For track day use with the much higher horsepower my Corvette now has over stock (481 HP versus 205 stock), improved braking was essential. Fortunately, C5 Corvette (1997 to 2004) front brakes are an easy swap.
The original 1984 Corvette front rotors are 11.5" in diameter (0.78" thick - 20mm), C5 front rotors are 12.8"1 in diameter (1.26" thick - 32mm), and weigh ~18.7 pounds each (versus ~13 for the original rotors). C5 Corvette brake rotors are directional; the vanes are designed to pump air through the rotors more efficiently to help cool them. This means there is a right rotor and a left rotor, and they must go on the correct side to cool properly.
The pads (in red hatching in the illustration above) in the C5 calipers are much larger than in the 1984 Corvette pads (shown in blue hatching), and this should mean they will wear less in hard use.
The larger calipers/rotors will not fit under the stock 1984 16" wheels. Later model 17" 5-spoke ZR-1 Corvette reproduction wheels (aka. "A-molds") were installed at the same time as the brakes.
The wheels are attached with ARP 100-7708 wheel studs. These are 8740 chrome moly (190,000 psi), heat-treated and cadmium-plated. They are 2.5" long (12mm x 1.5 thread). The stock studs are 1.65" long. The extra length of the ARP studs allows a safety margin for a nut backing off, as well as a quick visual reference that a nut is not loose (my wheel nuts are open-ended).
C5 calipers are dual piston aluminum floating calipers, the originals were single piston aluminum floating calipers. The twin pistons apply a more even pressure to the back of the pads, resulting in more of the pad doing effective braking work. The calipers are made by PBR Brakes. These calipers are pressure cast which makes them stronger than gravity cast calipers. (Apparently Corvette C6 standard calipers [not Z06] are dimensionally equivalent to C5 calipers and are interchangeable.)
The C5 Corvette calipers use the same brake line fitting as the C4 Corvette calipers (10mm x 1.0 banjo bolt), and for this conversion new stainless braided brake lines were installed in all positions (front and rear). The slightly longer lines go on the rear.
Doug Rippie sells stainless steel pistons for these calipers, the original pistons are made of aluminum. The steel pistons transfer heat more slowly from the pad to the brake fluid, decreasing brake fade: dougrippie.com/?p=425
To make this conversion you will need steel adapter brackets that bolt to the stock spindle, and have mounting holes for the new calipers:
The adapter bracket bolts to the steel caliper bracket (which holds the caliper), as well as to the spindle:
You can see the adapter bracket in the picture above, it is the bluish plate between the spindle and caliper abutment bracket. Below is a better look at it:
And here it is assembled on the upright:
These adapters do a number of things:
These can be supplied by a number of sources (try Google or eBay). These brackets are typically supplied with bolts and washers, I drilled all of the bolts for safety wire use.
Note that there are different brackets for 1984 Corvette versus 1985-1987 Corvette - the caliper bracket to spindle bolt size was increased from 12mm to 14mm in 1985, and the bracket needs to reflect this. (There was a recall [NHTSA: 83V064000] regarding 1984 Corvette caliper bolts loosening due to the factory applied teflon anti-corrosion coating. In 1985 the bolts were made larger and the teflon was eliminated.)
The larger 14mm bolts that attach the adapter bracket to the caliper bracket are torqued to 125 ft·lbs, while the 12mm bolts attaching the adapter bracket to the spindle are torqued to 70 ft·lbs. Safety wire and red Loctite is used on all bolts.
The dual 40mm pistons in C5 calipers increase the front brake pad pressure by 9.74% (= 2513mm2/2290mm2) over a stock single 54mm piston caliper due to their larger overall area. This pushes the brake bias to the front by a commensurate amount. In addition, the larger rotor provides a longer torque arm, and this applies a 11.3% larger brake force (= 12.8"/11.5") at the tire for a given pad pressure, so the total braking force increase at the front is 22.14%. Below is a calculator, with my before/after values as defaults, so you can see how changes affect the braking:
To restore the brake bias, there are a few options: there is the simple shorter, stiffer Doug Rippie brake bias spring #10-101, and the more complicated, but much more adjustable Wilwood 260-8419 proportioning valve. Even more complicated is a balance bar setup with dual master cylinders.
Don't forget that changes to the hydraulic brake force (but not the rotor torque arm length changes) affect the volume required from the master cylinder (and hence its diameter) as well as the pedal force required. In the C4 to C5 swap, the 9.7% volume change in the caliper flow requirement is small enough to use the stock master cylinder without volume issues (though the brake bias still needs to be attended to).
