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Discussion Starter #1 (Edited)
So...'09 non-ABS with about 50K miles on the ODO that has been owned and maintained by me since about 8K miles. No wrecks, original rotors and calipers, brake fluid replaced regularly, calipers cleaned and slider pins lubed recently, newer SS lines and HH pads.

Symptom is that when riding at speed (>35MPH) with only intermittent front brake application, the front brake lever has more play on first application, i.e., lever movement takes longer to pad drag, than when using the brake frequently. One pull and the brake lever action returns to normal operation. No air in the system, lever is firm both on initial and subsequent application, brake feel is normal, and there is no surging, pulsing or squealing during braking. If I could detect a pulsing through the lever, I would suspect pad knock-back from a warped rotor, but no indication this is the cause. Only other possibility I can come up with is worn front wheel bearings causing the wheel to move slightly resulting in pushing the pads/pistons into the calipers.

Thoughts? :confused:
 

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Have you tried putting new bleed valves on the calipers? Rebuilding the calipers? Cheap o-ring kits on eBay think mine were from brake craft..? Popping the Pistons out and just cleaning them up, checking for scaring is simple enough and free.
This happened with the swap to stainless lines? Going down that path I always try to ask myself what changed. Keeping it simple as possible which is hard to do sometimes if your mechanically inclined which it seems you are. If the problem presented itself at the brake line upgrade then that's where I would start. Check the bleeders first, check the seat of em in the calipers for foreign material or scarring. Pop some new ones in since that's cheap and easy w minimal bleeding.
If that presents the same results I'd put the old lines back on, bleed bleed bleed the brakes again and we'll...you know. Prob end up cussing a few times and maybe ordering another set of shiny lines.
Best of luck to you. Brakes are nothing to skimp on I know. Esp the fronts.

Sent from my SM-G965U using Tapatalk
 

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Most likely cause for the scenario you describe is the chambers inside the master cylinder are leaking internally, fluid transfer inside the master cyl. Try a rebuild kit, fairly inexpensive, (new puck, spring, etc.) If the walls inside the M/C are too badly worn, you may need an entire new unit.
 

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If you end up installing new seals or rebuild kits, use Suzuki OEM only.

Do NOT waste money on the imitation garbage.

Only thing that comes to mind is a tiny air bubble hiding somewhere (you'll still get a firm lever once it compresses the air) or wheel bearing/spacer play.

Get the front in the air and look for runout or wobbliness. Even if you don't have a dial indicator, you might be able to detect an issue by feel and eye.
 

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Sounds like a leaky or sticky master cylinder. If you don't want to buy a rebuild kit, you can try to clean the master cylinder and reassemble with the old rubbers. I once did this with success when I wanted to be on the road before my master cylinder arrived. But is was on an oldtimer with a very sticky master cylinder. For the effort involved, I would buy a rebuild kit and do the work properly.
Pad drag or sticky calipers are quite unlikely. Air in the lines would result in an overall spongy feel as well, so if the brakes are firm the master cylinder is the most likely culprit.
 

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If the brake lever feel is hard there is no air in the system. It is possible that the rubber cup or cups are bad but I would put my money on a small amount of lateral movement of the rotors.
 

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The soft feel to the lever seems straight forward(Air in lines). However the pulsation could be due to contaminates on the pads and rotors. As miles build up I've had this to some degree. Whenever my front wheel is off(Tire changes usually) the pads are removed and sanded on a flat surface. Then I scuff up the rotor with a Scotchbright pad. Brakes always feel much better w/ no pulsation.
 

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Discussion Starter #9
Thx for the replies and suggestions. As I stated, there is no sensation of pulsing or surging when braking, and it is highly unlikely that it is air in the system. Lines were installed about 15K miles ago and the issue has only arisen recently. The only time there is an unusual amount of play/pull/movement in the lever is on initial application after I have ridden a long time without brake use, i.e., at least 10-15 miles on the x-way. Once the first pull is applied--and the lever is still firm then, just a longer-than-normal pull--the brakes are completely fine without any mushiness or spongy feel. I'm leaning toward the master cylinder needing a rebuild (almost 50K miles of use) but would like to hear how a worn master piston seal would contribute to this. Is it likely that the bypass/return orifice is the cause? Anyone out there willing to share their knowledge about the "mechanics" of the master cylinder?
 

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The rebuild kit will be part #2, and the rubber puck is supposed to keep the fluid in the forward part of the M/C, when fluid is allowed to escape to the rear half of the M/C you will get that travel on first pull, then it will revert to normal as the fluid is forced back to its proper place on the second pull, only to bleed back over time. If the walls of the master are badly worn, the rebuild wont work, but for $30 its worth a shot.
 

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If the master cylinder sticks (meaning it doesn't move all the way back out after being pressed in by the brake lever), the bypass orifice stays open and pressure from the brake line is slowly equalised with atmospheric pressure.
 

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Someone mentioned to use OEM Suzuki rebuild kit only. The master cylinders are supplied by third parties like are the calipers, R/R's, forks, shocks and dozens of other parts. When I rebuilt my V65 Sabre master cylinder I used a kit labelled for a Yamaha FZ7 or something. This was a K&L kit. That's the brand most shops use and there is nothing wrong with K&L Supply parts.

Cheers,
Glenn
 

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Discussion Starter #13
Thanks for the great information, gents! Looks like I'll be ordering a rebuild kit and tackling that over the winter after the cold, rainy weather limits my daily rides.
 

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Too late now but having done a rebuild I'd just buy a replacement master cylinder next time. For all it looks simple it's incredibly tricky to do and if there's wear in the bore it won't be that effective. That said, I did mine at >100,000k's so the wear was likely a lot worse.
 
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