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I can tell you I upgraded my front brakes to the brakes of the GS. The increased stopping power is noticeable, but it's not like night and day.

If you are looking to upgrade with a low cost, the GS brakes are very nice and I haven't experienced any warping or petal vibration.
 

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It was noticeable because you went from the regular 12" rotors and small calipers to the J55 13" rotors and calipers.

All 13" corvette brakes are the exact same as the GS brakes, the only difference is the corvette logo.
 

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I was told the GS bracket is a beefier design as compared to the standard 13" caliper bracket.
 

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BubbleHead said:
I was told the GS bracket is a beefier design as compared to the standard 13" caliper bracket.
I was wondering if anyone had a documented brake comparison... like a road and track article on the 1995 braking distance... compared to the 1996.

:confused:
 

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zelement said:
It was noticeable because you went from the regular 12" rotors and small calipers to the J55 13" rotors and calipers.

I know, that's why I went with the 13" GS brakes and ditched the 12" stockers. I wanted more stopping power.:)
 

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I bolted on the 13" GS brakes onto my 85, using the DRM adaptors. WOW!!! what a difference. Everyone told me the extra weight would make me lose a tenth, but it was worth it.
 

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Patrick96LT4 said:
I was wondering if anyone had a documented brake comparison... like a road and track article on the 1995 braking distance... compared to the 1996.

:confused:
In 1995 Chevrolet included RPO J55 "Heavy Duty Brake Package" on all models. Previously it had only been available with RPO Z07 and RPO Z51. Source: Corvette Black Book 1953-2002 pp 102. The brakes on the 1996 GS were RPO J55 with black-painted calipers and Silver "Corvette" lettering. Source: Corvette Black Book 1953-2002 pp 105.

Road tests which include braking data are all over the map in terms of braking distance since each tester has different reflexes, the sufrace conditions and temperature vary, and the condition of the vehicles and tires vary dramatically. This is componded by the fact that some rags (er, sorry, magazines) test from 60mph, while at least one tests from 70mph. I have seen a high of 121 feet from 60mph to a low of 104 feet from 60mph.

Believe it or not, braking distance in cars today is more a function of the grip of the tires, the amount of brake bias, the amount of weight transfer, and not a function of the brakes themselves.

Practically every car produced today has disk brakes capable of easily locking up all four wheels because the tires are, beyond a certain limit, unable to handle the decelerative forces and will begin to slide. Sliding friction is not as high as rolling friction so a sliding tire produces less decelerative force than a rolling one. That is a secondary reason for having an ABS system.

The primary purpose of ABS (contrary to popular belief) is to permit the tire to brake (threshold-braking) while turning. Braking introduces one set of forces into the tire, while turning introduces a second set of forces. The tire can usually handle both up to the limit of adhesion, at which point the tire stops rotating. ABS senses the reduced rotational speed of a tire/wheel in this situation and reduces the brake pressure to that caliper by allowing brake fluid to bypass the caliper and return to the master cylinder. This reduces the decelerative force on the tire to the point where it will continue to roll while still dealing with the turning force induced by the steering.

Braking on the street or drag-strip is much different than braking in autocrossing or road racing. In these environments the problem is not so much braking ability as it is brake fade.

Brake fade is caused by several different things all initially caused by heat. The brakes slow the tires, the tires stop the car. The brakes convert the kinetic energy of motion into heat energy. That heat must be disappated, and in autocrossing or road racing it must be disappated quickly.

The primary cause of brake fade in a stock vehicle is boiling brake fluid. The brake pads generate friction when they squeeze the rotor. The rotor gets hot, the pads get hot, and that heat is transferred to the caliper. The brake fluid runs through the calipers and picks up heat. It can eventually pick up so much heat that it will boil, producing gas bubbles. Gas is compressible, hydraulic fluid is not. When the gas bubbles compress they produce a mushy-feeling brake pedal. In extreme situations the brake pedal will go all the way to the floor and the vehicle essentially has no brakes. Changing to a brake fluid with a higher boiling point will help a great deal (e.g., Motul 300 C, and it takes one and one half cans to completely flush the brake system of the old fluid).

