[Closed] Wandering Bite Point - What actually is it?

I put some Saint brakes on a DH bike years ago and that was my first experience of it. The first pull of the lever would always hit the bar. They would take a few pulls to pump up, feel normal and make great power, then they'd fall off again. They do this all day long, during every ride. Not ideal when you're on a proper DH track on a big bike.

They act exactly like they need a bleed, so that's what I did. Over and over again. I was mates with the LBS at the time so free to spend loads of time in the workshop and none of us could make it work using every method in the book. They were always crap and stupidly, I got injured and let the 2 year warranty period expire, foolishly thinking I'd finally figure it out once I could ride again.

I've known loads of people with the same problem since then and obviously, it's all over the internet. I have no idea what causes it but I sacked them off years ago. I wasn't a Shimano hater, I had SLX and XT brakes which worked perfectly.

Loads of people on this very forum don't believe there's a problem and will line up to tell you you're an idiot who doesn't know how to bleed brakes.

Also, what actually causes it?

Air.

They need a good bleed.

Air.

They need a good bleed.

^^^See what I mean!

The symptoms you describe are air in the system - possibly a bubble moving from below the diaphragm in the reservoir to into the line and back out again.  Just takes a wee bubble hiding in a corner somewhere.

Another reason why I prefer hopes - simple conventional bleeding

I think it's just air, small amounts getting stuck and then moving around between places where it's not that important and places where it really is. TBF there's not an awful lot else that it can be, though some brakes have issues with reservoir bellows putting a little pressure on the system it doesn't fit well for Shimano's design.

sharkattack
Full Member

Loads of people on this very forum don’t believe there’s a problem and will line up to tell you you’re an idiot who doesn’t know how to bleed brakes.

It's like old Elixirs imo- yes it was possible to give them a perfect bleed. But so many people have difficulties with it, including time-served pros, that it's obviously an issue with the brakes. Even if that issue is just "really hard to bleed properly" or "really easy to bleed wrongly but not realise", it's still an issue.

I like my Formulas for this- they're pretty easy to bleed but also, if you don't get it right it's completely bloody obvious because they just don't work. There's none of this variableness, they're either right or rubbish.

Look up Santa Cruz syndicate marshy bleed on YouTube for the fix.

My xt m8000 used to wander all over the place until I used that method. They work perfectly now.

What tips do we have for getting a good bleed on an internal routed hose?
Back in the good old days I used to bleed off the bike with lever on a dummy bar in a vice and caliper on the floor.

^^^See what I mean!

Had to be done 😂

It’s like old Elixirs imo

It is, but worse. Elixirs never did it straight from the factory, whereas I warrantied 2 sets of SLX and had a Zee turn up from Canyon with the problem

You can still tilt the bike in a stand to get as vertical a run as possible.

If you follow the Shimano instructions you'll see they also recommend tilting/tapping the levers a couple of times at the end of the bleed to release tiny air pockets.

FWIW I've had the wandering bite problem twice on my own bikes and solved it both times with a good bleed. There's certainly an argument that it shouldn't be so difficult.

There are some cases where people have linked this to temperature. However, these seem to be sub zero fat bikers so doesn't cover all cases. If you look at the spec of Shimano brake oil, the viscosity does vary a lot at extremely low temperatures.

There's no denying that some people have cure their issue with a good bleed. Not sure what makes the Shimano porting any more convoluted than anyone else though.

Finally, some people have found that the bore in the master cylinder can seem rough and sticky. They say it appears to be anodised then machined rather than the other way around.

What is curious if it is just poor bleeding, why are shimano so willing to warranty and why aren't vacuum bleeding methods employed?

A pair of ancient SLXs have just started doing this. I put it down to them being 10-11 years old as they seem to resist bleeding. However after trawling YouTube I applied the system mentioned above and they have been fine.

Air.

They need a good bleed. Etc. etc...

But that won't solve it because they let air in to the system during normal usage...

get used to interim bleeds every 10 rides or so.. or replace with something made properly.

The prevailing view in some quarters is that the lever reservoir volume is insufficient once the pistons start extending. Leading to air being drawn into the master cylinder.

Postulated solution is to top up the reservoir once pistons are out.

My zees are adjusted with the lever almost to the bars so I dont seem to suffer much from this, but I tried it and it did seem to mitigate what little trouble I had.

Air is only one possible cause of wandering bite point. Even then bleeding isn't the only issue, as things like a lever seal can let air in, which then causes problems until it works it's way up into the reservoir.

