Brake Pad & Rotor Selection

[Snakeskin347]

Hi guys, I think I have all the major components of my butcher build purchase rebuilt, reworked or replaced except for the brakes which I probably should of paid more attention to before some other things on the car.

The way the car is set up now it feels like I have to put way too much effort to make the car stop. It is a non-power system and has a Wilwood reservoir, master cylinders and pedal kit but has a cheaper caliper(PBR), rotor and pad setup.

I would like to keep the calipers if possible and try to achieve better stopping power by replacing the pads and rotors with something that will generate more friction.

Does anyone have the similar setup or is there anyone with some experience in regards to what I'm dealing with that could help me out?

Thanks!

[NAZ]

Can you lock up the brakes on all four wheels? If so, do you know what line pressure it takes to do that?

[Snakeskin347]

No, I can't even come close to locking up the tires! It is so bad that I probably shouldn't be driving it. I know nothing about the pressures and I'm hoping that it just crappy rotors and pads? The pedal feels rock hard and it is not squishy at all.

[Jim Stabe]

Try a smaller master cylinder. You probably have a high pedal now that feels like you are pushing against a concrete wall. I have a dual master balance bar setup and I went from 3/4" to 5/8" masters and it made a big difference. Pedal was a little lower and it had more feel and stopping power increased. Not sure what setup you have but look into a smaller master.

[NAZ]

The most frequent cause of this that I've seen are using the wrong pad compound. A street car needs high cold brake torque and if you get a race pad designed for high temps, these usually have very poor cold brake performance. Quality manufacturers will list their pad compounds on a chart that shows the coefficient of friction at various temps. You want high coefficient of friction at low temp (100F). If the manufacturer does not list this info, find one that does. But be advised that to properly troubleshooting heavy pedal / poor stop issues, it helps to know what pressure you can generate. It may take 800-1000 PSI to lock the brakes and that's OK. But if you can generate 1200 PSI and the brakes won't lock, that's a problem and it won't be cured by changing the size of the M/C. There are adapters for check the pressure: https://www.summitracing.com/search?SortBy=BestKeywordMatch&SortOrder=Ascending&keyword=brake%20caliper%20pressure%20gauge

[jts359]

I recently purchased a Mark II that has the same problem , It has 93 Mustang front disc drilled and slotted and 94 Mustang cobra rear disc brakes , It has a 7/8 bore m/c . I replaced all the brake hoses with braided line and installed Power Stop brake pads, It is better than when I first got the car , But not great but I feel more comfortable with it and I can lock up the front brakes There is a post where a person installed a booster on a MKII and I may do that this winter , Ed

[Snakeskin347]

Thanks for all the input Jim & NAZ, I'm going to look into some good pads that hive a high friction coefficient at low temps and get some good quality rotors to match. I was reading up on some of EBC's products and they have a pad called Bluestuff NDX that seems like it might be what I am looking for. I will also go on the Summit site and see what they offer. If that doesn't solve my problem I'll defiantly look into checking the pressure and look into what size of master cylinder was installed when the car was built.

Thanks again guys!

[Snakeskin347]

I recently purchased a Mark II that has the same problem , It has 93 Mustang front disc drilled and slotted and 94 Mustang cobra rear disc brakes , It has a 7/8 bore m/c . I replaced all the brake hoses with braided line and installed Power Stop brake pads, It is better than when I first got the car , But not great but I feel more comfortable with it and I can lock up the front brakes There is a post where a person installed a booster on a MKII and I may do that this winter , Ed

Are you saying that you went from not being able to lock the tires up to being able to lock the front brakes up after putting Powerstop pads on?

[NAZ]

Brake systems stop a car by turning kinetic energy into heat through friction between the pad and rotor. Friction is influenced by clamping force (this is why system pressure is important) and the kinetic (sliding) coefficient of friction of the pad & rotor. Rotors are typically made of cast iron and pad compounds are made from a wide array of materials that have a large range of friction coefficients. The pads are critically important to how well a brake system works and there is a night & day difference in how effective different pads are for specific applications.

There are literally more than a thousand brake pad compounds out there, all claiming to be the best so how do you choose? Rather than make a decision on something as important as brake pads by reading some marketing hype, I prefer to use technical data that can be compared to other manufacturer’s products. The trouble I’ve found with EBC is it’s difficult to find technical data on their products so comparing their pads to others is impossible. For example, what is the coefficient of friction to heat curve on the EBC Bluestuff NDX? If you find a source for that, please share as I’ve yet to find a mu curve for EBC compounds.

Click on the link to see what a coefficient of friction curve looks like: https://www.hawkperformance.com/compounds/motorsports These curves make it easy to compare products and provide some technical reference to help determine how suitable the compound is to your application. As a point of reference, the kinetic coefficient of friction of steel (think backing plate on worn thru pads) sliding on cast iron (brake rotor material) is .4µ which will give you some idea of how effective a race compound is at 100F.

[CraigS]

My experience is w/ Hawk pads. I understand that the EBC are good too but haven't used them. Hawk HPS5.0 will help a lot and don't dust much. HP+ will transform the car but dust much more. I REALLY like them though. I use this to help fight the dust
https://www.armorall.com/products/wheels/brake-dust-repellent
And I have a small shop vac w/ a brush on the end that is my dedicated wheel cleaner.

