Science me about brake res/calipers

[davesax36]

I have sean's busa caliper on a 320mm rotor on the front. Great idea. Looks good. Blah blah.

But... I have fjr masters. I have bled the front a few times now. The brakes work.... But the lever travels really far. I really haven't ridden it much with the setup, but I'm wondering if I have a mismatched master/caliper issue happening.

I also wouldn't mind just having any working combinations on here. I can get other masters if I need to, but I'm sure it's something I did wrong.

Fluid will shoot way up right at the beginning of the lever travel, so I'm not sure if it's an air issue or a plunger volume issue.

Anyway. Have at it, guys.

 

[Fire-medic]

Years ago I posted about a chart showing how to determine the master cyl size required for the # of pistons you have. You might want to search for that.

Ah, here it is, MaxMidnight you have to thank. http://www.vintagebrake.com/mastercylinder.htm

Not to be confused w/this guy, who drank lots of Ovaltine:

Anyone know who this is (the character he played)? Babyboomer or older to know, I reckon... . Besides Superman, he was my favorite tv show as a kid

 

[davesax36]

That's pretty cool. Has the chart been expanded to 6-piston calipers? I've got a 14mm master and it seems like I might somehow have a ratio up around 30 or something.

 

[Traumahawk]

Have you tried the 6 piston with the stock Vmax master cylinder? I have it on mine with the FZR 6 piston calipers. The stock lever starts grabbing after 1/4 of total travel.

 

[davesax36]

No, I haven't because I'd already swapped the Masters. I'm also only running one caliper, which I thought would make it seem a little more grab per travel. I don't have any stock parts here.

 

[Redbone]

Here is some further info:
http://www.venturerider.org/forum/showthread.php?60986-Master-Cylinder-Caliper-ratio-chart

 

[Fire-medic]

Who is the guy on the left? And, why does he drink Ovaltine? To become big and strong, so his hand can make the three-opposed piston dual calipers work?

If you read thru the thread, you will find info about the number of pistons in the calipers, and the number of calipers.

 

[davesax36]

I'm going to do another bleeding session tomorrow since it's raining and cold right now. I'm pretty sure that the difference between a 5/8" master pushing two calipers worth of pistons and a 14mm master pushing one caliper of pistons is not the problem. I just don't believe the difference in volume could be causing the squishy lever problem.

Any other suggestions?

 

[wildweasel_pt]

The problem is not quite the amount of pistons but their diameter as the same amount of fluid pushed by the master pushes a smaller piston further and stronger than a bigger one

 

[davesax36]

Well there are six pistons that are all smaller than the four from my r1 calipers that used to feel awesome. I'm sure it's my fault.

 

[one2dmax]

The feel should be great so you likely have an air bubble in there somewhere.

 

[davesax36]

How far should the lever travel? I can pull it pretty much all the way to the bar on 5 out of 6 on my adjustable lever (6 is most open, 1 is close). They did feel better when I just went out, but there's something sketchy going on. I can see the adapter plate moving as the rotor floats.

 

[dingy]

The Ventures are notorious for being difficult to bleed. One trick that has worked for me is to pump brake lever several times, then zip tie the lever as tight as you can and leave it overnight. Then release zip tie, don't pump lever yet, slightly loosen banjo bolt at the master and gently squeeze lever to bleed air. Containment of brake fluid expelled is very important for paint.

I know it sounds weird, but I have seen it work on brakes I couldn't get to bleed with mighty vac, speed bleeders etc.

Also gently tapping lines while lever is tied back can help small bubbles break free and migrate to top.

Gary

 

[Fire-medic]

Something to my way of thinking is seriously wrong. That plate should be solid w/the slider tube. Properly bled, my stock lever/master cyl will come about 1/2-way to the bar when it stops.

I know there are many guys who do like Dingy does, and fasten the lever to the bar overnight, which I guess is leaving a path for the slow migration of any small air bubbles upwards.

In my experience, the reverse-bleed using a ~60 ml syringe to push fluid from the slave cyl upwards does the same thing, except a lot more-quickly. Start w/a filled slave cyl & syringe, leave the lid off the handlebar master cyl, and open the slave bleeder and start pushing fluid upwards. Keep an eye on the fluid level in the handlebar master cyl, empty it by about 1/2, and keep pushing fluid up.

If the master cyl fluid isn't perfectly clear to begin with, evacuate the master cyl & fill it about 1/2 w/fresh fluid. When you begin to push the syringe plunger, you should see discolored fluid entering from the two holes in the master cyl. If the level approaches full, evacuate the master cyl until the holes are still covered w/fluid, but not exposed/dry. Refill your syringe if needed, and keep pushing fluid up from the slave cyl bleeder nipple until the master cyl fluid is clear, w/no trace of dirty fluid. Now close the slave cyl bleeder.

If you are careful, you should be able to carefully and SLOWLY squeeze the brake lever, and be rewarded w/a small geyser of fresh brake fluid coming from the hole in the bottom of the master cyl. Now replace the master cyl lid. Fan rapidly the lever, and almost immediately you should be rewarded w/a firm lever, and the point at which it stops moving should be about 1/2-way to the bar on a stock lever.

How far should the lever travel? I can pull it pretty much all the way to the bar on 5 out of 6 on my adjustable lever (6 is most open, 1 is close). They did feel better when I just went out, but there's something sketchy going on. I can see the adapter plate moving as the rotor floats.

 

[davesax36]

I'll work on it more tomorrow. Maybe not enough torque on my mounting bolts? We'll see what I can get done. I had to order those swingarm spacers anyway. I was, however, very happy to go ride today. A little tuning will get things dialed in soon enough.