Big Block from Hell, Part 13
The rest of everything youd ever want to know about 65-82 Brake Service
by Hib Halverson
©1994, 1999 No Use Without Permission
BBfH 12 began a miniseries on 65-82 disc brake service. In lucky number 13, we are going to talk more about brakes but from a racing and street high-performance perspective more characteristic of the project car.
First thing we did was install heavy-duty front brake discs from Vette Brakes and Products (p/n 13752). They consist of a NASCAR brake disc bolted to an aluminum hub. These are heavier castings of higher quality iron that improves durability and heat dissipation. The weight penalty is negated by the T6061 aluminum hub. These brake discs were prepared for use as discussed in Pt. 1 of the brake series with the exception of one additional modification.
One cause of brake fade is gas emissions from the brake pads when they got very hot. These gases form a boundary layer between the pad and the rotor which degrades contact between the two. When this happens, braking action decreases.
Some brake pads have grooves to help vent these gases. Grooving the rotors is an even better relief method. BBfH brake work is done at Global West Chassis Components. Its Director of Engineering, Doug Norrdin, milled spiral grooves in both VB front rotors and the production, Chevrolet units we used at the rear.
Timkin wheel bearings were packed with Red Line CV-2 synthetic grease and installed into the front hubs. We use synthetic grease because it maintains lubrication under the thermal stress put on the brakes during aggressive driving. If you pass on synthetic, at minimum, pack the bearings with a grease intended for use with disc brakes.
The front brake discs were then installed in the normal manner. BBfH 12 described correct wheel bearing adjustment. For performance street driving or racing, we cant emphasize enough the importance of proper adjustment.
From 1966-1975, Chevrolet offered "special, heavy duty brakes" intended for Corvettes used in competition. They were a stand-alone option (J56) in 66 and 67 and later were generally part of "special purpose" or "off road" option packages L88, ZL1, ZO7, ZR1 or ZR2. J56 included specific brake calipers fitted with insulated pistons, special brake pads, front caliper mounting reinforcements and an adjustable brake proportioning valve.
Most HD brake items are long gone from the Chevy parts book, but the front pistons (p/n 5463823) are still available. Since the front brakes work hardest, heat transfer to the brake fluid is greatest there. The thermal insulators on these pistons outer ends resist heat transfer, so we ordered a set and sent them to Vette Brakes and Products for installation into the front calipers installed on the car for Pt.12 of the series.
We had a set of the old, J56 front caliper bracket supports, so we had Global West install them. Stock caliper mounting brackets may flex under hard braking which degrades pedal feel and causes uneven pad wear. The bracket supports prevent that.
We mentioned in Pt. 12 that street drivers, occasional canyon racers and autocrossers can use stock or ordinary semi-metallic brake pads. However, if you regularly run hard on the street or do any racing, we suggest a brake pad designed for high-performance or racing use.
On the Big-Block from Hell, we installed "soft" racing brake pads from Porterfield Enterprises. Andy Porterfield was a two-time SCCA B/Production National Champion in a Corvette during the late-70s and currently races a Camaro in West Coast, Super Production and SCCA Trans-Am events. His company specializes in performance and competition brake pads.
The pads (p/n R4) Andy supplied are a carbon/Kevlar formulation intended for very aggressive street use and short-duration competition events. Porterfield also offers a hard racing pad (p/n R42) popular with vintage road racers. All Porterfield, 65-82 Corvette pads are available in single- and double-pin configurations. We do not recommend these pads for normal street driving as they have high effort when cold, tend to squeak and emit lots of brake dust, but boydo they work great when youre running hard!
For brake fluid, were using the Ford fluid discussed in Part 12. We do not recommend silicon brake fluid for high performance. It compresses slightly at high temperatures, so no matter how well you bleed the system; brake pedal feel is always a tiny bit soft and brake system response is not as crisp. Additionally, silicones higher viscosity makes bleeding difficult. That, with the 65-82 brake systems inherent air trapping abilities furthers bleeding problems.
For hard driving, we like stainless-steel brake hoses because they offer a slight improvement in pedal feel by eliminating the expansion of stock rubber units. We used hoses supplied by the Aeroquip Corporation. They are made of "TFE Racing Hose" which is flexible, extruded Teflon tubing covered with a braided stainless steel shell. We used a pair of 14-inch long, -04 hoses (p/n FBPA0400-14) for the front and a pair of 8-inch long -04s for the rear (p/n FBPA400-8). We also ordered four, 37°-compression-to-male-inverted-flare adapter fittings (p/n FCM2927) and four 37°-compression-to-female-inverted-flare adapters (p/n FCM2937) to fit the braided hoses to existing brake line connections on the car.
