CuttingEdgeRacing Posted March 2, 2010 Report Share Posted March 2, 2010 Just finished up a racecar for a customer, who provided me with an amazing set of pedals he wanted installed. So I installed them, along with his new BIG calipers. The brakes have been bled, 1200 - 1400 PSI at each caliper. Brake pedal is ROCK HARD, with ZERO modulation. So we figured it would get softer once the pads bed in. After saturday's test session, we still had ZERO brakes. No matter how hard you push, once you reach a point, it feels like you're stepping on a brick wall, it just doesn't move. We generate plenty of line pressure at the caliper, but the brakes have no stopping power. The pedals are ALCON, bias bar setup. Front master cylinder bore size is .937" rear master cylinder bore size is .8125". The brakes are AP racing 6 piston PRO 5000+'s in the front and Wilwood 4 piston SL-4 (superlight 4) in the rear. Car weights 3050 with driver. Mechanical pedal ratio is 12:1 We have been told by other people that the master cylinders are probably too big. So, we were considering putting the smaller master on the front side of the brake setup and then buying a smaller master for the rear. But, the ALCON cylinders are $600 each, so we need to make sure we're moving in the right direction. Can anyone help here? How can we determine what size master cylinders are the right ones? I've tried calling a few places, but have met resistance instead of assistance. Link to comment Share on other sites More sharing options...
rpfan Posted March 2, 2010 Report Share Posted March 2, 2010 You need to contact The Brake Man.com Link to comment Share on other sites More sharing options...
1-Crew Posted March 2, 2010 Report Share Posted March 2, 2010 The first thing to do is figure out what the ratio is between the master cylinder area and the caliper piston area. Just like you have a mechanical 12:1 ratio on the pedal, you will have a similar relationship with the master cylinder and the caliper. To figure the ratio, find the diameter of each puck in the caliper. Take the diameter and divide by 2. That is R or the radius of the circle defined by the face of the puck. The formula for area is 3.141 X R X R. Multiply this by the number of pucks. You already know you have .685 sq. in. area for the front master and .518 sq. in. for the rear. The front should have a higher ratio than the rear, depending on weight distribution. Link to comment Share on other sites More sharing options...
Pacecar Posted March 3, 2010 Report Share Posted March 3, 2010 For an asphalt car, the smaller MC is installed on the front brakes. Link to comment Share on other sites More sharing options...
Ford27 Posted March 3, 2010 Report Share Posted March 3, 2010 pedal ratio is the #1 mistake for most but if your runnin a 12:1 and getting 1200-1300psi at the calipers it should only take 100 pounds of force to stop your car which is right on the money. Double check your pedal ratio using the formula A = height of pedal B = center to center measurement of the lower arm C = pedal ratio A divided by B equals C My example 9" divided by 1.5" equal 6 to 1 ratio. I was'nt clear if it was hard to stop or didnt stop at all. if it's not stopping at all or real poor check to make sure your caliper piston are working properly(take em off have someone slowly apply the brakes and see if the piston moves) or not stuck. third double check that your pads are in correct .certain pads can bind and glazed pads might not work at all. sometimes you can grind a little off the pads to see if it helps but uneven pads can leave ruts in rotors so be careful on that idea.not sure if any of that helps but good luck Link to comment Share on other sites More sharing options...
CuttingEdgeRacing Posted March 3, 2010 Author Report Share Posted March 3, 2010 I am mistaken in two things: pedal ratio is 11:1 ... 12" pedal, M/C pushrod is 1" below the pedal pivot point. front master cylinder is the smaller of the two I posted them incorrectly. We get 1200-1400 psi at the caliper, but as soon as the pads hit the rotor, there is nothing left, like I said, the pedal just stops. Perhaps I should take the pads outta the caliper and press the brakes to exercise the pistons, perhaps they are stuck? The front brakes are 100% new. The car doesn't stop at all (at speed) Link to comment Share on other sites More sharing options...
GINGERBREADMAN Posted March 3, 2010 Report Share Posted March 3, 2010 My question is how do you know your getting 1200 to 1400 lbs of pressure at the caliper. Do you have a load cell your putting in place of the brake pad? Are the rotors new ,used or what? If used are they hard glazed where pads can't get a grip no matter how much pressure you apply....on all our cars 400 lbs of line pressure has the tires locked up and sliding at any speed...Brakes are very simple...but need more info or to look at what you have to be able to help with your problem... Link to comment Share on other sites More sharing options...
