Nobody can tell you for sure. Shimano is silent on the cause of the problem and the fix. There are lots of theories that people propose, I believe some of them, but honestly I just use Shimanos if they're OE until they develop persistent problems, then ditch them. This has happened with every set I've owned, except for the ones on my wife's bike (old two piston SLXs). 4-piston XTs seem to be particularly bad about them. The good news is that it's not the old days any more, there are lots of manufacturers who are objectively better to their customers.

 

What IS this wandering bite point (very specifically, I know the general complaint). I had deore brakes, xt brakes, slx brakes, and ultegra brakes with shimano and with hope rx4 calipers, as well as several hope tech 3 sets.

They are all... fine? I mean obviously the hope feel very different, but they all were/are pretty consistent. Only issue I had was the slx which one had a slow leak.

I ask cause I have have a theory, but I may be misunderstanding the issue and my theory does not apply.

 

I often wonder, too.

 

There are plenty of brakes out there that don’t suffer from this problem.

 

I would say its the combination of ceramic pistons, and home maintenance by hobbyist mechanics, not by professionals. The combination of the two is pretty MTB specific. Add to that weight obsession that results in tiny reservoirs.

The floating bite point is typically not a result of a bad bleed, even though angry internet people will immediately yell that at everyone. Perfect bleeds can get air back in the system in a few rides on MTBs, and let's face it, getting the air out of a shimano system is very simple process.

 

Normally I’d agree completely with this as I cannot say I’ve really experienced it on properly maintained and bled brakes but too many professional mechanics and high level riders have called out the Mavens for me not to believe it exists there. If they can detect it and the people working on them cannot resolve it then it either exists on properly bled brakes or they are too difficult for even experts to nail.

I have one set of Mavens and they seem fine but in talking to people that are much better at maintaining it than me, they say that it is inconsistent. I don’t know. All I can say for sure is that I’ve been using Trickstuff almost exclusively for the last four years on nearly all of my bikes and if the problem exists, it is a bad bleed which would be my fault. When I’ve fixed the bleed then there is no issue. Piccolas are particularly finicky to bleed correctly and that’s why I don’t recommend them.

 

because Shimano doesnt make car brakes

 

I've experienced two forms of wandering bite point with Shimano 4 pot XT brakes, M8120 to be specific...

The first occurs when rapidly applying, releasing and applying the lever in succession. The bite point moves out, away from the grip, with each successive application of brake. Slow down this repeated application OR pause before applying the brake again, and it goes back to the "old" bite-point.

The second occurs slowly over time as the pad and rotor wear. The bite point move in, toward the grip, over time. The pistons don't seem to advance well through normal use. When the bite-point move too close to the grip, I manually advance the pistons. This can be done with the pads removed, lever fully depressed, and pads reinstalled. You may have to fully depressed more than once to achieve the desired bite-point.

IME and riding, the first occurrence is very infrequent. Most recently it happened at a park day, earlier in the day and then it went away after a couple laps. It may also align with days right after bleeding the brakes and/or setting the bite-point too far out. Its hard to nail down, because its so infrequent. Put it this way, 4 years of riding Shimanos, I can count maybe 1 hand how many times its been noticeable... from park days, to trail, to Whistler/Squamish/BC.

The second form takes a long time, and can be "reset". So less of a big deal.

Only other form I've read, but not experienced is suddenly loosing all braking power... lever goes straight to the grip and requires rapid application to bring back braking power. This to me sounds more like a poor bleed, than "wandering bite-point".

Regarding why... the first issue could be poor design on Shimano's part regarding porting in the master cylinder. As in, when the lever is released the design doesn't allow fluid to return fast enough to the master cylinder. So in rapid applications of the brake it "pumps" up.

 

The first occurs when rapidly applying, releasing and applying the lever in succession. The bite point moves out, away from the grip, with each successive application of brake. Slow down this repeated application OR pause before applyign the brake again, and it goes back to the "old" bite-point.

Exactly

 

And on the steep stuff...if you can "let go" long enough, they DO reset...it's those times though where you can't let go the brakes that long due to how steep it is.