We caution the reader when selecting Aeroquip brake hoses. Their units are made to order. From 65-82, Chevrolet made several changes in brake hose routing and mounting. Before ordering, inspect your existing hoses for length, ends and mountings, then consult the Aeroquip Performance Products catalog. That way the correct hose configuration will be ordered the first time.
While braided brake hoses offer a performance increase; they can have one problem if there are sharp bends near hose fitting crimps. Flexing of the hose as a result of suspension movement and steering can cause the braid to rub against the edge of the crimp. This can cause a failure of the braid and that, in turn, will bring failure of the Teflon hose underneath. That type of failure will be catistropic and can cause loose of control of the vehicle. If you use braided brake hose: 1) choose a length and routing such that sharp bends near fittings are eliminated and 2) inspect the hoses a couple of times a year.
The standard 65-82 brakes relied on different piston diameters (1.875 in. vs. 1.375 in.) for brake pressure proportioning necessary to prevent rear wheel lockup due to weight transfer. However, with BBfH, stock brake proportioning may not be acceptable, so another racy thing we hung on the car was an adjustable, brake proportioning valve from Willwood Engineering. It will allow us to reduce rear brake pressure in relation to front pressure by turning its adjuster knob. Global West mounted the Willwood valve near the master cylinder.
For ultimate performance, the proper adjustment method is to begin with the valve open (full pressure to the rear brakes). Load the car with weight typical of the driving you will do. Go testing where its safe to perform maximum effort stops from 60-80 mph. Warm the brake pads with a couple of moderately hard stops then, do it again with maximum braking. If the rear wheels lock prematurely, give the valve a half-a-turn. Make additional, but finer adjustments in either direction until all four wheels reach the threshold of lock-up at about the same time.
That type of brake bias is appropriate for drivers who are experienced in high-speed driving and at limit handling. If that is not you; for safety reasons, we suggest adjusting for brake bias thats just a little less aggressive. Adjust the Willwood valve so the rears lock-up just slightly before the fronts.
We spent quite a bit of time in Part 12 covering rear spindle preparation. There is one additional spindle step we recommend if your engine produces 450 lbs/ft or more torque. It is especially important, if you have a manual transmission or your motorsport is drag racing. We suggest you Magnaflux the spindles. Magnaflux is nondestructive testing that finds invisible, "hairline" cracks that could be the cause of a catastrophic failure. Even new axles, such as the Chevrolet units (p/n 3872476) we installed in the Big-Block from Hell, should be "Maged". We took ours to Taylor Engine Rebuilding in Whittier California. Taylors owner, Jay Steel, specializes in race engine work and has a full Magnaflux inspection set-up. He checked our axles and they passed with flying colors.
We think larger wheel studs are an important safety upgrade for race cars. At the rear, this required enlarging the wheel stud holes in the axle flanges, a job we suggest be done on a drill press. Global West then pressed Dorman 1/2-20x1 3/4 studs (p/n 610-258) into the spindles. The front brake discs already had 1/2-inch studs installed as theyre an option for HD rotors from Vette Brakes &Products.
Another item we installed during our BBfH brake work is those snazzy, Global West trailing arms. While a rear arm change should be covered in a suspension article, during the preparation of the brake series, we had the rear axles and brakes off, so that was the time.
Global arms for 65-82 Corvettes are made from heliarc-welded, 1020, seamless, steel tube stock in short: bullet-proof construction appropriate for an M1 tank. They are stronger than the stock arms at about the same weight. Globals Doug Norrdin shaped the arm and placed the e-brake cable mounting brackets such that wider tires on wheels with larger back spacing can be used. Since the e-brake cable mounts are in a revised location, adapter sleeves are supplied to preserve the production cable geometry. The Global arms are available powder coated in a variety of colors.
The stock bearing carriers bolt right into Globals arms as do rear stabilizer bar mounts. The arms come two ways: to accept either a spherical bearing (p/n TBC-9) or a urethane bushing (p/n TBC-10). The stock arms we took off the BBfH had been modified with spherical bearings. However, experience showed they contributed greatly to ride harshness. As the trailing arm end bushing is a major noise and harshness path; we decided to downgrade this particular part of the car yep, you read it right! There is a limit to our boy racerness!