CuttingEdgeRacing Posted March 3, 2010 Author Report Share Posted March 3, 2010 My question is how do you know your getting 1200 to 1400 lbs of pressure at the caliper. Do you have a load cell your putting in place of the brake pad? Are the rotors new ,used or what? If used are they hard glazed where pads can't get a grip no matter how much pressure you apply....on all our cars 400 lbs of line pressure has the tires locked up and sliding at any speed...Brakes are very simple...but need more info or to look at what you have to be able to help with your problem... Brakes ARE simple!?!!!! I know! I've built probably a hundred race cars, this is the first time I've experienced this. The rotors are brand new, the pads are brand new. I put pressure gauges on all the calipers, like I said, 1200-1400 psi on the gauge. I think that the rear calipers are locked up. I'm going to work on them tonight if I get a chance. Ya'll tell me if this scenario makes sense to you: If the rear calipers are locked up, and the pistons wont move (past a certain point, cause they do move enough to engage the pad to the rotor); would that mean the 1.5 - 2.0" we can move the pedal is the front pads/rear pads moving...but once the rear pistons get locked up, the pedal goes hard? Does that make sense? Link to comment Share on other sites More sharing options...
Ford27 Posted March 4, 2010 Report Share Posted March 4, 2010 possible i guess. you might be able to get that much pedal from fluid movement and line bulge( dont know what else to call it...lines get bigger under pressure).11:1 pedel should still be okay.I would think it was piston lock for some reason but all four at once is not real common.. You might double check the pads are free moving and id check the piston take the caliper off take off the pads hit the pedal and it should move the piston. if the piston moves it might be the pads, if it doesent move you eliminate the pads....etc.....just work on one wheel and take one part out of the equation at a time and you'll br able to narrow it down from pads to caliper to lines to mc etc....good luck Link to comment Share on other sites More sharing options...
GINGERBREADMAN Posted March 4, 2010 Report Share Posted March 4, 2010 I don't see how you could have 11 to 1 ratio pedal assy...7 to 1 is the biggest ratio I can find...what brand pedal assy. do you have?...also I looked at your m/c's and they appear to have a really short stroke...need to check and see if your bottoming your m/c...need more info or pictures Link to comment Share on other sites More sharing options...
CuttingEdgeRacing Posted March 4, 2010 Author Report Share Posted March 4, 2010 I don't see how you could have 11 to 1 ratio pedal assy...7 to 1 is the biggest ratio I can find...what brand pedal assy. do you have?...also I looked at your m/c's and they appear to have a really short stroke...need to check and see if your bottoming your m/c...need more info or pictures We're certainly not bottoming out the M/C's. I've checked that. These pedals came outta one of J. Johnson's short track car's (supposedly). Like I said, pedal length is 12 inches. Distance from pedal pivot to M/C is approx one inch. Ratio should be 11:1 or 12:1 right? Pedals and M/Cs are Alcon (except clutch, which isnt an issue). These brakes were pushing some serious calipers at one point. I just don't see how they couldn't work in our scenario. Link to comment Share on other sites More sharing options...
1-Crew Posted March 5, 2010 Report Share Posted March 5, 2010 The issue could be the compound of the pads. There are some pads that are formulated to work best at elevated temperature (road race). When cold they just don't grip.. Do some research on the compound used for pad material.. Link to comment Share on other sites More sharing options...
CuttingEdgeRacing Posted March 5, 2010 Author Report Share Posted March 5, 2010 The issue could be the compound of the pads. There are some pads that are formulated to work best at elevated temperature (road race). When cold they just don't grip.. Do some research on the compound used for pad material.. Thanks for the advice, but unfortunately we've ruled this one out. We took it to the Harris Hill road course in San Marcos, with these very thoughts in mind. After a nerve racking 10 minute session, the rotors were hardly wiped. Link to comment Share on other sites More sharing options...
jwmbishop Posted March 5, 2010 Report Share Posted March 5, 2010 Just WAGGING - is the diameter of the cyl so big that just before its pushed enough fluid to the calipers it's bottoming out? Easy check is stand on the brakes and have someone pop open a bleeder - you should get at least an additional inch of pedal! Also look at the resevoir - when you step on the pedal is the fluid circulating? maybe the M/c has an internal bleed off return to resevoir side (many do as a way to circ and cool the fluid)? Put the guage on line out and check to make sure you can exceed the 1200-1400 wheel pressure with the m/c alone. This would rule out almost anything at the M/c - your focus would then be on the calipers (mechanical bind - are they sliding all the way? shim them toward the wet side if single side hyd), pad material (its possible that with an incorrect pad/roto combo you aren't making enough heat period no matter how long your test session. What did the infrared therm say when you hit the rotors after the test session?), rotors themselves (crushing or too thin - try shimming the pads - at full rest with the calipers forced fully open you only need about 1/8 clearance). I am assuming they bind enough to stop in the shop just under speed you have the problem. as little as .010 inch caliper short travel can be the difference. man good luck on that - as I often say with any custom work, nothing works or fits until you f^&* with it for an hour or two. Link to comment Share on other sites More sharing options...
77bomber Posted March 8, 2010 Report Share Posted March 8, 2010 What about putting spacers in the calipers Link to comment Share on other sites More sharing options...
jwmbishop Posted March 9, 2010 Report Share Posted March 9, 2010 Well.... Are ya going to keep us in suspense? Link to comment Share on other sites More sharing options...
