Shimano brakes: Pull lever fast works, but pull lever slow goes to bar

My problem is related to wandering bite point, but a bit different.

After the last bleed my XTR M-9000 rear brake works without wandering bite point like it should while riding, but if I squeeze the brake lever slowly it goes to the bar; whereas, when I squeeze the lever rapidly (just one squeeze & not the repeated squeezing to pump it up), the pads contact the rotor when the lever is half way to the bar (or where ever I adjust it to)

I had the stereotypical wandering bite point and did the brake bleed where you remove the caliper from the bike to hang vertical and removed the bleed screw completely and let the brake oil flow down from the funnel and out the caliper into a rag while rotating and tapping the caliper around in all directions. Finished off by bleeding normally and burping some more oil out after pads stepped and adjusted pad to rotor spacing.

I have used all bleed methods recommended including gravity bleed to hose attached to bottom bleed screw, syringe from the bottom, syringe from top and bottom, tapping, rotating, hanging etc.

When I burp the lever (attach oil filled funnel and squeeze lever to pump air bubbles out and nothing more) when the pads are partially worn, I get oil squirting out the bypass port in the lever and onto my grips, but the brake works after (either correctly or when pumped up for wandering bite point), so after the initial squirt there is not more oil loss.

I am wondering why the difference between slow vs fast squeeze.

I finished my ride about 4 hours ago and just now tested the lever again by first squeezing fast (it worked perfectly), but my second squeeze was slow and the lever went to the bar

Maybe the inside of the master cylinder is worn (almost 5 years old now) or burping the lever so that the bypass port was damaged? Does anyone know of another reason?

Hope someone has a solution for you. I went through so many hours messing with wandering bite point issues just like yours. Throw in the towel and put some Magura calipers on there is all I have to offer. https://www.bike-components.de/en/Magura/MT5-Carbotecture-Disc-Brake-Set-p45429/

My bite point hasn't moved in the two years I've been running Shigura.

You could spend the time reading the 50 page thread on ridemonkey covering brake shenanigans... But the consensus seems to be that shimano anodise their levers before machining the MC bore, so the piston gradually wears the raw aluminium away.

I'm full shimano across the fleet, but am tired of how disposable they are, it'll be TRP next I think. 

Good luck.

Velocipedestrian, I hope you’re sub 160lbs. I bought TRPs DH brake when it was first released and could not get enough power out of them despite trying shimano pads and larger rotors.

Posted by: Cheez1ts

Velocipedestrian, I hope you’re sub 160lbs. I bought TRPs DH brake when it was first released and could not get enough power out of them despite trying shimano pads and larger rotors.

No... Not by heaps, probably 175-180 geared up, but I do love the Saints, so power is important. 

I've heard the DHR evo with the thicc rotors is better, but won't go there if the power is lacking.

Sounds like master cylinder is bypassing. Need a new lever. A quick tap and fluid can't bypass the orings,  but steady pressure it is leaking past.

Posted by: velocipedestrian

You could spend the time reading the 50 page thread on ridemonkey covering brake shenanigans... But the consensus seems to be that shimano anodise their levers before machining the MC bore, so the piston gradually wears the raw aluminium away.

This is why you can bleed a Shimano brake and after 1 ride the fluid is black. Its all aluminum impurities.

Posted by: Kenny

Sounds like master cylinder is bypassing. Need a new lever. A quick tap and fluid can't bypass the orings,  but steady pressure it is leaking past.

Thanks Kenny. That is what it looks like.

I pulled another bl-M9000 lever from my scrap bin apart for practice. Pulled the piston and spring out of master cylinder and there were some streaks in the bore (scouring?) and the piston was very sticky and I could barely get it to move (which is why it was in scrap bin)

I saw some titanium pistons from China online.  But don't see the point if the cylinder bores are already pooched.

Anyway I found another new lever, and in the mean time I will remember to always pull the lever quickly (at least to the engagement point)

So where's a good place to get a deal on Magura levers/pistons?

Jenson has MT5s in stock

Posted by: syncro

So where's a good place to get a deal on Magura levers/pistons?

I've bought a couple pairs from the sketchy German site linked above/\ 

Note you'll need the Magura hose olive and pin too if going Shigura.

Posted by: syncro

So where's a good place to get a deal on Magura levers/pistons?

I've bought a couple pairs from the sketchy German site linked above/\ 

Note you'll need the Magura hose olive and pin too if going Shigura.

Posted by: Hepcat

Posted by: syncro

So where's a good place to get a deal on Magura levers/pistons?

I've bought a couple pairs from the sketchy German site linked above/\ 

Note you'll need the Magura hose olive and pin too if going Shigura.

They’re not sketchy, more like the Chain Reaction of Germany. 

Just ordered a set of MT5 brakes complete about a week ago and delivery should be any day.

Posted by: Hepcat

Posted by: syncro

So where's a good place to get a deal on Magura levers/pistons?

I've bought a couple pairs from the sketchy German site linked above/\ 

Note you'll need the Magura hose olive and pin too if going Shigura.

Saw that. I was curious though, why use Magura calipers and Shimano levers if the issue seems to be with the Shimano lever and the wear in the master cylinder piston bore?