So i bought this used, modified kent trouvaille on Facebook marketplace with generic IIIPRO E4 4 piston brakes. For the first couple of months the bike ran really smooth with no issues. I then started experiencing rotor rub in the rear due to a warped rotor.
So I took it upon myself to order new pads, a new rotor , and a bleed kit. Im not super competent yet but im mechanically inclined and I want to learn. Well I attempted the bleed which was a disaster as none of the adapters were labeled. I thought I bled it properly but alas my brakes had no pressure and I couldnt figure it out so I took the new rotor, pads, and my bike to a shop to have them do the bleed and install the new parts.
So I get my bike back and im having rotor rub that I cannot for the life of me fix. Ive tried aligning the caliper by hand for hours. Ive thoroughly cleaned, massaged, and lubed all 4 pistons. Ive tried the trick where you slightly loosen the caliper bolts, hold the brake lever and tighten. Nothing. Ive spend hours messing with it and a couple of times i actually got really close BUT the final synch down of the caliper bolts always pull the caliper out of alignment which I cannot prevent by physically pulling the caliper the opposite way. I've tried and tried and right when I feel like I fixed it that final tightening of those 2 damn bolts makes it rub again. And yes I am alternating between the 2 bolts as I tighten, doing them each little by little.
I'm seriously stumped and im wondering if I need to get the mounting area faced. But If that's the case i dont understand how for the first couple of months I had the bike before I started working on it it was in good alignment and worked perfectly fine.
Anyone here have any tips or ideas??
by thirdeyeblind999
6 Comments
Squeeze on the brake so the caliper self center and tighten down the bolts, you don’t need a ton of torque. If you still have rub look at the disc to make sure it’s straight.
You can try tightening one of the two screws while holding the brake, then tightening the second screw supporting the caliper with your hand to keep it visually lined up. I’ve had to do this when the last stage of tightening shifts the caliper.
Even though your brakes look pretty new, could the pistons be getting stuck and not retracting? A worn/missing pad spring? Anything that is decreasing the available gap between the pads.
The actual perch that the caliper sits on is misaligned. A bike shop can “face” the mounting points to make them level. It might be as simple as scraping paint from them, but sometimes a bit of metal needs to be shaved, very precisely.
For the tightening trick, re-doing it a few times over is important, they won’t settle instantly and perfectly unless you’re lucky. For extra luck, add a thin piece of cardboard or a folded paper sheet on each side, between the rotor and pad. There are thin metal tools available for this role, it helps centering the caliper with some leeway.
The goal with the trick isn’t to hit the perfect pitch, it’s reaching a point where you just have a tiny bit left to adjust, usually an imperfection in the rotor which is battled out with a disc straightener and a lot of eyeballing and listening for rub.
Please note i have also heard about these aliexpress brakes being a little badly designed and that they’re sometimes struggling with pistons returning/air entering at the lever. Make sure there is no such shenanigans worsening your day.
Is the adapter centered too? Sometimes the brake and the adapter moves when you align them and when you tighten them. It might need some tinkering
Is the caliper tight in that picture? It looks like there’s light coming through between the caliper and the adapter. If the caliper or frame, or even the adapter, aren’t flat, tightening it down could be distorting the caliper and causing the rubbing.
Try taking the pads out and seeing if it’s the pads or the caliper body that are rubbing. If it’s the pads, maybe pushing the pistons back a little will eliminate the rubbing and not make the lever pull too great. If you squeeze the lever with the rotor out, it can advance the pistons too far and not leave enough clearance.