 

This makes sense, cause the fluid is cooling, shrinking

 

And specifically on the 9000 non-servo. I used to have them on my racing fatbike. I would deal with the on/off switch function in the cold, but when the lever eventually puked and shimano replaced em...I put Hopes on...that basically work at -20 the same they do at +80. Yeah, a little slower...but not like shimano where the engagement point was way out there like an on/off switch and they were filled with glue. Comparatively, the Hopes worked like they do in Summer. And then on my XC race bike...the two issues of the weeping pistons and the engagement point moving out on steep descents (like in the Whiskey Off Road Copper Basin drop-in) was just too much after a few years.

 

Weird, I never have any of these issues.

At the root, this is the lever not being able to compensate for fluid changes. I wonder if the port is just too small. Mineral oil is a lot more viscous than DOT after all? Anyone ever try drilling it out slightly bigger?

 

I also tried the Putoline HPX 2.5 oil to see if thinner oil would fix the wandering point. No appreciable difference. Maybe slight, but still did all the stuff above.

 

Well, like I said, I tried thinner fluid. But yeah, it's like it can't "reset" and the fluid is too thick for the port.

But I totally get that some people's braking just never approaches where this is an issue. The best I can suggest is to get onto a 45% grade slope of decent distance where there's no "runout", no place you can just let go the brakes and slow down/let them cool. You gotta stay on the brakes under load and then try the quick resets, but it's not going to happen unless it's one of those "ass way back below the saddle" descents that isn't a "roll out". It's when you are nearly constantly on the brakes.

 

Well, like I said, I tried thinner fluid. But yeah, it's like it can't "reset" and the fluid is too thick for the port.

But I totally get that some people's braking just never approaches where this is an issue. The best I can suggest is to get onto a 45% grade slope of decent distance where there's no "runout", no place you can just let go the brakes and slow down/let them cool. You gotta stay on the brakes under load and then try the quick resets, but it's not going to happen unless it's one of those "ass way back below the saddle" descents that isn't a "roll out". It's when you are nearly constantly on the brakes.

I don't probably brake hard off road, but I sure cook them on road - I live on a cliff I've seen rain sizzle on the ice tech rotors. No issues with the ultegra levers which are, at least in principle, exactly the same as xt. (and yes I do have hope calipers, but I don't feel like they are part of the equation here)

 

Oh wow, more engagement that I expected.
The reason I bring it up is because I was thinking about splurging on the beringer set of brakes because I love my super-Moto beringers, and haven't found a MTB lever I really like the feel of yet. But the only review of them I can find mentions a bit of this "wandering bite". I figured if any company would be immune, it would be a company that makes professional race brakes for moto and race planes. So it got me wondering if it had something to do with the general design of MTB brakes in particular.
From the feed back here, it does sound like it could be a knockback sort of issue. Where the pads resting point is further away from the rotor than it should be, so your initial press has to move fluid to move the pads into contact with the rotor before increasing in pressure to brake. Then when you quickly release the lever and reapply force again, the pads don't have enough time to return to the normal resting position. So pressure rises sooner in the lever stroke. Do Shimano pads use a spring that pushes the pads out and away from the rotor like I see some pads do?

 

From the feed back here, it does sound like it could be a knockback sort of issue. Where the pads resting point is further away from the rotor than it should be, so your initial press has to move fluid to move the pads into contact with the rotor before increasing in pressure to brake.

This is somewhat the exact opposite of the problem.

 

I think MX brakes are a whole hell of a lot more like the V1 Magura Gustavs...and then MTB had to go and screw things up and try and reinvent them too many times.

 

Speaking of mags.. you mentions the older ones. Magura also being the only other "big boy" using mineral oil.

I have a dead SLX here, But I don't really have the inclination to experiment with it.

 

Because sram....

 

shimano issue first. and some other brands had it even earlier.

In mtb our brakes are small and use Very small channels with Large pistons and for whatever reason MTB'ers want to use mineral oil.....
Mineral oil, small channels with almost no mechanical advantage to retract pistons often means bleeding is a pain as air can get stuck behind pistons etc (which is the issue with MAvens)

Mineral oil is **** for bleeding, just doesnt flow as nice and once it has air mixed its hard to fix.


Hope brakes use an Automotive style and any clown can bleed them.

 

Any clown can also bleed shimano brakes. It's actually know to be the easiest system to bleed with the funnel.

 

Based on all the wandering bite point of shimanos. I'll have to disagree, they are just easier to bleed to get them in a way usable state.

