Let’s diagnose a hard brake pedal

[honeybadger]

Searched for this topic after a track day at Road Atlanta last week. I have driven this track 3 other times and it never happened before. However, last week I experienced it several times on the back “straight” heading into turn 10. Can confirm that each time I was at WOT and then transitioned quickly to the brakes. Went away when I lifted and then reapplied the brakes.

I don’t have a fix to offer, but everything that was said about it being a vacuum issue makes sense.

I've seen this as overcooling the brakes a bit. What pads are you on? Try having an exponential ramp up on the brake pedal pressure - so have half second with a tiny bit of pressure before you begin pressing hard. If that fixes the issue, you're likely overcooling the brakes on the long straight.

Sponsored

 

[Tonymustang302]

Ive been experiencing this after i did major upgrades (cage, fire supression etc etc) and have been working with kevin and steve. So far the solution has been the 1/2 second light pressure applied followed by harder pedal.

one thing i did do was the throttle body changed it to solar. Imma try going back to stock and test

 

[G8rbcn]

I've seen this as overcooling the brakes a bit. What pads are you on? Try having an exponential ramp up on the brake pedal pressure - so have half second with a tiny bit of pressure before you begin pressing hard. If that fixes the issue, you're likely overcooling the brakes on the long straight.

I am currently running Carbotechs XP10 and XP12 with Motul DOT4 BF. This is the first time I’ve run RA with this combo.

 

[honeybadger]

I am currently running Carbotechs XP10 and XP12 with Motul DOT4 BF. This is the first time I’ve run RA with this combo.

FWIW, I talked to a few folks that have had ice pedal/hard brake pedal using the Raybestos ST pads. It seemed those pad had some issues with pad deposits/glazing causing issues.

Could be some type of conditions that cause similar issues with the carbotechs. Try dragging that brake a tiny bit and see what happens. You can also pull the pads out and see if they’re glazed at all.

 

[bnightstar]

FWIW, I talked to a few folks that have had ice pedal/hard brake pedal using the Raybestos ST pads. It seemed those pad had some issues with pad deposits/glazing causing issues.

Could be some type of conditions that cause similar issues with the carbotechs. Try dragging that brake a tiny bit and see what happens. You can also pull the pads out and see if they’re glazed at all.

Did you eventually figured what was causing it for you and fixed it ?

My car started doing the same the last few track days first 2-3 brake zones is fine but the last brake zone hard pedal but the car stops. I was thinking brake pads glazing so moved from R10 to R12 but still after a few hard laps the R12 are doing it as well. Though now they skeak a lot so I guess I glazed them.

I wonder if it's a sign of brake booster going wrong as I often have spongy pedal as well or is it just overheating because of the AR-1 tires and a lot of hard braking without cooling on my local track.

Would love to find a solution.

 

[honeybadger]

Did you eventually figured what was causing it for you and fixed it ?

My car started doing the same the last few track days first 2-3 brake zones is fine but the last brake zone hard pedal but the car stops. I was thinking brake pads glazing so moved from R10 to R12 but still after a few hard laps the R12 are doing it as well. Though now they skeak a lot so I guess I glazed them.

I wonder if it's a sign of brake booster going wrong as I often have spongy pedal as well or is it just overheating because of the AR-1 tires and a lot of hard braking without cooling on my local track.

Would love to find a solution.

My specific issue was cam lockouts resulting in too little vacuum generated by the engine for the capacity held in the booster. Adding a canister fixed it for me - but you shouldn't have to do that.

If you're still having issues, I still lean towards a pad/rotor issue. What does the surface of your rotor/pad look like?

A bad booster is pretty easy to determine - they will wheeze and fully depress when the engine is off.

 

[bnightstar]

My specific issue was cam lockouts resulting in too little vacuum generated by the engine for the capacity held in the booster. Adding a canister fixed it for me - but you shouldn't have to do that.

If you're still having issues, I still lean towards a pad/rotor issue. What does the surface of your rotor/pad look like?

A bad booster is pretty easy to determine - they will wheeze and fully depress when the engine is off.

But your issue was vacuum. My rotors do look like they were heat checked as I have a few spots on them (brand new blanks). Obviously don't know how the pads look like. But they do sound like a train while they didn't before the track day. However when the car stays for a few days the brake pedal gets really hard but got soft when engine start. Also my pedal is mushy though it looks like my brake fluid doesn't have air in it. I'm not sure what to think but I also still lean towards pad temps considering it only does it ones every 10-12 laps or so.

 

[bnightstar]

To go back to that topic. Installed brand new Power Pack 3 and the car is doing something funny when revving the engine stationary like 2000-4000 rpm the brake pedal is moving up and then goes back down when I depress. I start to lean towers bad brake booster check valve :? I was also getting hard pedal when car is stationary for a few days even before the Power Pack 3. But when engine on the pedal does drop. That issue is going to drive me nuts not to mention it doesn't sound safe.

 

[NightmareMoon]

To go back to that topic. Installed brand new Power Pack 3 and the car is doing something funny when revving the engine stationary like 2000-4000 rpm the brake pedal is moving up and then goes back down when I depress. I start to lean towers bad brake booster check valve :? I was also getting hard pedal when car is stationary for a few days even before the Power Pack 3. But when engine on the pedal does drop. That issue is going to drive me nuts not to mention it doesn't sound safe.

If it started with the PP3 install, could be something with the plumbing on the new intake manifold.

I had my brake booster replaced a while back but that didn't fix it (although lately I haven't have the issue as often - increased my RPM limit and now I'm being a wuss and not running it to redline at the braking zone as much because I'm not used to the new limiter).

If you know where the brake booster check valve lives, I'd love to check mine (no pun intended). My mechanic thought maybe a bad check valve too. IIRC the S197s had it near the booster.

 

[bnightstar]

If it started with the PP3 install, could be something with the plumbing on the new intake manifold.

I had my brake booster replaced a while back but that didn't fix it (although lately I haven't have the issue as often - increased my RPM limit and now I'm being a wuss and not running it to redline at the braking zone as much because I'm not used to the new limiter).

If you know where the brake booster check valve lives, I'd love to check mine (no pun intended). My mechanic thought maybe a bad check valve too. IIRC the S197s had it near the booster.

Will do a better investigation tomorrow the check valve lives on the end of the brake line where it connects to the brake booster. It's a 10-25$ part. I lean towers ordering it and figuring out if it's that or not. The PP3 install seams fine I think this is just an issue that was present before that.

 

[NightmareMoon]

Will do a better investigation tomorrow the check valve lives on the end of the brake line where it connects to the brake booster. It's a 10-25$ part. I lean towers ordering it and figuring out if it's that or not. The PP3 install seams fine I think this is just an issue that was present before that.

Later, get me a picture if you can. It would help me tremendously.

 

[bnightstar]

Later, get me a picture if you can. It would help me tremendously.

Ordered a new one it's 20$ part with the rubber seal on the brake booster.

Here is a photo of how that shit looks like.

P.S. I was thinking of ordering it prior to the PP3 install so I'm officially an idiot 2 weeks wait. Track season is here though.

 

[Nfs1000f]

First thing I would’ve done is checked with Mrs. Brake Pedal to help out.
Sorry.

Sponsored