Front brakes rub after rebuild.

[kstylian]

Hi All,

Just got the CB650 on the road after a long overhaul and now I'm just trying to sort out a few items.

I rebuilt the calipers with new pistons (aftermarket stainless items) and new Bike Master pads. The pistons slide smoothly in the bore and the caliper slides smoothly on its pins. I pushed the pistons all the way into their bore when installing the new pads and the calipers did mount on the forks and over the rotors, but tightly. I could spin the front wheel, but there was a definite drag/rub from the pads rubbing on the rotors.

I thought this would free-up a after a bit of riding - the pads would wear in and maybe the pistons would retract a bit more. Not the case. After about ~5 miles the rotors will get hot (can't hold hand on the rotor for more then 2-3 seconds) and the drag/rubbing does not seem to be getting any better. I've put about 35 miles on the bike so far, but don't want to ride for an extended period in fear of warping the rotors.

My question is, is this common? Will the pads eventually wear/bed-in? Or is there something wrong (maybe pads too thick or aftermarket pistons too tall)?

Any remedies for this issue (sand/file the pads a bit, etc.)?

Thanks all in advance..........

[MiGhost]

Did you rebuild/replace the master cylinder as part of the complete system?

If not. It is highly likely that the return port in the master cylinder is plugged, and not allowing the pressure to be released from the calipers.

Ghost

[kstylian]

Yes, I rebuilt the MC as well and made sure the return valve was not plugged. I cleaned the small little hole in the reservoir with a guitar string and brake fluid. As a side note, when I placed the calipers/pads back over the rotors there was no fluid in the system and the system bled easily with speed bleeder valves installed.

I do have an aftermarket MC, but not convinced it's the culprit.

[MiGhost]

What year is your bike?
There are at least 4 different calipers that were used on these bikes. I know that the single disk systems have problems if the caliper mounting bolts get mixed up.

Ghost

[kstylian]

It's an 81' CB650C with the dual caliper/rotor's.

I should have measured the aftermarket pistons with OEM before I replaced them.

This just seems a bit fishy and haven't been able to pinpoint the issue yet. Was hoping someone had a similar problem with a quick adjustment/fix that I may overlooked. Probably just need to dig in a bit deeper to inspect/resolve.

My next issue is a doozy in comparison...

[Volker_P]

This is not normal. Can you feel a resistance turning the front wheel in the air?

As it seems on both sides, it is probably a hydraulic issue related to the master cylinder. You may verify by opening a bleeder so the resistance on turning should reduce or vanish.

If it does, verify the order of parts in the master cylinder (and again the small hole to be free): viewtopic.php?f=4&t=1804

Another option might be a swollen (to inside) brake line. Check by blowing through.

[kstylian]

Can you feel a resistance turning the front wheel in the air?

Yes, on both sides. Verified that rotors are hot after a short ride. One more so than the other.

As it seems on both sides, it is probably a hydraulic issue related to the master cylinder

The rubbing/resistance was there prior to any fluid in the lines and bleeding of the system. I'll open the bleeders, spin the wheel and see if this helps.

Another option might be a swollen (to inside) brake line

Brand new stainless lines from slingshot.

[Volker_P]

The rubbing/resistance was there prior to any fluid in the lines.

You need some play to install the calipers on the disk.
So they were rubbing already after installation with a still dry brake system?
This sounds like you installed the piston rubber seals in the wrong direction and/or the glider bolts are not moving freely.

[kstylian]

So they were rubbing already after installation with a still dry brake system?

Correct

This sounds like you installed the piston rubber seals in the wrong direction

Are you talking about the piston o-ring/seal or the dust cover? The o-ring didn't look tapered as to suggest a front/back orientation and installing inside-out is almost impossible. Glider bolts are new and greased as well. Havent had a chance to dig in yet, but will report back.

[Volker_P]

The o-ring didn't look tapered as to suggest a front/back orientation and installing inside-out is almost impossible.

It is the close to square piston rubber ring where orientation may play a role.
In fact this off-square shape serves to slightly pull back the pistons after pressure realease mechanically a bit. This will work the opposite way, too.
Not sure if CB brake piston seals are like that, but worth a closer look and a try.

[kstylian]

Did a bit more tinkering, but no obvious solution yet.

I replaced the rebuilt OEM MC with an aftermarket unit.

Pads still rub on rotor and the rotors do get hot after riding 3-4 miles.

I removed the pads from the left caliper and pumped out the piston a bit. It would not retract when trying to pry back in with large screwdriver. Opened the bleeder and the piston retracted fine when pried. Closed the bleeder and pumped out the piston again, cracked the line at the MC and it retracted fine again when pried. I did notice when the piston was pumped out it would retract a little when the brake lever was released. So, the piston is pulling back, but possibly not enough? When bleeding the brakes, I did notice air bubbles from the pressure relief hole, so I'm assuming it is not clogged.

Is it possible that this aftermarket MC is designed to retract the pistons just a little, then hold pressure?

Another thought is that the pads are new and even with the piston fully retracted, there is barely any room between rotor and pads. I don't want to sand the pads down to allow more room for the pistons to travel, but I'm leaning towards that route.

Next step will be to install the OEM MC and retest the above procedures.

Thoughts?

[Bongskit]

grease in the outer part of the piston before installation? when you install the new pads and the piston fully flushed in, looks like did you had a little trouble mounting the caliper.

pushed the pistons all the way into their bore when installing the new pads and the calipers did mount on the forks and over the rotors, but tightly.

hows your old pads? totally unusable? i was thinking if its still possible to still use it for a bit with the new piston. or at least use 1 old pad on each side paired with a new one and see if that helps. if that fixes the issue, then I think you can go the sanding route.

you are not using brembo double opposed piston are you? i would be jealous. if only i could use my scooter's caliper.

[kstylian]

Going to search for the old pads today and see if they help the issue.

[kstylian]

Found the old pads and put them in. Problem solved! No rubbing and the rotors were nice a cool to the touch after a short test ride. Initial hunch was correct.....apparently the new pads were too thick. I'll sand down new pads a little and put them in tomorrow. FYI: These are Bike Master brand brake pads.

Can't believe such a simple thing caused so much drama......

[jagans]

The rubber O-rings are not O-rings. They are supposed to be torrus Torri? In other words, a square O ring. When pressure is applied, they deform into a parallelogram in cross section, (If this makes sense) and they return to square once the pressure from the MC is released. This deformation, elastic memory is what backs the puck off just a bit to retract the pads. Pretty neat. The torruses (Torri?) have to be in good shape to perform this function. Obviously round in cross section will not do, as there is no deformation/return. Did you install new torruses? Torri?