In addition to the bracket, these are the parts required parts for the C5 front brake conversion:
|1||12530682||172-2219||C5 right front caliper|
|1||12530683||172-2220||C5 left front caliper|
|1||10445856||177-853||C5 right front rotor|
|1||10445857||177-852||C5 left front rotor|
|2||10333772||176-1008||C5 front brake hose|
|2||22163795||---||10mm x 1.0 Banjo bolt|
|4||10139097||---||Banjo bolt washers|
Here are some optional part numbers:
|2||88895128||172-2263||Z06 right front caliper (red)|
|2||88895129||172-2264||Z06 left front caliper (red)|
|4||12530697||179-2009||C5-Body caliper guide pin|
|4||12530703||179-2008||C5-Body guide pin boot|
For the C5 calipers on the front and the original calipers in the rear, I used a set of 4 SB1010S speed bleeders (similar units are also available as Earl's P/N 280040ERL). These are 10mm x 1.0 thread, and have a 32mm overall length.
This conversion will require C5 brake pads on the front, obviously. There are a number of good pads out there. For combined street/track use, I typically choose between:
Hawk rates these pads as follows:
Pegasus Auto Racing Supplies is a good supplier for any of these: www.pegasusautoracing.com
For the rear pads, I generally use C4 Hawk HP+ pads regardless of the front pads specification: HB112-HPPLUS-.540, these less aggressive pads help ensure that the bias won't shift to the rear if the brakes get very hot.
My 1984 Corvette cam with a 0.800" tandem master cylinder and a 3.5:1 pedal ratio. Later C4 Corvettes had master cylinders with larger bores:
Stock C4 Corvettes had a 3.5:1 pedal ratio until 1992, then it went to 4.0:1 (with the 0.930 master cylinder). All C4 Corvettes have vacuum assist power brakes.
The later models specify line pressure at 1160 psi front and 680 psi rear with 100 pounds pedal pressure. However, the C5 brakes increase the front braking force by 22.14% (see above), so the corrected balance should be close to 1160/1.2214 = 949 front and 680 rear.
Here is a calculator to see the effects of changes in the braking system (the defaults are stock 1984 Corvette values):
A master cylinder change isn't strictly required for the C5 brake upgrade. However, for my car, my goals with the master cylinder choice were to:
One choice for a mater cylinder upgrade is a Wilwood 260-9439 aluminum tandem master cylinder. These sell for ~$200 on eBay or at Summit. These master cylinders have a 7/8" (0.875") bore, giving ~20% extra volume for the larger C5 calipers (the master cylinder has a 1.1" stroke). This master cylinder has a rebuild kit available under part number 260-9606 (~$40).
I moved the pushrod hole up 1.25" on the brake pedal (to a 5.3:1 pedal ratio) by drilling a new 3/8" hole to match a 3/8-24UNF rod end.
Then I fabricated a ½" aluminum adapter plate to plug the firewall hole and mount the master cylinder using the 3.375" square booster mounting pattern. The aluminum adapter plate located the master cylinder (on 3.375" spaced mounting holes) higher by 1.25" than the brake booster input rod had been positioned to keep the push rod geometry correct. Note that the upper bolts must not protrude through the adapter, or they will interfere with the master cylinder. The firewall had to be modified a bit to ensure clearance for the pushrod. Here is a draft layout for the adapter (dimensions not verified!):
Combined with the 19% larger master cylinder bore area and 22% increased brake torque from the C5 front brakes, this 5.3:1 pedal ratio results in a slightly higher (7.5%) brake force at the pedal as before the brake, booster and master cylinder modifications for any given stop (neglecting the effect of more aggressive pads, which would further reduce the difference).
The original master cylinder had 10x1.0mm threads with ISO bubble flares for the two front fittings, and one 12x1.0mm fitting with an ISO bubble flare for the rear fitting. The Wilwood master cylinder comes with several adapter fittings to adapt the 1/2UNF master cylinder ports to various brake lines. There is:
The Wilwood proportioning valve (Wilwood 260-8419) has two 1/8"NPT ports, and is supplied with two 1/8"NPT to 3/8-24 internal flare fittings (Wilwood 220-0628).
Other adapters are available from www.fittingsandadapters.com, such as the 1/4" tube with 7/16-24 to 1/8" NPT (2200x4 @ $1.11 each), and the matching 7/16-24 nut for 1/4" tube (2105x4 @ 47¢ each).
One short 'custom' brake line was made up to go from the master cylinder to the proportioning valve. It is 1/4" in diameter and has a 1/2-20 inverted flare nut on the M/C end and a 7/16-24 inverted flare nut on the proportioning valve end.
