Brake masters ... for Ckau and others ...
 

Been doing some "research" trying to get to the bottom of getting better braking out of a dual system off a master designed for one caliper.

I'm not positive my woes stem from a mismatch in the master to the 2 caliper volume, but really feel it's there. New brake pads may resolve some of it, but before i go that route i'm doing some "testing."

a buddy of mine gave me a master off a 250 quadracer, darn near identical to the yerf master C and I are using. externally, they're both basically the same. internally the bore is a 1/2 and the bore depth and stroke limit is the same length. so apples to apples, until you get to the piston. I'd been thinking about the fluid passage design of the piston and the width of the spacing. thought the yerf had narrower passages and maybe widening them would help. thoughts were actually backwards. :biglaugh: the yerf has a very wide spacing as shown.

springs were also the same size, but different rates, I put the softer one in.
after doing cleanup on the suzuki piston (the rod pocket end was snug in the bore), i installed it in the yerf master.

Along with the suzuki master, my friend also gave me one off a yamaha, think it's an old yz-125. bolt pattern is a mismatch, but that can be fixed.

What' i've found is that most name brand masters have the internal bore size cast on their sides. the yammer is a 14mm. it was in really bad shape, but managed to get it apart, clean it up and make it safely functional. depth and stroke are the same, so overall, it will push a 1 mm larger bore size of fluid per stroke. no i'm not doing the math!
this may be enough to get me what i need.

At this stage, I still need to refill/bleed the lines (at least i came up with a tried and true easy method)

I won't be able to test the "combo" master for awhile since i've torn down the front steering system to improve it.

My thoughts right now are that the piston difference may only affect the firmness of the stroke and most likely not move any more fluid. if this proves out, then the yamaha master goes in for a test.

Just wanted to start a thread on this so if anyone else goes down this road, they know what to expect.

C ... i've also found a couple other used masters on e-bay with 11/16ths and larger bore sizes with essentially the same mount pattern and line placement. key is to look for the inch or metric number cast on the side of the master. on on used quad brake assemblies sold as a whole, it's typically hidden by the plate it's mounted on.

piston -- yerf left, suzy right
master -- suzy left, yerf right

You know, I have been pondering a similar question once I replaced the rear master on my RM80, and I swear it is identical, except for the clevis that attaches it to the lever. I want to place the master up front right off the pedal, and since space is a bit limited, I needed to find a good master prior to fabbing mounts and linkages. I have a front master for my SV1K somewhere, but the push rod set up is a little odd, but I know it would work for dual calipers. I was thinking the lines might have been the culprit on mine, and was planning to upgrade to a dual piston caliper out back.

master, pictures of the master and any measurements as to bore, stroke & volume are more than welcome! (i'll let the peanut gallery have a ball with that sentence ... )

pretty reasonable 5/8ths bore master cylinder, being used in two caliper systems.
http://wheelsca.com/MASTER-CYLINDERS.html

looks like a bolt in match. i'll probably go this route and quit playing with the junk.

The difference between the yerf and "susy is quite obvious. I'm curious to know which spiral configuration is more efficient. Would the "susy trap more fluid or less? How do the two piston compare in function ? Would the susy work in the yerf casing? Have you tried this? :confused:

I wish I had something to contribute to this thread but all I got are questions.:dunno:

The dual piston calipers exert force over a bigger area, although the pressure may be less, especially if set up incorrectly, or haphazardly. The increased surface area, including the pads, resulting in greater heat transfer and less brake fade, and better stopping power. The one thing you would need to be concerned about, is the fluid volume from the master cylinder. Plus, with the bike calipers, you would have more and better options as far as pads, including organic and ceramic pads. I know there is a difference in pads, I replaced the stock ones on the SV1K with EBC double-H, and wow what a difference, almost endo'd myself off the first time I hit the lever.

I really have no answer for the spiral question, I'm sure it would be easier to swap it and see, but since X downed the buggy, it would be some time before that is possible.

Metalstudman1 wrote some time ago, that he switched out the calipers on his yerfs with motorcycle calipers, and reported no issues, and I think better braking response, but that was some time ago, and did not mention doing anything with the master.

