Power Bleeding Brakes PDF Print E-mail
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.

Peter Szymczak

Bugeye Drum Brakes

I noticed one day a small amount of fluid on shed floor. On investigation, using the reliable taste test I discovered brake fluid. Further investigation revealed a back wheel cylinder was gone. Gone to God !

Speaking to John Whitburn, who had just done up his brakes, and me being somewhat afraid of touching brakes, John suggested we both get together and do the job ourselves. John joined our Club about 18 months ago, and is very keen to solve problems related to Sprites.  So I ordered the parts from the Bug-Eye Barn and Tony Bennetto explained the wheel cylinder will fit after some filing down. Yeah right !

So John arrives one morning, we quickly remove the wheel cylinder, unpacked the new one and attempted to fit it. Well yes, after plenty of careful filing we get it in, and  re-connect every thing, then attempt to bleed the brakes. Well no amount of bleeding would do anything but a soft spongy pedal. We called it a day and went off to think. I then pulled all the drums off, and found a few surprises. One front brake was working, one not, the other rear, very suspect. I decided to ring Tony Bennetto and order wheel cylinders all round. They duly arrived and we fitted them, but still a soft pedal.

dsc08126.jpgWhat could it be that was  not allowing us to bleed up a full pedal. Rang Tony again, he suggested new hose lines and two brand new front drums as they were measuring far too big. During the fitting of the passenger side front wheel cylinder we pinched the steel brake hose running across the front of the car, so new one was ordered.

John made a few light modifications while David went inside to phone in some new parts…..

So now we had a lot of fitting to do. Putting on the 3 rubber hoses was simple, and tried bleeding again but to no avail. Now the tricky job of fitting the steel brake line across the front cross member. Out came the radiator. Tony had bent the line up to match an original line, but mine had been fitted in a slightly different position, so some minor bending was needed. We needed a pipe bender, but had to be very small as Sprite brake lines are  very small.

John being very inventive came up with a tiny pipe bender made from split copper pipe and other bits and pieces. It worked beautifully. We were able to bend the pipes in situ , which was great. It was then time to bleed the brakes. John came up with another invention to easily bleed the brakes. What it consists of is a garden sprayer with pressure gauge and a spare master cylinder cap fitted to a couple of metres of clear plastic hose.

We filled the master cylinder with brake fluid, then slowly filled the sprayer with brake fluid making sure we did create any air bubbles. Then we slowly pumped the fluid up the tube the attached it to the master cylinder. After that we pumped in about 10PSI and wheel by wheel we did the bleed. Then we fitted the new drums and had to sand paper a bit off the linings to allow the drums to fit. The radiator was re-fitted, re-filled with the new Penrite Coolant that does not contain glycol.

dsc_4647.jpgNow it was time for a test drive around the block. Brakes got a bit hot, and pedal was the same as it had been for many years. Then a longer drive after more sanding of the linings, and suddenly a big strong short travel brake pedal was felt. Finally our goal was reached.

The players in this saga – David and John.

Of course as any Sprite owner knows I await the next problem, which had already arrived. That’s another story for another day.

David Low