0Todd TCE

Good discussion...many folks don't understand how the work so it's not uncommon.

Changing the master won't have any impact in this case; there's only one doing the work thus total pressure is more or less to each end of the car. To achieve the goal you'd need two of them, a common F/R twin set up for this very reason.

Yes changing the rear caliper can make a difference but not by the caliper itself but the piston area. Larger bores; more clamping smaller less. But before one does all this it's a good idea to have a blueprint of what the car has now and evaluate the proposed changes too. There's always a side effect of these changes- again because you have only one mc to work from. Making smaller changes is more ideal so not to effect the other end of the car.

For the most part the rotor OD change is usually the most effective way- it increases or decreases the lever arm of the caliper and doesn't upset the hydraulic balance. (unless you go to stupid changes where you'd have more rotor size making a huge swing in bias) The nice thing is that you pick up more rotor mass for better heat management.

BTW a Prop valve should never be installed in the front system for somewhat obvious reasons....at least not a street car. Maybe a rail dragster or such.

Churchkey

Good info in post 42.

Some brake data I compiled when contemplating a brake upgrade for tracking the vette.

90 Vette = 7/8 master cylinder (91 Vette is listed as having the same size master cylinder bore).

7/8 master cylinder sq in area = .60

Front caliper bore = 1 & 1/2

Front caliper combined area (4 pistons) = 7.07 sq in.

Hydraulic ratio front = 11.78



Rear caliper bore = 1.591

Stock Rear caliper combined area (2 pistons) = 3.976

Hydraulic ratio rear = 6.627


-------------------------------------



C5 front caliper bore 40.5 mm = 1.62 diameter.

Front caliper combined area = 8.245 sq in.

hydraulic ratio front with 7/8 bore master cylinder = 13.74


When the hydraulic ratio is increased numerically more clamping force is applied by the caliper.

Suggest balancing the system with C5 rear calipers.

If rear wheel lockup occurs before front wheel lockup an adjustable prop valve can be used in the rear
hydraulic line. I use a Wilwood, one turn out from fully seated = a 5% reduction in pressure to the calipers.

Have contemplated (speculation) a Wilwood mechanical E brake caliper. They have shims between the caliper halves which would make them adjustable for rotor thickness. A fabricated mount bracket would be required.

Ricky 91 vette

Here i am as i promised before that i would be back with the results and pics of my rear brake upgrade, i did a week ago, and to be honest i'm glad that i decided that because my brakes improved a lot, i'm noticing the brake pedal is softer now or with other words i dont need to step at the brakes as hard as before to stop the car, the brakes feels just perfect and less nose diving and less dust on the front wheels, which means my pads will last for longer time and my rims will stay clean for longer time too!!!

Ricky 91 vette

and here are some pics of the adapters i for the rear c5 brake upgrade made by dale, he sent them to me with no time with all the hardware needed for the installation

Ricky 91 vette

see how i needed to use a counter sink to make the flat head bolt disappear from the surface to provide the needed clearance with the abtumant bracket

Ricky 91 vette

here is a pic with the abtumant bracket installed on the adapter notice the clearance with the flat head bolt

Ricky 91 vette

here is a pic with the rotor and the caliper installed too, the only problim was that the adapter mounts the caliper lower than the stock brakes, so my ss brake lines became short for them, and as u see i had to jack the suspention end to be able to mount everything , i havent changed the brake lines to longer ones yet, they r working fine but in case i need to lift the car i will have to do it from the suspention end, so longer brake lines are in my to do list

Ricky 91 vette

i painted to rotors with brake caliper paint from autozone, so it look bettter and doesnt rust on the area that the pads dont reach, and with the black rims and red calipers it came out really nice



and here how it was before

Ricky 91 vette

so i did the same to the front ones too

Ricky 91 vette

and i took off the e brake wires from there roots and they were 3 pieces, i had to remove the driver seat to be able to do that, i'm thinking of instaling the electronic e brake switch that a member here mentioned

Kubs

I put those brackets on my car also. I have not driven with them yet though. Are you using the Z51 size calipers or the base model? Do you have the C5 12.9" front rotor or did you upgrade to the 13.4" Z51 rotor?

I have some brake calculations that I cannot get to cause Im on my phone at the moment. Basically it shows what you (and myself) experience. The C5 front brakes put too much bias in the front even with a DRM spring. I was also locking up the front with stock C4 rears and DRM spring.

Putting the 13" C6 Z51 rears on will put waaay to much in the rear. Especially with the smaller C5 rotors in the front. If it feels good to you now and you are happy thats what matters.

