Issue with Wilwood brake setup

[rickster]

Hello all, I have not been on the forums in a while, but I got back in the seat this spring and decided to look further into my brakes and get them sorted once and for all.

I completed the car in 2015 and have put 600 only miles in it since then. The brakes are custom built and sourced by my self.

The parts:
Mark4 Wilwood pedal box w/ .75" MC front & .625 MC rear

Front:
Wilwood Forged Dynalight calipers - 120-6815 (1.75" pistons x 4)
13" rotors (2006 corvette w/ re-drilled bolt pattern)

Rear:
Wilwood Forged Dynalight calipers - 120-6805 (1.38" pistons x 4)
13" rotors (2006 corvette w/ re-drilled bolt pattern)

Pads:
Hawk - PC (Performance Ceramic) (all four corners)

I have never been able to get this setup to stop really well for me. Just the other night I reviewed all the calculations, and I should be able to lock the tires at about 50 lbs of pedal force. On the road, I need to put everything I have into it to make this happen.

So I decided to start by measuring the pressure seen at the calipers with a WilWood gauge tonight. I suspected that I would see low pressure. Perhaps from a hidden air bubble, leak or obstruction somewhere, but that was not the case. My readings showed 1000lbs at the front caliper, and 0ver 1500 at the rears ( I know I need to adjust the balance bar...)

This equates to:
Front @ 1000psi * 2.40 (piston area) * 4 (pistons) = 9600lbs of clamping force to the rotor (x2 for each wheel)
Rear @ 1500psi * 1.49 (piston area) * 4 (pistons) = 8940lbs of clamping force to the rotor (x2 for each wheel)

Even 1/2 that amount should try to put me through the windshield?

I checked for any interference that may be keeping the pads from engaging the rotors. but found nothing. All rotor surfaces seem to be getting smooth even contact.

I also have an ABS controller from a early 2000's Mustang in-line, but the pressure seems to getting past that just fine by my tests...

Any ideas?

Thanks,
Rick

(Edited to include the correct MC sizes and brake pads)

[rickster]

My next step is to validate the front passenger side caliper pressure (I only tested the drivers side). I assume that the passenger rear is good to go as it tee's from the same line as the drivers rear.
Then I will pull the pads to make sure they are not glazed. Not sure how that would happen though, as it hasn't been run really hard.

Thanks,
Rick

[CraigS]

Does Wilwood have a grippier pad compound available for your calipers?

[Jeff Kleiner]

I’m kind of going the same direction as I think Craig is. Clamping force does not=friction. If the pads are not correctly bedded or are not a proper compound clamping force alone won’t do the job. Have you been through the bedding procedure?

Jeff

[NAZ]

Rick, you have plenty of pressure and clamping force as you suspected. Clamping force, rotor diameter and coefficient of friction are what affect braking torque. The Wilwood pads have very poor cold friction which is what you need for a street car. Try a set of Hawk pads with their DTC-30 compound. They have an aggressive initial bite with high cold torque and still plenty of high temp fade resistance. They easily stop my car from over 150 MPH and I can lock up all four tires with less than half the clamping force you have and my rotors are smaller than yours.

[Jim1855]

The pads are BP-10s. Nice but not great. Switch to BP-20s more friction but more dust.
Been there, done that with a similar system. The 1-3/4" front, 1-3/8" rear calipers should be good.
Jim

[rickster]

You guys are awesome! (as always) I'll get some new pads and report back once I have them installed and tested...

Thanks,
Rick

[NAZ]

I've tried a variety of Wilwood pads and have always seen disappointing results, including BP10 & BP 20. In fact, you will only make cold stopping worse with BP 20 compound as it needs to get ~300F to equal the friction coefficient of the BP 10 when cold.

147617

Switch to the Hawk DTC-30 compound and you will see a night and day difference. Summit Racing carries them.

[rickster]

Ordered the DTC-50 pads today from Summit. I'll report back once they are installed!

I was looking back at my receipts, and it appears that I was using the Hawk ceramic pads, not the Wilwood - 150-8850K as my spread sheet showed...I can't seem to find these online anymore, maybe they were discontinued?

Thanks again,
Rick

[NAZ]

That number corresponds to a BP-10 Wilwood pad. https://www.wilwood.com/BrakePads/BrakePadsProd?itemno=150-8850K

I think you're going to be happy with the Hawk.

[tonywy]

Just want to throw this out there, Hawk and Wilwood all good stuff but, I have been using EBC with even better results. Yellow Stuff on my car and Green Stuff on my daily driver and MGB.

[Railroad]

Anyone have the part number for the EBC stuff to fit the Wilwood 6 piston front on a Mk IV?
I am digging, but slow, hoping I can use your knowledge, thanks.