CuttingEdgeRacing Posted March 10, 2010 Author Report Share Posted March 10, 2010 I'm in suspense myself!?!! Everything works, but the car don't stop! I'm waiting to hear back from Alcon. Their engineer (eric) is looking at the overall setup and going to recommend the next step. I still think the master cylinders are too large. I think the smaller of my two cylinders needs to go to the back brakes, then step down two sizes (to like 5/8) on the front. I really am dumb founded, its gotta be something so easy, I'm not seeing it. Link to comment Share on other sites More sharing options...
jwmbishop Posted March 10, 2010 Report Share Posted March 10, 2010 its gotta be something so easy, I'm not seeing it. My personal experiences are that it usually is.... Link to comment Share on other sites More sharing options...
CuttingEdgeRacing Posted March 15, 2010 Author Report Share Posted March 15, 2010 Ok, the saga continues. Alcon told me to test everything and come back with results...as if I haven't tested everything. SO, I did it again. All 4 calipers are in working condition. I don't feel like the front pistons are moving as much as I'd like, but they are moving. I re bled the entire system again today. There is just nothing I visually see, that wrong. Is it possible to have a bad master cylinder that works "just" enough? Link to comment Share on other sites More sharing options...
jwmbishop Posted March 15, 2010 Report Share Posted March 15, 2010 I don't feel like the front pistons are moving as much as I'd like....Is it possible to have a bad master cylinder that works "just" enough? If the master is at the end of expected travel - thats possible - (most are designed to only travel about 70% of the way down the tube) there may be a bleedback port in it somewhere. But the pedal would sponge (maybe it is but just not enough to really feel with those steel toed shop boots you should be wearing). You described solid. Try putting 18guage sheet metal between the pads and calipers just for fun (cut it to exactly match the shape of the pad backing). THis should eliminate "mechanical travel" issues as far as calipers moving as much as you'ld like and the only thing left would be hydr. And the shims are for trouble shooting only - do not under any circumstance race with them in!!!!! A few hot laps would be okay - and if the problem is solved get some thicker rotors. If not then yes the M\C would be the first thing I change. Reminds me of my Dad's 49Chev PU - we put a 454 in it and the brake transverse link would hit the header after very little shoe wear. Had to adjust the brakes every week! Link to comment Share on other sites More sharing options...
CuttingEdgeRacing Posted March 16, 2010 Author Report Share Posted March 16, 2010 . Try putting 18guage sheet metal between the pads and calipers just for fun (cut it to exactly match the shape of the pad backing). THis should eliminate "mechanical travel" issues I don't have room for a spacer, the pads are brand new and ON the rotor. Ugh...I'm ready to throw these things on ebay and go with something a little more normal...but I dont own them. Link to comment Share on other sites More sharing options...
jwmbishop Posted March 16, 2010 Report Share Posted March 16, 2010 I don't have room for a spacer, the pads are brand new and ON the rotor. even with the caliper plunger pushed all the way in? wow - there is usually about an 1/8 inch extra even with new pads. Sounds like you may have to try a different parts mix. Link to comment Share on other sites More sharing options...
CuttingEdgeRacing Posted March 16, 2010 Author Report Share Posted March 16, 2010 So here is from alcon: Keeping a 1/8” split in front to rear MC’s, here is the total braking torque and pedal travel based on their setup. On the piston area, AP 5000, piston sizes 27, 31.8, 38.1mm = 50.14 cm2 Wilwood Super Light 4-Piston, piston sizes 47.8, 44.5mm (1.88”, 1.75”) = 67.00 cm2, greater then front caliper I am not guaranteeing a change of master cylinders will fix the braking issues, based on their setup (AP 5000, Wilwood Super Light 4 –Piston, 1200F-1400R), the front braking torque percentage is 44.0%. Which cannot be right as the car will spin-out with this percentage of rear brake, if everything was in working order. Typical, GT cars usually use between 60-65% front brake. Something in the system must be off, causes · Pedal going over center · Bad Master Cylinder, MC cannot apply pressure to calipers · Balance Bar Issue, bind in balance bar which will only allow pressure to be applied to front or rear brakes · Restriction in Master Cylinder Fluid Reservoir, reservoir cannot supply fluid fast enough (to master cylinder) to keep up with pedal travel. As MC travels, fluid is displaced from reservoir to MC, air has to be supplied to reservoir to fill void of movement of fluid to MC, if the reservoir cap(s) do not allow air to enter cap fast enough, fluid flow to calipers will stop. If you are having this issue, pedal will travel slightly then stop. Way to test, remove reservoir cap(s) and see if issue goes away · Crushed Brake Lines, fluid cannot get to front or rear calipers SO, with that being said, perhaps the chart is correct and my .850 travel is all I'm going to get. Before changing, I'm going to try removing the master cylinder caps to see if thats the problem. I realize now, our rear brakes are too large. Any other thoughts from you guys? Link to comment Share on other sites More sharing options...
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