Rival brake issues

TheLurker!

Member
Running two 2019 rivals with jr drivers. Both run the chassis supplied heel risers. The pressure they place on the pedal in an avoidance situation such as a spin out in front of them causes the riser to bend up, this pushes the pedal away from them. Anyone come up with good solutions for this or even experienced it? When we got these they were set up and assembled for us by a reputable dealer who did out last karts as well. Kids went out on them and said they were hard to stop. I assumed that they were just not used to the new master cylinder/ brake pressure. Saturday one completely lost brakes and I had to catch him at the end... that sucked. I found no leaks, emptied all fluid from the master cylinder lines and caliper, installed new dot five brake fluid, and bled. Brakes seem to be OK now but I just don’t understand what failed. Fluid was full. It almost had to be air.
 

flattop1

Dawg 89
Or may have boiled the fluid . Should have been able to see it glowing if at night . Extra thick rotors help dissapate heat . Also mcp had softer pads for the mini lite .
For me the brakes barely fit the definition .
If they are bending the pedals there pushing pretty darn hard .
 

TheLurker!

Member
The pedal extensions offered for the kids are really thin and they’re not bolted to the floor they float that’s why it’s bending up. I know the fluid did not boil because we run momentum tracks and I can touch the brake every time they come in the only time they hardly ever use the break is during a crash scenario or a caution. We had multiple red flags in red plate due to someone’s engine shutting off and not being able to get the restart in. when he would try to stop for the red flag he could not there were no brakes. This was 2 laps in. After the race when I got it on the stand we could push the pedal all the way down and I could rotate the rotor by hand with a little resistance. I appreciate the feedback.
 

TheLurker!

Member
It would not pump up because he was showing me as he was coming by. taking his foot and pumping it back-and-forth with his hands in the air LOL I will check the gap again but like I say since changing the fluid and bleeding I cannot push through it anymore and our other kart had brakes all night and are equal and comparable to the one that broke is after repaired. I did notice a little fluid in the rubber caps covering the two bleeder screws this may just have been residual from when they were bled initially it was not dripping from them nor were there any wet spots anywhere else.
 

TheLurker!

Member
I’m starting to think it is gap after reading my post back to you. The pedal would not go all the way down but just would not apply enough force to lock the rears up it was letting them push through? If the gap was set too wide no matter how much you pumped it should it come together?
 

flattop1

Dawg 89
I do not think so its a itty bitty piston against a big diameter caliper , double piston .
Fluid returns pretty fast , line flex . The mini lite on our phenom acted the same way , pads had to be close to disc .
 

TheLurker!

Member
Ok our gap is 1/8 inch on both sides of the caliper. Should I close this? Because I know cars and their brakes almost touch. I understand this is not ideal in karting as it creates drag but should I try 1/16” maybe?
 
1/8" is where it needs to be on both sides. How are you bleeding the brakes? Gravity feed or with the bleeder tool? I would also check the fittings going into the master cylinder and into the caliper just to be safe.
 

TheLurker!

Member
I will check those fittings. This is the 3rd race on these so we’ll see. As far as bleeding goes I did the old tube off the bleeder into a jar of fluid.... pump the master and hold... the crack the bleeder and close. Add fluid and repeat. When there are no more air bubbles in the jar I topped it off and left it. If this is wrong let me know. Just the way I’ve always done cars by myself.
 

flattop1

Dawg 89
I usually gravity feed the brakes..... I do it about every other race just to make sure.....
This worked best for me .
Pumping them just did not seem too work , though i did not use the fluid in the jar .

Reverse bleeding with a syringe seems like a good method also .

Lost the key once - they weren't poor , they were non existent .
 

Phiddy

Member
Soft pedal sounds like air. I have seen pads get glazed up, but that has a firm pedal and it sounds like you barely use the brakes. Make sure you are not mixing two brake fluids that are not compatible. Dot 5 is Dot 5, nothing else. I have seen this Dot 5.1 stuff and I don't think its compatible.
 

krtrcn

Member
This worked best for me .
Pumping them just did not seem too work , though i did not use the fluid in the jar .

Reverse bleeding with a syringe seems like a good method also .

Lost the key once - they weren't poor , they were non existent .
Been there done that. Was not fun
 
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