We installed urethane bushings supplied by Energy Suspension (p/n 3-3122) into Global Wests arms. Based on previous success with polyurethane, we feel the slight compliance of polyurethane compared to the spherical bearings no compliance will improve the Big-Block from Hells harsh ride at little cost to handling.
Installing new trailing arms forced a session on Global Wests alignment rack. The settings we used were: front; -3/4 camber, +3 1/2 caster and 1/16-inch toe in and rear; -3/4 camber and 1/32-inch toe in per side. These are specifications we like for aggressive driving where tire wear is not a consideration. For a car that sees a lot of street use a more conservative alignment is suggested.
The last performance-related change was new tires and wheels. Since the Big-Block from Hell has always been an exercise in conspicuous consumption; one of the big raves in Corvette wheels: the, 17-inch five-spokes (p/n 10214046, front and 10214047, rear) used on the 94 and 95 ZR1s.
These units are manufactured using the "squeeze-cast" technique which makes an aluminum wheel with less porosity, higher strength and more uniform density. The outside surfaces are treated with a glossy, silver coating that is corrosion-resistant and attractive. Chevrolet did such a great job with the style and engineering of this product, its hard to understand why someone would look anywhere else but Chevrolet for a cool set of Corvette wheels.
Fitting the 94/95 ZR1 wheels to BBfH required a set of Vette Brakes & Products adapters. For several years, VB has cataloged these for customers wanting to install 84-87, 16-in. wheels on 68-82 Corvettes. On special-order basis, they also can supply adapters in most any width up to three inches, in quarter-inch increments.
We used their 2.75 in. unit (p/n 13772) in the front and their 3.0-in. unit (p/n 13773) at the rear. VB had these sizes on the shelf so quick order filling, along with three-day UPS service, had the pieces in our hands in four days. One of the reasons we like Vette Brakes and Products is their quick turn-around on orders.
A hot tip: these new wheels, in the front size (17in.x9.5in.x56mm), will bolt-on any 88-94 Corvette base Coupe or Roadster. Additionally, they can go on 84-87 cars if a set of VBs 3/4-in. adapters (p/n 13760) are used.
Hardware is included with the adapters, however, not all of it may be usable. The adapters are bolted to the brake rotors with deep-reach lug nuts and flat washers. Observe the markings on the washers as to their orientation on the lugs. Torque them to 80- ft/lbs. The ZR1 wheels do not have steel seat inserts so they must use a nut with a wide bevel to prevent damage to the aluminum. The nuts supplied did not have a wide bevel and, not wanting to screw-up our new wheels; we found the right pieces at Tucker Tire Company. Youll need a wide-beveled, acorn nut in either 7/16-in. or 1/2-in. thread.
The only tires appropriate for the Big-Block from Hells new wheels are original equipment on the ZR1: the Goodyear Eagle GS-C. We ordered up the Kings rubber in 275/40ZR17 for the front and 315/35ZR17 for the rear. Going GS-C had significant advantages for us. The first was better ride quality compared to the shaved, 255/50ZR16, S-compound VR Eagles we used before. The GS-C casing is a newer design incorporating advanced technology that reduces noise and harshness. GS-C is a much better tire in the wetand, no; were not afraid to drive our project car in the rain. Lastly, even with full tread depth and the GS-Cs pleasability-driven changes; we expect ultimate performance on dry roads very close to the shaved VR-S we ran before, but with more predictable, at-limit handlingan important difference between the GS-C of the 90s and the Eagle VR-S which is mid-80s design.
As for the optimum pressure level to run in these new tires? Scott Allman, the GM engineer who did much of the ride and handling development of Corvette tires from 89-94, once told me 30 psi is suggested for speeds up to 170 mph and 35 psi for up to, ah200. Will the BBfH go that fast? Well set the tires at 30 for now, thank you very much.
Lets talk about clearance when installing tires this large on a 68-82. The change required fender flares, which were on our car before we got it. However, the flares it has were designed to house racing tires and are really too large. As a result our adapter thickness selection was predicated on positioning the wheels so they look reasonably correct in those existing fenders.
VB offering adapters in 1/4-in. increments will allow us to eventually position the wheels as far inward as possible which will be better from a performance standpoint. Once thats done, we will have smaller flares in the rear and maybe none at all in the front. That change will come in future installments of the BBfH series.
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