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pads are new front rotors are new.....had other dealership do full manual bleed of everything including master cylinder etc etc..........I am convinced going back to semi metallic stock pads and see now that system is bled correctly what I have got. Can tell you this these carbo tech etc brakes are much different that the stock semi metallic yes I know compound differences on t0ack may be great I would rather deal with dust and sharper stopping brakes normal driving!
pads are new front rotors are new.....had other dealership do full manual bleed of everything including master cylinder etc etc..........I am convinced going back to semi metallic stock pads and see now that system is bled correctly what I have got. Can tell you this these carbo tech etc brakes are much different that the stock semi metallic yes I know compound differences on t0ack may be great I would rather deal with dust and sharper stopping brakes normal driving!
Thanks for info
David
So still crappy pedal feel after second dealer bled brakes? That would suggest first dealer did things correctly. I would agree, swap pads to stock pads if you can and see the difference. I was running Carbotech XP12 and XP10 for the track and pedal didn't feel different although needed to get heat into the brakes for them to work well. Still had a firm pedal.
Ken,, would love to hear in painful detail your best practices on bleeding brakes. Please. I have new calipers and lines that need to be installed and remain confused between gravity, pressure or the old tried and true two-man method. Note that I only have my wife for the two-person method. I love her but don't want to go there if possible LOL. Any insight would be greatly appreciated.
This is not the easiest thing to describe in a post.
I have 8 bleeder bottles. They have magnets. I have all the bleeders cracked/ready.
It will flow at 14.7 psi. Just slowly.
The good news with pressure - don't matter how many bleeders you have open - they all see 14.7 psi. (Less in Colorado - sorry...)
Let them run - and KEEP THE MC FULL.
(Which of course is a pain on the C8 because of whatever that stupid baffle on the MC is supposed to accomplish)
That flushes all four calipers.
Then I close three - and do the 2-man unfortunately 8 times. I could probably omit that but it's measure three times and cut once. "Pump it up,2,3, hold, (crack and close bleeder), Release!"
I am not going to out the dealer because I don't know for sure they didn't actually install the Motul 660, and I also don't know for sure that the reservoir filler neck wasn't aready damaged from BGA. The scratches are small, but enough to prevent the standard cap from sealing and pressure bleeding.
Here's a pic, and also a pic of the tesla cap that I got that works (and just barely fits).
The damage to top of filler neck made a gouge and displaced some plastic (arrows). I am thinking to carefully cut away the uplifted plastic with a razor, or maybe just heat up a blade and try to smooth it out again next time I try pressure bleeding. There is still a channel there though for air/fluid to escape.
That dealer needs to fix your car.
The cap at least partly seals from moisture.
I was pushing the C8 really hard at the time brakes failed. Newbs will brake too soon and hold the brakes too long which actually heats them up more.
I do not think physics agree with that.
The first order conditions, consider power. If you are decelerating more - that costs more power. More power = more heat.
And in selling brakes for 19 years you can likely guess who wears out more brakes and it is not the slower drivers.
I do not think physics agree with that.
The first order conditions, consider power. If you are decelerating more - that costs more power. More power = more heat.
And in selling brakes for 19 years you can likely guess who wears out more brakes and it is not the slower drivers.
Well, since you brought up Physics I actually went to college for dual degree in physics/electrical engineering.
Edit: I think BLUF I am not talking about braking more, I am talking about making braking duration LESS, but when you need to brake, you need to get to the max speed safe for going into a turn in the shortest amount of time possible so you can get off the brakes and allow them to start cooling. So I am not talking about "decelerating more".
If you are on the brakes longer (during a single application of the brakes - aka riding the brakes), then you are on the accelerator less often and the only way to get better lap times is to increase your average speed around the track. So that said, you want to favor the gas pedal in a "related rates" problem.
Also the pad material takes heat with it and the heat is generated at the contact surface of the pad and rotor. The longer you are generating that heat, the longer it has to soak or transfer into the caliper through the pads vs having the caliper open and air carrying that heat away in the opposite direction.
