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Fixing Shimano Wandering Bite Point

Lelandjt

Lelandjt

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Apr 4, 2008
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One of my rarely used bikes has a 2 year old set of SLX brakes that are nearly new and always felt perfect (I did the install and bleed). On the last two rides the rear started doing wandering bite point. The end of the stroke is still firm, whether it's engaging at the normal spot or close to the grip. While it was engaging close to the grip I looked at the caliper and the pads were sitting the same distance from the rotor as when it's working normally, so it's not that the pistons are overly retracting sometimes. Doing the quick repetitive pumps thing doesn't really shorten the stroke. I just have to wait for it to return to normal.

I'm going to try cycling the pistons in and out with a funnel on the lever, maybe I'll even do a full bleed, but I'm not optimistic that this is fixable since I can't figure out exactly what's causing it. So, the real fix will probably be replacement. It's the lever that's causing the problem and needs replacement, not the caliper, right?
 
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Toshi

Toshi

butthole powerwashing evangelist
Oct 23, 2001
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My 4 piston XTs do this. Persists after a bleed.
 
Jm_

Jm_

sled dog's bollocks
Jan 14, 2002
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Yeah, sometimes I end up having to do a "double pump" thing where when I'm braking hard, like down Skyline the other weekend, I have to let off and not just let the rotor cool momentarily, but do a intermediate squeeze to reset it so it's ready for the next time I use it hard again...because the bite point pumps up.

Supposedly Putoline HPX R 2.5 WT is light enough to not force the lever to have to "reset" every time you pull it for a hard braking event, discussed in this thread, look towards the end:

forums.mtbr.com

Shimano XTR BR-M9120

Has anyone tried the new XTR 4 pot brakes yet? I am keen as a bean for them but I am worried they will exhibit the same wandering bite point and odd lever feel as most recent shimano brakes have.
forums.mtbr.com forums.mtbr.com

That said, seems like it'd be more orientated towards cold conditions if anything and really, the brakes are fucked any way you look at it. My 000-series levers on my turner are starting to seep at the lever and the rear gets a little soft now under hard braking, as in it's passing fluid. The way to fix this for sure is to hold on to the brakes, put them in a box, buy some hopeguraomulas and wait until the next big race with all the reps and then chuck that shit in their tent. I'm going to in the Spring.

I'm going to try the above poutine on my winter xtr brakes to try and get a bit more life out of them, hopefully at least this season, but as this stuff fails, I sure as hell ain't replacing it with dumbass shimano.

Titanium master cylinder with seal if you are feeling brave.

As to your "2 year" finding...I cornered the Shitmano reps at a race and when you tell them about the wandering point, the lack of replacement seals/piston/cylinder/parts they say "yeah, you should get a couple seasons out of them". Then you are up fuck creek waiting for them to catastrophically fail at some point because you couldn't rebuild them before the season...
 
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Lelandjt

Lelandjt

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Apr 4, 2008
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It's the first time since they ditched the radial mount master cylinder that I've encountered this on a Shimano brake that also had a firm end of stroke, ie not needing a bleed. I've read about it online but never experienced it. I own plenty of this generation Shimano brakes that don't do it, including the left one on this bike. Is the consensus that I should replace the lever, not the caliper?
 
slimshady

slimshady

¡Mira, una ardilla!
Dec 20, 2007
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A long time ago, in a galaxy far, far away...
I said it on the Frankenbrakes thread, if you don't rebore the master cylinder's inner bore you'll be at the same position you are now in no time. The replacement titanium piston would help if it conforms to the new MC diameter.

EDIT, ask @kidwoo about his experience with Chinese brake replacement pistons...
 