Another cause of brake fade has to do with the pad surface. Some compounds actually melt and produce gas or liquid which acts as a lubricant between the pad and the rotor. This problem can be ameliorated or eliminated entirely by slotted or cross-drilled rotors. The slots or holes allow the gas/liquid a place to escape to so that it no longer remains between the pad and rotor. Cross-drilled rotors must have the holes chamfered to reduce (it can't be eliminated) stress cracking of the rotor around the holes.

Vented rotors have curved vanes which radiate out from the center of the rotor. Their pupose is to dissappate heat from the rotor. Some owners confuse vented rotors with cross-drilled or slotted rotors.

Getting cooling air to the braking system goes a long way towards disappating heat. The front brakes perform the overwhelming proportion of braking so they get hotter. The C5's brake cooling vents in the front help but need to be augmented for road racing. The rear brake cooling ducts on the Z06 are a nice visual addition but do little since the rear brakes (on front engine cars) do relatively little work, even in a race car. That's why all cars have a brake bias valve and a brake proportioning valve. The rear brakes actuall apply slightly before the fronts (while there is still weight over them) and pressure to the rears begins to be reduced as weight transfers to the front suspension in order to avoid rear-wheel lockup (bad car, produces oversteer on corner entry, felt as "twitchiness" at the rear).

Baer racing produces cross-drilled rotors with chamfered holes and an anodized finish to prevent rusting when they get wet (the rust gets sanded off the first time you apply the brakes but it's visually unappealing).

Many companies produce brake pads with compounds that resist melting (e.g, Porterfield Racing) made from a variety of materials including carbon-Kevlar but be aware that they generally squeal when cold and produce prodigious amounts of brake dust which is corrosive if left on the wheel too long. Caveat car-nut.

Hope this is useful to someone.

Ray
 

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Fascinating.

So, a considerable upgrade (yet simple) would to go with a better brake fluid (any specific brand?) to reduce boiling and replace the rotors with slotted or cross-drilled rotors?

Now, since my foot and tires are the majority of my stopping ability, it would make sense to hang on to the stock GS calipers? What would the expected life be on those? How do I know when they should be tossed in the trash?

The car has 33k miles, running all original brake hardware and it still stops violently when necessary (when my Escort 8500 says "Laser". )

Patrick
 

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Patrick96LT4 said:
Fascinating.

So, a considerable upgrade (yet simple) would to go with a better brake fluid (any specific brand?) to reduce boiling and replace the rotors with slotted or cross-drilled rotors?

Now, since my foot and tires are the majority of my stopping ability, it would make sense to hang on to the stock GS calipers? What would the expected life be on those? How do I know when they should be tossed in the trash?

The car has 33k miles, running all original brake hardware and it still stops violently when necessary (when my Escort 8500 says "Laser". )

Patrick
I would go with replacing the fluid first. It's cheaper and gives you the biggest bang for the buck in the Whoa! department.

Brake fluid is hydroscopic (absorbs water easily) and any water that gets into the system will boil very quickly (causing bubbles) causing fade. That's why you need to keep bottles of brake fluid tightly closed (a better solution is to not use any bottle that has been opened for more than a day). Motul 300 C is affordable and as I mentioned you will need one and a half cans. Make sure the old fluid is completely flushed out by continually bleeding the calipers until virgin fluid comes out consistently (start with the caliper furthest from the master cylinder and then move to each closer one, then do the master cylinder. You probably know this, but NEVER use Silicon-based fluids (it will eat the seals) use only D.O.T. approved fluid.

If you hire someone to perform this work watch them like a hawk watching a field mouse. If it's done sloppily it's worse than if it wasn't done at all. If you do it yourself and don't have a pressurized bleeder, get someone reliable to step on the brake pedal upon your command and hold it down until you retighten the bleed screw. Be obsessive when working with brake systems.

Slotted or cross-drilled rotors look sweet on a road car but are, for all intents and purposes, overkill unless you autocross in hot weather on long courses that have tight corners at the end of long straights. A spirited drive through the twisty roads in the Sierra Nevadas will generate enough heat that they may actually become functional, but that's an exception. However, they aren't that expensive and do look damned cool on any car, especially a C4 or C5 (because the wheels allow you to see so much of the rotor).

