Pulsating Brake Pedal

[jhv48]

I’ve got Superformance #2932 with 36,000 miles. Front brakes are pulsing when applied. Could be either brake pad buildup or warped rotors. Should I have the rotors resurfaced or just replace them altogether. And, if I should replace them, where can I get replacement rotors. I know they’re Wilwood, but can’t find any part number.

[twobjshelbys]

My experience the last few times for regular cars was that new rotors only cost a few dollars more than the cost of labor for turning the existing ones.

[rt.collins]

I would price out both options. My son just had his 98 Mustang GT rotors turned at half the cost of new rotors.

[Grubby]

Modern rotors are too thin to turn. Waste of money - they will warp quickly.

In the ‘90s I was a product engineer at GM. They advised against turning then.

John

[rt.collins]

Actually, looking at rotor thickness specs (ratio of thickness relative to diameter) from the 80's to 90's, rotors increased in thickness...

[Dominik]

Somebody who knew once, said about brake shudder:

"In more than 40 years of professional racing, including the Shelby/Ford GT 40s – one of the most intense brake development program in history I have never seen a warped brake disc.
To induce that kind of permanent deformation, you would need to heat your rotors to a sustained temperature of over 738 degC then rapidly quench them in order to convert the thermoelastic instability generated hot spots to martensite instead of the ferritc/pearlitic matrix you started with.

Your basic brake pads will begin fading around 350 degC. Your high performance pads will begin fading around 550 degC. You will start to break down the surface of your rotor into cementite hard spots around 610 degC.

Your basic Dot III brake fluid will begin to boil as low as 140degC. High performance brake fluid will only take you to around 300 degC.

Bottom line - Your brakes will fade into near uselessness long before you can achieve the conditions necessary to warp your rotors.

Uneven deposition of friction material results in this thickness variation or run-out due to hot spotting that occurred at elevated temperatures."

[jhv48]

So how do you get the remove pad deposits from a rotor without resurfacing it?

[rt.collins]

Originally Posted by Dominik

Somebody who knew once, said about brake shudder:

"In more than 40 years of professional racing, including the Shelby/Ford GT 40s – one of the most intense brake development program in history I have never seen a warped brake disc.
To induce that kind of permanent deformation, you would need to heat your rotors to a sustained temperature of over 738 degC then rapidly quench them in order to convert the thermoelastic instability generated hot spots to martensite instead of the ferritc/pearlitic matrix you started with.

Your basic brake pads will begin fading around 350 degC. Your high performance pads will begin fading around 550 degC. You will start to break down the surface of your rotor into cementite hard spots around 610 degC.

Your basic Dot III brake fluid will begin to boil as low as 140degC. High performance brake fluid will only take you to around 300 degC.

Bottom line - Your brakes will fade into near uselessness long before you can achieve the conditions necessary to warp your rotors.

Uneven deposition of friction material results in this thickness variation or run-out due to hot spotting that occurred at elevated temperatures."

"Somebody who knew once, said about brake shudder:"

"This person" obviously never spent time in the automotive service industry working with the general public. Warped rotors are very common and one can achieve this quite easily on your standard car - you could do it in minutes given the right situation. After years in the auto service industry and teaching with Ford, it is all too common to see people with this issue.

JHV48, I suggest contact Superformance, let them know what car you have; ask them to provide the details on your brakes and then either get the minimum thickness spec from them or Wilwood for resurfacing. Or buy new rotors with the information you receive about your brakes.

[cycleguy55]

Originally Posted by jhv48

So how do you get the remove pad deposits from a rotor without resurfacing it?

Find the manufacturer's pad / rotor bedding procedure and follow it - precisely. I've had success doing exactly that in the past for so-called 'warped rotors'.

[Grubby]

Warped rotor vs uneven pad deposits on the rotors is debated in the auto industry. I am not sure what the answer is.

I have measured numerous rotors for runout and thickness when pulsation was felt (50+ rotors over 30 years). My personal observations are;

1. used auto rotors are always below minimum thickness;
2. auto rotors are right at minimum when new;
3. light duty truck rotors are above minimum, but too close to minimum to bother turning when they pulsate
4. when rotors pulsate, I have noted typical runout of .003" to .005" total. That could be material build up or warped.
5. new rotors with measured runout of 0" certainly cures the issue
6. turning a rotor that is at minimum thickness to remove pad material build up would yield a rotor that is below minimum

I will continue to install new quality rotors when pulsation is felt. Good quality rotors typically have runout of 0" and can be purchased for about $50.

