|Power Bleeding Brakes
|Note: brake repair should only be carried out by people with a good understanding of brake systems and only to the highest levels at your own risk especially in the case of single circuit braking systems as in Sprites.
Just the other day I had great difficultly bleeding the air from the brake lines on my Mk111 after replacing the rear hydraulic flexible line. I started with a “one man brake bleeder kit” only to find it’s just a bottle with a magnet on it and some clear hose, a poor investment of $20.00. After a number of attempts with the “one man bleeder” and a spongy pedal I decided to go back to the old two man method. There were some minor improvements but still the spongy pedal remained. (I’ve never had so much trouble in the past with any other car I owned!) I then tried using the close bleed nipple when the helper releases the pedal and open the nipple as the pedal is depressed method with no improvement and half a bottle of brake fluid later. Could there be something else causing the problem and not air in the lines, although all new hydraulic lines, a rebuilt master cylinder, and rebuilt callipers had been fitted? After discussing the problem with a friend who has owned and worked on a number of English cars he advised a method which he saw a mechanic use which entailed the use of compressed air to pressurize the entire brake system through the cap of the master cylinder which he called ‘power bleeding’. I decided to give bleeding one last go using the power bleed method. SUCCESS! The pedal is rock hard with little travel.
This is how it’s done.
First find a cap which fits the reservor on the master cylinder. I used the top from a Metho bottle with the child safe fitting removed.
Drill a hole just a bit smaller than your compressed air fitting, retaining the seal and punch a hole through it.
Using plumbing tape to reduce some of the air loss and screw the air fitting into the cap.
Fill your reservoir with brake fluid and fit the cap with the air fitting.
Apply regulated pressure started at 10 psi and open the bleed nipple on the wheel cylinder furthest from the master cylinder (passenger rear). Use a piece of clear tube and a jar if you don’t want fluid all over your garage floor.
Increased in 10 psi steps until the fluid flows well, I ending up at 50 psi where I found the fluid flowing in a constant flow where I saw the bubbles finally make their way out.
Close the nipple, refill the reservoir and continue to the other rear wheel making your way around the car remembering to refill the reservoir after every wheel as a lot of fluid flows from the system finally to the wheel closest to the master cylinder.
|Bugeye Drum Brakes