Overflowing master cylinder?

Still new to karting, on my first outing i had a bit of brake issues. Completely lost brakes, pedal straight to the floor. From then on i had the same issue. I was able to start pumping the brakes and eventually got them to bite. The mychron picked up i was not able to hit near the max rpm (LO206) and felt like there was a possible drag.

I bleed the brakes before my outing everything seemed solid, pads had good life no leaks that i can see.

I have a ven05 system with a floating rotor and righetti rolf master cylinder with a reservoir (brand new) I feel like i may have overfilled the master but i dont see a fill line indicator on them.

Has anyone else experienced this? Any ideas of what may have caused it?

I plan to rebuild the caliper get new pads and a rotor to eliminate those.


Either you have a LOT of air in the line, your level isn’t actually high enough, or a seal someplace is not holding pressure. The last should be obvious if its the brake caliper. Not so much if it is inside the master.

Did you bleed the system well before getting on track?

The only way this situation can happen is air in the system. Air compresses, brake fluid does not which is why the pedal goes through its full travel without doing anything if there is air in a sealed system. If you are able to regain brakes by pumping again it points to air. The harder part is determining where the air is coming from. Most of the time it just hasn’t been bled out completely. It is possible air is being allowed in even after bleeding but determining where can prove challenging. Things to look at:

Make sure the bleeders are completely sealing and tight
Make sure all joints are tight, some might use joint tape or compound to further help with sealing.
Check for leaks. Brake fluid leaking would show where air can get in when there is a vacuum.
If it is a split caliper make sure the connection between halves is good, sealing and tight.
If you are able to build pressure likely the Master cylinder is sealing well so that likely is not the issue. The reservoir needs fluid, if it is low that can be the source of air. Make sure the reservoir is tight too if you have one. Make sure the bleeder port on the MC has a o-ring or washer.
If you have excessive brake travel from worn pads either shim the pads or replace.

I wouldn’t worry to much about what the gauge is showing. If you know your brakes are not up to 100% you’re not going to be able to drive 100%. Get the brakes consistent then address the issue if you are

Derek, it sounds like your axle might be slipping. Check that all grub screws are tight.

1 Like

Thanks you all for the suggestions. I thought i had strong bleed prior to going out on track, it was seemingly working till about 5 laps in.

Austin, you were correct some of the grub screws were loose :confounded:

Im assuming that would constantly push the pad and pistion back too far when taking a corner, thus causing having to pump the brakes. And im guessing it created a drag as well.

Also, what do you guys fill your MC to with a reservior? I cant find a max fill line on mine.

This is the one i have

1 Like

Yes, the rotor sliding back and forth pushes the pads away and creates a very long pedal (or no pedal at all) until you pump them back up and get the pads to readjust. And yeah, the brakes will drag as well then.

Common issue. I check my grub screws before every session because of this.

1 Like

Thanks guys, lesson learned that is for sure.

My goal is to eliminate as much as possible air under the rubber bladder. However, the pistons need to be in all the way too if the MC is full. If your pistons are out some and you fill the MC completely to the bladder you will have a mess when or if the pistons are pushed in. Filling the MC and inserting the bladder can be a little messy so have some towels around to catch the overflow.

Hey guys just following up.

Took it to the track yesterday, slapped new pads and rotor on there and a solid bleed. tightened every single screw and nut.

Can 100% say kart is running great, i had brakes and confidence going into every corner :sweat_smile:

Thank you all for your help.