Anyone have any Brake Questions?

[Peter Mc Mahon]

This is good stuff, thanks for the input so far!

[csouth]

This is great thread and its good to have someone with such vast knowledge helping us that need need it. I only have one suggestion :maybe people asking questions in individual threads and placing OG racing in the title if they want you to answer. I could see lots of good questions and your replies getting buried 8 pages deep in this thread by New Year....

[Skip Fix]

Got one for you on my 97 Chevy 1/2 ton I use to tow the hot rods. Front calipers have a 2.94 piston and a 4.95x2.99 inner/5.50x 2.35 outer pad size. The 3/4 ton calipers bolt on and have a 3.15 piston and a 4.95x3.37 inner/5.80x2.32 outer pad size. Worthwhile swap or will it affect pedal feel much being a 7% larger piston? Good pad for a street tow truck? Hawk has a truck pad.

[OG_Racing]

Got one for you on my 97 Chevy 1/2 ton I use to tow the hot rods. Front calipers have a 2.94 piston and a 4.95x2.99 inner/5.50x 2.35 outer pad size. The 3/4 ton calipers bolt on and have a 3.15 piston and a 4.95x3.37 inner/5.80x2.32 outer pad size. Worthwhile swap or will it affect pedal feel much being a 7% larger piston? Good pad for a street tow truck? Hawk has a truck pad.

your going to have a 7% larger front piston area. is that good for increasing brake tq? yes it is. 7% is also a good area to incrementally increase pressure by. But how is the braking balance? by increasing the balance of the system forward your removing braking duty from the rear. if your system already has a heavy Front balance (if you have rear drums a heavy front bias could be the case) then a larger piston will be shifting even more bias to the front, making the braking overall performance even worse. this could result in higher braking temperatures on the front rotors, if the rotor temperatures get too high you would loose all braking performance. When towing you have allot of weight and increased traction over the rear wheels. if your looking to increase the stopping performance i would look to adding more tQ to the rear of the truck. take advantage of all that extra weight you have.

For increase braking demand i would look to the PFC .10 compound. it's made from an old nascar race compound but modified to not squeak or dust too much. it can take a rotor temperature in excess of 1600* (most street pads fall off around 800*). we have the PFC 0369.10 for 1997 chevy 1500's for 57.64. i would also look to see if there is a rear disc conversion for your application. FYI going drum -> rotor does require an aftermarket proportioning valve.

[Skip Fix]

Thanks, looks like staying with the stock calipers is the way to go. The 97s have ABS and barely use the rear brakes the way the stock setup is. I think I have over 100K miles on the shoes and still plenty left! Engage the ABS and the pedal feel real good. Been weird since new.
The PFcs have a real good cold bite also? Most moron drivers pull in your stopping distance then hit the brakes themselves expecting you and 5000lbs of trailer and car to stop n a dime!

[OG_Racing]

Thanks, looks like staying with the stock calipers is the way to go. The 97s have ABS and barely use the rear brakes the way the stock setup is. I think I have over 100K miles on the shoes and still plenty left! Engage the ABS and the pedal feel real good. Been weird since new.
The PFcs have a real good cold bite also? Most moron drivers pull in your stopping distance then hit the brakes themselves expecting you and 5000lbs of trailer and car to stop n a dime!

the cold bite is there, but the hotter they get the better they work.

[Skip Fix]

rear shoes that match the pads for coeff?

[Mr Nick]

Proper way to set an adjustable proportioning valve?

I was told "slam on the brake and adjust it so the back doesn't lock up" but that just didn't seem right.

[Skip Fix]

Nick not a "expert" but that is kind of how you get the initial setting. I usually find a gravel driveway/road first as you can hear see it without as hard a "slam". But remember at the track street things are my dynamic -what was fine in a straight is totally different in a turn, harder braking can unolad the rear more(esp if soft front springs/large sway bar setup) do rear can lock up easier. Rear suspension too tight(springs/sway bars) in a turn inner rear can lock up. So you have to find the right spot to balance all of those, or tune to specific tracks, driving.

[OG_Racing]

rear shoes that match the pads for coeff?

i don't do shoes, sorry. I would strongly recommend upgrading to a Rotor/ Floating caliper for track days. The brake drum is not a very good braking design, they are heavy, don't cool well, and can reach unbelievably high temperatures at a track day. a rear disc conversion kit is strongly recommended.

[OG_Racing]

Proper way to set an adjustable proportioning valve?

