Sticking Brakes

[Bill Cary]

What would cause the brakes on an AM29 (3 yrs old) to bind against the brake rotor when hot but retract fully when cooled? This issue just seemed to arise at the end of the season after 8 races with no problems.

[angus' dad]

too much pressure. until you get the right answer from the pro's, easy thing is to let a little brake fluid out in the caliper end. might not be the best thing to do, but it will fix that.

[Marc Miller]

Angus' Dad has the point I would make.

But for the sake of things, let's ask these questions:

Is the fluid 3-years old?
Do you top off the fluid - or have you changed it out?
Could it have been overfilled?

Remember that just like tires, brake fluid heat cycles as well and any moisture that finds its way into the system now adds to the expansion of the fluid. The closer it gets to boil, the more it expands pushing the pucks out to the rotor. Relieving some of that pressure is a fix - but you should likely always make sure you keep your brake system clean and the fluid somewhat fresh.

[Garry Lobaugh]

My experience:
Some drivers may be dragging their foot on the brake through the corner. We try to teach drivers to be either on the gas or on the brake.

Often I have seen fluid too full and the brake cap too tight. If you bring the kart off the track, pop the brake fill cap, let it drain out (over the top) and then replace the cap while hot. This will allow for needed room for expansion when the brake fluid is hot.

Is your fluid clear or dark and dirty? I'd bleed the brakes but not over fill the master cylinder. Those are my best answers for the moment.

[Garry Lobaugh]

From the symtems described by the customer, I doubt that there is a piston problem. If there was it would have shown itself in the first year of racing. Anything is possible. I would urge exhausting all of the other suggestions before jumping into a piston diagnosis.

[pjavan]

Although I'm new to this, I had the same problem this weekend on a kart that I just bought and hadn't been run in over a year. The piston in the master cylinder was getting stuck. After rebuilding it and cleaning out gunk, the brakes would release.

[Steve Miller]

The word "gunk" makes me feel the fluid is quite old. As the fluid gets dirty and hot the boiling point of the fluid gets lower each time. If you want to send it in to MRP we will look at it. Another point, is that when the kart sits for any length of time the seals "shrink" causing a loss of brake fluid and moisture to enter the system which also lowers the boiling point of the fluid. Or, if the air gap is to large between the pad and rotor the piston goes out further then it should this will also give a mushy feeling to the barkes. Hope this helps.

[Bill Cary]

I went wholehog and got the master cylinder and brake caliper both rebuilt at Team AZ. The brakes no longer hang up when hot. But even after bleeding the system several times, the brake pedal has much more travel to achieve the same pressure on the brakes. Why?

[Steve Miller]

What is the air gap between the brake pad and the disk? This will give you a "long" travel on the brake pedal. The brakes are not self adjusting and as the pads wear they need to be shimmed to keep the pedal travel as it was when the brake pads are new. Bleeding and rebuilding will not cause a long pedal travel.