Robiwan

Sometimes you really don't want what you wish for. Finally got my day at a road course and fried my brakes within 2 laps. Course had two long "straights" with tight turns at the ends, and I cooked them puppys. I installed SS brake lines, the bias brake spring, cryo slotted rotors, stock pads and Valvoline synthetic brake fluid before I went, and still burned them up. I have bleeded them twice and with the engine off, the brake pedal is rock solid after depressing about 1". Turn on the engine and down the pedal goes and sponginess is quite apparent. Do I need to turn the rotors, replace the pads or could there be something with the brake boost?? Appreciate any help.
Thanks, Robi

Jim 47

Robiwan:

I hope that "synthetic" Vaovoline brake fluid is DOT-3 or DOT-4 and NOT the silicone fulid. GM recommends DOT-3 fluid. If you mistakenly put silicone fluid in your brake system, then it needs to be completely flushed out and replaced with DOT-3 or DOT-4 fluid.

Secondly, your brakes should NEVER have given you trouble after only 2 laps even with factory pads, unless you were riding the brakes most of the way around the track. I assume you were not.

This leaves a mechanical problem with the booster. I don't think it is air in the line or you would feel a mushy peddle with the engine not running. If this condition continues, then take it back to the dealer for diagnosis and repair. Good luck :lol:

SweetSavannah

IMO your problem can be traced to one or more of the following areas with the most likely culprit listed first & the least likely listed last.

1. Brake pads - It is highly probable the stock pads aren't up to the task, that the heat they absorb alters their coefficient of friction leading to a 'spongy' pedal after a few turns. You need to upgrade to PF 90s (if you can still find a set), 97s, Hawk Blues or something else.

2. The rotors, even after slotting & cryo treating, aren't up to the task. Sounds like you did these things to the stock rotors and, as the old saying goes, you can't make chicken salad out of chicken poopie, or, if you prefer the more genteel, you can't make a silk purse out of a sow's ear.

3. There's still air trapped somewhere in the lines even after bleeding. Ergo, bleed 'em yet again using either a pressure or vacuum procedure.

4. The Valvoline syn fluid isn't up to the task. Not likely, but an outside shot after other changes have failed. As I recall the 2 highest dry ot wet boiling point fluids were Castrol SRF (?) and Motul 600 in that order.

5. The whole braking system is inadequate. You'll get lots of varying opinions on this, but that was my conclusion after chasing problems for 18 months. Solution was to go to Mov'it's Porsche/Brembo '993T 'Big Red' adaptation. Like the movie of the same name, problems were 'Gone In Sixty Seconds'!

Should you eventually pursue this last course, I think the 4 best systems on the market are:

a. System from Dave Dilusi (www.dilusi.com ???)
b. BAer/Alcon system from DRM (www.dougrippie.com)
c. system from Lou Gigliotti (www.lgmotorsports.com ??)
d. Porsch/Brembo 'Big Red' system from Mov'it (www.movit.com) distributed by The Ulimate Garage (www.ultimategarage.com)

Good luck! Bad brakes give you nightmares.

Godspeed

Robi,

How did you replace the stock fluid with the Valvoline? You didn't completely drain out all the fluid first did you?

Here is what I would do to get your brakes up to par with the minimum out of pocket expense.

New Parts

1. Order a set of Speedbleeders. They are very cheap, make bleeding much easier, and take the guess work out of bleeding
2. Order 2 500ml bottles of Motul 600 fluid. It 's DOT 3/4 compliant and for the price you can not beat it.

Install & Bleed

1. Replace the stock bleeder valves with the Speedbleeders
2. Take the cap off the master cylinder
3. Attach a hose and catch can to the valive, open the bleeder, and pump until there are no more bubbles.
4. Bleed brakes in this order - RR, RL, FR, FL
5. Monitor master cylinder and fill with the Motul 600 as needed - don't let it get empty.
6. After two full passes you should have flushed all the fluid and there will be no air left in the lines.

