[Blatant]

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.

 

[Sloth Monster]

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

 

[67King]

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.

 

[155K98]

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.

 

[Adodero]

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.

 

[Mudguard]

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

Yeah I've found Tech 4s virtually impossible to get feeling decent. A friend has two sets. I've had Formula, Shimano, SRAM and Hayes and I've found bleeding those Hopes a PIA.

Shimano the easiest, then dual syringe for Hayes, SRAM and Formula.

The Hopes we bled pulling from the bottom, which means topping up the reservoir with a spare hand so it doesn't run dry. Both sets I suspect have air stuck in the caliper that we cannot shake free.
Don't get me wrong, I love the way they feel and look. But there's way too much lever travel for my liking.

We've tried bleeding from the bottom up too and had the same result.

Shimano, partially filled funnel on the lever, bleed up from the caliper. Done.

 

[TylerVernon]

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.

 

[Jayem]

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.

The wandering bite point of the shimanos has nothing to do with bleeding.

 

[Shark]

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

 

[Picasso_the_Impaler]

This is somewhat the exact opposite of the problem.

How so? If the first press of the brake has to move more fluid before biting, the lever is going to pull further in. You let go, quickly pull lever again before the springs or whatever could pull the pads and pistons back to the resting position, less lever throw would be needed to get to the bite point.

 

[plummet]

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.

 

[Adodero]

Yeah I've found Tech 4s virtually impossible to get feeling decent. A friend has two sets. I've had Formula, Shimano, SRAM and Hayes and I've found bleeding those Hopes a PIA.

Shimano the easiest, then dual syringe for Hayes, SRAM and Formula.

The Hopes we bled pulling from the bottom, which means topping up the reservoir with a spare hand so it doesn't run dry. Both sets I suspect have air stuck in the caliper that we cannot shake free.
Don't get me wrong, I love the way they feel and look. But there's way too much lever travel for my liking.

We've tried bleeding from the bottom up too and had the same result.

Shimano, partially filled funnel on the lever, bleed up from the caliper. Done.

I have bled several sets of T4s and never had a problem. Which caliper are you using? V4? I will agree the lever feel is lighter than others and if you value brakes with a lot of lever feedback then the V4s in particular probably aren't the best option, you can pull and barely feel the bite point.

The problem IMO is people tend to get too inventive in the bleed process and don't follow instructions or completely replace the recommended process. I found this with Magura and Trickstuff also, people complain they couldn't get a bleed but then you ask what they did and it's not what the instructions state, they just sorta invented their own process and never do anything the manufacturer recommends. I've added my own steps to bleeds at times but I always finish with the manufacturers suggestions and I've rarely had a problem with any modern brakes and getting air out. I think the same applies to Shimano, people start pressurizing or overfilling the system then wonder why the bite point wanders worse than when you do it with the instructions (despite this I've never gotten rid of the problem entirely when cold). You can do whatever you want before but IMO it's important to follow the manufacturer guidelines on the bleed process when you finish, from top to bottom, before closing it off.

For the T4 V4s I've bled, I do add a step before finishing with their instructions and I extend the pistons out using two rotors put together, zip tie them in, then do the bleed as stated by Hope. I then push the pistons back in and repeat the process as outlined by Hope. IMO the biggest challenge with them is the last step, which is rolling the bladder in and avoiding air getting trapped there, along with the fact it's an inherently messy process. I got the pitchforks showing up at my doorstep last time I said this, but I find the Hope bleed process janky in comparison to others that keep the whole system sealed (Hope, Trickstuff, Intend, Magura, Formula, SRAM, etc). It takes a bit more work to get it right.

It's also worth remembering that Hope brakes are hyper sensitive to caliper alignment. They have some STL files you can 3d print, both bleed blocks and a caliper alignment tool, using these makes this process a lot easier as do the marks on the caliper.

 

[Picasso_the_Impaler]

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.

 

[Picasso_the_Impaler]

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.

 

[CrozCountry]

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.

I will repeat what everyone else here said, wandering bite point is not a bleed issue.

 

[Wabatuckian]

I've noticed wandering bite point in my Tektro 4-pistons:

First, if I make a hard, sharp turn, it seems that I get enough flex in my front wheel to make the rotor push against the pads on one side a little bit, enough to change the engagement point but not enough to keep the brakes from engaging.

Second, if I'm riding my brakes, release and reapply, they engage sooner. I suspect this has to do with heating the fluid.

 

[smashysmashy]

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

Yes, I mean the port from the master cylinder to the reservoir. This is where excess oil is supposed to go when you release the lever. Seems it may be travelling too slowly for "quick" lever motions. I mean this is the principle behind pumping up brakes. you flick the lever a bunch of times to force oil INTO the line before it leaks back out into the reservoir. So maybe we are getting the reverse here.

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.

That is the root of the problem, Fluid expands, but it clearly not making its way into the reservoir fast enough when the lever is released. More than like this is gets super exaggerated by servo wave because even a tiny bit of fluid expansion deep in the lever travel will move the "power point" a lot. And given the nature of the design, it could also be inconsistent. I bet a larger port might resolve most of it.

I don't think the master cylinder would be over filling and pressurizing, but that is an interesting thought.

 

[smashysmashy]

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.

 

[smashysmashy]

I've noticed wandering bite point in my Tektro 4-pistons:

First, if I make a hard, sharp turn, it seems that I get enough flex in my front wheel to make the rotor push against the pads on one side a little bit, enough to change the engagement point but not enough to keep the brakes from engaging.

Second, if I'm riding my brakes, release and reapply, they engage sooner. I suspect this has to do with heating the fluid.

Your first issue about cornering will not be part of this. the rotor pushing on one piston necessitates it release the other. The rotor is not getting fatter

Second issue sounds like packing up, but its hard to know. The issue with shimano is HIGHLY specific. ALL brakes pack up to a degree, but none but shimano seem to have this very specific behavior.

 

[Picasso_the_Impaler]

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.

The lever shouldn't have a slow return if the pistons do. It should pull from the reservoir and with the pistons staying in its extended position. That's what it's for.
But you are right, the MC would still potentially be the problem in my scenario as well.