In dry weather, it's worth keeping an eye out for any dampness around the lever, as it only takes a very minor leak to cause problems. Unfortunately in the UK, minor leaks are often very hard to locate until they become bigger leaks, as it's rare to ride in enough dry weather to notice a small damp patch that doesn't get washed off.

Piston/seal/bore tolerances can also be a cause.
Early Hope Moto V2s suffered from this, which caused the piston to retract too far, resulting in excess lever travel if the brakes weren't applied for a period of time.
The tolerance around using square seals to achieve consistent piston retraction can be quite problematic, as the actual result depends on groove width/shape/depth, amount of seal deformation, tolerance between piston and seal groove, and lubrication.
It wouldn't surprise me if mass produced callipers slip past QC with poor bore tolerances, and no amount of fettling/bleeding will resolve the issue.

Master cylinder volume theory is an interesting one. Should be easy enough to test I imagine.

Postulated solution is to top up the reservoir once pistons are out.

Over the years I have had a couple of sets of XTs (of different generations) that have come back to the bar. Open them up, stick a bit more fluid in, problem solved. I did wonder where the fluid had gone to, but they work, so I don't worry about it.

So I have some Shimano MT420 4 pots and I have noticed that sometimes the lever needs to be pulled further before they bite and sometimes not - this doesn't vary during a ride and they will stay the same for weeks on end.

I have noticed though that the pistons don't come out uniformly. I have watched them with the pads out and they all move but 2 seem to protrude further. I have cleaned them and lubricated with silicone but it seems to make absolutely no difference so I wonder if sometimes all four are applying pressure evenly on the pads and sometimes not, hence the difference. My thinking is that it will take more fluid to push out four pistons so the lever will travel further???

I have a brand new set of front and rear XT levers and callipers which I keep as spares currently but I'm tempted to fit them and see if they work better (routing the new hose will be a PITA though I suspect as it's an ebike so the hose has to go past the motor and battery etc - that'll be another thread no doubt - how do I... !)

Where you pull the lever and the bite point isn’t where it was a second ago… on the flat it’s a bleed, on long descents, the theory I’ve heard is that with heat the ice tech rotors warp slightly and push the pistons back slightly. Cheaper shimano rotors, or something thicker like the galfer ones I use, work well. Also check your discs aren’t wobbly, makes a massive difference. We spend quite a bit of time fixing peoples rotors as they are warped and are pushing the pads back in.

Pistons will never all move at the same time, as the easiest to move will always move first.

Once a set of pads are in and against a disc, the extra resistance means pistons will then apply equal pressure, unless there is a more serious issue, such as a seized piston.

Pistons will never all move at the same time, as the easiest to move will always move first.

Once a set of pads are in and against a disc, the extra resistance means pistons will then apply equal pressure, unless there is a more serious issue, such as a seized piston.

Yeah I sort of assumed that might be the case.

My rotors are true - well by eye anyway. I watch the gap between the pad and the rotor and spin the wheel - gap stays the same.

I actually don't think I have a real issue as the brakes work fine, I was more curious if the wandering bite point was what I am noticing, which it doesn't appear to be, and to be clear I'm not talking about a massive difference. It's not like the levers are going all the way to the bars sometimes and only moving a few mm at other times. One side or the other sometimes just feels a bit different when I pull the lever and goes a bit closer to the bar before it bites - it could be the weather..🤷‍♂️ This is the first bike I have owned with hydraulic brakes so I've got nothing to compare it to.

Thanks for all the responses though.

It wouldn’t surprise me if mass produced callipers slip past QC with poor bore tolerances, and no amount of fettling/bleeding will resolve the issue

Reminds me of the shimano chain issues back in the 90’s. Loads of people complained of chronic chain suck, loads of people said they was nothing wrong with them and they must be doing something wrong. Eventually shimano found an issue with one of their two chain making machines that was causing tolerance to sporadically alter

If a bleed doesn’t solve it, and it likely won’t, check your pistons.

Cleaned and lubed them recently?

One of the reasons The Marshy bleed works so well is that it also gives the pistons a lube at the same time.

I have had wandering bite point a few times and sorting the pistons out not bleeding has always solved it.

The prevailing view in some quarters is that the lever reservoir volume is insufficient once the pistons start extending. Leading to air being drawn into the master cylinder.

This is what I think. Both my Shimano brakes are completely dry at the caliper end, including numerous sets of pads over years and yet I still end up with an air gap, at the master cylinder, after as little as a ride. I'm constantly bleeding them!

Both sets (Deore and SLX) produce bubbles constantly at the lever. I've tested it by bleeding it for lengthy periods. A lever pull instantly produces little bubbles in the bleed bucket, it never completely stops, no matter how long you persist!

