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Discussion Starter · #1 ·
OK......so I give up and need some advice. Bout three months ago received all kinds of great advice on gettin the air outta my front brake system after I had to unhook the master cylinder from the hose for a handlebar mod(if interested read thread "where does the air hideout" )

For three months have had the symptom of whenever the ambient air temp. rises even 10 degrees the front brake begins to drag and will bring you to a stop. have a little 8mm wrench wired right to the base of my brake fluid reservoir and must release just a little when it starts to tighten up. Tried everything imaginable, unsucessfully to fix this 06 GSXR-1000 with 7000 miles (when problem began.) So if I'm going to start replacing parts i guess I'll start with the master cylinder because for some reason I suspect that it is entraining air into the system whenever the brake lever is released from the compressed position>> As I've completely disassembled both the calipers completely and the master cylinder and only ever found light scuffs on the master cylinder piston as the only abnormality.

If I'm buying a new master......do you guys suggest switching to an aftermarket one? is there even an aftermarket one available. I do no racing whatsoever and just ride the streets. Guess I'd like to have one that has the bleeder on the master cylinder if possible

Things I've tried:

-six foot 1/4 inch tubing to the ceiling bleeding method
-Mityvac. bleeding holding the calipers hoses,and master cylinder
in various positions as the oil flows through them.
-COMPLETELY removing the entire front brake system from the bike INTACT(had to take the front master and reservoir down through the front faring compartment and out the bottom) without unhooking any hoses so that I could bleed the line from the master cylinder up to the right caliper with that caliper ABOVE the master cylinder..used vacuum bleeding as you couldn't easily compress the brake lever unless you put somethin between the pads I guess
-have pushed all eight pistons as far back as they will go in attempt to get any air out from behind them..did this three different times holding the caliper in different positions in case that makes a difference in whether the air can get out
-used tapping methods during all these various methods to try to move bubbles up to the bleeder I was evacuating fluid from
-first month and first six bottles of DOT 4 was cheap prestone synthetic stuff from walmart........in last several attempts have completly taken system down and caipers completley apart and cleaned a second time and then changed to MOTUL racing 600 DOT 4 fluid......two bottles at $17.95/bottle
-have inspected all the lines and no aneurysms anywhere
-micrometer on both front rotors showed less than two thousanths of and inch wobble in either disk.

Please someone make me feel like a complete FOOL with the correct diagnosis of this problem or tell me where to get a different master cylinder, if I should. Only thing NOT stock about front brake is when I moved the clip ons above the triple clamp I had to turn the hose connector where it hooks to the master cylinder upside down and then slightly bend it to make it clear everything. No leaks of fluid anywhere.
 

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did you reuse a crushable washer when you put it back together? Just a thought. There isn't much to those systems. Do you ever see a leak anywhere? Even the slightest amount of fluid?In those temperature settings, I would suggest pumping the brakes(while bike is not in motion) and look for any leaks. My guess is that if the problem did not start until you performed that handlebar mod, it is probably something to do with the reassembly.
 

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Discussion Starter · #4 ·
all stock hoses.......and yes did reuse the crushable washers at all the banjo bolts.....will watch closely for any leaks at all but haven't had any yet.......last night for the first time on the way home on a slightly wet road the front brake suddenly came on harder than it ever has and almost skidded the front wheel before I got it whooooaed ! ..........system was pressured up and when I cracked the master cylinder bleeder fluid squirted out and I squeezed the lever to get a little more fluid out and then it was fine......disks on front wheel were very warm
 

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rotaredom
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if it were me, i would replace the oem brake lines with an aftermarket brand as you may be getting some expansion in the lines when applying brake pressure. failing that i would get it to a shop before something bad happens.
 

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:headscrat sounds to me dollars to donuts the master is not letting the fluid return into the resivoir, which in turn is causing brake drag, when the fluid heats up in the calipers the problem worsens, you said you had to flip and bend the fitting for the master, i am thinking that you have caused a restriction in the system not allowing the fluid to return properly, i would think that even after you install a new master with the same flipped and bent fitting that it will still be a fault, try and re-route another way without flipping and bending the fitting, just my thoughts
 

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:headscrat sounds to me dollars to donuts the master is not letting the fluid return into the resivoir, which in turn is causing brake drag, when the fluid heats up in the calipers the problem worsens, you said you had to flip and bend the fitting for the master, i am thinking that you have caused a restriction in the system not allowing the fluid to return properly, i would think that even after you install a new master with the same flipped and bent fitting that it will still be a fault, try and re-route another way without flipping and bending the fitting, just my thoughts
This sounds very possible to me and for sure something is not letting fluid to return to the MC that would account for the brakes being applied when there is an increase in temp change.
 

