylinder goes where it has never been before and that part of the bore is rusty... tearing up the piston cups...= new master cylinder. PM writer said to put 2x4 under brake pedal to keep pedal from going all the way to the floor when PUMPING the brakes to bleed the system. or do a brake job... plan on new master cylinder as if very old the bore is pitted anyway and pretty much non rebuildable by avg home tinkerer and such a mess to make it not worth the effort... depending on yr, make/model. and ... never time to do it RIGHT THE FIRST TIME, BUT ALWAYS TIME TO DO IT AGAIN... and again, cuz saved some money by not doing it RIGHT the FIRST TIME. I like the plastic syringe and clear hose that fits the bleeder thing. $1/each on E bay, or a little more at farm supply store.


brake fluid swells up the piston rubber in the syringe and degrades the plastic so the syringe wont last but mostly for one time use, so for $1/each might want to get 5 sent from HK at a time. 2+ wks delivery though
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post #4 of 5 (permalink) Old 04-07-2019, 07:28 PM Thread Starter
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Quote:
Originally Posted by redwing52 View Post
I too have …etc... What do you think?
I guess it's possible, I don't know. My basement may get as low as 60 degrees in winter. Not a lot of fluctuating. I went down awhile ago to check, was checking air in tires too, couldn't rotate tires on 1200 and thought "Oh hell, now it's a seized caliper" …. I forgot for a brief moment that the rear pedal was strapped down.




Glad I ran carbs dry when parked the 1200 in late 2016 and I even unhooked vacuum line to petcock on 1500 and did same in 2017. Gonna use battery siphon pump and vacate the tanks of old sta-biled gas this week, & put some fresh (non-ethanol from Co-Op) in both.
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.
.
.
1997 GL-1500 SE / 1998 Lehman GTL Trike
...(Candy Spectra Red )
GWRRA, NRA, & VSPA Life Member

"Make Courtesy Your Code of the Road!"
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post #5 of 5 (permalink) Old 04-07-2019, 08:50 PM
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Quote:
Originally Posted by redwing52 View Post
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?

I have another theory..............

This happened to my GL1500 during warm weather. I could tie the brake pedal down for a day and then have almost a full pedal. One week later the brake pedal was back down all the way.

The only permanent solution was to replace the pistons and seals. That corrected the issue.

Tenp changes had nothing to do with my issue..........!!!

A similar situation occurred with my friends 1996 GL1500.
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