I ran several bikes with Shimano brakes. No problem. Then I had a problem set. The rear M8000 XT 2 pot just was random. Sometimes it would pull short. Sometimes long.

I swapped the calipers between the hoses front to rear. Problem was now on the front brake.

Swapped back; problem at the back. Did the swap twice more. Yup. The caliper is the problem.

Not the m/c. Not air.

Dismantled and there was impacted swarf from manufacturing in the piston surface that was snagging the seal. That was as far as I gave a damn in sorting it out. New brakes please.

Having experienced a really bad caliper I paid closer attention to other Shimano brakes; they had some similar tendencies. The piston retraction is slow. If that's friction or fluid viscosity, I don't know. Combined with servo-wave, a small change in the rest position of the piston results in a bigger change in the lever pull on next use. It shows up in intense use (Alps etc.)

Shimano brakes try to retract the pistons further than other brands, with servo-wave bringing them back in contact on next use. I prefer now brands that run less clearance but work predicatbly. Formula Cura has been a good find.

I'm a Shimano brake fan but as above my most recent set did have a bit of swarf pop out during installation bleed.....

Sometimes it's the barb / olive causing the issues. Either misalignment or overtightening the retaining bolt. Both can cause restriction of oil flow which you don't notice when you apply the brake, but the oil can't flow back into the master cylinder fast enough when releasing and quickly reapplying the lever. Hence the pads can't retract fast enough. First squeeze = long lever throw. Second squeeze short lever throw. I've had this before, including a couple of days ago when I wasn't happy with a bleed. Replaced the barb / olive and the lever feel was then perfect.
I'm not saying this is always the case, but it's one scenario.

Four year old XT/SLX brakes. Big fan of the Marshy method (plus rotating the levers 45 degrees above/below bars and squeezing at end of process, plus silicone grease on piston edges with a cotton bud before working them in and out). Do this once a year and have had no problems - except once...

I'd put a new hose on the rear SLX due to a frame swap, using the Marshy method to fill the system. Felt fine for 400km, then started getting the symptoms described here. Uh oh. Another Marshy bleed failed to solve it, so I bought an Epicbleed kit and did it as per their instructions. Sorted, no reoccurrence in the last 18+ months. I assume there was a small air bubble trapped somewhere which the EB process forced up through the system. I still use the Marshy method for a general bleed/fluid refresh and piston lube.

Marshy bleed now bookmarked. Cheers

Look up Santa Cruz syndicate marshy bleed on YouTube for the fix.

Good video!

I just use the "Shimano" method as described in their techdocs.

Previously I've followed the Epic brake bleed instructions, which seem more complicated than the SC method above...

An observation, I was having some issues with my SLX brakes, bleed them still had issues. Then noticed that the pads and rotor were thin. Now after replacing them the issues have gone away.

I am wondering if as the rotors and pads wear this might cause issues around oil volumes and how the brakes adjust for wear.

had this loads on various shimano brakes.. and the syndicate video work for all of them

I had an issue a bit like this on my Sram Codes recently. I'd set them up at home feeling nice with not too much lever throw then get on the trail and after a few descents the lever pull would increase dramatically to the point where it almost hit the bar.

I figured it was air in the system but it persisted after a very careful bleed. In fact the problem was sticky pistons causing them to get unbalanced and slightly skewed.When I took the pads out I could see that they were worn unevenly.

I cleaned up the pistons again and this time lubed them with Hunters silicone lube following advice on this thread and they felt better than new. A really even pad spacing, nice sharp lever feel and it stayed that way the entire next ride.

I'm not saying this is always the issue, it probably almost always isn't the issue but it did help in my particular case so worth considering.

I am wondering if as the rotors and pads wear this might cause issues around oil volumes and how the brakes adjust for wear.

Yes. If the reservoirs are underfilled there won't be enough fluid to take up the movement. If there's air in the reservoir, that can get into the master cylinder much more easily than when the pads are new and the reservoir is full.

I cleaned up the pistons again and this time lubed them with Hunters silicone lube

This is a really good point and a good data point from another brand's brakes.

The piston/seal interface is the complicated part of hydraulic brakes. If there is dust and muck, they won't work as designed. I use most changes of brake pads as an opportunity to clean up brake dust and trail crud while the pistons are pushed out and to ensure they're moving evenly.

I think Marshy's bleeding technique has the really useful side effect of lubricating and cleaning the pistons.

+1 Marshy vid, I'll be trying that later as my front Zee was playing up yesterday.