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Date:         Sun, 14 Dec 1997 09:39:27 -0500
Reply-To:     Mark Hudgik <mhudgik@THE-SPA.COM>
Sender:       Vanagon Mailing List <vanagon@gerry.sdsc.edu>
From:         Mark Hudgik <mhudgik@THE-SPA.COM>
Organization: remodeling@homewrecker.com
Subject:      Re: Air in Brake Circuit
Content-Type: text/plain; charset=us-ascii

Mike,

It's not clear whether you're closing the bleeder screw before lifting your foot off the brake pedal, but it sounds like you are sucking air back through the bleeder screw when lifting your foot off the brake pedal. I use a manual hand pump attached to the bleeder, it has a clear cup on it to collect the fluid and allows me to see when all the air is out of the line, (your can pick up a hand pump at your FLAPS for less than $30). The pump setup allows you to bleed your system without requiring a second person. I prefer it even when a second body is available as it is faster and cleaner. Below is some generic information on bleeding brakes that may be of interest....or not ;)

-------------------------------------

Bleeding is a service procedure that involves purging the master cylinder, brake lines, calipers and wheel cylinders.

If there are air bubbles in the fluid, they will compress when the brakes are applied, causing either a low or soft pedal. Bleeding gets the air out, leaving only non-compressible brake fluid.

Air can enter lines when the system is opened for repairs. Air can also enter the lines if the master cylinder reservoir gets too low.

To remove air, bleeder screws on the calipers and/or wheel cylinders are opened one at a time. Old fluid, along with any air, is then drained, pumped, pushed or siphoned out while fresh fluid is added to the master cylinder reservoir.

Manual bleeding is usually a two person job. One person pumps the brake pedal while another closes the bleeder screw after each stroke to prevent air from being pulled back into the system. Gravity bleeding doesn't involve any pumping. The bleeder screws are opened and the fluid is allowed to dribble out.

Gravity bleeding is slow (and is less likely to get the air out) and seldom used except on certain import applications. Most professionals use power bleeding because it is fast and does not require a helper. Compressed air is used to force new brake fluid through the master cylinder to push out the old.

Another method sometimes used is vacuum bleeding. Special equipment is used to siphon old fluid out through each bleeder screw.

To get all the air out, brakes must be bled in the proper sequence. Depending on how the hydraulics are split (front/rear or diagonally), the usual sequence is to bleed the wheels furthest from the master cylinder, then the closet wheels.

On most rear-wheel drive vehicles, the recommended sequence is RR, LR, RF, LF. On front-wheel drive cars with diagonally spit brake systems, the sequence is RR, LF, LR, RF.

If the master cylinder is being replaced, it may have to be bench bled before being installed.

-------------------------------------

Hope this helps.... Mark - 91 Carat

Michael A. Radtke wrote:

> Hello, > > '84 GL. > > Yesterday, my brake pedal started going nearly to the floor. So, I checked > the rear drums and the brakes were in good adjustment. The disks have no > adjustment. From this, I concluded that I needed a new master cylinder. > No further tests were done. > > Today, I installed a new master cylinder. However, I am not able to bleed > the front brakes. The first sign of trouble was when I started getting a > fine foam out the bleeder ... almost like whipped cream. Finally, that > quit, but I still get air. No matter how long I bleed them, I still get > air from both front wheels. > > I am lost. What should I do next? > > Help please, > Mike > > Michael A. Radtke - Z74 Voice: 602-862-4897 > Bull FAX: 4853 > 13430 N. Black Canyon Hwy. > Phoenix, AZ 85029 Email: m.radtke@bull.com


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