I was told "slam on the brake and adjust it so the back doesn't lock up" but that just didn't seem right.

like it was said before braking is dynamic. that means Different actions will bring up different reactions. Example if your driving down a straight road and slam on the brakes your Fronts will lock up first. with the exact same setting If your entering a turn you might slam on the brakes and the rear tires will lock up first. all factors of your chassis set up will change these retractions. the factors in your chassis set up like weight distribution, speed, tires size, tire compound , brake pad, shock settings, spring rate, driver input, brake pad tq, ect. The rear brakes locking up will cause the rear to "step-out", "over-steer" or "trail brake". This is because in a turn, your inside wheels are unloading. The weight is shifted from a neutral state to forward, and left or right. this shift in weight will shift the traction forward and off the rear tires. An overseer condition caused by the brakes is called "trail braking". Trail braking is used by Racers to turn the car into a corner. To a novice racer trail braking can be surprising. Without knowing how to control trail-braking It can result in a spin, spins can result in crashes. for my beginner drivers i try to avoid all trail-braking. i want them to have the car slowed before the turn. once they have mastered slowing the car before the turn, then we can learn how to use trail braking. For a street application i would crank the brake bias knob +2-3 turns from off. this means that the rear brakes are mostly off. most of the time with this setting your front wheels only will lock up. that Lock up also called under steer". under-steer is disable in a panic stop situation. on the street it's easier to recover from under-steer then it is to recover from Over-steer. it will keep the car pointed in a straight line in a panic stop. To tune the prop valve take the car to an autocross. start with the valve shut. every autocross run open the bias knob a half turn, until you feel the rear of the car want to step out under braking, then back the knob off 1/2 turn. Then your at a Happy medium with brake bias pressures. record how many turns the valve is from off, and that will be a good autocross starting point. When driving on the streets crank that knob back 2 turns to remove pressure from the rear. This will insure that if your in a panic stop situation you won't spin out into the weeds.

[Skip Fix]

Drums for the tow truck.

[79-TA]

Proper way to set an adjustable proportioning valve?

I was told "slam on the brake and adjust it so the back doesn't lock up" but that just didn't seem right.

It's a good starting point. Assuming the surface isn't overly dusty or slick, that will let you make a good guess at the brake bias for straight line braking.

A bit more thorough explanation might be find the point where all four wheels lock up at once and then remove rear pressure/bias.

Most likely, you have a pressure limiting switch on the rear lines (this kind of knee point adjusting device should never ever be on the front brake lines). Start with as little rear pressure as possible and gradually add more rear brake line pressure/braking torque. Once at the point of 4 wheel lock up, back the rear pressure off at least two turns.


There is a pitfall to this sort of testing, especially if done in a parking lot. Often times, the convenient long stretches of asphalt with low traffic don't have the best traction. This limits the coefficient of friction which limits the rate at which the car can slow down. For ideal bias, the car will need more braking torque in the front for higher rates of deceleration with more weight transfer. It would then be possible to think you had the bias correct only to find the rears locking prematurely at a driving event with a more ideal (clean) racing surface.

Autocrossing can help reveal whether or not the bias is appropriate for dynamic situations, but this does not replace straight line testing. The typical autocross course doesn't have a significant enough braking zone to test threshold straight line braking at high rates of deceleration. Conversely, getting the bias safe in a straight line does not necessarily guarantee that the car will turn in without the rear losing traction first. Both are important tests. If in doubt, run less pressure in the rear.

[OG_Racing]

Drums for the tow truck.

Oh got ya, thought you where talking about your TA. sorry i don't have any shoes for drums.



saw this today. ugghhhh love!! Big old PFC brake kit.

[Mr Nick]

Thanks to you guys for the input on setting my prop valve. It's cold here in Chicago, so this will have to wait till Spring. The GY Supercar tires have poor traction under 50*, so no point in setting it now.

[cdrod]

Johnny:
Thank you for starting this thread and for your willingness to share your knowledge and experience with the rest of us. I'm building an Olds 442 convertible as a daily driver. I don’t plan to autox this car or race it, but I do want to upgrade to 4-wheel disc brakes and get rid of the 42-year-old drum brakes. I've chosen a rear disc set-up from an '01 Chevy Blazer running the stock 295mm rotors (which are 20mm thick) and the caliper has a single 48mm piston. I want to use C5 Vette parts for the front brakes, which use a 325mm rotor and the caliper has two 40.5mm pistons.

Using some aluminum parts (heads, radiator, AC compressor, etc.) I am removing 300 lbs of sprung weight in the front and the C5 brake parts along with aluminum rims will reduce the front un-sprung weight by 14 lbs per side. I think the overall weight of the car will be around 3500-3600 lbs (without driver) but I don’t know the F-R weight distribution or the weight transfer rate. Since I’m removing 300+ lbs of weight in the front, I should be moving the F-R weight distribution closer to the ideal 50-50 balance.



