Hey everybody, I noticed at our last practice day, that my son’s brake pistons aren’t retracting fully or evenly when the brake pedal is released. I can seat the pistons back in all the way, and center the rotor between them, but when I pump the brake, they dont come out evenly, or retract fully and one side tends to drag.
What’s the best bet? Full caliper rebuild and bleed? Or am I missing some simple service/lube that I should have been doing?
I would try bleeding the brakes first before doing anything
Bleed first, are you sure if it is not your master cylinder stuck?
I’ll take a closer look at the master cylinder first.
Assuming you have a free floating brake disc, it is my understanding that you do not want the pistons to retract but to stay (loosely) against the back of the brake pad. This gives you a quick reacting brake and much less pedal travel. HOWEVER, you must also be careful not to “rest” your foot on the brake pedal or to drag the brakes when you are nervous – something you otherwise might get away with if there is significant pedal travel before the pads bite the disc.
I have also wrestled with uneven piston movement. I have found that this is normally caused by air in one side of the caliper. Correctly bleeding the system should eliminate this.
It’s a fixed brake disc, not free floating. I will pickup some DOT 4 this weekend and do a full flush/bleed and see where that leaves me before I do anything else.
Pistons shouldn’t fully retract, but allow an air gap that is 1/16-1/8 on each side. When is the last time the caliper was apart? Depending on the design it could be several things. I had CRG brakes where the caliper bore became out of round and the piston would come out unevenly. The rubber rings can wear too causing the same issue. If your pads are past half life they might be to far out of the caliper too which can cause them to not be square either. It could be as simple as just needing a cleaning too as the pistons sometimes get like a gummy residue. If it has been more than a year or two since you have done anything then a complete cleaning and fresh fluid would be recommended.
I’ve only had this chassis for my son for 1 year, and it was supposed to have been fully serviced by the dealer when I got it. It probably wouldn’t hurt to rebuild them completely. The main issue is that they don’t retract evenly, one side stays out and drags while the other side retracts. Lots of life on the pads, I’ll start with a flush and go from there.
I would start with cleaning and fresh fluid. You probably do not need new o-rings or whatever is sealing the pistons. I misspoke about how some pistons work, The CRG I mentioned has springs that always pull the pads back in regarless of how much pad is left. However, some do not use this method, they have a deflecting o-ring that only returns the piston a small amount. In either case a gummed up piston or o-ring will prevent them from doing what they are supposed to do.
So there are 2 types of caliper.
The spring return type pulls the pads back until the back of the pad hits the brake casting or the piston is pushed back into its bore as far as it will go.
Identified by 4 visible springs external to the caliper body,and mainly found on older karts.
The self adjusting type has ’ clever’ seals which should pull the piston back when line pressure is released.
The pad is ‘attached’ to the piston usually by a small magnet.
Retraction is 0.2-0.5 mm per side. No springs.
Almost universal on modern karts but inferior imo. to the older type.