How to remove excessive play from front brake engagement

[motoguy]

2006 Ulysses. It has excessive (IMO) play / movement in the front brake lever. I'm moving the lever a good portion of the available travel before the front brake becomes loaded. I've bled the brake system, replaced the fluid, zip-tied the lever down overnight, etc. It's not just free play in the lever. I'm watching the brake activate / move the piston before pressure begins to build.

I normally like a little bit of lever free play before the brake begins to load, but this is more than I'm used to. I'm curious if this is just a ZTL thing or if there's more I can do to reduce the issue. I guess it could be a piston seal issue as well, but I haven't gotten that far into it.

 

[Pushr0d]

Maybe your disc is not properly aligned, or it has a warp. That would push the caliper puck away, so every time you apply the brake, it has to travel further.

Or, the boot is sticking and pulling the puck back.

 

[motoguy]

Maybe your disc is not properly aligned, or it has a warp. That would push the caliper puck away, so every time you apply the brake, it has to travel further.

Or, the boot is sticking and pulling the puck back.

The bike hasn't left the garage since I started dinking with this issue. So it's not a rotational issue. It's a stiction, leakage, compression, or design issue. I'm just trying to figure out which, and what the fix is.

 

[Kurlon]

Unbolt the caliper from the fork, slide it down the rotor a little so the only thing locating it is the rotor, you'll need to hold it up with your hand. Better, find a friend to hold the caliper in place. Now try the brake lever, see if after a couple good squeezes that excess travel is gone. If it is, the rotor is pulling one side's pistons back due to either warpage, or it's not floating on it's mounts correctly, etc.

 

[motoguy]

I'll pull the caliper and check the slide pins and piston. I didn't have time to do that the other day. Actually if I'm going that far I'll probably just swap on the ZTL2 setup from the parts bike.

 

[Cooter]

There should be almost no free-play once the lever contacts the piston and it travels past the feed hole in the reservoir. Fluid doesn't compress*.

Theres no slide pins, the caliper is solidly mounted to the fork leg with pistons on both sides. If you see the rotor moving/flexing when applying the lever, some ting wong.

It's usually the M/C not the caliper. Try loosening and rotating the M/C on the bars so brake line output is the highest point. That will allow any trapped air bubbles to travel down the line. And a M/C re-build kit is super cheap. 19mm is the size for ZTL-2 if you go that option you'll need that M/C..

No weird old wives tales bleeding BS needed, like stories of rubber banding the lever closed etc. But a vacuum bleeder is useful. In extreme cases, I will leave some fluid room in the resevoir and completely (slowly and carefully) compress the caliper pistons entirely in their bore to drive all the fluid back up into the MC. Then pump the lever SLOWLY while re-filling the res.

 

[motoguy]

There should be almost no free-play once the lever contacts the piston and it travels past the feed hole in the reservoir. Fluid doesn't compress*.

How much piston travel occurs before it's moved past the feed hole?

It's usually the M/C not the caliper. Try loosening and rotating the M/C on the bars so brake line output is the highest point. That will allow any trapped air bubbles to travel down the line. And a M/C re-build kit is super cheap. 19mm is the size for ZTL-2 if you go that option you'll need that M/C.

I did the usual tricks. Tapping the lines with a screwdriver, tilting the bike so the exit from the MC was the highest point, etc. I'll try removing it completely and cycling it "banjo bolt high" for a bit.

But a vacuum bleeder is useful. In extreme cases, I will leave some fluid room in the resevoir and completely (slowly and carefully) compress the caliper pistons entirely in their bore to drive all the fluid back up into the MC. Then pump the lever SLOWLY while re-filling the res.

I used my metal Mityvac but as mentioned, didn't loosen the MC and rotate / tap on it to knock bubbles loose. I'll do that in a few days when I'm off and have time to mess with it again. Running the pistons in is a good idea I overlooked as well. Thanks.

 

[Barrett]

Excessive lever "slop" in an aging Nissin/Harley Davidson system is always a failing master cylinder.

 

[Starman]

I'm with Barret, I would pull the master, clean and install new rubber parts. Quick easy job.

 

[Cooter]

How much piston travel occurs before it's moved past the feed hole?

Not much. You can literally see it if you look. I'm just saying it won't build pressure until the cup seal is past that point. You can have VERY good brakes with the stock system.

 

[motoguy]

I'm with Barret, I would pull the master, clean and install new rubber parts. Quick easy job.

Outstanding. That makes me happy. I'll see if I can find the parts to rebuild it.