Take a frying pan, put it on a burner at max heat. Put your hand on the frying pan, now a minute later take the frying pan off the heat. Your hand will be fine.
Now put the frying pan on a medium burner, put your hand on the pan and leave it on the burner for twice the duration. Be sure to have plenty of aloe vera handy!
This is due to the physical properties of materials known as thermal conductivity (K). (copper being one of the best materials at conducting heat, aluminum one of the best radiators of heat, etc. this is why some passive heat sinks will use a copper interface material with the heat source to draw the thermal energy away from the part you are protecting and then use aluminum to radiate that heat into the atmosphere.) The K value for the pads (Kp) is generally less than the Kd of the disc (Kp < Kd), so the brake disc is taking more heat away so if you shorten the braking time you are also increasing the time where the brakes are cooling and the rotor is more likely to take the lions share of the thermal energy converted from all the kinetic energy you had to get rid of. The biggest concern there is the rotor getting so hot it undergoes thermal distortion or coning, but at least your fluid isn't boiling... haha!
Last edited by dohabandit; Feb 13, 2024 at 02:43 PM.
I am a mechanical engineer, I've worked with brakes for 20 years, and I consult with a tenured physics professor at NC State. Let's put the resume contest to rest and continue to offer real world explanations and solutions to interested parties.
Braking harder from XX to xx creates more heat. You can use a power equation, you can use an energy equation or you can use a momentum equation. They all go to the same place. If you brake harder you create more heat. And heat is the enemy.
I can't even understand why you would disagree with that. The conductivity of the rotors vs pads would have to differ by magnitudes to affect first order energy calculations.
C8 Z51's on track eat front pads and thus the fluid - if not prepared - can fail.
C7 Z51's are even worse. The pads are a bit bigger so they don't fail as quickly but the fluid can boil
C6 Z51 - that's archaic ****. You bring spare everything and expect to change something.
I am an engineering director for the last 20 years, but not in the area of mechanical engineering. I am not saying that if you have more kinetic energy braking in a shorter distance ("harder") will generate less heat, we aren't going to violate the first law of thermodynamics.
It necessarily will generate more heat, but over a shorter duration of time with a higher flash temperature at the pad/disc interface and the thermal conductivity of materials involved favors the heat transfer to the disc material. It's difficult to generalize due to the complexity of the system, heat transfer, conduction, and dissipation, repeated braking cycles, heat soaking of the disc, etc.
The issue with the heat transfer from the pad material into the calipers (usually made from aluminum to help radiate that heat and reduce un-sprung weight in high performance applicaions) and brake fluid was related to me by a professional driver / instructor.
It seemed logical to me at the time. Maybe the one thing we can agree on is it is a complex topic and it's important to have good working brakes? 8)
I am an engineering director for the last 20 years, but not in the area of mechanical engineering. I am not saying that if you have more kinetic energy braking in a shorter distance ("harder") will generate less heat, we aren't going to violate the first law of thermodynamics.
It necessarily will generate more heat, but over a shorter duration of time with a higher flash temperature at the pad/disc interface and the thermal conductivity of materials involved favors the heat transfer to the disc material. It's difficult to generalize due to the complexity of the system, heat transfer, conduction, and dissipation, repeated braking cycles, heat soaking of the disc, etc.
The issue with the heat transfer from the pad material into the calipers (usually made from aluminum to help radiate that heat and reduce un-sprung weight in high performance applicaions) and brake fluid was related to me by a professional driver / instructor.
It seemed logical to me at the time. Maybe the one thing we can agree on is it is a complex topic and it's important to have good working brakes? 8)
Well when I go in the room with the physics guy I often leave with more questions than I started with.
For a Z51 - I know that car is underbraked in the front - and pretty badly. Does not mean you can't track it - just means you should have fresh racing fluid, proper race pads, and running the pads down is going to be sketchy.
Some things that are done as needed - Ti shims to slow the transfer from pad to AL pistons. Castellated pistons to shrink the path for heat transfer, Piston materials that transfer heat much more slowly (stainless steel and Ti) and even ceramic piston 'tops' (which sucked for BMW's and P-cars - they didn't last)
