FF: Forks Kawasaki Discs On My Vin Got Weak

[CarlHungness]

Don't know how many miles I have on my Kawasaki disc brake conversion but today I note the brake lever seems
to be pulling in further and visual inspection of the disc brake pads sure seems to show there's plenty left. Fluid level
is fine. I did note the discs themselves had somewhat of an oily covering, not one you could feel with your hand, but
very evident when wiped with a paper towel and brake cleaner.
It seems to follow that if the brake lever is pulling in quite a bit then the only problem can be worn pads. I see no
air bubbles in the master cylinder when pulled in ever-so-slowly...and that's how I wound up bleeding them upon
installation. I filled the system, pulled the handle slowly and saw bubbles rise to the top. A couple of hours later
and a couple thousand lever pulls the bubbles were all gone, and the brakes sure seemed like one could lock up
the front wheel. Now, they're not nearly as efficient, so I think my only option is to replace the pads.
Since I'm not the most mechanical among us thought I'd ask for suggestions. I continually discover I don't know
as much as I think I know.

 

[Robert Watson]

Caliper seals leaking a bit?

 

[CarlHungness]

Caliper seals leaking a bit?

Don't think so, but will re-check.

 

[passenger0_0]

I suggest you check the hydraulic lines, as like may things, these soften with age.
Pads also absorb moisture and accumulate dust and road grime so best to replace these too.

 

[John Cone]

Are you using rubber hoses or Aeroquip braded? if rubber there could be a pin prick of a hole spraying fluid on to the discs

 

[Gary Gittleson]

And then there's the master cylinder. It's a piston moving in a cylinder. A common problem is corrosion and pitting of the cylinder. Or, you have the same problem with the calipers. Your mention of a possible leak would suggest that. Brake fluid is hygroscopic. It absorbs water. The best practice is to flush out the fluid at the beginning of riding season.

With the bike on the stand, you should depress the brake lever hard and hold it to see if it continues to creep back to the handlebar. That would be caused by bypass in the master cylinder or the calipers, assuming there's no air in the system. If it does that, you would need to take things apart and check the bores for pitting. If they're all OK and rebuild kits are available, that would be the next step. Otherwise, you'd need new calipers and/or a master cylinder.

 

[CarlHungness]

And then there's the master cylinder. It's a piston moving in a cylinder. A common problem is corrosion and pitting of the cylinder. Or, you have the same problem with the calipers. Your mention of a possible leak would suggest that. Brake fluid is hygroscopic. It absorbs water. The best practice is to flush out the fluid at the beginning of riding season.

With the bike on the stand, you should depress the brake lever hard and hold it to see if it continues to creep back to the handlebar. That would be caused by bypass in the master cylinder or the calipers, assuming there's no air in the system. If it does that, you would need to take things apart and check the bores for pitting. If they're all OK and rebuild kits are available, that would be the next step. Otherwise, you'd need new calipers and/or a master cylinder.

I didn't think of holding the lever in, good suggestion. Will try tomorrow.

 

[Bill Cannon]

Check the pads for free movement in the caliper. They could be stuck on one edge and hence returning too far when lever released.

 

[Nigel Spaxman]

Often I have found a huge improvement in the feel and power of a disk brake by putting a little dab of grease on the part of the lever that pushes against the piston.