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Discussion Starter #1
Need help to cure front brake.

So this happened two days in a row: I lost front brake on a bumpy steepish downhill. Lever would go down to the bars without braking.. pumping up would help but only somewhat. Brake would get back to "normal" once we got back to road sections, though lever would feel spongy like there's air in the system. The loss would be gradual and could have been counted by constantly pumping lever. First time it happened I ended up running wide into ditch (my fault got distracted by turkey.. but not having front brake didn't help)

No visible leaks, brakes were bled 4 times (last time removing brakes and hanging them high). Probably bled 32oz bottle through.

Have a couple theories:
- air in abs unit which would get released only when abs engaged and it did buzz on occasions
- failing master cylinder
- there's a leak somewhere

If anyone knows a way to bleed abs unit pls let me know!

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Yup, that's the cause a speck of crap in the ABS valve. Be warned it may take some effort to move it, I have a large grassy back yard and picked a rainy day.

Up to 30-40kph, hit the front hard, skid 10m or so, pull up, turn around repeat. It took a lot of passes but it did fix the problem but I was covered in sweat at the end - far end of my yard either way has quite a big drop ;).

You may get lucky, but plan on twenty or so passes.
 

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Discussion Starter #6
Thanks for replying guys!

I will bleed front brake to see if there's any air there if is it must have come from abs.

I wish there was a way to bleed abs unit itself.. BMW used to put bleeders on servo pump was pain but at least you could do it right.
 

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Not a biggie activating it on gravel, that's what worked for me. I like the bumpy hill idea. I'm not sure how the factory does it. Maybe there is a remote abs controller to cycle the valves.

Sent from my SM-G930V using Tapatalk
 

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The factory diagnostic tool has an option to cycle the ABS, the problem is that you have to use the front brake HARD at the same time to move whatever along. Not confident a dealer mechanic will bother with that.
 

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Discussion Starter #12
The factory diagnostic tool has an option to cycle the ABS, the problem is that you have to use the front brake HARD at the same time to move whatever along. Not confident a dealer mechanic will bother with that.
thanks for info I will have to talk to them and see if they do it and how much they want.

I was suggested to do reverse bleeding will try to see if it helps. Was also pointed out that front wheel bearings and fork deflection could be causing it.. need to check if I tightened brace after servicing forks.
 

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Brakes slowly head into the bars if you apply them gently, still grip well if you give them a hard poke ?.

Several people have had that now and I'm the only one I know who's managed to fix it short of a new ABS unit (others, please chime in). If it's that then you can bleed the system as long as you like, it won't help. Your only hope is that the crap stuck in that valve can be persuaded to move.
 

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Discussion Starter #14
Brakes slowly head into the bars if you apply them gently, still grip well if you give them a hard poke ?..
No they were fine on the pavement but I lost them on steep loose wet downhill. Ran wide on one of the switchbacks and ended up in the ditch was a contributing factor. Came back after repeated pumping and were soft but useable next day until we got off pavement than it happened again. This time on flat/uphill but I was waiting for this so started pumping them right away. That wasn't BTW from any heavy use I was going slowly so not brake fade.

My mechanic also thinks it's an abs valve or pump doesn't kick in due to electric contact getting loose/corroded but I think I have air in the system too. Feel spongy with bike off. Bled 4 times but brakes never felt right after 4-pot conversion.

Could be also mc but I don't have the symptoms aka lever slowly falling to the bars at light application (bike/abs off) or no brake after not using it. Interesting to know that leaking abs valve could cause similar symptoms.

I will bleed and see if there's any air if there's it must have been in abs and got released from abs use.
 

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Same problem here. Had to "throw er down" before running off a steep WV switch back. Really I just turned in till front end washed out, let the Tusk box do the rest of the stopping. Fun was standing the bike up without throwing it rest of the way off the mountain.
Also cycled the ABS repeatedly while doing a MSF rider class. Lots of little grassy spots growing on the course.
Debating weather to put a 2 pole switch in front of the 2 ABS fuses. Or a 2 pole relay with a holding coil so it resets when ignition is cycled.
 

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Another scenario besides ABS issue could be rotor runout. If the rotor/wheel has some free play it will push the brake pads back during rough sections and create an air gap that will feel like a spongy brake until the pads move back it to place against the rotor.

Simple enough to check for free play in the front hub or rotor. I've had this happen on cars with bad wheel bearings.
 

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From the detailed description there's nothing wrong with the ABS other than maybe they need bleeding.

IF you just grab a handful and hang on the result you got is the expected one. To get current ABS brakes to work in those conditions you grab a big handful and when you feel the lever shuddering (ABS kicking in), release the lever and try again.

The reason for that is that the master cylinder only traps a small amount of fluid when you engage the brakes, everytime the ABS fires it releases a little fluid, once the trapped fluid has gone, no brakes unless you back off the lever to let more fluid in. Also bikes stop better when the front wheel isn't actually skidding, so releasing and hammering them hard again on loose surfaces drives the front down (gets more grip) until the wheel starts to skid.

I've seen a very good (Pro enduro rider) make 'the mistake' on dirt because it was the first time he'd ridden an ABS bike offroad. I explained how the ABS brakes worked to him once we'd picked the bike up, light came on and he had no problems from then on.

It's not that ABS is no use on dirt , for me it's wonderful because the odds of a front washout go down massively and I can use much more front brake - BUT - the rider has to do their bit as well.
 

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Discussion Starter #19
I agree with Pete on Wee ABS useable on dirt I have an ABS switch (not EB the mod which let me turn on/off on the fly) which I wired in preparation for class and I never use it.

The Nissin unit Suzuki used is very nice lever would buzz for a split second when front wheel hops over bump then business as usual. This is on steep loose downhill where rear is pretty useless.
 

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You don't even need a gravel road to activate the ABS; just do it in the grass. Anything that'll reduce the friction with the ground enough that the ABS kicks in will do the trick. If you have a yard where you live, just spray the grass with a hose and then ride the bike over that patch of ground and grab the brake hard. On something as slick as wet grass, you shouldn't need much speed.

I've always bled the ABS brakes by riding down my gravel driveway and grabbing the brakes hard, then going back and bleeding them one more time. It seems like a bad idea, especially with the front brake, but it works just fine. I've never had anything bad happen by doing it that way.

Back when I had a Harley Road King, I would have weird issues sometimes with the front brakes. I solved it by opening the master cylinder cover, putting a piece of saran wrap loosely over it to keep out debris, and then bungee cording the brake lever to the grips to slightly pressurize the system. I'd leave it that way for a couple hours, so any residual air bubbles in the system had time to rise up to the master cylinder. Since the cover was off and the system wasn't sealed, the air could escape. Brake fluid is hygroscopic, but I wasn't worried that it would absorb that much moisture in that short an amount of time.
 
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