GR Yaris Failing brakes/stiff pedal/track driving/timeattack

[Gunsmoke Motorsport]

I have a GR Yaris 2021 with BCB upgraded brake calipper pistons, brake booster and larger master cylinder.
Turbosystems hybrid turbo, Kelford Cams/valve springs, 408hp
Rev limiter at 7600rpm.
Car has 6000km on the odo.

When I was competing at the last timeattack competition at Mantorp Park I had a suddenly stiff brake pedal at the end of the long strait (top of 5th gear, 220km/h)
This hapened 3 times under about 40 laps in total, everytime at the same place, after the long strait.

The last time I went of the track.
I brake at the 100m sign so no time for error or stiff pedal/ the feeling of "no brakes"

Seems like a loss of vacuum, but I don't know why... maybe the vacuum pump cant deliver enough vacuum at those circumstanses? failing check valve?
The vacuum pump shows no signs of overheating, it looks like new.

Any ideas?

Br, André, Sweden

 

[Sekred]

Never heard of that problem before.
As you mention, stiff pedal could indicate loss of vacuum.
Non-OEM brake components complicates the issue.
I would vacuum test the system, meaning hoses, check valve and booster.
Does it hold vacuum overnight?
Vacuum also operates the waste gate actuator, so no vacuum, no boost.
Let us know how you go.

 

[Michael Knight]

Do you have steel lines + fresh pads? Worn pads can cumulate heat to fluids. But as you described maybe its vacuum related.