We remove the bleed nipple and screw in a syringe and vacuum the caliper.

Hope brakes is literally funnel, open an close caliper while pulling lever. Done.

 

I feel bad for everyone who struggles with brakes.
Little bit of knowledge and know how makes these products work much easier.

All good mate if your struggling. Pop to the bike shop if you need help.

 

Fun fact, in the hope corporate tech 3 bleed video, THEY have issues I get a strong feeling you've never done this before.

 

Ill be honest an say I've never touched tech 3.
T4v4 is the only brake worth owning from them... no issues at all.
As I said, you can take yours to a bike shop if you are having issues 😅

 

Ill be honest an say I've never touched tech 3.
T4v4 is the only brake worth owning from them... no issues at all.
As I said, you can take yours to a bike shop if you are having issues 😅

So you try to mock people about brakes you know absolutely nothing about. Yeesh.
What's in the water today?

 

Wandering bite point is not an MTB thing in general. In recent years, it’s a Shimano thing. I haven’t experienced it on any modern brake other than Shimano. Every single Servowave system I’ve owned has exhibited this. Nothing on the current non-servo on one of my bikes.

 

I've never had this issue in 14 years of Shimano brakes.
I've only bought levers and calipers separately and bled them myself for installs.
Always mixed and matched ie xtr race with zee, xtr trail m9000 with xtr 4 Piston.
My wife's AliExpress SLx has no problems

 

I've only seen mention of servo-wave once throughout here, but I believe that that probably amplifies the issue to a HUGE degree. I personally can't stand the servo-wave, as modulation is more difficult, but it seems that more people than not prefer the binary response of them. I switched out all of my XT levers to XTR's (M9100's, not the 9120's) mostly because of modulation, but the wondering bite point hasn't been an issue since then, either. It seems to be a bigger factor for other people than it does me, perhaps that's because I'm more an XC/trail guy than a downhill guy.

Another factor that likely is coming into play is something called viscosity index. The DOT 5.1 stuff that SRAM specs probably has a higher viscosity index (VI) than mineral oil, as mineral oil typically has a low VI. This means that as the fluid heats up, its viscosity doesn't change very much, so the effort required to push it through orifices doesn't change. A fluid with a lower viscosity index will get thinner as it gets hotter, reducing how much effort is required to get it through orifices. COmbine that with thermal expansion (they aren't related - VI improvers are added to increase the VI), and this is probably a major factor.

 

When talking about channels or ports do you specifically mean piston ports or in the master cylinder in the handlebar?

So what technical changes could be made to the master cylinder to reduce the brake packing effect? Here are some theoretical and very random ideas:

• modify the brake fluid = Likewater or Putoline (doesn't seem to work)
• modify the ports/channels in the caliber/master cylinder
• 3d print additional fluid reservoir on top of the master cylinder
• change the spring in the master cylinder = longer?
• change the pad spring to make pads return more quickly
• change the diameter and thickness brake disc

I only get the packed feel in my Shimano Saint brakes like has been mentioned here previously: a relatively long downhill track where I have to brake for a long time, release, and brake again, and suddenly, the free movement in the handle is almost zero.

 

I didnt' read the entire thread to see if this was answered, but here is my observation.

I've had several brakes that have this problem, either due to incorrect installation/bleeding or manufacturing/design defect. In both cases, it seems like the problem occurs when the pistons don't retract fast enough and/or get stuck, then someone pulls the lever again. When the pistons don't fully retract, the system retains too much fluid beyond what it was designed for and it isn't the 'neutral' level, so the second pull then presses even more in before the fluid level can return to neutral. So the bite point moves further and further out. You can observe this on any brakes exhibiting this problem by pulling the lever and watching the pistons retract. It's very obvious in some of them.

My observation is that people who don't have issues with Shimano brakes in particular use a different braking technique than those that do. If you tend to rapidly on/off the brakes then you are more likely to have issues with them in the cold in particular. If you tend to make infrequent brake pulls with a gap between them or make minor adjustments, then you are less likely to have issues. I've yet to get on a set of Shimano brakes, setup by me or anyone else, that didn't have this problem when temps got below freezing and I've tried many on my bikes, demo bikes, and friends bikes, even those who said they don't have the problem, the brakes are still doing it. They just don't have an issue because of how they use their brakes. So technique can play a part in how people perceive this issue.