[tonywy]

Get your Wilwood pad # and go here. https://ebcbrakes.com/articles/wilwood/

[CraigS]

I happened on Hawk way back when and have used most of their street compounds and like them a lot. I have called Hawk a few times to get their advice and their tech people are very helpful. I understand EBCs are good also but have not tried them. OTOH, Mark at Breeze always has good answers and he sells the EBCs, so my bet is they also work.

[Railroad]

With help from tonywy's links, I have found my MkIV 6 piston, front, Wilwood calipers to be DP6A.
The EBC yellow pads are DP 4055R.
Summit racing does not show these available, although they would probably order.
Anyone care to verify my numbers and maybe provide a source for the pads.
TIA
I will contact Mark, also.
The pads that fit my Wilwoods are no longer available.
I guess it will be the Hawk pads.
I might wait on a report from rickster.

[rickster]

I ordered a set of EBC Yellow stuff pads too. Not sure when the Hawk pads are going to ship. First set to get here wins first test drive!

Rick

[Railroad]

I ordered a set of EBC Yellow stuff pads too. Not sure when the Hawk pads are going to ship. First set to get here wins first test drive!

Rick

Rick do you have the 6 piston Wilwoods? If so where did you find the pads?
thanks,
Never mind, I see where you have the 4 piston calipers.
How about a report on the results?

[Mike DiGiorgio]

ive only used EBC pads on my motorcycle, but they are my go-to pad for bikes as they stop so much better

as stated, your pressures seem fine. so this is likely a friction issue. when you were bleeding the wilwoods did you blead both sides of the caliper? if not the pedal will have some sponge. i have found this is usually a multi step bleed process

[Railroad]

Well, 6 piston Wilwoods really paint you into a corner for pad selection.
EBC's are practically non existent. Hawk does not offer anything closer to a street/strip pad than the DTC-30.
Wilwoods are less street friendly than the Hawks. Still hoping someone has some experience with the Hawk DTC-30s.

[NAZ]

Railroad, I'm using Hawk DTC-30 pads front & rear on Wilwood calipers. My fronts are the same as FFR supplied, Dyna Pro-6 (6-piston) with pad plate # 6712, Hawk pads # HB645V.490. My rears are Dynalite Pro 4-piston calipers that I spec'd so they are very different than what FFR supplies.

[Railroad]

Railroad, I'm using Hawk DTC-30 pads front & rear on Wilwood calipers. My fronts are the same as FFR supplied, Dyna Pro-6 (6-piston) with pad plate # 6712, Hawk pads # HB645V.490. My rears are Dynalite Pro 4-piston calipers that I spec'd so they are very different than what FFR supplies.

Thanks for the information. With help, I have determined I have the same set up on the front, other than having the BP-10 pads. I assume you like the braking provided by the DTC-30 pads??
I was considering changing out the front pads first and seeing how that works, but would listen to more experienced users.
Thanks again. With your confirmation, I will be ordering some DTC-30s.

[NAZ]

With the Wilwood pads I could not lock the tires at any speed even at 1200 PSI (I have pressure transducers on front and rear brake circuits so I know the actual pressures). With the Hawk pads, even before bedding them, I could lock up the 29" tall 16" wide tires with only 400 PSI and moderate pedal force. I have 12.88" front and 12.19" rear rotors, a Wilwood balance bar pedal assembly with a 6:1 ratio pedal. The only change was the pads -- that is a significant difference with just a pad compound change.

I can slow the car from ~150 MPH and take the first turnout at Wild Horse Pass, usually that's the lower powered street / street machines that use the first turnout.

147845

[CraigS]

I can never find it when I want it but there is an industry wide # system for all pad shapes and sizes. If you can find that listing it's easy to measure what you have currently, find the industry #, and then find other pads that have the same # and same dimensions. Also, pads are just pads. 35 yrs ago I ran a couple of seasons of SCCA IT class in a 280ZX. No good pads for the rear. So I bought pads that were about an 1/8 inch too tall and cut them down in my bandsaw. I had a respirator on and the shop vac set to catch the dust. I took them outside for the final edge finish w/ a power sander.

[rickster]

Well the Hawk DTC-50 pads showed up first! What a difference! After bedding it now stops like I want it. The pedal is a bit squishy, but I am going to chalk that up to rear end axle movement. I re-bled all the calipers with a power bleeder while I had the tires off and saw no air bubbles, so I am pretty sure that is not an issue.

I also noticed that I was using a 5/8 MC for the rears, so I am going to edit the original post in case someone refers to this in the future.

Thanks all!
Rick