Help with hydraulic brakes

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hhsmiley

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Just got this to the point that I can drive it around. Seems to work OK and goes pretty fast for as heavy as it is with as small an engine as it has. This will be for my son who's a lot lighter, so plenty of go.

The problem is not enough STOP. The brakes "work" but just do not grab the disk hard enough and you sort of gently coast to a stop when you brake hard instead of really stopping.

I used this caliper and cylinder which I got from Amazon. The caliper seems more heavy duty, with larger pads that you typically see on "go kart" brakes. I have definitely bled all of the air out of the system, and I've thoroughly cleaned the pads and disk, so I'm not sure why I'm just not getting enough stopping power.

Ideas?
 

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Whitetrashrocker

Whitetrashrocker

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That should lock the axle up easily. I have the same master cylinder. The first one i got didn't work. It just wouldn't bleed properly. I got a new one and it bled just fine. It won't push all the way to the floor. Gets a firm pedal now.
What method did you use to bleed it?
 
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hhsmiley

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The rotor diameter is about 9.5 - 10". I don't think it's stainless, a magnet stuck to to like it's just regular steel.

I bled/filled fluid by using a large syringe/pump that I attached to the bleed nipple on the brake cylinder. The I pumped fluid from there, from back to front until all the air was purged and the reservoir was full. There's no way to introduce any more air doing it this way as only fluid is going in from the pump and it sure seemed like all the air was purged, and I repeated this process twice.

It almost seems like the master cylinder just doesn't have enough "throw". Like the pedal needs another 1/2" of travel. But then again, I would think these components would work for what I'm doing.

This brake cylinder has two places where you could attach a banjo connector. I think on the ATV it goes on a line goes from one of those to another cylinder. I didn't think it would matter which I hooked the brake line into, so I connected it to the one circled in red and blocked the other off. Would that have made a difference?

???????
 

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hhsmiley

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I have taken the caliper off and watched it as I press the pedal. Even when I press the pedal/master cylinder through it's full range of motion, the caliper only moves a little bit. It takes 2-3 pedal pushes to get the cylinder to extend to the point where it would really be pushing on the pad.

I have no idea if this is normal, but that's why I say that I think the master cylinder should have more "throw". The pedal push barely moves the caliper, and subsequent presses just don't generate enough force to really clamp down.
 
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Alex Johnston

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That’s weird, those brakes should have enough power to stop that kart, I have those brakes on mine and they stop good. Maybe they don’t work? You may have to send them back and get new ones. Also I found they were bled well enough from the factory so I just left them. I’ve heard that once you try and bleed them they just don’t work. Hope this helps.
 
Master Hack

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I had the same problem. I found two things:
Bleeding these things is an absolute bit**. I resorted to the gravity bleed method.
Another thing I found is:
The stroke where the MC works is very short and in my case is was not in the right spot in relation to the pedal.
The piston was not in the sweet spot when the pedal was pressed. Sounds weird, but adjusting MC rod in relation to the pedal helped alot.
To put it differently, the MC piston travels farther than necessary, and if it is not where it needs to be when called into action nothing happens.
Also if the caliper bleeder is not at the top ya never will get the air out of it.
I have seen instances where the caliper bleeder was at the bottom. I had to take the caliper off put a piece of wood in it, turn it over, bled it then re installed it. Don't over look the small things!
It took a few minutes to install the whole brake system and another day and a half to get it working properly.
All this probably has nothing to do with your situation, but was my experience.
Good luck!
 
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hhsmiley

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I'm still working on this. Would the type of fluid make a difference? I put DOT 3 in.
 
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hhsmiley

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Master Hack said:
When the goin gets tough and the tough cry uncle, the tough get a Mity Vac!
Click to expand...
Interesting.

What we tried today was taking the brake caliper off and raising it up so it was higher than the rest of the system, attaching this to the bleed nipple thing, and trying to suck the air out of the system.

https://www.amazon.com/dp/B0CGCZ8HZC?ref=ppx_yo2ov_dt_b_fed_asin_title&th=1

Never did get to the point where we were getting only fluid. In fact it was almost all air, but I think it was outside air that was getting past the bleed nipple, not air from inside the line.

I would assume this Mityvac will generate a lot more suckage than this little pump thing I have. Is the secret also to just barely open the bleed valve/nipple so you're only sucking air from within the brake lines and not from outside?

I'll give that a shot.
 
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hhsmiley

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I measured the thickness of my brake disk and it's about 3.5 mm. This brake caliper is supposed to be for a Polaris Sportsman 4 wheeler and the brake disks for that are 4mm. Would that be contributing to the issue? Would "shimming" one of the disks to take up that little bit of extra be something I should try?
 
Master Hack

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1/2 MM is roughly .020 inch. I would think the caliper has more than .020 in travel, so my guess is probably not.
At this point i would suggest taking the MC apart and check the orings. Think about the country of origin and the fine craftsmanship that goes into every product they sell. After ya fix anything ya may find, bench bleed and test the MC. Then try again. I believe every one that has ever had one of these things has had the same problem. Its a DIYGK initiation, hazing in a most cruel way. Good luck!
 
Whitetrashrocker

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Here's what it looks like inside. A rubber cup and a seal. This was an old one i was trying to refurbish. It was corroded inside and would never seal.
20240103_144607.jpg

I bought a new one. Couldn't get it to bleed. I tore it apart and didn't find anything wrong. Put it back together and still could not get it to push fluid with pressure. It would push enough to blow out the bleed screw.

20240103_144615.jpg


I bought another one and it bled right away and is still working just fine.
 
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hhsmiley

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Didn't mess with this over the winter but recently got everything to work. The problem was I had over 6 feet of brake line and the flexible brake line was swelling so much when braking that the brake would not clamp tightly.

To simplify things, I used a 1 foot flex line at each end and then just one straight piece of steel brake line in between.
 
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