The three original brake lines on the car must be cut, SAE nuts slipped on (2 @ 3/8-24 for the front brakes, 1 @ 7/16-24 for the rear brakes), and then the lines must be re-flared to a standard SAE 45° inverted flare. The metric brake lines are slightly smaller than their SAE equivalents. If the flaring tool slips, wrapping a piece of sandpaper once or twice around the tube may provide better grip.
The master cylinder comes with a pushrod that has a 3/8-24 UNF thread (3½" long). A female 3/8" rod end was used to attach the pushrod to the new 3/8" hole in the brake pedal. The rod end was adjusted to make sure the pushrod was perpendicular to the line between the pedal pivot and the pushrod hole when the brake were firmly applied.
Dual Master Cylinders
An alternative to a single tandem master cylinder is a dual master cylinder and balance bar set-up. These use two master cylinders mounted side-by-side, with and adjustable balance bar to distribute the brake force from the pedal to both cylinders.
In my case, a swing brake pedal assembly with a 7:1 pedal ratio with two 0.750" bore master cylinders works well. The pedal effort is increased by a negligible ~2.8% (neglecting the increased coefficient of friction of more aggressive pads). A 58.2% front bias achieves the correct front/rear pressure ratio with these master cylinders. To see the full results, set 'dual master cylinders w/ balance bar' in the calculator above.
The balance bar works by moving a pivot point (in the form of a spherical bearing) between two threaded rod joint ends (that is, the portion of the rod end that the 3/8-24 balance bar passes through is threaded). The rod ends are also pinned (you can see the roll pin on the rod joint below, the roll pin axis is in blue), so they can't turn within the housing (shown in red) once the master cylinder pushrods are attached (the rods ends are like nuts on the bar - the balance bar moves through them when it is turned but the distance between the rod ends stays the same). The rod end can still swivel (shown in green) around the pin's axis (blue dashed line), and rotate on the threads, of course.
The housing of the rod end is threaded for the standard (for these master cylinders) 5/16-24UNF pushrods and locknuts.
The rod ends themselves can't move from side to side when the balance bar is turned, because the large washers prevent them for moving into the bore from either side (and their spacing is setup to match the master cylinder spacing). Thus, turning the balance bar forces the spherical bearing to move laterally, since the bearing is locked to the rod with two nuts. Moving the bearing increases the portion of the pedal force applied to the master cylinder it has moved towards, and reduces the force on the master cylinder it has moved away from. The total force is the same, it it just shared between the master cylinders differently.
This setup allows the required mechanical front bias on on the balance bar of ~58.2%, giving room for adjustment either way, as the balance bar can be adjusted by ~¾" (=18 turns with a 3/8-24UNF thread, or 9 turns either way from the centered position) for bias range from 65%F/35%R to 35%F/65%R.
The balance bar is typically set to less than the 58.2% front bias calculated above, because the car has:
The balance bar moves bias about 1.7% for every full turn (i.e. adds 1.7% to one end and removes 1.7% from the other end). Here is a calculator to compute the bias introduced by turning the adjuster on the balance bar:
I used a Wilwood 340-4990 remote brake bias adjuster cable so that these adjustments can be made from the driver's seat. The adjuster has detents for each ¼ turn of the knob (which turns the cable and threaded rod the same amount).
A 0.875" bore master cylinder for the rear brakes also works well with a 0.750" bore front master cylinder, and creates a balance bar position of that is very nearly centered (50.6%, which is 0.35 of a turn on the balance bar) while also reducing pedal travel, but at the expense of a 18.4% increase in pedal effort over the stock setup (and requires one more spare/rebuild kit for repairs at the race track, if needed).
These popular racing master cylinders have two vertical 0.40" flange mounting holes on 2.25" centers. They are available from Girling, Tilton, Afco, Howe, Coleman, and Wilwood, among others. They typically cost around $40 to $60 each.
I went with Tilton 73 Series master cylinders.
The master cylinders have a single 1/8"NPT port per cylinder, so a tee for the front brakes and some NPT/inverted flare adapters and nuts are required.
The existing brake pedal support has to be extensively modified to work with the dual master cylinder pedal. A number of modifications to the firewall will be required. A bracket for the stop light switch will also have to be fabricated, or a hydraulic brake switch can be used as shown in the diagram. The brake light switch is available as:
Note that with a dual master cylinder, a proportioning valve is not needed, as the bias is set with the master cylinder bore sizes, and can be adjusted using the balance bar.
One thing to keep in mind when doing a C5 brake upgrade is that the mini-spare may not fit over the larger brakes. This means if you have a flat on the front, you may have to put the spare on the rear and move the full-sized wheel from the rear to the front.
2 Early C4s with 11.5" rotors use a single 54mm piston caliper. Later C4s with 12" rotors use a dual 38mm pistons caliper. C4s with 13" rotors use dual 38mm calipers.