John

[eschaider]

Jim,

I have an original Superformance service bulletin for brakes on our cars. It will give you all the name, rank, and serial number information you need to both check and replace your rotors. The document exceeds the CC website file size maximum for PDF files of 39K.

PM me your email address, and I will email you the document. It will solve your problem.

[patrickt]

Originally Posted by jhv48

I’ve got Superformance #2932 with 36,000 miles. Front brakes are pulsing when applied. Could be either brake pad buildup or warped rotors.

Uhhh, Jim how do you know that the pulsing isn't coming from your foot and not the brakes?

[jhv48]

I talked to several brake experts and they all recommended re-bedding the existing pads if there was enough material. Since they have 36,000 miles and are 14 years old, I bought a set of EBC Redstuff pads and will install and bed. Hopefully that will remove the old pad buildup and improve braking.

[Laughing_Jakal]

While riding my Harley in Florida one day, I got the proverbial opposing traffic left turn in front of me. I got on both brakes hard....standing on the rear pedal and managed to stay upright. I avoided disaster, but pulled over and sat on the curb to settle down. When I rode the bike home I noticed that the rear brake pedal "had nothing". I pulled over and pumped that brake pedal and it got firm...thinking I had ingested air, I went home and was determined to bleed brakes.

When home, I pumped the brake pedal a few times and the pedal was as firm as it ever was. I then went to ride, and after I rode a few feet, the pedal was slack again. So I checked the reservoir (Full), then bleed the brakes...no air. I wasn't very mechanically inclined then and had no clue. I took it to the local Harley dealer and they said there was nothing wrong with the brake system....said that it was probably master cylinder had air in it. After paying their diagnostic fee, I found out that it was cheaper to buy the part than pay another service fee..

I figured I would change the master cylinder myself and got the same results with the new master cylinder.

I had the rear wheel on and off a few times, checking the caliper, (after re-aligning the rear wheel with the front using an 8' square tube aluminum extrusion per the Harley manual) I was sitting with my FIL ...an old motorcycle guy explaining the problem to him. He was also flummoxed as we had completely replaced all the fluid at this point and there were no leaks.!

While we were talking and drinking a beer, I spun the rear wheel out of frustration and I caught motion.....The rear rotor was so warped I could see the warp (Run out)....the runout was so severe on that skinny rotor that when the rotor spun with no pressure on the caliper piston, it would push the piston more than the distance it travelled when pressing the brake pedal one "throw"....when I pumped up the brake with multiple pumps, the piston would eventually cause the pads to make contact and it would temporarily unwarp the rotor.

When the brake was released and the rotor turned it would then push the pads far apart again. Which is why at a standstill I could pump up the brake and get it firm and it would then apply normally after pressure was built, but then after rolling a few feet, the pedal would go slack again.

Wheel off one more time, replaced the rotor (20 years ago it was $100).....haven't had a problem since. That rotor absorbed so much energy it warped.....it didn't owe me anything...lit saved my life and I learned a heck of a lot about motorcycle brakes.

[Dominik]

Originally Posted by rt.collins

"Somebody who knew once, said about brake shudder:"

"This person" obviously never spent time in the automotive service industry working with the general public. Warped rotors are very common and one can achieve this quite easily on your standard car - you could do it in minutes given the right situation. After years in the auto service industry and teaching with Ford, it is all too common to see people with this issue.

JHV48, I suggest contact Superformance, let them know what car you have; ask them to provide the details on your brakes and then either get the minimum thickness spec from them or Wilwood for resurfacing. Or buy new rotors with the information you receive about your brakes.

lol, hilarious - ask at Ford if they heard about Carroll Smith and the GT40 program ;-)

In another thread about brakes I referred to Mac Tilton. Nobody wanted to hear about that either and asked instead who the man is. Well, go-ogle it. He is basically a “nobody” in the brake industry.

"warped" disk means: deposits of pad/friction material.
Take a flapper disk and sand it off (but you didn't hear that from me).

Or, like the service industry prefers, buy a new disk - from Superformance :-)

In the EU we also advise to replace disk. It's more cost effective. Labour is expensive.

I worked in service readiness, too. I would have to check my own manuals, but we may not even list a disk minimum thickness anymore. Replace disks and pads when pads are worn and get on with life.