Gunk in Front Brake Caliper Pistons

[philipviana]

Relatively new rider here, which means I am also an inexperienced mechanic. 5 months of riding and 3500 mi on my rc390. After about a month of riding, my front brake became very squeaky and squealy, particular when coming to a stop around the 15mph to 0mph range. I looked into it and bought CRC Disc Brake Quiet, which seemed like a smart choice at the time, but dear lord has this stuff become a nightmare. The bottle says to "apply liberally" to the back of the brake pads, which I did. I effectively coated the entire back of the pad with a 1-2mm layer of the stuff, let it set for a few minutes, and then installed the pads. The noise disappeared. However, after 7 or 8 weeks, the squeak returned.

Amazon.com: CRC Disc Brake Quiet 05016, 4 Fl Oz: Automotive
Today, I took the pads out and took the caliper off, and dear god has this stuff gotten messy. It seems like the piston heads effectively pushed their way through the Disc Brake Quiet onto the metal backs of the brake pads, meaning that the metal was contacting the metal, so the goup was having no effect. What worried me was that A) it was extremely hard to remove and clean up this stuff, even with various degreasers and scrubbing tools, and B) it seems like now the residue/goup has contacted the sides of the pistons, which means it might have worked its way into the seals by now.

To nip the noise in the butt the second time, I decided to avoid this product and instead tried sanding the surface of the brake pads as well as cleaning my rotor with a brake cleaner. I cleaned it all up as best as I could, reinstalled everything and rode around the block at low speed and tested the brake. It's hard to tell how it was performing, but I want to say that the brake felt a little less responsive than before. I'm a little worried about the brake now.

Wondering if I should just chuck the entire caliper and get a brand new one, or even upgrade to a nicer Brembo or aftermarket brand since the brake has always been a little soft. Ideally, however, I just keep the existing caliper and get some words of wisdom from you folks so I can have some peace of mind. Hoping that the goup won't ruin the cylinders and that I can keep riding like normal. What do you think?

Thanks.

 

[zaster]

Before you spend big bucks on a new caliper, I would give a set of pads a shot since the OEM pads are crap.
I just installed EBC Double-H Sintered Brakes at a cost of $35 and they feel a lot better after being bedded in properly.

 

[Ryanthegreat1]

The stock pads are junk but typically very quiet. Sounds like they might need to be bedded in with a dozen or so moderately hard stops.

I am running the EBC HH pads and they were crazy loud until they had a track day and several hundred spirited miles on them. Now they are quiet.

 

[Diploman]

The OEM pads are arguably the first thing a 390 owner should change. They are very hard, sometimes do not bed in evenly, and are clearly designed for long life (ie economy) rather than a high coefficient of friction. HH rated pads from EBC, Brembo, SBS, Vesrah, etc. will make a very significant improvement - but HH pads require a significantly long bedding-in process. The ABS unit does rob the brake system of a little feel, (some racers remove it) but it is such a valuable safety factor that it would be very counterproductive to take it out of the system. The ByBre caliper seems robust and stops well when matched with good pads.: not a problem. The weak link in the system, IMO, is the ByBre master cylinder, which seems to flex, have a long travel before engagement and feels a bit "spongey" no matter how well the system is bled. An upgrade to a Brembo, Accossato or Frando 15mm radial MC will improve initial engagement, firmness, lever effort needed, ability to modulate braking effort and overall braking power.

 

[philipviana]

Thanks all. Any thoughts on the cleanliness of my existing ByBre caliper? Should I be worried about gunk getting into the piston seals, or are they typically pretty hardy?

 

[philipviana]

Thinking I might just bite the bullet and buy the new caliper. The idea of that gunk getting into my brake's hydraulics is really scaring me.

I found a used, good condition + 14 day guarantee caliper here:

301 15 KTM 390 Front Brake Caliper | eBay

That plus the EBC HH pads seems like a good clean way to refresh my braking system. I'm prepared to flush my front brakes and do all that for the first time.

Seriously, you should all see how impossible to clean this CRC Disc Brake Quiet shit is. The website says to use normal degreaser or brake clean to clean it - doesn't work at ALL.

 

[ToraTora]

A slight bevel on the leading edge of the pads usually stops the vibration which is responsible for most squealing.

 

[philipviana]

The OEM pads are arguably the first thing a 390 owner should change. They are very hard, sometimes do not bed in evenly, and are clearly designed for long life (ie economy) rather than a high coefficient of friction. HH rated pads from EBC, Brembo, SBS, Vesrah, etc. will make a very significant improvement - but HH pads require a significantly long bedding-in process. The ABS unit does rob the brake system of a little feel, (some racers remove it) but it is such a valuable safety factor that it would be very counterproductive to take it out of the system. The ByBre caliper seems robust and stops well when matched with good pads.: not a problem. The weak link in the system, IMO, is the ByBre master cylinder, which seems to flex, have a long travel before engagement and feels a bit "spongey" no matter how well the system is bled. An upgrade to a Brembo, Accossato or Frando 15mm radial MC will improve initial engagement, firmness, lever effort needed, ability to modulate braking effort and overall braking power.

Diploman, when you say the HH pads require a signifcant bed in time, exactly how long are you referring to? I plan on putting the HH pads in the day before a two-day track weekend, and was thinking that a few hours of riding on the street the day before would be enough.

 

[Diploman]

Right out of the box, I found my EBC HH pads better all around than the OEM pads. I did about 20 stops initially from 50-20 MPH to get them working, avoiding extreme stops and heat, and giving the rotor and pads time to cool between stops. This will give you a strong brake that requires less lever effort than do the OEM pads. However, at this stage, the HH pads are by no means definitively bedded-in. Over the next 5-600 miles of normal street usage, with occasional hard stops, the pads continue to slowly conform more closely to the rotor surface. I think it is important to clean the rotor regularly (ie every 200 miles or so during this process to remove residue from the bedding-in process as well as any possible oily contamination. After about 600 miles I felt the HH pads were finally comfortable and snug against the rotor, requiring far less of a squeeze than at the beginning of the process. When fully bedded-in, the HH pads are remarkably powerful and low-effort, easy to modulate. But it does take a while to reach this end-state: be patient. With racing use, this process is likely to be accelerated with the severe braking that is typical. Both rotor and pads will experience greater heating (and possibly warping?) than with a moderate street bedding-in. But most racers using HH pads seem to find them very effective and recommend them highly.

 

[philipviana]

Awesome. Thanks for the thorough breakdown!

 

[big_sur]

You can bed pads on the track in a session if you're getting on the brakes pretty good, just follow the initial bed-in procedure before you really get into it so you don't glaze them. Your rotor won't warp and the fewer miles on your rotor, the quicker the pads will bed.