Exactly! you hit on the million dollar question. That's the term I was searching for. Which piston increases " fluid volume"? With X being down, focusing on other items, he's got me in suspense!

right now the suzy piston is in the yerf master, bench bled, installed in the buggy and awaiting final bleeding. i'm considering tossing my tie rods back on for some test drives to settle the brake question . problem i have is no misalignment spacers on one side, but i can get around that i think since i won't need to be hammering it over any bumps. Meanwhile i can make parts to redo the tie rods.

if the suzy piston doesn't do it, (i'm doubtful it will as i think the seals dictate the volume moved and hte spirals likely control "feel") then i'll most likely go with the 5/8ths master--there's also a used 11/16ths one on e-bay that i can buy new if it's priced right, just have to find the auction and get the make/model it came off of. before i go to new pads, i want to have effectiveness out of this setup as the pads aren't totally worn out.

Should you decide to put it together for testing, isolate one side at a time, and see of the brakes get better, this is probably the fastest and easiest, and cost effective way to effective way to see if the master can hold both calipers.

My gut says the master is designed for a single piston caliper, and thats where the fault lies, every bit of info I have found pertaining to caliper upgrades, from vettes to miatas, the same thing comes up, make sure the master can push the required volume to the calipers.

I tried that before the race as a means to make sure both calipers were functional. i did have good clamp that way--by "hand turning" feel. I also looked at two-pots (ckau's) vs singles (mine) since i do have a pair of yerf two-pots. i never tested them, but they may have less volume in them, which would help ckau's system. I decided not to run them as i have to mess with the roketa mounts and wouldn't have an e-brake system ready to go if I want, which i do have. just nee to weld in the handle mounts if i want to put it in.

All that said, i'm already in countdown mode to the next race and with 1 day a week off and only a few of those to spend with my daughter before school i'm really in crunch time.

So instead of re-prepping the front end to test the master, i tore the rack out, and started fabbing drop mounts for new tie rods.

X-bird,

What are the brake problems that you are experiencing? Spongy pedal, too much pedal stroke, poor braking? I tried to look through your build thread to find what your problem was, but I couldn't find it. Also, what method are you using for bleeding your brakes? These little MC can be a real pain sometimes. Also, what type of brake lines / hoses are you using?

I just don't get enough apply pressure/pad travel. i can slow to a stop, but not lock up the rears. likewise, it can't hold on a hill forward or reverse. I've tried every bleed method in the book and then some and have come up a pretty solid method--no concerns with air in the lines or master. lines are braided, a little extra long, from the roketa gk-29 the trailing arms/calipers came from. they check out as good. there's snippets on page 6 of my build thread. Clutches and gearing took priority over the brakes to make the race. as long as i had a little braking i decided to run it. next race, i need something real--was almost in a bad way in this last race when i was running out of fuel 3/4 way up the hillclimb and had to go to neutral to get revs--she started roliing back--my reverse visibility is as bad or worse than a countach--and believe me, i know how bad those are first hand. ))) CKau and i have been pm'ing a lot about this setup since his is very similar so a lot of brainstorming isn't on the forums.

X-Bird,

Any update on the brake issue, inquiring minds want to know.

not yet, new 5/8ths master is sitting on the bench, yerf/yamaha "mix" master is hooked to the lines, but not bled. as usual, brakes are going to be the last or 2nd to last item on my list. 18 days and counting ...

I assume that both you and Ckau are still having trouble with you brakes. If not disregard this message, of course you can ignore it as well :lol:. This topic has been eating at me and I just wanted to run something by you. The MCs that both you and Ckau are using are essentially motor cycle MCs. I've had quite a bit of experience with them and they can be a pain to work with on a good day. The main problem with them is that they do not move very much fluid when they are compressed. This can making bleeding them a chore. Since you are using disc brakes, once they are bled, there should not be any problem with braking power (unless the lines are expanding). If you were using drum brakes, where the shoes move in and out, I would think that the MC was too small. However, with disc brakes, the distance that the pads move is miniscule, so you do not have to move the pedal much to engage the brakes.