[jts359]

Yes after putting powerstop on I can lock up the fronts ,, But I got to thinking based on the size of the rear brake pads and the size of the rear tyres would I ever be able to lock up the rear tyres ? Maybe with a booster , Ed

[NAZ]

Yes after putting powerstop on I can lock up the fronts ,, But I got to thinking based on the size of the rear brake pads and the size of the rear tyres would I ever be able to lock up the rear tyres ? Maybe with a booster , Ed

If you mean the size of the pad as in contact area, that has little to do with brake torque. A larger pad (contact area) of the same compound will last longer. It is also a bigger heat sink so will resist fade longer but will not increase friction or brake torque. If you need more brake torque on the rear you need more clamping force (more line pressure or larger caliper pistons which increases the force at the same line pressure), a larger diameter rotor, or compound with a higher coefficient of friction. The other thing that affects the ability to lock up a tire is the tire diameter (smaller is easier to lock up) and traction (less makes it easier to lock up).

[Snakeskin347]

OK, I see what you mean in regards to the information on the Hawk Performance website. I would definitely feel more comfortable buying their product knowing what I am actually getting! Is there any issues with me putting on a race pad such as the HT-10 over a street rated pad like the HPS-5? The race pad seems to have more bite with similar characteristics in other aspects.

[NAZ]

Looking at the mu chart, HT-10 looks like it might work for the street as it shows ~56µ at 100F, which is on the higher side but the description shows the min/max operating range as 300-1300 so I think I'd call and talk to an application engineer before using these on a street car. Street cars require higher cold braking torque (and so does drag racing and autocross).

I run DTC-30 on my street legal race car and find they work excellent on the street and on the strip. My car routinely stops from 150 MPH and has great initial cold bite, good modulation, and while my rotors can get 800F on a hard stop from that speed, I've never had a hint of fade. Also, the HP Plus looks interesting but I have no direct experience with it. But I recommend you stay away from anything that looks like the DTC-80 curve as you would not be happy with the performance on the street or an autocross course.

Thought I should add that I can lock up all four tires with only 400 PSI of line pressure. Using a variety of Wilwood pads, I couldn't lock the brakes even at 1,200 PSI. The moral of this story is that pad compound makes a significant difference.

[Snakeskin347]

Thanks NAZ, You are a wealth of information and I really appreciate the time that you took to help me out with my braking issue. It is no huge rush but it is something that I have committed myself to fix by the end of the year. I am going to take your advice and maybe not rely on marketing so much and I'll spend a little bit more time understanding what really makes a good product for my application. My next step is probably to talk to a tech at Hawk and see what they have to say? Anyways, thanks again for your time!

[CraigS]

The problem w/ the usual Fox Mustang brakes on an FFR is the Mustang weight distribution is maybe 55% front / 45% rear while the FFR is about 47% front 53% rear. So generally it is real hard to get the brakes balanced because the FFR need significantly more rear. The Wilwood dual MC w/ balance bar really helps w/ this. A 3/4 front and 5/8 rear MC is common and then, of course, you can adjust the bar. Before I upgraded to a CNC dual MC (unfortunately they went out of business) I ran Hawk HPS on the front and HP+ on the rear so I got my balance improved via compound stagger.

[jts359]

Do we know if there is a larger caliper and with emergency brake that will bolt on to the 1994 Mustang rear ? And fit under 15" compomotive wheels , Ed

[NAZ]

Check the Wilwood site for other brake options. You'll be looking for an internal shoe type e-brake combo. I run 12.19" rotors on the rear under 15" forged wheels with Dynalite Pro calipers. For a parking brake I use a hydraulic block valve on the rear circuit. When I designed my brake system I selected parts carefully to get the correct rear bias and supercar performance -- I'm very happy with my braking system. My car has 52.1% of the weight on the rear axle with me in it. On paper, my car will stop from 60 MPH in 90', that's 1.34Gs and takes into consideration load transfer, brake bias, and traction on dry pavement. I've never measure that -- it's just from my calculations when designing the system as I was using the C7 braking performance as a project goal. However, the seat of the pants perception is it's better than the wife's little Mercedes sports car which itself is quite good.

So you can get great performance and fit the brakes under 15" wheels if you work at it.

[CraigS]

Back in the day there were some Lincoln calipers that some used. I never tried them because Hawk didn't have many pads for them. One builder actually made adapters to mount Mustang front calipers on the back which I thought was a great idea. I have the drawing for the adapter plate that he published at the time but unfortunately it doesn't have his name anywhere so it would be hard to find him and this may have been 10 yrs ago. Your 15 inch wheels are a huge restriction but that is what it is. I would call Gordon Levy because he has had a lot of experience putting Wilwoods on FFRs.

[lee82]

No, I can't even come close to locking up the tires! It is so bad that I probably shouldn't be driving it. I know nothing about the pressures and I'm hoping that it just crappy rotors and pads? The pedal feels rock hard and it is not squishy at all.

Make sure you don't have a piston partially stuck. I had one of the front PBR calipers partially stuck and dragging and it made my pedal feel just like you describe! After swapping calipers and changing the brake fluid it definitely stops much better and has some squish back in it. No, it doesn't stop like a 911 with 15" rotors and brembo calipers, but I have confidence I can stop quickly enough.

[johnnybgoode]

A good thread below on the various OEM caliper/rotor and various pad combinations. This is from several years ago and I remember Hawk did not supply their more aggressive pads for some of the rear calipers. I think that may have changed since. In any event, some good info if you have the time to read.

https://www.ffcars.com/threads/brake-bias-concern-and-a-warning-for-safety.245120/

This thread helped me to get my MKII stopping much better. Scott