HardtailHack

HardtailHack

used an iron once
Jan 20, 2009
7,663
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Damn, I thought this was going to be about a baitcaster reel.
I fixed my Shimano brakes by replacing them with some made by a company that doesn't make fishing products. My MT5s have had one bleed in 18months and the rear pistons are just starting to get sticky so it will be time to do some maintenance soon.
 
kidwoo

kidwoo

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Lelandjt said:
It's the first time since they ditched the radial mount master cylinder that I've encountered this on a Shimano brake that also had a firm end of stroke, ie not needing a bleed. I've read about it online but never experienced it. I own plenty of this generation Shimano brakes that don't do it, including the left one on this bike. Is the consensus that I should replace the lever, not the caliper?
Click to expand...
You're right that the newer ones are way better in that variable engagement isn't an entirely regularly occurring feature every single ride. But it also means that you're about to start getting the variability type that goes from "have brakes" to "lever to the bar, holy shit I'm going to die where is the braking?" between turns.

Are your calipers leaking around the pistons yet? Like when your bike sits without riding it for a few days, you notice your pads squealing? If not, just replace the levers. If so replace the calipers. Or just be smart and go to a bike shop and say you need to warranty both complete setups, because shimano WILL replace them since they know damn well this is a problem.


@Jm_ : rock scissors paper to decide who tries those replacement pistons first? I mean they're titanium and suspiciously cheap, what could go wrong?
 
Nick

Nick

My name is Nick
Sep 21, 2001
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I think I asked this to the RM brain trust before, but what do we think the optimal material would be for replacement pistons in say a set of Saints or XTs?

I'd have protos made up, if I knew what the hell to do.

edit: specific to the caliper issues, as that seems to be the larger problem.
 
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Jm_

Jm_

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Nick said:
I think I asked this to the RM brain trust before, but what do we think the optimal material would be for replacement pistons in say a set of Saints or XTs?

I'd have protos made up, if I knew what the hell to do.

edit: specific to the caliper issues, as that seems to be the larger problem.
Click to expand...
I dunno, ceramic seems like a good idea for heat resistance, the problem is they don't make replacement seals so you can't prevent them from blowing out the next season. There are two big issues though and that is only one of them and can generally be handled by baking the pads at 400 for 15 min and cleaning the rotors. The arguably bigger issue is the wandering bite point caused by the master cylinder in the cylinder bore, this end is just all F-ed up and eventually self destructs. Then you are really out of options unless you try one of those aftermarket cylinders, but then you are left with the leaky piston at the caliper. Warranty them like Kiwdoo says and sell the new ones quick with the hype that they are "shimano" and superior to everything else.

In this world of floating ocean trash and plastic in the digestive tracks of food sources, Shitmano has managed to invent disposable brakes.
 
troy

troy

Turbo Monkey
Dec 3, 2008
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One thing I have noticed recently, while performing some bleeds for my clients was that the master cylinder was not returning fully after pulling the lever. It was just a 1mm or two, but it led to lever going straight to the bars next time You pulled the brake lever...
 
Electric_City

Electric_City

Torture wrench
Apr 14, 2007
2,047
783
Some people put quality over looks.

Monkeys put fashion over life.

I'll never put myself at risk with Shimano or waste my money annually on sram.
 
kidwoo

kidwoo

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Electric_City said:
Some people put quality over looks.

Monkeys put fashion over life.
Click to expand...
That's a good point. Can you tell me which ones look the best? If there's one thing I've definitely never even mentioned here ever, it's the performance of a hydraulic disc brake, it's so irrelevant. I just need to know which ones look the best. Doesn't even matter how they work, I'm not going to put fluid in them anyway.
 
Jm_

Jm_

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kidwoo said:
That's a good point. Can you tell me which ones look the best? If there's one thing I've definitely never even mentioned here ever, it's the performance of a hydraulic disc brake, it's so irrelevant. I just need to know which ones look the best. Doesn't even matter how they work, I'm not going to put fluid in them anyway.
Click to expand...
Trickstuff Dementia and Hope Mono M6 definitely look the best, with an honorable mention to Gatorbrake 8 pistons.
 
kidwoo

kidwoo

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Yes einstein, I was able to put those two together, thank you.