Cross-drilled rotors look cooler, but slotted-rotors are cheaper and have less of a problem with stress cracking around the slots. You are more likely to see production-based race cars running slotted-rotors than cross-drilled (cost and and sometimes rules). Only the cognoscenti will appreciate the subtlety.

Calipers flex under braking loads. Cheaper ones flex more. The stock Corvette calipers are more than sufficient for normal and aggressive street driving and will probably outlast the engine. They are actually incredibly good parts considering the Vette is not a limited-production prohibitively-expensive vehicle.

If the calipers become deformed you will experience a symptom very much like that produced by an out-of-true rotor, i.e., a vibration in the pedal when braking. Check the trueness of the rotors (use a dial-gauge, follow shop manual directions) and when you have the brakes serviced make sure that when/if the rotors are resurfaced (if they are so bad they need to be "cut", toss them) they are done on the car. If you go to a real brake shop they'll use a stone hone to produce a cross-hatch pattern on the rotor which aids in new pad break-in and good contact.

If you do go with aftermarket calipers your best bet are calipers from AP, Stop-Tech, or Brembo. Baer makes repalcement calipers but I have no experience with them.

My 6-speed '92 LT1 with the Z07 package had 70,000 miles on it when I unloaded it to get the Z06. It stopped like the day it was new and I autocrossed it and ran a couple of Solo I events (single car qualifying on a road course like Willow Springs or Buttonwillow). The main thing I did was to replace the fluid. I also installed braided stainless steel hoses (the stock rubber ones will, with heat and age, start to bulge when they fill with higher pressure fluid causing what feels like heat-related brake fade). Be careful however because different manufactureres make them in varying lengths. If they are too short or too long they chaff the wheel sensor lines and will cause a code to be set indicating a wheel sensor failure which disables the ABS (on the front and rear) and the traction control (on the rear).

My '92 LT1 generated 1.5Gs under braking, measured with an in-car accelerometer, on a consistant basis. That was good since my cornering style has charitably been described as "Obsessive Kamikaze" in terms of late braking. Remember, slow in, fast out. Get most of the braking done in a straight line, then trail-brake through to the apex, and smoothly bury the pedal as you unwind the wheel.

If you replace disk pads do not follow the loony-tune advice of some who tell you to take the car up to 100mph and slam on the brakes to "bed" the pads. All you will do is warp the rotors and/or warp the pad back-plates. Drive for about 100 miles on the street braking normally. Do not attempt aggressive braking until the pads have had a chance to make friends with the rotors.

When selecting a pad, keep in mind that life is full of compromises. Do not install racing pads if you aren't going to the road race course because they will not work well at all when the brakes are cold (and I'm talking Southern California cold here, not Flin-Flon, Manitoba cold) they will not grip the rotors very well and the car will actually require a longer distance to stop. They also squeal like you wouldn't believe (some produce an ear-splitting screech when cold), and produce so much dust that the wheels will be almost completely black after about 20 miles of around town driving. They are made of highly ablative material and will wear faster than most people can afford. The good news is that, incredibly, racing pads, or street-track pads, don't cost any more than stock pads from the Chevy dealer.

I learned most of this stuff the hard way, so they are lessons well learned. I thought I'd post this information so that other Corvette owners can get 3-wire stops without the cha-ching.

Ray
 

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Excellent Information

Thanks for the great information Ray. I've read a lot of information lately on the slotted and cross drilled rotors and have decided to just stay with my stock setup. The only thing I am going to change that you made mention of are the brake lines. This summer I am upgrading my brake lines to the braided flex lines and will do the flush and fill with the brake fluid you mentioned. Thanks for the information.
 

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Re: Excellent Information

GS487 said:
This summer I am upgrading my brake lines to the braided flex lines and will do the flush and fill with the brake fluid you mentioned. Thanks for the information.
Motul 300 C gets its name from the fact that it has a boiling point of 300 degrees centigrade (572 degrees Fahrenheit). It is 100% synthethic fluid and is D.O.T. approved.