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Discussion Starter · #10 ·
thanks everyone for helping here ...........so is that what the tiny tiny hole in the side of the bore of the master cylinder is>>>is the passageway to the reservoir....so that when your not squeezing the lever and the M.C. piston is in its fully retracted position that the fluid in all the hoses down to the calipers and including the fluid in the calipers is exposed to the pressure created from the column of brake fluid in the reservoir (THUS THE REASON YOU NEVER WANT TO HAVE THE RESERVOIR OVER FILLED) ? but then the instant you squeeze the lever some, the seal on the piston then immediately covers that hole ,which is only about say 15 thousands of an inch in diameter, and then no fluid can get away and all your lever pressure is applied directly to the fluid in the hoses and calipers....but then the instant you release the lever then the hole should immediately be uncovered again allowing the pressure in the hoses to equalize with the pressure created by the column of fluid in the reservoir (Which is obviously very low) ? called stealership today and can get a new piston kit for 42.00 and a whole new master with all the guts for 164.00
 

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I would try replacing the brake lines sense you bent the banjo fitting and I don't have a pic so I can't ascertain the degree you have bent it or the radius of the bend. The lines will be cheaper than the MC and the lines will be an up grade in the long run. If i remember this started after the bar replacement during which time you had to bend the banjo fitting correct? Just me but I would start with the lines and go from there.
 

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thanks everyone for helping here ...........so is that what the tiny tiny hole in the side of the bore of the master cylinder is>>>is the passageway to the reservoir....so that when your not squeezing the lever and the M.C. piston is in its fully retracted position that the fluid in all the hoses down to the calipers and including the fluid in the calipers is exposed to the pressure created from the column of brake fluid in the reservoir (THUS THE REASON YOU NEVER WANT TO HAVE THE RESERVOIR OVER FILLED) ? but then the instant you squeeze the lever some, the seal on the piston then immediately covers that hole ,which is only about say 15 thousands of an inch in diameter, and then no fluid can get away and all your lever pressure is applied directly to the fluid in the hoses and calipers....but then the instant you release the lever then the hole should immediately be uncovered again allowing the pressure in the hoses to equalize with the pressure created by the column of fluid in the reservoir (Which is obviously very low) ? called stealership today and can get a new piston kit for 42.00 and a whole new master with all the guts for 164.00
that is excactly what i was talking about, from the sounds of it like jet said replace the bent fitting and go from there, good luck hope i helped
 

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Discussion Starter · #13 ·
You guys were exactly right about the fluid not returning to the reservoir.....I was sure with closer inspection I would find the brake lever or the spring loaded aluminum piece that is actually inside the brake lever that reaches down and actuates the brake light switch HITTING SOMETHING BECAUSE OF MY MODIFICATION.

Earlier when I said that I had to bend the banjo fitting .....I didn't bend the actual round part that your bolt goes through to attatch the hose to the master cylinder, but the metal part of the hose that is the first piece leaving the round part of the banjo fitting. Obviously you couldn't seal the fluid if you did that.

Here's what I found>>>that aluminum piece inside the lever(looks like its held in place by the same bushing that the bolt that holds your whole lever in place>>>that piece moves some back and forth and I think is spring loaded>>>but the blasted thing is against the plastic brake light switch and has wore a tiny groove in the light switch. All the time for the last four months its been held up there tight and not letting the MC piston come back all the way against the piston. Thought maybee I had the switch outta its little centering hole but no I double checked it....so when I walked out to the bike today it was already warm down here in florida and the front wheel was already locked up......in other words, in neutral you could hardly push the bike.....took the nut off and the bolt out removing the entire front brake lever and then the bike is free again. I'm dumbfounded? Then took out the little shaft with the rubber dust cover and the ball with lube on it that reaches in and presses against your piston and I could then see the snapring and piston....piston is free in there and comes back and freely rests against the snapring every time. Also made sure that the end of that little plunger shaft was fitting ALL the way into the little movable socket there is in the previously mentioned aluminum piece inside the brake lever. So there ain't nothin wrong with my master cylinder or any of its contents, or the hoses or the fluid and calipers now cleaned and replaced FIFTY times, at all.....but what's up with these ALL stock parts that are in a bind??>>>>to put the brake lever back on bike you must press on that inner spring loaded aluminum part(tried to look the correct name of that piece up on the online K5 service manual today and locked the puter up and had to do a power off and then realized the hard drive went outta it....so that's why I've been late replying here. So when you try to put lever back on bike one end of that inner piece is against the plastic brake light switch and the other end is against the plunger shaft tight to where its holdin the piston slightly from commin all the way back. The only thing I can think that might be going on is maybee there has accumulated a significant amount of dirt between the brake lever and this moveable aluminum piece I keep talkin about that is spring loaded in there and reaches down to actuate your brake light switch>>> maybee that that piece isn't moving and as free as it should be within the brake lever>>>>but it looks like to take that apart one would have to take a proper sized punch and drive that long silver bushing outta the brake lever and that the aluminum moveable piece would then be seperate from the brake lever and also you would then have access to the little roller that changes the position of the brake lever from 1 to 6......ANYONE EVER HAVE TO DO THIS.....only thing else I can think of would be to grind off the inside of the tab of that aluminum piece where its contacting the button on the brake light switch so its not always in a bind, or I guess I could grind a little off the end of that shaft that goes in and contacts the piston(the one that has the ball on it and lube) until things are free again........I took the bike out with no front brake lever brake light switch on it and everything works beutiful like it did when new. ANY THOUGHTS ??? Man I tell you guys the other night when that thing decided it was going to tighten up on the way home from work(even when it wasn't gettin warmer) it wasn't to far from locking the front wheel on the wet payment.....it was like twilight zone and someone with there hand suddenly on your front brake lever and you feel the engine start bogging in sixth gear:headshake
 
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