Disc brake issues

[GCC]

I am finishing up my granddaddy project. I have the MCP disc brakes installed and bled ( I think). There seems to be good pedal, but I can’t lock up the rear wheels. I am using a fair amount of pressure on the pedal (more than the grandkids will be able to apply) but the wheels will not lock up. The pads are moving. Any suggestions? I assume they should lock with not excessive pedal pressure. Thanks

 

[Kent]

It sounds like the pads are not squeezing down on the disc far enough. Some calipers have an adjustment bolt to move the pads closer to the disc. I think your pads should be just barely touching the disc when no brake is applied or just barely off the disc. Is the brake system new ? I have read on this forum where some people have bought thicker disc's to get better contact. Maybe the pads are worn down.

 

[GCC]

Everything is brand new

 

[Kent]

Does the caliper have the adjustment bolt ? Can you watch the pads as someone pushes the brake ? Maybe you can see how much the pads are moving before making contact. Should be very little. Seems like the pads should be okay if the manufacturer supplied them. It could be the disc is to thin. The disc wasn't part of the brake kit was it?

The brake pedal should not be bottoming out after you bled them.

 

[GCC]

Everything is part of the kit. The pads are almost touching the rotor before the pedal is pushed. The pedal is not bottoming out now, but the wheels don't lock up until I have alot of pressure to the pedal. Maybe this is normal and I am just used to power brakes in the car.

 

[Joe-405]

Pictures would help.

I have the MCP ones on my barstool racer with the MCP master on the hand lever and it locks them up everytime. But yes you gotta pull it firmly to do so.

if it stops good then I wouldn’t worry about it.

 

[anderkart]

When the MCP brake kit is fully bleed, it'll easily lock up the brakes on a 125lb racekart with 11" tall rear tires & one 250lb driver using just a medium pedal force.

But this brake kit can't be expected to work nearly as well if you & your Spidercarts GrandDaddy kart end up weighing a LOT more, and especially if your rear tires are a lot taller...

Is your brake pedal designed to give good leverage?

Also, do you have your brake linkage rod connected to the top hole of the master cylinder lever to achieve maximum leverage?

 

[GCC]

I haven't driven the go cart yet to see how it stops. I have just tried to push it while someone pushes the pedal. If the pedal isn't pushed really hard I can push the cart. My concern is that my 9 yr old grandson won't have the leg strength to push hard enough. The linkage is set up for maximum leverage. Is there a screw to adjust the pad clearance? Photo shows what I have. I also have 18" tires.

 

[jamyers]

When pushing on the pedal, does it go down a bit, then get a LOT harder to push, or does it "squish" on down? If it's squishy, you've still got air in there somewhere. Bleeding can sometimes be a royal pain.

 

[Kent]

I'm no expert but to me, given the problem your having, that looks like to much clearance between pads and disc. If the unit has a provision to adjust the pads you should be able to see it on the caliper.

http://mcpbrake.com/default.html

You could try calling MCP and they may have the answer for you.

 

[madprofessor]

Something nobody ever seems to question is the size of the brake disc. Whether it's part of your problem or not, just remember: The more diameter, the more braking. I have an 8" solid disc on my live axle, with a single cheap Chinese caliper on it. Very little pedal travel on my linkage setup, massive grip on disc. If you use one of those little 5" or 6" discs trying to get more ground clearance, you'll need logarithmically more pressure to the pedal. Discs that are slotted and/or perforated for cooling and weight reduction purposes reduce the square area of contact to the pads to boot.

 

[Phil2]

I had a really hard time initially bleeding the brakes, red beard garage has a good video on youtube about it. if you closely follow the instructions on mcp website and have another adult to help you should be able to get stock setup to work. The hard part is that it is a dual piston caliper and has very specific bleeding instructions. a 1/4" combination wrench (I think that is bleeder screw size) really comes in handy. i have rounded off a few bleeder screws using pliers.