One thing to be aware of is that when you start this you may notice that the level of fluid in the master cylinder is lower than the fill-to line. If the pads are about 50% worn (or more) this is normal. As the pads wear the pistons must push them further to make contact with the rotor (in essence this is "self-adjusting"). When this occurs more fluid leaves the master cylinder causing the level to appear low. While you should keep plenty of fluid in the master cylinder while bleeding (to avoid sucking air into the system if the level gets too low) you may want to note the original level and make sure that when you are finished bleeding the level is about the same.

The reason for this is that if you choose to replace the pads at some point, you will use a spreader to push the pistons back into the caliper bores (don't be tempted to use a screw driver). If the master cylinder is full when you do this it will overflow. If you replace pads at the same time as the brake fluid then you should fill the master cylinder to the fill-line.

You can buy a small hose (with a spring wrapped around the outside so it will hold a bend) that fits over the bleed screw. Put the other end in a clean plastic cup half-filled with clean brake fluid. Keep that end below the level of the fluid in the cup. As you bleed you will get a visual indication when air bubbles stop coming out. Also, if the pedal gets relaxed while the bleed screw is open, fluid will get sucked back into the caliper and not air.

The '96 GS is a nice autocross car. Best of luck with it.

Ray
 

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Pressurized Bleeders

Ray,
You mentioned pressurized bleeders. What about the vacuum bleeders? I've used these on the older non-ABS systems and they worked great but have no experience on a car with the ABS. Does this do anything to the ABS system? I know the vacuum mechanicsm when attached to the bleeder will get all the air out and will draw fresh fluid in the older systems to the caliper or the wheel cylinder. Now I've heard and read some things about the ABS systems and the porportioning valves when you pressure bleed but haven't gotten too far into it. I guess it is time to break out the shop manual and read it while it is still cold out and figure out the best way the old general wants to bleed the brakes.
What type pads are you running on your Z06? The previous owner had just put some new ones on mine, don't really care for them too much. He gave me the stock ones with the car and I might just switch back when I do the hoses and fluid this summer.

Leo
 

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Re: Pressurized Bleeders

GS487 said:
Does this do anything to the ABS system?
Leo
I do not recall any warnings in the shop manual with respect to using any type of "one-man-bleeder" and the ABS. And I always followed the shop manual guidelines (I'm an engineer not not a mechanic) to the letter and they recommend using a one-man-bleeder.

Given the number of times I flushed the brake system over the years on three ABS-equipeed C4s I would think that if there was a potential for damaging the system we would not be communicating now. :laughing:

I haven't autocrossed the Z06 so I had no incentive to change brake pads. The best policy to follow is use whatever pads are easiest on the rotors. An aggressive pad compound will literally destroy a set of rotors in a suprisingly short amount of time. Pads that are advertised as producing less brake dust are suspect since they need to be harder (and therefore less rotor-friendly) than the stock pads which are a necessary compromise with respect to a variety of variables (pad wear, noise, heat, and cost).

Keep in mind that on the street, in an ugly situation, you really only need to make one violent, short-distance stop. You are not repeatedly, sometimes within seconds, thresehold-breaking as you would on a road-racing course. Therefore issues such as brake temperature and pad composition are irrelevent.

Ray
 

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Re: Re: How much faster does a 1996 Grand Sport stop versus...

-=Jeff=- said:
Won't be much if anything.. all 96 vettes had the 13 inch rotors and calipers.
Only the Gran Sport and the Collectors edition had the upgraded brakes.

RanMan:D
 

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Re: Re: Re: Re: How much faster does a 1996 Grand Sport stop versus...

-=Jeff=- said:
Starting in 1995 ALL Corvettes had 13" brakes,

Although, the GS and CE had the Corvette logo
Okay, maybe they were all 13", but the GS and the CE came with more than just the logo. Chevy calls it the "J55" heavy duty upgrade.:nuts:

RanMan:smokin:
 

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Re: Re: Re: Re: Re: How much faster does a 1996 Grand Sport stop versus...

RanMan said:
Okay, maybe they were all 13", but the GS and the CE came with more than just the logo. Chevy calls it the "J55" heavy duty upgrade.:nuts:

RanMan:smokin:
J55 was the same on ALL cars with 13"

in 89 the 13" upgrade was an option.. the RPO.. J55

Only difference is the Logo and color
 
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