The one single fluorescent yellow brake in the entire world of mountainbiking deserve it. That doesn't mean they don't work and that doesn't mean the way in which they work is irrelevant. It means they're fluorescent yellow. Which is funny.
 
maxyedor

maxyedor

<b>TOOL PRO</b>
Oct 20, 2005
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The fix for day-glow yellow Maguras is obvious, angle grind it nao!


+


+


=

www.magura.com

MAGURA Disc Brakes - MT Technology

Magura Brake Discs Series for all mountain bike disciplines: MT8 MT7 MT5, MT4, MT Trail
www.magura.com www.magura.com
 
Flo33

Flo33

Turbo Monkey
Mar 3, 2015
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kidwoo said:
The sleek italian styling makes all the worth. I don't even bleed them. Just stare lovingly at the black coctail dress sensibility.
Click to expand...
Can I convince you to hop over and do the same to my RORs? We got steep rough trails and pow atm. During my last ride the rear suddenly started to drag heavily on a climb, bite point at 3 mm of lever movement. Did pump it a bit and all of a sudden it was gone again. Any ideas?
 
kidwoo

kidwoo

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That's weird, especially on a climb. Did you go suddenly from sea level to 10k elevation? Cuz that sounds like air expanding but shouldn't be pedaling uphill obviously.

I never owned a set of RO gens so I don't have any real experience with those. I was just going along with englertracing making fun of my drab curas.
 
Nick

Nick

My name is Nick
Sep 21, 2001
24,861
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where the trails are
That's like the rubbing issues I was having with my 4s. Sometimes even on climbs. Argh.

I'm not opposed to trying those Miami Vice Maguras, I mean if they haven't killed @Da Peach peach yet they're probably good to go.
 
6thElement

6thElement

Schrodinger's Immigrant
Jul 29, 2008
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Nick said:
That's like the rubbing issues I was having with my 4s. Sometimes even on climbs. Argh.

I'm not opposed to trying those Miami Vice Maguras, I mean if they haven't killed @Da Peach peach yet they're probably good to go.
Click to expand...
You're welcome to come look at the sealed boxes I bought for the wife :D
 
HAB

HAB

Chelsea from Seattle
Apr 28, 2007
11,589
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Seattle
I've got two pairs of RORs, and they've (by a mile) been the most reliable, dependable brakes I've ever had. The older pair is over 3 years old at this point and they're still great.

I assume that, by typing that, I've caused both sets to spontaneously combust and burn my house down.
 
Da Peach

Da Peach

Outwitted by a rodent
Jul 2, 2002
13,773
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Nick said:
That's like the rubbing issues I was having with my 4s. Sometimes even on climbs. Argh.

I'm not opposed to trying those Miami Vice Maguras, I mean if they haven't killed @Da Peach peach yet they're probably good to go.
Click to expand...
Pretty sure you can buy all kinds of custom
Coloured bits to get all matchy matchy.

They’re great brakes.
 
Flo33

Flo33

Turbo Monkey
Mar 3, 2015
2,135
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Styria
kidwoo said:
That's weird, especially on a climb. Did you go suddenly from sea level to 10k elevation? Cuz that sounds like air expanding but shouldn't be pedaling uphill obviously.

I never owned a set of RO gens so I don't have any real experience with those. I was just going along with englertracing making fun of my drab curas.
Click to expand...
Nope, no rocket propelled elevation changes. I did bleed them with a proper bleed kit in late September and the result was the best I ever had on them. I also pumped out the pistons and lubed them with the Finish line Fluoro magic stuff Udi recommended, because one was a sturdy sticky bitch, esp. with the red Trickstuff power pads. Bite point was flawless and very consistent, did some lift laps on them - no problems.
The front is trouble free since the purchase in March 18. Will bleed again, maybe there is some air in it somewhere and change the piston seals while I'm at it.
 
Bikael Molton

Bikael Molton

goofy for life
Jun 9, 2003
4,088
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I’m fine with Codes but miss the bite strength of sorted Shimanos.
I hope they fix the issue sometime so that I can go back.
 
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