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Shimano Brake wandering bite point cure...sort of

May 4, 2021, 9:46 a.m.
Posts: 267
Joined: March 6, 2017

So I finally got fed up and dealt with my issue. I'm running Shigura with XT levers, MT5 calipers. I decided to take my masters apart and figure out exactly causes the wander. The system is as simple as possible IMO, a rod pushes a piston that pushes the fluid so wtf could it be? I wish I took pictures but I didn't so it is what it is. The problem with Shimano brakes is that the piston gets filthy dirty when you push the shitty fluid up from the caliper during a bleed, so the Marsh gravity bleed technique is your best bet. Even after clean fluid was filling up my bleed cup, the system was still 'sticky' because the piston o-rings were so dirty. The wander is from the piston not retracting all the way fast enough so when you grab the lever again there's already fluid in the system and you're just introducing more. The second problem is the pin that the lever rotates on is press fit into the plastic 'cams' and rotates inside. My pin and plastic were worn so bad I almost threw the levers away. All I did was rotate the pin 180 degrees to take up some of the slack when I put back together. SRAM uses bearings on their higher end brakes which gets rid of this issue. So my advice is to gravity bleed always and keep your levers as clean as possible at all times so mud and gunk doesn't get in there and make the wearing issue on the pin even worse.

Also it was interesting seeing how the 'Free Stroke' screw actually works. It just pushes on a piece of plastic that pushes the piston in, pretty simple, when you unscrew it the piston comes out which is how the system should be bled. Cheers.

May 4, 2021, 11:10 a.m.
Posts: 1399
Joined: Nov. 8, 2003

Nice, thanks for jumping into the guts T-mack. Marshy knows a thing it seems.

Interestingly I haven't had the wandering bite point since going Shigura. I'm running non-servo XTR race levers wonder if that has anything to do with it.

May 4, 2021, 11:13 a.m.
Posts: 267
Joined: March 6, 2017

Posted by: Hepcat

Nice, thanks for jumping into the guts T-mack. Marshy knows a thing it seems.

Interestingly I haven't had the wandering bite point since going Shigura. I'm running non-servo XTR race levers wonder if that has anything to do with it.

Could be. I'm willing to bet the 'Servo-Wave' is actually those plastic bits in my levers come to think of it

May 4, 2021, 4:14 p.m.
Posts: 187
Joined: Feb. 24, 2017

Awesome information, thanks! I have always bled my brakes top down. Given the amount of crap that gets flushed out of the calipers this just makes sense to me.

May 4, 2021, 7:04 p.m.
Posts: 91
Joined: Feb. 24, 2017

According to the 30+ page thread on ridemonkey, the bore in the MC is machined after anodising, so it's not hard enough to stand up to the plunger pushing, so it wears... The dark grey fluid in the MC is aluminium particles. This doesn't cause the wander, but it makes any issues worse.

May 4, 2021, 8:07 p.m.
Posts: 267
Joined: March 6, 2017

Posted by: velocipedestrian

According to the 30+ page thread on ridemonkey, the bore in the MC is machined after anodising, so it's not hard enough to stand up to the plunger pushing, so it wears... The dark grey fluid in the MC is aluminium particles. This doesn't cause the wander, but it makes any issues worse.

Oh that makes sense too! I was always shocked at how quickly the shimano fluid got dirty.

May 4, 2021, 9:03 p.m.
Posts: 362
Joined: Feb. 24, 2017

Good to know. I always wondered how the pad contact adjust worked. I always turn it out until the lever stops moving then gravity bleed. Seems to work. I also will do a burp whenever the brake starts feeling like the lever is getting too close. 

I’ve read somewhere some time ago that many modern brakes don’t have a lot of oil volume so when pad wear and disc wear add up the lever gets too close. Not enough oil volume to account for a lot of wear. What does the hive mind think?

May 5, 2021, 7:35 a.m.
Posts: 14884
Joined: Nov. 20, 2002

I find when it gets to that point its probaby time for new pads  so replace them but don't add brake fluid

May 5, 2021, 9:58 a.m.
Posts: 1208
Joined: Nov. 23, 2002

Posted by: T-mack

Posted by: Hepcat

Nice, thanks for jumping into the guts T-mack. Marshy knows a thing it seems.

Interestingly I haven't had the wandering bite point since going Shigura. I'm running non-servo XTR race levers wonder if that has anything to do with it.

Could be. I'm willing to bet the 'Servo-Wave' is actually those plastic bits in my levers come to think of it

Yeah the Servo-Wave is those plastic bits and simply changes the leverage ratio of the lever so the pads move more in the initial part of the stroke. Servo-Wave is external to the master cylinder and has nothing to do with the wandering bite point. The part about the non-anodizing leading to increased wear has me a bit suspicious tho, how much wear can a rubber seal cause on an aluminum surface when it's bathed in oil? Either way the gravity bleed part makes sense and I'm going to do the same as you T-mack and pull it all apart to clean everything properly. I'm also going to try out the automotive mineral oil I picked up. If nothing else it's an inexpensive way to flush the lines and clean everything out.

