How did the factory fill brake systems?

[Verle R.]

How did the factory fill and bleed the brake systems in our old Corvettes?

How do they do it now?

Thank you,

Verle

[Michael H.]

Re: How did the factory fill brake systems?

Hey Verle -

As far back as I can remember, the factory used a pressure bleed system which forced brake fluid through the master cylinder down to all the lines. Corvettes (especially disk brake models) are notorious for being difficult to bleed using the "pump the brake pedal" method. I have a tool called a Phoenix Injector that works quite well, provided you bench bleed the calipers and master cylinder. The Phoenix Injector is made by Phoenix Systems (www.phxsyss.com) and reverse bleeds the brakes by "pushing" brake fluid from the calipers back through the master cylinder. The theory behind this approach is that it is easier to "push" air bubbles up rather than try to force them down, since air rises in fluid.

However, I am going to invest in a high quality pressure bleed system since they are so fast and thorough. A Phoenix Injector is a good investment if you bleed brakes once or twice a year.

[Terry M.]

Re: How did the factory fill brake systems?

John Hinckley or Mike Hanson should be responding to this, but if I recall John's previous posts correctly. The fluid fill station first pulled a vacuum on both the brake and cooling system, and then injected the fluids.
We should wait for their comments though because I know C2- C3 the disk brake system will not hold a vacuum well. Once the vacuum pulls the pistons all the way into the bore the lip seals tend to leak and the vacuum decays rapidly.

[John H.]

Re: How did the factory fill brake systems?

Until the mid-60's, a pressure bleed with vacuum-connected tubular bleeder wrenches was used, which wasted lots of fluid and made a mess - the operation was done over a sump pit with steel grating over it. Later, the evacuate-and-fill system was implemented; an adapter was clamped to the master cylinder and a large vacuum pump pulled the system down through the compensating ports, held and checked for any decay that would indicate a gross leak, then fluid was injected at 40 psi with the system still under high vacuum - the bleeders were never touched, and no fluid was wasted; this operation was performed on the Chassis Line, well before body drop, and the master cylinder was secured to the firewall (or booster) after body drop. Essentially the same system is still used today, although with better controls; similar evacuate-and-fill systems are also used for A/C refrigerant, anti-freeze, and power steering fluid. Today's hydraulic clutch systems (master and slave cylinders and lines) are received filled and pre-bled from the supplier.