 

[Joe-405]

I haven't driven the go cart yet to see how it stops. I have just tried to push it while someone pushes the pedal. If the pedal isn't pushed really hard I can push the cart. My concern is that my 9 yr old grandson won't have the leg strength to push hard enough. The linkage is set up for maximum leverage. Is there a screw to adjust the pad clearance? Photo shows what I have. I also have 18" tires.

Should be 2 Allen headed screws on the side for adjusting clearances after they are bled. So yes there is adjustment

 

[SDcarting]

I haven't driven the go cart yet to see how it stops. I have just tried to push it while someone pushes the pedal. If the pedal isn't pushed really hard I can push the cart. My concern is that my 9 yr old grandson won't have the leg strength to push hard enough. The linkage is set up for maximum leverage. Is there a screw to adjust the pad clearance? Photo shows what I have. I also have 18" tires.

I have this problem with the MCP brakes, I cannot lock them up. I am a healthy 43 year old man really biting into them. I have the MCP bleeder kit and I also have a stiff pedal. I cannot seem to apply enough pressure to lock them up or even stop with what I would consider reasonable distance.

 

[Denny]

What is the rotor material made from?
What kind of pads?
What is the rotor diameter?
What is the rear tire size?

 

[SDcarting]

It looks like mild steel.
The pads come with this kit. https://www.bmikarts.com/1-or-1-14-Hydraulic-Brake-Kit--Black-Shim_p_10491.html
Rotor = 6in inches. (BMI sent me the wrong rotor the kit supposed to come with a 7 inch)
The tires are 18inches.
With someone setting in the cart and pressing the brake, I can push the kart with someone applying brake pressure. I don't think this should be possible.

 

[Denny]

Big tires need a big brake rotor. I would step up to atleast an 8”.

 

[bullseye670]

I have the MCP brakes on 2 of my carts. 6" slotted brake disc. Stops great. I wouldn't say that they lock up on grass, but the definitely lock up in the sand. My pedal movement is about 1/4". That's on my bigger(red) kart with 22" tires. It takes some work, but you have to get them bleed. I don't see how you can't stop if you have a stiff pedal. 3/16" brake rotor. A lot of the small ones are only 1/*" thick. I wanted to keep things simple and went with the single line. And yes, they must be adjusted down to the rotor. That picture from the original post difinitely looks to wide.

 

[SDcarting]

I have the MCP brakes on 2 of my carts. 6" slotted brake disc. Stops great. I wouldn't say that they lock up on grass, but the definitely lock up in the sand. My pedal movement is about 1/4". That's on my bigger(red) kart with 22" tires. It takes some work, but you have to get them bleed. I don't see how you can't stop if you have a stiff pedal. 3/16" brake rotor. A lot of the small ones are only 1/*" thick. I wanted to keep things simple and went with the single line. And yes, they must be adjusted down to the rotor. That picture from the original post difinitely looks to wide.

Ok, so I have about a 1/16 inch gap on both sides of my pad to my rotor. Closing the gap increases the force and ability to stop?

Big tires need a big brake rotor. I would step up to atleast an 8”.

If I stick with this hobby it will be on my next build. I am getting anxiety, I had the brake lines pop, the throttle cable come off on both ends and the brake key slide out after securing with with set screws waiting for my locking collars. It deserves its own post. I am risk adverse and went out of my way to build this safe as possible and I feel like it wants to kill me. It is way faster than I thought on video. It hauls too much!

 

[bullseye670]

I can't argue with Denny about the bigger the better for the rotor. I looked into a bigger one myself. However, the way Manco built my 388 make a larger brake rotor impossible for me. In one of my greater moments, I mimicked the construction on my smaller 285 when I restored it. Then I put the exact same setup for the brakes. That mechanical "disc" brake everyone upgrades to sucks. At least it did in my opinion. Like I said, I don't lack braking power with this set up. I couldn't be happier.
Edit: Just took a spin. Brakes lock up great on the gravel road. The kart comes to a pretty quick stop on the grass, but I wouldn't say they lock up. Great stopping power. Remember, I'm driving a 55 mph kart.