However, do to the orientation of your MC, I am not sure that you are getting all of the air out of the system. The first drawing is of how a motorcycle MC is mounted. Notice that the air bubbles naturally rise into the brake line area where they can be displaced out of the calipers by bleeding. However, since your MC is upside down, the air bubbles tend to move away from the brake line and tend to collect in the MC plunger cup where they may become trapped. Is there a way that you can dismount the MC flip it over and compress it by pushing it on the floor of the buggy.

Also, Ckau may be having the same issues because his MCs are mounted horizontally. In this case the air bubbles may be rising to the top of the MC bore and becoming trapped. In his case he might try jacking the brake line side of the car as high as possible, then try bleeding the brakes in this position.
These ideas may or may not help you, but your problem has been gnawing at me a long time.

Good luck.

I hope the bleeding helps, but I am still skeptical about the volume of fluid needed to engage both calipers, and the volume the single master puts out. I hope the single master is enough to do the job, as I would also like the option to add an additional caliper.

Just to add to what toomanytoys said, the majority of these type masters are mounted vertically, as were all of our yerfs. Keep that in mind while bleeding as well.

Thanks for the input, i'm still pretty sure, at least with my single pot calipers, that its a volume issue.That and the amount of loose, flexible line i have looped on the floor. that may be more of the problem than i realize. i've been doing the bleeding with the master flipped, then bolting it in place afterwards.

X-bird,

Is the flexible line standard or steel braided? If it is the standard type, it may be swelling like a balloon when pressure is applied. In short runs, this may not be that big of a deal. However, with a long run it can really affect the braking power. That is one of the 1st mods we do on a dirt bike if the braking is poor, switch over to the steel braided lines.

here's some interesting reading http://www.grc.nasa.gov/WWW/K-12/Win...principle.html
this link has the formula to calculate the effectiveness of a hydraulic system. I've been meaning to try this out but I keep forgetting to get the caliper piston size while at the buggy.
if you know the dimensions of your system you can calculate what it will do

They're braided, but chinese braided if you know what i mean. clear covers where you can see braiding inside them. I don't think they're swelling, rather, it's almost like when you "lose" initial hit engine power to torque flex in the motor mounts. I think application of pressure "moves" the lines, taking a small percentage of effective pressure away, as they have a ton of extra length and a lot of the line length is just looped on my floorpan. I intend to have fastenal make me a set to match the buggy, just don't have the time or $s right now.

if you have a spare caliper, put the piston at it's correct retracted position and use a syringe to fill it to find the volume. move it to extended position, add more and you've got your amount needed from the master's stroke.

you'd think i'd have taken the time to do that by now :doh:

One way to check the volume issue (non-math) is to push / rock the buggy while you slowly apply the brakes. Then take note of the pedal travel needed to just barely apply or drag the brakes. If it used up most of the pedal stroke, you have a volume issue. If you still have a lot of pedal movement left, you have some other type of issue. This can also help you to determine whether you have brake line flex or not.

The brake lines will not swell when just a little bit of force is applied at the pedal. However, when you try and stop and put a lot of force on the pedal, this is when they will swell. Remember that the brake lines are seeing 200 psi and up (in a hard stop). If your brake lines are moving around, then they are swelling. A hydraulic line will become more rigid when it is pressurized, but it shouldn’t move or flop around. Also, if I remember right, the piston size on my Hammer Head are 1/2" and they control both of the front calipers fine.

Since you have all the time in the world and the money as well :rolleyes:, your best solution may be to run a long piece of steel tubing back to a tee and then use short piece of flexible line to each wheel. That is if the above test shows that you have enough pedal movement.

i still have the 5/8ths master to toss in. i cranked hard enough on the pedal to bend the mount and only get minimal brake effect. for the last race i ran with the pads run into the rotors to a hair off light drag and was nearly out of brakes by the end. started out as enough to hold it in place on the trailer ramp, not enough to do that at the finish. used first gear engine braking a lot to slow down.

Another area to explore is to make sure that the MC is returning all of the way. If its not, the port to the reservoir may not be fully uncovered and you are not able to pull in fluid to the MC to make up for expansion and / or pad wear. This is another common modification to the MCs in the dirt bike world. You can buy them, but I just find a spring that fits over the rubber boot of the MC and use a flat washer to hold it. If I remember right, my spring was used to hold a brake shoe on VW.