Frequently Asked Questions
Ask the Corvette Specialists!
Q: I bled the brakes on my C2 / C3 Corvette but I still have a soft pedal. What went wrong?
A: There are several possibilities in this situation. The first thing to check is that you are bleeding the calipers from all bleeders. There are two bleeders on each of the rear calipers that often get missed; missing either of these will allow air to remain in the system.
As you are bleeding, tap the caliper with a rubber mallet to coax the air bubbles out of their hiding spots. The best way to do this is to use one of our Motive Power Bleeders, which allows one-person bleeding where you can control the pressure in the system.
If you are using silicone brake fluid, make sure you treat it gently. Shaking, pouring quickly, or “slopping” the fluid into the master cylinder reservoir can result in tiny air bubbles in the fluid that are very difficult to remove afterwards.
Q: I want to use silicone brake fluid in my brake system. Will it mix with my old fluid?
A: NO. Silicone (DOT5) fluid is not compatible with DOT3, DOT4, or DOT5.1 glycol based brake fluids. The two mixed together will form a gel and could cause rubber brake seals to swell and fail.
The best time to install silicone brake fluid is when you are doing major brake work such as installing one of our Super Brake Kits, which replaces all four calipers, master cylinder, and rubber hoses.
We recommend silicone brake fluid for Corvettes that may not get driven very often, as it does not absorb water the way glycol fluids do. It also has a higher dry boiling point and is good for light track use.
Additionally, modern cars with ABS brake systems cannot use DOT5 silicone brake fluid. The quick cycling of the brake system will cause silicone brake fluid to aerate, introducing lots of tiny air bubbles.
To learn more, read our article on Converting to Silicone Brake Fluid.
Q: What is rotor runout and how do I fix it?
A: Rotor runout was the bane of the 1965-1982 Corvette brake system. It is caused when the rotor face is no longer parallel to the plane of wheel revolution, causing a “wobble” inside the caliper. This can be caused by rotor warp, bearing play, or a spindle that is no longer true. Runout can cause reverse oscillation in the four piston lip seal calipers, which causes the pistons to act as air pumps, bringing air into the brake system and causing low/soft pedal or complete brake failure.
Runout can be combated a few different ways. One way is to shim the rotors. There are rotor shims available on the market from various vendors. Another way to eliminate runout is to have the rotor machined on the car. High end shops and dealerships will have on-car brake lathes that can machine the rotor while it is still on the vehicle, eliminating any high spots.
One way to deal with the reverse oscillation problem without addressing the rotor runout issue is to install O-ring seal calipers. This caliper has a different style seal than what was originally installed on these cars and is not susceptible to reverse oscillation.
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