I’ve built a spreadsheet to allow me to quickly change brake parameters to evaluate the performance of my brake combination and gauge the performance relative to the stock Olds 11” disc w/rear drum system. I have attached a pdf version for your reference – numbers in blue are data inputs, numbers in yellow are important results. My goals are to modernize the brakes (need to be able to stop when those damn Mini Coopers cut you off and slam on the brakes-lol) using readily available OEM parts that can be purchase at any auto parts store. Here are my questions:

1. Do you see any errors in my spreadsheet? I've included a “notes” column to show the formulas used to calculate the results.

2. What is an ideal target for front to rear bias? I plan to run a 285-40R17 tire on the rear so I think the braking could be increased to match the increased traction. My spreadsheet shows a 65-35 balance front to rear. I plan to test drive the car to dial in the prop valve under real-world conditions, but I want to make sure my system bias is close so I don’t have to reduce the rear pressure too much. Does this look OK?

3. What is a good pad CoF for a daily driver? I used a 0.3 CoF in my spreadsheet, should I use a higher value? I don’t want to be too aggressive with the pad CoF to the point I’m changing the pads and/or rotors every 20k miles, but I want the car to stop well.

4. What would be a good master cylinder/booster combination for this car? The booster size shown in my spreadsheet is the stock Olds size and the master cylinder is a 15/16” bore from a Monte Carlo SS. I could use the C5 booster/master cylinder, just not sure how this would work out with the larger 48mm Blazer calipers in the rear. Also, I think the C5 Vette had a quick take-up style master cylinder and the rear brakes had a 45mm caliper.

I’m looking forward to your comments, and anyone else's with more knowledge and experience than me.

[OG_Racing]

Johnny:
Thank you for starting this thread and for your willingness to share your knowledge and experience with the rest of us. I'm building an Olds 442 convertible as a daily driver. I don’t plan to autox this car or race it, but I do want to upgrade to 4-wheel disc brakes and get rid of the 42-year-old drum brakes. I've chosen a rear disc set-up from an '01 Chevy Blazer running the stock 295mm rotors (which are 20mm thick) and the caliper has a single 48mm piston. I want to use C5 Vette parts for the front brakes, which use a 325mm rotor and the caliper has two 40.5mm pistons.

Using some aluminum parts (heads, radiator, AC compressor, etc.) I am removing 300 lbs of sprung weight in the front and the C5 brake parts along with aluminum rims will reduce the front un-sprung weight by 14 lbs per side. I think the overall weight of the car will be around 3500-3600 lbs (without driver) but I don’t know the F-R weight distribution or the weight transfer rate. Since I’m removing 300+ lbs of weight in the front, I should be moving the F-R weight distribution closer to the ideal 50-50 balance.

I’ve built a spreadsheet to allow me to quickly change brake parameters to evaluate the performance of my brake combination and gauge the performance relative to the stock Olds 11” disc w/rear drum system. I have attached a pdf version for your reference – numbers in blue are data inputs, numbers in yellow are important results. My goals are to modernize the brakes (need to be able to stop when those damn Mini Coopers cut you off and slam on the brakes-lol) using readily available OEM parts that can be purchase at any auto parts store. Here are my questions:

1. Do you see any errors in my spreadsheet? I've included a “notes” column to show the formulas used to calculate the results.

2. What is an ideal target for front to rear bias? I plan to run a 285-40R17 tire on the rear so I think the braking could be increased to match the increased traction. My spreadsheet shows a 65-35 balance front to rear. I plan to test drive the car to dial in the prop valve under real-world conditions, but I want to make sure my system bias is close so I don’t have to reduce the rear pressure too much. Does this look OK?

3. What is a good pad CoF for a daily driver? I used a 0.3 CoF in my spreadsheet, should I use a higher value? I don’t want to be too aggressive with the pad CoF to the point I’m changing the pads and/or rotors every 20k miles, but I want the car to stop well.

4. What would be a good master cylinder/booster combination for this car? The booster size shown in my spreadsheet is the stock Olds size and the master cylinder is a 15/16” bore from a Monte Carlo SS. I could use the C5 booster/master cylinder, just not sure how this would work out with the larger 48mm Blazer calipers in the rear. Also, I think the C5 Vette had a quick take-up style master cylinder and the rear brakes had a 45mm caliper.

I’m looking forward to your comments, and anyone else's with more knowledge and experience than me.

I do see some errors. The spreadsheet your using doesn't allow for rotor sizes to be entered. that does Play a huge role into brake TQ and balance.

2 brake bias before using a proportioning valve should be closer to 40-50%. if you where to remove a prop vales the car should be undriveable. that's why a balance bar or a Proportion valve are so important.