My theory is the reason it happens is due to the fluid getting too thick when it gets cold and it can't retract fast enough. It could be compounded by the seals getting stiffer in the cold but I would expect the issue to go away as the caliper heats up if that was the problem, so I think it's in the lever somewhere. My observation being that it gets worse when people do a "lever bleed", because it overfills the system and gives the fluid less room to retract if you fill the MC entirely with fluid. I've only ever had this issue with mineral oil based fluids (not all of them, though, mainly just Shimano), no brakes I've had that used DOT fluid had this problem provided the bleed was correct (My Kahas did until I bled them).

In some cases, it could be improper setup. In the case of the Mavens, I was warned by my LBS when I got them to do the piston massage procedure by shoving two rotors in then pulling hard against the lever to align the pistons. Prior to doing this, you could watch the pistons slowly retract in the last 20-30% after pulling the lever but after doing it then retracted quickly. I suppose it's possible the pistons could get out of alignment and it could cause them to not retract fully? A bad bleed can cause it, also, regardless of fluid type

As for why it doesn't happen in other areas - most other brakes use DOT fluid, which doesn't do this. Most other fields, you are more likely to find professional work done where you expect things to be installed correctly, even some bike shops can't manage to do this properly but in cars/moto/etc I think you expect a higher level of experience/professionalism. You also have a lot more fluid in other applications where weight and space isn't as concerning.

 

Pistons of brakes shouldnt retract much at all. That's something I've noticed with MTB brakes, the pistons move a TON. The square seals on calipers are meant to rock back and forth just a bit when the pistons squeeze down to take up the movement. The pistons are only supposed to slide up the seal as the pad wears. I'm wondering if it's a design choice to have lots of pad movement to pull them away from the rotor to make sure there isn't extra friction from the pads rubbing in their static position vs a car or moto that have pads that are always in contact with the rotor. I wonder if they used a higher leverage ratio on the lever and let the pads float right next to the rotor like on these other brakes if it wouldn't be a problem.
I kinda wish I had a set of brakes that have this issue so I could try a couple things out.

 

What about mineral oil's thermal expansion characteristics? For a 100F temperature change, the volume is going to change about 4%. That could cause a system overfill during long braking if the system isn't designed to compensate.

 

Agree, I only use Hope brakes. Since 2005 I think?
Never an issue.

 

To me it's simple. You have very tight tolerances, small pistons in both caliper and lever, heat, particilate, flexible bendy rotors. Small bolts....

It's called tolerances stacking. Stack them all up in thr wrong order abd bloom. Shitty brakes.

Because of the limited piston travel pad wear equates to some non aligned pumped out pistons and funky bite.

 

To anyone who has this issue and wants to try something out, try pulling off the spring clip that hold the pads together and seeing if that changes anything. I really feel like it has something to do with the pads normal resting position being further away from the rotor than the square seals on the pistons to take up with their designed rock. And not being able to slide back up the square seals with a quick release and reapplication of the brake. There is a huge amount of friction between a piston and it's square seal when it slides along it, but they shouldn't slide along the seal. The seal should just rock the small amount that is needed to make contact and start building pressure without the piston sliding inside the seal. But I could absolutely see the pad pushing back through the seal if the MC is designed for too much fluid movement and pulling the pads back too far by not being able to pull fluid from the reservoir fast enough. Or because of a quick release and application, the friction of the seal on piston holds the piston out and within the seals rocking operation range. But when you keep the brakes unapplied for a bit longer, the spring between the pads and the jostling of the pads from chatter pushing the pistons back through the seals and back to the resting position the rider is used to.
Also may be 100% wrong lol. I wish I had a set of these to test stuff with, but I'm not gonna spend the money to find out.

 

To anyone who has this issue and wants to try something out, try pulling off the spring clip that hold the pads together and seeing if that changes anything. I really feel like it has something to do with the pads normal resting position being further away from the rotor than the square seals on the pistons to take up with their designed rock

It will not/ can not be a function of the calipers.
If the caliper has a slow return, the LEVER will also have a slow return. A lot of us that ride in -30c will know this. everything just moves slow. The wandering bite point can really only be due to the lever.