Front brake lever normal-soft-normal

vgazer

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Sorry if this has been posted somewhere, I did my best searching.

Just finished replacing the front tire on my 2017 non-ES using the removal and installation instructions on the Tire part of this forum.

After putting it together, the front brake lever seemed fine. Starting my test ride and while moving, the front brake lever had zero pressure and pulled all the way to the grip. I stopped, squeezed a few times and the pressure returned to normal. Once I pulled away again, the lever went loose again.

Seems to only lose pressure when moving. Went up and down my driveway: pressure when stopped, coast backwards 20 feet, power forward, no pressure in lever, stop, squeeze lever a few times, pressure builds.

Rear brake seems to operate normally.

At a loss on what to do next. Thanks in advance.
 

WJBertrand

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Sounds like the rotor is pushing the pistons back in for some reason. Spacers in correctly?, Bent rotor?


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EricV

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Sounds like the rotor is pushing the pistons back in for some reason. Spacers in correctly?, Bent rotor?
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I agree with WJB. This happened to me with bad wheel bearings. There is play in the front wheel for some reason and the rotors are not spinning true and that pushes the pads out. Do NOT ride the bike until you sort this out.

The easy explanation would be that you tightened the pinch bolts before you torqued the axle and it's just loose. The painful explanation is that you have a damaged rotor or bad wheel bearing.

Or as WJB mentioned, a missing spacer. Make sure the small collar bushing is in place and the speed sensor cover is located correctly in it's notch matching up with the fork leg.
 

vgazer

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Sounds like the rotor is pushing the pistons back in for some reason. Spacers in correctly?, Bent rotor?


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It's the rotor for sure; my dumbass must have bent it while putting the tire on. Put a screwdriver in the suspected low spot and turned. You can listen below if you're curious.

Lesson learned.


Guess I'm getting new rotors this week...

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jeckyll

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Did you get the front wheel off the ground and spin it to see that it's warped? They're not usually that easy to bend unless you're really ham-fisted...
 

OldRider

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With the lever coming all the way back to the grip, I don't think you have the caliper lined up right. Loosen everything up, tighten the axle nut, spin the wheel and hit the brake a few times and then tighten up the pinch bolt. Make sure the axle isn't too tight in the right fork leg and drawing it in when the axle is pushed through it.
 

steve68steve

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It's not clear from your driveway experiment whether the pressure is lost every time you move, or every time you release the brake lever.

If you just lose pressure after pumping the lever, it could be a problem with the lines - bad fluid, an air bubble, a fluid leak out, an air leak in.

I'm not saying your rotors aren't warped and that that's not the real problem, but your screwdriver video doesn't do a good job of communicating how MUCH they're warped, and I'm sure there's some tolerance specified in the service manual. Put a dial indicator on it, or rigidly mount the screwdriver with the disk spun to the highest point so it just touches, then spin the wheel until you find the point with the most clearance and measure the gap with feeler gages between the disk and screwdriver. If you only have a .005" of runout, that would be enough to produce the video you posted, but probably not enough to produce your braking symptoms.

Mostly just throwing this out there because no one else has - there's a great chance I'm way off base. Having said that, it would be a shame to replace a disk and find it didn't cure the problem.
 

Longdog Cymru

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Just a thought before you spend money, the front disc rotors are floating. Maybe, just maybe one rotor has cocked and jammed on the hollow spools that it floats on and just needs to be re-seated?

Apologies if you have already investigated this.
 

Don in Lodi

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What Longdog said. That's the idea behind floating rotors, they're self centering, unless one of the pucks gets jammed up.
 

jeckyll

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If one of the plugs is stuck there are some decent videos on YouTube on how to service it
 

vgazer

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Just a thought before you spend money, the front disc rotors are floating. Maybe, just maybe one rotor has cocked and jammed on the hollow spools that it floats on and just needs to be re-seated?

Apologies if you have already investigated this.
I haven't explored this option yet. From my "scientific" tests, it seems like one section of one rotor is misaligned.

Can the buttons/spools be adjusted or do they just need be replaced?
 

Longdog Cymru

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You need to check that they are free to rotate. One way to do this is to put a bolt through each spool in turn and tighten a nut onto the bolt. Then, using a wrench, turn each spool in turn. It can be a bit tedious but it could save you money and at least you will have exhausted this option.