When you have more cash

1. Order some Hawk pads
2. Order some Eradispeed rotors


Hope you get the brakes working. :)

-Jeremy

Evil-Twin

do you know the difference between Fade and spongy??? is the pedal going to the floor ???a spongy pedal usually means fluid brakedown or air...
if you have fade.,.. you step on the pedal and it doesnt stop the car as quickly as it use too.. but the pedal does not feel spongy...using synthetic brake fluid is not a good thing... it absorbs moisture.... you should never keep an opened bottle of brake fluid... you need something in the 550 to 560 degree wet boiling point.. if you absorbed mositure and your fluid reaches 500 degrees , you can imagine what that will do to the moisture in the fluid...synthetic fluid is ok for a Garage queen.. the fluid is much more paint friendly... if you happen to get a bit on your 10,000 paint job..

Gary2KC5

I don't trust my brakes and I've done all the above with the GM system (see sig) I've bleed 2 liters of Motul through the system and had the dealer bleed the ABS unit with the tech 2. And they don't seem right...haven't been able to test yet, though.

When you say "the whold brake system" what componets are you talking about replacing...just the calipers and rotors right?

SweetSavannah

Whole system = rotors, calipers, pads, SS lines, fluid.

You've already done the fluid & SS lines.

Some might suggest the master cylinder and adding air ducts, but I found I needed neither.

vette-crazy

I don't know about this problem. However, after seeing the difference that my AP Racing adj master cylinder has made on my clutch I am thinking about doing the same thing for my brakes. I believe that Mel has this on his car and shows pics at this site...www.tradezone.com/vette. My car had spongy brakes before my upgrade to Baers.

corvette dave

Robi,
I have seen this problem many times.
The pads on these cars will taper with track use. This means the pads wear unevenly and do not mate with the rotor and the pedal will feel spongy, although a different spongy than air in the lines.
Get a new set of track pads or a known set of good pads and try them.
I get the same spongy feeling with my track pads, then when I put the stock pads on voila! Pedal is back.

Someone posted that synthetic fluid is bad. It is not! I have used it for years.
Silicone fluid is bad. Do not use it. The two get confused often.

Robiwan

Thanks to everybody's responses!!! Lots of good info out there. I know its hard to believe that it only took two laps to get brake fad, but its true. The vette is a heavy car and slowing it down from 100 to 40 twice a lap, burns up a lot of energy. Just to clear up some questions:
1- The synthetic brake fluid is NOT silicone, it is Dot 3/4 and higher boiling point than standard (500F dry)
2- Not riding brakes or have the parking brake on.
3- I thought I had flushed the entire brake system as I could see the new clean brake fluid coming out of every caliper. It took almost 2 quarts to do it.

Maybe an upgrade to new brakes would be good, but since I don't race or get to a track that often, don't know if the cash out is worth it. I will try upgraded pads and see what happens.
Thanks again to everybody!
Robi

SweetSavannah

Corvette Dave makes an excellent point. Most systems, stock or aftermarket, taper the pads which will lead to a spongy pedal.

I can't speak to the other systems I listed, but the Porsche/Brembos from Mov'it generate no pad taper in either direction. I've run pads down to the last 16th of an inch - unintentionally - and there's still an even amount of material left both east & west as well as north & south. This has the side benefit of being less expensive since you get to use virtually all of the pad rather than only 2/3 of it. On a prior aftermarket system, I've had pads which had almost half the thickness on one side and were down to the backing plate on the other.

My last comment is that I don't understand why so many people want to 'economize' on braking components when that middle pedal is so much more important than the others. To paraphrase a current TV commercial:

Rotors: $200
Pads: $100
Peace of Mind: Priceless!

MY 2002 Z06

Here is my 2 cents. I track my Z06 about once per month. I use Castrol SRF (>500 F WET boiling) and Performance Friction Pads. (I don't care too much for them so I am going to Hawk next). I use a set of speed bleeders and bleed my brakes after each weekend. It takes maybe an hours to do all four corners.

My pedal also loses some feel toward the end of the weekend. Front brake cooling is a shortcoming in Corvettes. If you rig up some sort of home make duct, it will help prevent the soft pedal. Of course, as others suggest, brake upgrades (rotors, caliper etc) will provide better performance. Upgrade as funds allow or as needed.


[Modified by TorchZ06, 4:37 PM 11/17/2001]