The Mustang Forum for Track & Racing Enthusiasts

Taking your Mustang to an open track/HPDE event for the first time? Do you race competitively? This forum is for you! Log in to remove most ads.

  • Welcome to the Ford Mustang forum built for owners of the Mustang GT350, BOSS 302, GT500, and all other S550, S197, SN95, Fox Body and older Mustangs set up for open track days, road racing, and/or autocross. Join our forum, interact with others, share your build, and help us strengthen this community!

S197 3V Brake Pedal Travel

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.

This is my first post with a lot of contend, so please bear with me.

2009 GTSC
ST XTA Coilovers, single adjustable (rebound) Set at 10 front and 2 back, on a scale of 0-16, 0 being full soft and 16 being full hard.
Strano front and rear swaybars, front full stiff, rear full soft.
Camber plates, set at -3, toe -.07.
JLT CAI, with 93 tune.
18x11 wheels, I in spacers in front, with 285, 200tw tires.
2012 GT performance package front brakes.
G-LOC R16 front, R8 rear.
SS brake lines.
STR 600 brake fluid.
4in brake cooling ducts.
Corner balanced.

This is not a daily driver, only time I drive it on the street is to get gas or go to a local Autox. Primary goal is SCCA T3 (That’s why the 285 tires) and Autox between track events.

I have been doing autox and track day stuff for about 5 years. Started the first year with everything stock. The next year upgraded to 14in brakes with R10 in front and 18x10 wheels with 340tw tires. All the upgrades have been added a little each year, but my primary concern has always been the brakes. They have never been consistent since I put the 14in brakes on. I am always getting brake fade and or excessive pedal travel. There are some other things I have questions on, but the brakes are number one.

I ran VIR (first time) about 6 weeks ago and lost it in turn one twice when the brakes would not grab. Checked the system for any air and all was good. Therefore, I just took it easy the rest of the weekend. Being the track was new to me, I could not determine if it was the car or me. My best time for that weekend was 2:30.4.



Last weekend went to NCCAR. I have run NCCAR 10+ times, so I am comfortable with this track. During the first session, the brake pedal travel started getting longer and longer. By the end of the day it felt like the pedal was at the floor by the time the brakes really started to grab. It stayed this way for the rest of the weekend. In the past, even with the pedal travel getting longer, with R10s in the front, I could brake at the 300 mark and make a smooth transition at turn 11 (Braking zone of 120-130 to 25-35). With the R16, I was braking at the 500 marker. I tried to brake at the 300 marker and it just did not feel right so I stuck with the 500 marker. This also creates a problem when I just want to “tap” the brakes to set the car prior to corner entry at turn 7. Feels like a long pedal travel before I get the brakes to respond.

Once the long pedal travel starts, it stays this way until everything cools off and I bleed the brakes, but I never get any air out. I have checked everything I can think of with the brakes. The brake booster checks good. No system leaks. If this is something to be expected, so be it, I will learn to work with it. Any thoughts on what I may need to do.
 

captdistraction

GrumpyRacer
1,954
1,698
Phoenix, Az
knockback (common on mustangs particularly) is when the lateral loading of the tire (and some give in a worn wheel bearing for example, or flex in the suspension assemblies or upright) results in the rotor "pushing" the pads back in, compressing the caliper pistons in. Then the resultant gap (however small) results in the pedal throw being very long (as the hydraulics need to take up that gap before you get the brake pressure intended).

Sometimes, you'll see brake traces on drivers have a double press (see the pink arrow in the below picture) to A) see if the brakes are there, and B) take up any knockback travel:
1619639209624.png

There's various ways to mechanically resolve/reduce knockback, and they include:

  1. Better spindle/upright
  2. replace a worn wheel bearing
  3. True floating rotor assemblies
  4. anti-knockback springs in the brake calipers
  5. motorsports caliper/brake systems
 

TMSBOSS

Spending my pension on car parts and track fees.
7,530
5,247
Exp. Type
HPDE
Exp. Level
10-20 Years
Illinois
Knockback is when the pads get moved away from the rotors or Knocked Back from the rotors. The extra pedal travel comes from the pistons having to move further before contact between the rotors and pads happen. It can be caused by out of round rotors, excessive build up on the rotors, loose wheel bearings and other issues.
Did you feel any pulsing while applying the brakes?
Have you considered adding titanium shims to protect the pistons from excessive heat?
 
Rotors, pads were new when i went to VIR. No pulsating noticed. I tryed pumping the brakes, it was no better. Was hoping to install the shims, but when pads were new, there wasnt enough clearance to install. Just checked wheel bearings when i installed brake pads and rotors and all were tight. I'll check wheel bearings again and try the pump the brakes in the next day or two. Thanks
 

TMSBOSS

Spending my pension on car parts and track fees.
7,530
5,247
Exp. Type
HPDE
Exp. Level
10-20 Years
Illinois
Did you have time to bed the pads before VIR?? I have had issues with this exact problem new pads, no bedding at Road America. I chased out of round and other issues, found nothing until I inspected the rotors and had a few spots which looked like hot spots but were pad material. This was on my boss, I believe they are the same brakes you are running.
 
I did not bed the brakes, i got them directly from G-loc prebedded. When i talked to G-loc, they said no bedding required, pads are race ready.
 

captdistraction

GrumpyRacer
1,954
1,698
Phoenix, Az
pre-bedded means they were burnished / thermally cycled once which is important, but bedding also means transferring a layer of the friction material into the rotor surface - that cannot be done before you have the pads and rotors in your hands.

I've had good luck with the R18 compound with just being able to bed it on a practice session - but other compounds may require more specific temperatures or cycles to accomplish a good transfer.
 
I did not bed the brakes, i got them directly from G-loc prebedded. When i talked to G-loc, they said no bedding required, pads are race ready.
Also, if it was a bedding problem, would that not have cleared up by NCCAR? I did a autox the week before NCCAR, they felt weak then, but G-loc said R16 pads will not bite good until they get hot. Autox doesn't get the brakes hot.
 

captdistraction

GrumpyRacer
1,954
1,698
Phoenix, Az
Short answer - sure*

Long answer - depends on the compound and its needs and ability to cleanly transfer.

Based on what I know of the compounds you're using, I don't think that's the answer. I think its more related to either the shims (as if fluid gets hot - and it did for me on the 4 pots when I ran those), or knockback
 
Checked brakes today, rotors check out at <.002 deflection. All pads are in contact with rotors, EXCEPT the passanger side onboard pad. It has a .007 gap between the pad and rotor, had someone press the brake to observe pad movement, pad makes contact and when brake is released, gap comes back/ returns. Assuming this could cause the excessive pedal travel ?
 

Grant 302

basic and well known psychic
Checked brakes today, rotors check out at <.002 deflection. All pads are in contact with rotors, EXCEPT the passanger side onboard pad. It has a .007 gap between the pad and rotor, had someone press the brake to observe pad movement, pad makes contact and when brake is released, gap comes back/ returns. Assuming this could cause the excessive pedal travel ?
Sounds like enough flex to create a knock back problem. Those tolerances are probably worse when hot.
 
1,246
1,243
In the V6L
Checked brakes today, rotors check out at <.002 deflection. All pads are in contact with rotors, EXCEPT the passanger side onboard pad. It has a .007 gap between the pad and rotor, had someone press the brake to observe pad movement, pad makes contact and when brake is released, gap comes back/ returns. Assuming this could cause the excessive pedal travel ?
This might indicate a stuck puck on the passenger caliper inboard side. The brake application might actually be bending the rotor to close the gap.
 

TMO Supporting Vendors

Top