Good luck, I hope it works for you or there is another low cost solution for you.
 

Kyle_E

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Bobbins are a pain in the rear.

Best method I've seen is an arrangement of a bolt with some washers and a nut.
Use the washers to clamp the bobbin, and then use an electric drill to spin them while spraying with brake cleaner.
I've seen people use a few drops of oil, but I'm always afraid to get oil near my brakes.
 

WJBertrand

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I don't think there's enough lateral movement in those bobbins to cause the symptoms observed. The floating rotor design is mostly to accommodate radial expansion with temperature to avoid heat distortion. The dual action caliper pistons should automatically adjust to offset wear/centering.
 
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Don in Lodi

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The front calipers are fixed, no automatic anything. The front rotors themselves do all the auto stuff.
 

WJBertrand

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The front calipers are fixed, no automatic anything. The front rotors themselves do all the auto stuff.
Note that I referred to the dual action pistons in the calipers, not the calipers themselves. Single action caliper piston, I.e. the piston(s) are only on one side of the caliper, require the calipers to be mounted on a slide pin to allow alignment. The reason the Super Ténéré has solid mounted calipers is because the pistons are on both sides of the rotor. Braking pressure will equalize on both sides of the rotor, even if the piston travel on each side is not equal. This design allows the pads to center/equalize pressure on the rotor laterally from both sides in spite of a rigid mounted caliper.

Note: I clarified my post to make sure the word floating I used applies to the rotor description and not the calipers.


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vgazer

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Thanks everyone for your input on this matter. My last question: if I do end up replacing the front rotor, is it recommended to replace both? With everything I'm learning from you folks on the rotors, dual pistons, etc., I'm wondering if I can save a few dollars without compromising safety. I plan on just buying another OEM rotor. Bike has 14k miles on it.
 

steve68steve

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Buy a rotor if you want, but the lever coming back to the grip and returning back to normal after being pumped a few times isn't a symptom of a slightly bent rotor. A bent rotor is going to cause some pulsating in the brake when applied. The worse it's bent, the worse the pulsating will be. I've seen rotors bent so bad it would almost shake you off the bike, but the lever didn't come back to the grip. Just my .02 worth.
This.

If the idea is that a bent rotor is pushing the pistons in too far, IMO there would be a pronounced effect on the feel and action of braking. You'd have different symptoms, or at least additional symptoms.

A lever going slack until pumped sounds like a classic symptom of hydraulic failure... as in, the hydraulic fluid column between the lever piston and the brake caliper piston is being interrupted by air. Air is compressible, fluid is not. If your master cylinder level is low, or your fluid is very dark...

Air could be introduced by a leak in a hose, the caliper/ piston seal, the lever/ piston seal, the master cylinder reservoir cap, the junctions where the lines change from flexible to rigid, probably the ABS unit... You could be losing a small amount of fluid in an out-of-sight location and not easily see it. You could be not leaking fluid at all, but sucking air in (I think this is how ABS unit leaks have manifested).
 

EricV

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There are a couple of things that can cause the brake pistons to be pushed in, so that when you grab the brake lever it has no effect until being pumped up. As I said before, I saw this exact symptom with failed wheel bearings. That seems unlikely in this case, but one of the reasons for the brake lever symptoms would be the wheel moving back and forth.

If you have not already done so, remove the calipers and the wheel check the bearings with your finger to see if they feel smooth or notchy/rought and re-install if they feel ok to you. Looking at everything while you do so.

You should have a spacer on the throttle side of the wheel and the speed sensor cover on the clutch side of the wheel. You should be aligning the speed sensor cover with the raised part on the fork leg so it can't rotate when you install the axle. snug the axle, then bounce the ftont wheel against the wall or a curb, etc a few times. Now, tighten the axle to 54 ft/lbs, then tighten the pinch bolts.

Before you re-install the calipers, with the bike on the center stand, use your shoulder to raise the front wheel off the ground and spin the wheel, try to move it side to side, etc. If everything seems normal, install the brake calipers. Weight the rear of the bike so the front wheel is off the ground and spin the wheel, apply the brakes until the lever is firm and the wheel stops. Repeat and see what happens. If it feels normal, run down the driveway again and see how that goes.

Cheap and easy to do stuff before you spend any money.
 
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