3. COF or Mu for a standard street pad is anywhere from .3 - .4... .5-.7 for race pads.

4. As far as the master cylinders go. the 15/16" seams too large for the corvette calipers. The corvette calipers size in with an area of 4^2" the old GM metric calipers where a 4.92^2". a difference of 20% larger to the old single pistons. It would be highly advisable to scale down the Master cylinder size too, or the pedal would fell like a rock. the C5 corvette uses a 13/16" master cylinder size. i am unaware of how much assist the booster provides or the pedal ratio.


My recommendation for your set up is to run an C5 master cylinder for you braking system. the K5 rear brake master cylinder is larger then the C5 rear calipers by 7%, but you have a 7% smaller rotor. so things will be quite even. one thing that allot of people over look when building a DIY brake kit is pad choices. Most mopar guys run into this issue. the selection of pads for the corvette is much larger then pad selections for a C5 blazer. You would be very lucky to find matching compounds front and rear.

[OG_Racing]

http://youtu.be/-bm5aW_tga4

Found this nice video from Stop Tech on how flexy Factory calipers are. before you start knocking the results remember that this test is at room temperature, with a hand pump. Normal Brake system will see 1200-1500psi. at a race a calipers can see >600*
__________________

[cdrod]

I do see some errors. The spreadsheet your using doesn't allow for rotor sizes to be entered. that does Play a huge role into brake TQ and balance.

2 brake bias before using a proportioning valve should be closer to 40-50%. if you where to remove a prop vales the car should be undriveable. that's why a balance bar or a Proportion valve are so important.

3. COF or Mu for a standard street pad is anywhere from .3 - .4... .5-.7 for race pads.

4. As far as the master cylinders go. the 15/16" seams too large for the corvette calipers. The corvette calipers size in with an area of 4^2" the old GM metric calipers where a 4.92^2". a difference of 20% larger to the old single pistons. It would be highly advisable to scale down the Master cylinder size too, or the pedal would fell like a rock. the C5 corvette uses a 13/16" master cylinder size. i am unaware of how much assist the booster provides or the pedal ratio.


My recommendation for your set up is to run an C5 master cylinder for you braking system. the K5 rear brake master cylinder is larger then the C5 rear calipers by 7%, but you have a 7% smaller rotor. so things will be quite even. one thing that allot of people over look when building a DIY brake kit is pad choices. Most mopar guys run into this issue. the selection of pads for the corvette is much larger then pad selections for a C5 blazer. You would be very lucky to find matching compounds front and rear.

Johnny:
Thanks for your reply. Actually, the second row of my spreadsheet has the rotor sizes. Not being defensive, just pointing out the data is there.

#2. What's a good brake bias balance after the proportioning valve? It seems to me that if I start out with a 50-50 front to rear balance before the proportioning valve I would be at the limits of the proportioning valve to reduce the line pressure to the rear calipers. Don't most valves max out at around 50% reduction?

#4. The stock Olds calipers on the front of the 442 were a single piston design with a diameter of 2.93" and a piston area of 6.7 sqin. In comparison, the C5 caliper piston area is approximately 4 sqin, which is 40% smaller than the Olds, but the C5 rotor diameter is 16% larger than the Olds 11' rotor. The stock Olds used a 1-1/8" MC (lots of volume to fill those huge calipers) but the C5 calipers should need 40% less volume for the same amount of piston travel. I came up with the 15/16" MC size by reducing the sotck Olds MC size by 40% (1.125 * .60) which falls between 7/8" and 15/16". I was also concerned about too much pedal travel with a smaller MC bore, and not sure how the MC size will affect pedal modulation.

I didn't think about pad availability for the Blazer rears, but couldn't this be fine tuned with the rear proportioning valve? i.e. a grippy pad in front, not so grippy pad in back, needs little more brake bias to the rear. And wouldn't I be able to find a good pad, If I stay with a less aggressive street pad (CoF .30 - .35)? Like a semi-metallic AC Delco pad? Remember, I'm not looking for autox or racing level performance, just good daily driver performance on par with a modern vehicle.

Thanks!

Rodney

[Hugger67RSSS]

I have a set of Baer 6S front calipers with 14" rotors that I want to use on my 68 Camaro. I have a 9" rear that has the new style ford ends. (Non floater obviously) and have been looking for a floating rear caliper. Will the wilwood D154 setup with a piston area of 4.12 work for the rear with my front brakes?
My front calipers have 1.62,1.37, and 1.18 Pistons. My car has a 7/8 manual wilwood master on it now.

http://www.wilwood.com/Calipers/Cali...ston%20Floater

Thanks!