hey, i race my 3rd gen in Time Attack - its a lot of fun. still having some crazy braking issues

Brake system is 12” front and 10.5” rear disk with Tilton prop valve in rear circuit. AND factory prop valve in place.
When threshold braking from 200kmh to 150kmh it was Ok, from 150 down, rear end skips and bounces.

So after much research, I remove the OEM prop valve and use just the Tilton in the rear circuit...

It got worse! Now, the back end skips and bounces as soon as I touch the brakes at high speeds as well - what happened???
In the video you can see that where I should be braking at 2 cones, I’m letting off at 3 1/2 cones and after the right hand kink, I tap the brakes and it starts a tank slapper...I had my ***** in my throat for that one lol!

Any help would be greatly appreciated!!

Matt

 

Brake hop is more often cause by suspension setup that brake bias. What the rest of the cars setup?

 

thanks for the reply;
in addition to the 1LE front brakes, it has the other 1LE parts as well...except the 12" rear brakes...KYB AGX shocks all around (currently all maxed), global west rear LCA's and track bar, Anti squat brackets, all Heim jointed, no poly bushes. front del-alum bushes, 5 deg camber, 34mm bar, wonder bar - unsure of spring rate, unsure of brake pad compound. Toyo RR's 245-45-16, 1 track day from new.

 

What are the antisquay brackets? Are the rear control arm relocation brackets? If so what hole is used?
Have you backed off the bias for the rear brakes since the last outing?

 

Looks like too much rear brake.

 

So at the last event of the season, I got the rear wing installed and changed the pads. Hoping that the wing would put some load on the rear end, increasing grip. After talking with a couple veteran F body road racers (from Firehawk series in the 90's) I put Hawk Blue pads in the front and the shittiest cheap pads in the rear in an effort to create front/rear bias with pad selection. The results were fantastic. For the first time in a couple years I could get on the brakes real hard and it was great, the back end stayed put and i dropped 2 seconds off my best lap time.

 

Very interesting.

 

It sounds like you have it solved. But how? Soft pads at the rear will fade at the higher temps you will inevitably be putting into them. Did you you try reducing rear brake with the proportioning valve? I'm interested because I may go NASA TT next year with my 88 T/A.

 

time will tell how effective the solution is. Track conditions were also a factor as the 2 corners that were my nemesis were also re-paved and my first time on the new pavement was also my first time on the new braking set up, either way, i could feel the huge difference and was still learning how to use the brakes again at the end of the day.
I had ALL the back brake dialed out and the wing was still only at 2 degrees. if the rear pads burn off at a 2:1 rate that's fine with me as they are only $22 a set, as opposed the $325 (all-in, Canadian $) i paid for the Hawk Blue's. Also, one of those guys told me he put hawk blue's on both axles and it was a huge mistake. i'm not about to re-invent the wheel, so that was sound advice coming from experience.
By the way - I just picked up the front brakes for a 2018 SS Camaro, 14" Brembo set up and i'm putting that on for next year with the 17" CTW's and 275/40/17's. so if you are interested in the 1LE front set up let me know, its now redundant to my needs.

As a side note; I tried the Tilton Brake prop valve with and without the OEM prop valve in line, and i can tell you with confidence that the OEM prop valve MUST be used with the Tilton. no exceptions.

IROC with Splitter and Wing

 

I've not experienced axle hop under light braking, but have had it under heavy braking. Your video seems to lock the rears under light braking.

I've tried a few combinations of pads with 1le fronts and 3G rears. Started with Carbotech XP10 front and XP8 rear. I've also tried the Porterfiled R4's all around.

I now have Wilwoods/C5 rotors on the front, and LT1 rears. I use Porterfields on the front, and Powerstop Evolution on the rears. A few fellow racers use the cheap parts store on the rears, but I wanted something that had a bit higher temperature range.

All that said, the biasing of the brakes is a bandaid from what I've been told. If I remember right, the cause as told to me by some former A-Sedan racers, more has to do with the torque arm binding under braking. The front of the torque arm is supposed to be able to slide forward and back as the rear suspension travels up and down. Under heavy braking with a lot of weight transfer, the torque arm doesn't slide in the factory rubber mount when the rear brakes are hard applied. The 'fix' was to put a spherical bearing for the front mount and replace the nose of the torque arm with a solid rod.

*edit* I have '10 SS Brembo's (14") on my streetcar. They are HEAVY compared to the Wilwoods.

 

Hey GMan 3MT, thanks for chiming in!
It's light pedal pressure, but high speed. In the video this happens at around190kmh (118mph) and becomes manageable down at around 100kmh or 64 mph. Another corner is a little slower (150kmh to 75kmh), but same issue.
Racers have been using pad compound to adjust braking for years so I don't really look at it that way, I look at it like tuning to the driving style and conditions, because effectively, that's exactly what i'm doing. I can make laps all day and never skip a wheel, but my driving style is to explore the limits to the best of my ability (safely) and this condition was a limit i needed to move past. The pad compound adjustment worked. Next year brings new challenges and i can't wait!

Yes, 100% you are correct, the OEM geometry is a contributing factor in this condition. Unbalanced Engineering and Detroit Speed are 2 suppliers that recognized this and developed a repair - well, a completely new rear system. This snazzy diagram shows how the instant center creates problems and how the de-coupled torque arm fixes this problem. Detroit Speed ditches the torque arm completely - and i'm not ready to do that just yet, so i've been looking into this de-coupled torque arm - however, i wont bother spending the time and resources if changing brake pads can produce the same result.
https://www.unbalancedengineering.com/Camaro/TA/

i'm looking for LT1 rears right now and plan to run those next year.

Matt

Oh, and thanks for the heads-up on the wilwood-brembo weights. i'm going to weigh the 1LE set up and the Brembo set up and see what it nets out at. hoping its not too bad. i added 5lbs for the splitter and removed 17 lbs for the SMC hood, so i'm still ahead of the game by 12 lbs lol!

 

What happened when you didn't use the factory prop valve? I'm curious because on my car I have C5 brakes on front and LS1 brakes on the rear with no factory prop valve, but a wilwood prop valve that I can adjust while driving. The wilwood possibly different than the tilton or just different brake package?