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Finally fixed free play in brake lever 2006 636

2.3K views 1 reply 2 participants last post by  RJ2112  
#1 ·
It's been a long story of progressively improving my front brakes on the 2006 636 which use the stock 4 pot Tokico callipers, the main issue I think is that these callipers are crap which is why the ZX6R changed to Nissin callipers in 2007.
I'll make a point list of every stage until the final fix.

1. Purchasing the bike in Nov 2020. Brake lever would easily go right down to the bar like there was nothing there at all. First fix attempt was simply to put new brake fluid and bleed the system.
- Result 70-80% free play in lever, only about 1/4 braking power when lever is maxed out to the bar.

2. Install Brembo 17RCS Master cylinder and HEL braided lines, new fluid and blead the system.
- Result 50% free play in lever and can achieve full brake power but is too close to the bar (not ideal)

3. New brake pads and rotors
- Result: No change in lever movement from step 2. (however fixed the minor wobble on hard braking that I had before)

4. Rebuild the front callipers with OEM seals and polished the calliper pistons
- Result: no change in brake lever still same 50% as points 2 and 3.

5. Put cable tie around brake lever to hold brake of +12hrs
- Result: Improved brake level to now 42%-45% free play.

6. The final fix that gives me satisfactory 30-35% free play
Before I explain what I did to get this I need to explain the main cause of my issues, the cause was what called piston "retraction".
The seals around the pistons in the calliper have a moderate grip on the piston (some people suggest this is caused by the dust seal not the actual piston packing and they remove the dust seals to fix this issue). Regardless, when the brake is pressed and the pistons move; the seals are sort of stretched and deformed because of the grip the seals have on the piston, when the lever is released the stretched seals pull the pistons back to where they were before the brake was pressed.
Also on a side note: if the pistons protrude "too much" (i.e. when pads wear) the piston yields against seals, if you were to see this happen it would look like a sort of pop or jerk of the piston, where the seal would momentarily let go of the piston a bit to then re-grab it further down the piston. This yielding is why hydraulic brakes are a self adjusting system and the lever does not need to get adjusted as the pads wear.

Anyway the issue I was having was that these callipers seem to have too much retraction (the pull back movement) and wouldn't yield easily.
- One solution that made an improvement was the cable tie around the lever for +12 hrs. What this does is as the seals stretch with the piston movement, if held long enough the seals will slowly relax back into normal shape while the piston is still protruded (there is a good animation of this online somewhere).

-The second solution which finally got me to be satisfied with my free play is to do the following process
1. undo and remove the calliper mounting bolts
2. push the calliper hard up against the rotor away from you into the rotor (don't push too hard as you can bend the rotor). push hard enough to remove any gap between the brake pads against the rotor on one side.
3. pump the brakes around 10 times.
4. now pull the calliper in the other direction (towards you against the rotor) this will remove the gap on the other side.
5. pump the brakes around 10 times.
6. Reinstall the calliper bolts with the correct torque.

Then after this do the cable tie around the lever and leave it for +12hrs, the lever does not have to be crazy tight just like light braking where the pads are hard up against the rotors.

The reason why I think this method works was when I pushed the calliper against the rotor on one side it caused a bigger gap on the other side, the idea is that gap is big enough to overcome the retraction and cause the pistons to yield closer to the rotors.

I hope this is clear and useful to everyone, please feel free to let me know if there are any issues with what I've said.