Ricky 91 vette

and as a bonus and during the bleeding procces after the installation, i had the engine running ( with the abs service light on as usual) i was moving the main rellay harness around to fit my rinch down there to bleed the abs unit when i notice the abs light turnning off while moving the harness!! so i tapped the relay and it turn off again, tapped it again and the light turns off again!!! so it was bad relay the whole time!!!! and that perfectly explains why the abs light was turnnig off some times when i was hitting some bumps!!!! i took the really off the conecter and examined its clips where it conects to the harness and examined the harness too and they both looked like new, after that everytime i would start the car and the abs light would stay on, i would just need to tap the relay once or twice to make it work again!! so i searched around next day for a new relay, but its discontinued everywhere! during the search i dropped the relay on the floor couple times and when i gave up on finding a new one that would fit without modifying the conecter, i put it back on the car, but since then its been working perfectly for 10 days now!!! i guess dropping it on the floor cleaned the carbon that was gathered on its switch and got it to work agin for a while...... but i''m really happey that i found the reason of my 4 years old abs problem !!!!

Ricky 91 vette

finally somebody agrees with me, the front c5 upgrade is great but its not enough with stock rear even with drm spring!!! u will need to upgrade the rear too if u wanna get the most of your upgrade which is better stopping distance!!!
i'm using the z51 rotor with c5 caliper and c5 abtumant bracket for the rear, and on the front i have the c5 caliper and abtumant bracket and c5 rotor, and i didnt need to remove the DRM bias spring becasue its just feels perfect now!!!! by the way the wheels are c6 zo6 style repleca 9.5 x 18 with 56 offset which is the stock offset for the late c4 cars so i had no problem with clearance at all!!! with my previous c5 zo6 style repleca chrome rims i had which u can see in my profile pic, the tire shops were having problems balancing them because even the thinest weights they used were not clearing the front calipers, so i sold them and bought those 18'' rims, tires are 275x35x18

Ricky 91 vette

i think if i would change the front abtumant brackets to the z51 ones and use the z51 13.4 rotors i would start having more bias on front than how much my car needs, as i said like now its just perfect!!! by the way Kubs ,, did u have to change ur rear brake lines hoses? mine are too short now and if i lift the car from the side or from the frame i may break them....

Sidney004

It's an elegant solution to the bias problem but I'll take the cheapscape's approach and get higher friction pads in the rear next time.

Ricky 91 vette

and i'm sure it will be cheaper to change the pads, it may improve the rear brakes a bit, mine even though i didnt have to buy the calipers because i bought them as a set 3 years ago with the front ones, but now i paid $160 for the adapters + $140 for the rotors + $60 for the pads plus $10 for caliper paint,and i still need to buy longer ss brake lines so around $400 total, it may sounds a lot but its much cheaper than the going to a body shop to fix the car after i reck it because of not good enough brakes, now and after running some braking tests i can drive with confedence

Kubs

Ok here are some of the calculations I have done. I do not know how the internal bias of the master cylinder is on a stock car, but these are purely the mechanical bias numbers. I believe the DRM spring would be the closest to these numbers.

Setup Bias F/R
Stock J55 front 12" stock rear 64.7/35.3
C5 front stock rear 66.3/33.7
C6 Z51 Rotors front and rear, larger Base rear caliper 60.7/39.3
C5 front with our combination rear 59.4/40.6

The balance felt best on my car with the stock J55 stock rear and DRM spring. My new setup includes the same rear you have (13" Z51 rotors and base C5 calipers) but my fronts are 14" C6 Z06 rotors and 4 piston Brembo Viper calipers. The bias for this setup is 63.3/36.7 close to stock with slightly more rear. I also have a Camaro MC with no internal bias adjustment like the C4 MC.

Edit: I also want to add that all these calculations are assuming the same pad compound front to rear. I will be using less aggresive pads on the rear, but pad manufacturers dont give out the friction coefficient of their pads so it is easier to just assume the same. My C5 front stock rear setup felt better with the same pad all around but still not the best.

Kubs

I have also done some simplified calculations that show front lockup vs rear based on vehicle weight, cg location, brake bias, etc. The C5 front upgrade locks up way before the rear. My new setup they should lockup almost at the same time with the rear locking slightly before the rear.

Kubs

Yes i installed custom hoses. I will give you a list of the part numbers i used when I can look them up. I will also snap a few pics this weekend.


Edit: Here are the part numbers:

These go in each caliper
http://www.summitracing.com/parts/RUS-641431/

These go on the hardline on the car
http://www.summitracing.com/parts/EAR-989534ERL/

These are the hoses I used
http://www.summitracing.com/parts/EAR-63010116ERL/

I chose hoses with straight fittings because I wasnt sure how close to the wheel the hose would get with 90 or 45 degree. You can try a different end. I route the hose in between the trailing arms, up to the fitting on the car.

All the fittings and hoses for all four corners cost less than a pre-made "kit" for a C4, and I can change hose length easily if I change brake setups in the future.

Ricky 91 vette

with my current setup the front are still locking up slightley before the rear, even though i kept the DRM bias spring in the master sylender!! but the stock rears never locked up while the new setup does....