Brake Bleeding / No Brakes

My teenage son and I picked up a go kart from a local seller, I dont have much back ground on who makes the cart and am struggling with the breaks. I see that when I depress the break the pads touch the rotor, but they provide zero stopping power.

I have tried to pump bleed the breaks - three pumps, hold, release the screws on the calipers to let air out with limited success. I got a reverse bleeding kit, but the plastic tube is too large and that turned out not to work.

I’ve looked into getting a bleeding screw but cant figure out what size it would be. The other thought I had is to get shims to see if that works.

Does anyone have suggestions on what to do? Also - can anyone provide me the maker of the calipers so I can match the pads / shims.

Appreciate any help!

So normally brake bleeding involves screwing a gravity feed tube full of fluid onto the master cylinder. From there you’d also unscrew a cap on the caliper (where the old fluid bleeds out). Gravity pushes the old stuff and air out.

You put up pics of the caliper but not the master. Any idea of brake brand?

Here’s our KP contributor Eric Gunderson explaining:

If it doesn’t have a gravity feed tube, then:

  1. fill the master with fluid
  2. crack the upper bleeder screw
  3. push and hold the brake pedal
  4. close the bleeder screw
  5. release the brake pedal
  6. repeat 2-5 until only fluid comes out, refilling the master as needed

Judging by looks those air fairly old brakes. My concern is the condition of the caliper where the piston moves. My first kart had been sitting for years with brake fluid in the system. Brake fluid is hydroscopic (absorbs moisture) so there was a fair amount of corrosion and pitting of the aluminum. You may be able to disassemble the caliper, clean it and re-use the existing seals, but it might also be a lost cause. If you need new seals it might be tough to source them based on the age and uncertainty as to the make and model. In the case of of my first kart I retrofitted a MCP caliper and master cylinder and with some trial and error they worked fairly well. Your rotor should be fine.

As for bleeding what you have looks very similar to the CRG used in the video posted by Dom. While the brake bleeders work great they are also expensive. I was able to source a bicycle hydraulic brake bleeding kit from AliExpress used with a syringe to basically do the same thing, which is create a little pressure to push out air and also have a reservoir of fluid for air to escape as well as not let it in.

Thank you for the response, the master cylinder is a wiliwood: Wilwood Disc Brakes - Master Cylinders: Kart Master Cylinder

I unfortunetally do not know the brand of the calipers - that’s one of the struggles. I talked to a friend and he said they looked like old motorcycle breaks.

If I have to go the route of getting a new caliper - any suggestions?

I’ll try the bleed method described above in the next few days and see how that works.

You should be able to get somewhere following this, though I’d change 6 to keep repeating until clean fluid comes out, then you know you’ve pushed the new fluid in and all the old fluid / air out.

Side note…….change the axle !

So you have a Wilwood reservoir type master cylinder with what I am pretty certain is an SKM/ Righetti Ridolfi 4 pot spring return caliper.
Bleed as suggested by Bryan Hall above. One side at a time. Fluid is likely to be normal DOT4 glycol but you can check using existing fluid. Should dissolve in water.
Check that the master cylinder piston is returning fully or it will not pump.
Pics of caliper and pads at kartstore Righetti/SKM.
The caliper is ‘European’ if I have it right.
Have you found any identification numbers etc. on the chassis? Common places:rear cross tube, rear axle bearing hangers, bottom steering column bracket.
Edit. Your link suggests that your m/cyl is only 0.5 inch bore. If so it is very small for that caliper.

As I mentioned above the least expensive route I found was MCP brakes. You can get a new caliper with pads and a master cylinder and line for about $200 - 250. There are 2 versions cast and billet, they are basically the same design, with the billet costing a little more. You may have to do some fabricating to get them to line up properly, but based on your photos I think they will work. Make sure to get the split line where each side is isolated that way you can adjust the spacing for your size rotor. The current MCP brakes use silicon based 5.1 fluid, do not mix with DOT 3, 4 or 5. There are several online vendors that sell MCP, TS racing out of FL and Fasttech out LV are 2 that I have bought from in the past.

With all that said, I wouldn’t be afraid to take them apart, clean them up and see what you have.

Thank you everyone that posted. I’m going to take the caliper appart this weekend and see what I can see. I ordered some shims to try to help get the pads a touch closer to the rotor - it’s definetally a project!

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Good plan Charlie Brown :+1:t3:

Another trick you can use with return spring calipers is to shorten the rod connecting the pedal to the master cylinder, effectively keeping some tension on the actuating lever.

Problem here is that the m/cyl has been changed? to a reservoir type as normally used on a self adjusting system.Any movement of the m/ cyl piston will block off the feed from the reservoir.
I am going to go out on a limb here and say that the main problem is that the new m/cyl is too small in the bore (about 1/3 the area of the proper one) and is just not moving enough fluid to press the pads onto the disc/ rotor .Excess pad to disc clearance or any air in the system will of course make the situation worse.
Easiest way to check this out would be to cut some al etc sheet to take up the clearance pad to disc and see if you could then get a good pedal with or without further bleeding.

Thanks all for the help here. After taking the caliper apart and cleaning it, adding some shims and doing a bleed I have breaks again. They are not the best - I think due to the smaller bore master cylinder, but I can at least lock the back tires with heavy pressure and stop.

Do you have any way to increase the mechanical leverage via holes on the pedal or master cylinder pivot points.

So this is the current configuration. What would you suggest to be different? Thank you!


Moving the bolt on the master cylinder lever to the higher hole should give more leverage and reduce the needed pedal pressure some.

That said, I’m a little concerned about how easily the pivot lever could slip away from the master cylinder pin :thinking:

Ideally there should be some sort of mechanical attachment there, for example a notch in the master cylinder pin that the lever would slide into, accompanied by a pin, or bolt going through the pin and lever.

Another concern, the rod should have a locknut on it at the end nearest the master cylinder as a precaution to prevent it from screwing itself out of the pivot pin.

I moved the linkage to the top hole on the master cylynder and tossed a lock washer on the rod. Trying to figure out a way next to secure the pivot lever to the cylynder pin!

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I would have agree that set up is a little concerning, however I think as long as the pivot is tight it should stay centered on the push rod.

I think James is referring to the clevis on the master cylinder not having a nut, but the other end does so I don’t think it will move.

I also notice the brake pedal has no tension on the spring and the stop doesn’t appear to be touching the frame. I would adjust everything so that as soon as you move the pedal it has an immediate effect on pushing the rod for the MC. There should not be any “play” in the set up. The spring should have tension to return everything so that the brakes are dragging.