braking issue

[camaro427-69]

hey folks

i already changed front and rear brakes. my original setup was disc front and drum back. front has the ssbc quick change 43mm kit and the back has the standard brake kit. i haven´t done any changes in the lines or master cylinder just swapped brakes. the only thing i changed was a vacuum pump connected to a can cause my bbc doesn´t make any vacuum. my problem is that the brakes don´t feel good at all and like i have no assistance. i have to push the pedal really hard to slow the car down. first i thought that the proportioning valve or the valve in the drum brake line is keeping the rears from helping to brake so i´ve put it on my mechanics brake test stand. you should have seen my face when the brakes made better numbers than brand new cars and were perfect balanced front and back. but brake stands and streets are two worlds. could another power booster solve that problem? what´s the difference between the 7" and 9" boosters? i would appreciate more space between valve covers and booster cause i have to use 2 cover gaskets to fit my roller rockers but tall covers won´t fit.

thanks,
pat

[Apogee]

My opinion is that the factory 1-1/8" bore master cylinder is too large for the new, smaller piston area front calipers (~4.5 square inches) versus the factory OE calipers with 2-15/16 pistons and 6.78 square inches of area. The SSBC calipers have the same size pistons as the 98-02 LS1 F-body applications. Those cars use a 1" bore MC and dual 9" diaphragm vacuum booster from the factory...not to mention typically make plenty of vacuum to function properly. A dual 8" booster gives close to the same boost as a single 11" booster and the dual 9" booster gives aproximately 30% more boost than each of those.

What vacuum levels do you get at your booster? Some electric vacuum pumps don't do a very good job supplying the necessary vacuum or volume required.

Tobin
KORE3

[camaro427-69]

thanks for your opinion tobin. i´m getting around 12" on engine and 18" on pump. but i don´t know if my gauge is that good but it´s a different number. the only difference i can tell is that without pump just with vacuum can i can barely brake. also like you said i´m feeling that when i brake first time i have way more assistance than after couple times in a row. is it a good idea to hook a vacuum can on if using a pump? probably i should hook the pump testdriving it.
hmmmmmmmm so did i swap something bigger stock to smaller aftermarket :hammer:. so where´s the improvement on that? looks like i did some "looks shiny i need it" buying.........

[Apogee]

Smaller, higher piston count calipers tend to give better support to the pads and better feedback to the driver, but the brake torque is strictly a function of the caliper piston area, rotor diameter, and pad coefficient of friction. In your case, that means less brake torque for a given system pressure...hence the need to reduce the bore size on the MC to compensate for the smaller piston calipers by increasing the system pressure.

Considering the tires tend to be the limiting factor with respect to brake torque, better modulation should yield more controlled threshold braking which is what stops a car quickest, not brake torque.

18" of vacuum on the pump should be more than adequate for any vacuum booster I can think of, although the fact that you say the performance deteriorates with use would seem to indicate that your pump may not be able to generate the volume required for aggressive driving. I know they make accumulators...but it just seems like putting a band-aid on top of a band-aid to me at times. If it gets the job done though, so be it.

Tobin
KORE3

[camaro427-69]

so right on the point what´s the best way to go? my setup now is clear and i´m not happy with it. should i try the 9" booster with master cylinder and proportioning valve or should i dump all the **** in my car to swap to a full big brake kit. i just want good brakes who work all day and don´t start to sweat if i take a couple fast laps on a round course. it should stay in some kind of a budget cause i need to put the same amount in euros onto what i payed in dollars (shipping and taxes to get stuff to europe are insane).

[Apogee]

You could swap your 11" single-diaphragm booster for a dual 9" and you should see about a 30% increase in boost. That said, it will also require more volume of vacuum than your current booster which is already marginal from the sounds of things.

When you've got vacuum issues and you want a brake system that will work all day and inspire confidence, manual brakes are usually the best solution IMHO. They're simple, relatively inexpensive, and work the same regardless of whether you've got an engine running in the thing or not. If you'd rather stick with power brakes, hydroboost is the easiest solution that doesn't require vacuum, but it does require power steering.

Most big-brake kits will give you more rotor mass to work with, so for a dedicated track car that gets flogged on a regular basis, it's hard to have too much rotor. As you know though, they don't come cheap...especially when you factor in shipping them to the kangaroo's winter wonderland.

Tobin
KORE3