May 5, 2021, 10:33 a.m.
Posts: 19
Joined: Oct. 23, 2019

Posted by: T-mack

So I finally got fed up and dealt with my issue. I'm running Shigura with XT levers, MT5 calipers. I decided to take my masters apart and figure out exactly causes the wander. The system is as simple as possible IMO, a rod pushes a piston that pushes the fluid so wtf could it be? I wish I took pictures but I didn't so it is what it is. The problem with Shimano brakes is that the piston gets filthy dirty when you push the shitty fluid up from the caliper during a bleed, so the Marsh gravity bleed technique is your best bet. Even after clean fluid was filling up my bleed cup, the system was still 'sticky' because the piston o-rings were so dirty. The wander is from the piston not retracting all the way fast enough so when you grab the lever again there's already fluid in the system and you're just introducing more. The second problem is the pin that the lever rotates on is press fit into the plastic 'cams' and rotates inside. My pin and plastic were worn so bad I almost threw the levers away. All I did was rotate the pin 180 degrees to take up some of the slack when I put back together. SRAM uses bearings on their higher end brakes which gets rid of this issue. So my advice is to gravity bleed always and keep your levers as clean as possible at all times so mud and gunk doesn't get in there and make the wearing issue on the pin even worse.

Also it was interesting seeing how the 'Free Stroke' screw actually works. It just pushes on a piece of plastic that pushes the piston in, pretty simple, when you unscrew it the piston comes out which is how the system should be bled. Cheers.

I agree with your description of the "pumping up" mechanism, this get worse at lower temperatures, the oil becomes more viscous and the seals probably harden slightly.

I personally haven't seen excessive wear on the lever axle bushings or axle, definitely develops some play over time though, it would be nice to have the option to replace those bushing though. You did take the Lever Axle Set Screw Out right?

It would be interesting to see an oil analysis of what's actually in the black oil, the aluminum particle theory makes sense, but the oil in the caliper is always so much worse than the in the master cylinder/hose, I always assumed that some brake dust was being pull through the seals when the pistons retract in the caliper and/or the heat from braking has some sort of effect on the additives in the oil.

Posted by: andy-eunson

Good to know. I always wondered how the pad contact adjust worked. I always turn it out until the lever stops moving then gravity bleed. Seems to work. I also will do a burp whenever the brake starts feeling like the lever is getting too close. 

I’ve read somewhere some time ago that many modern brakes don’t have a lot of oil volume so when pad wear and disc wear add up the lever gets too close. Not enough oil volume to account for a lot of wear. What does the hive mind think?

I've always burped the levers several times over the life of a pad. I figured there is technically enough oil but would bet that if you pulled the levers while the bike is upside-down with the pads 75% worn, you would introduce air into the lines. 

Although, maybe that doesn't actually line up with "burping". Burping does definitely improve lever feel/bite point, so either the extra oil being added into the reservoir adds weight to fill the master cylinder piston slightly more, or air is introduced to the master cylinder as the pads wear: maybe via air and oil mixing due to vibration during riding and then being pulled into the master cylinder?

I've found that there is some degree of venting/weepage in the lever from every shimano brake I've owned. I think this is through the reservoir vent, but could also be from the master cylinder seals.

I also loosen off the contact adjust screw for full bleeds, but I turn it in before closing the reservoir, otherwise, the excess fluid seems to vent out of the reservoir.

I like the Marshy bleed, but I find that covering the caliper with oil ends up being a pain to clean fully, and I often end up with slight contamination that needs to be burned out of the pads.

May 5, 2021, 1:20 p.m.
Posts: 113
Joined: Jan. 21, 2013

Somewhere between a bottom-up bleed and a Marshy bleed, is putting the (full) cup on top, hooking up a tube and syringe on the bottom. Open the bleeder most of the way. Pull the lever to push fluid through repeatedly. Each pull of the lever pushes a couple mL of oil through and into the syringe. Repeat until the fluid at the bottom is pink. Seal the bleeder, bubble burp the top. 

No pushing dirty fluid up. No messy oil all over the place. Full oil flush. It's getting to be my go to.

May 5, 2021, 1:53 p.m.
Posts: 1399
Joined: Nov. 8, 2003

By burping, do you guys mean attaching the cup up top and flicking the lever?

May 5, 2021, 2:25 p.m.
Posts: 113
Joined: Jan. 21, 2013

Posted by: Hepcat

By burping, do you guys mean attaching the cup up top and flicking the lever?

That's what I mean!

If it's an externally routed rear brake and I'm having a hard time getting a good bleed, I pull the rear caliper right off the frame to let it hang and maximize gravity too.


 Last edited by: mrbrett on May 5, 2021, 2:26 p.m., edited 1 time in total.
May 5, 2021, 2:54 p.m.
Posts: 91
Joined: Feb. 24, 2017

Posted by: mrbrett

Somewhere between a bottom-up bleed and a Marshy bleed, is putting the (full) cup on top, hooking up a tube and syringe on the bottom. Open the bleeder most of the way. Pull the lever to push fluid through repeatedly. Each pull of the lever pushes a couple mL of oil through and into the syringe. Repeat until the fluid at the bottom is pink. Seal the bleeder, bubble burp the top. 

No pushing dirty fluid up. No messy oil all over the place. Full oil flush. It's getting to be my go to.

This. Plus the added step of advancing and retracting each piston. Otherwise some nasty fluid always seems to be trapped around them.

May 5, 2021, 9:39 p.m.
Posts: 1186
Joined: Nov. 21, 2002

Posted by: syncro

Yeah the Servo-Wave is those plastic bits and simply changes the leverage ratio of the lever so the pads move more in the initial part of the stroke. Servo-Wave is external to the master cylinder and has nothing to do with the wandering bite point. 

I never really understood or cared to understand what servo wave was all about these past 10 years.  But once I got some 980 xtr levers, it became clear as day as the mechanism is external.  You can see in the picture below servo wave just refers to whatever pieces needed to get that wavy path so lever pull and piston travel are non linear at the beginning of the stroke. And I agree servo wave isn't the culprit behind the wandering bite point

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