Technical Forum (Read Only) > Braking Systems
Brake System and Diagnosis
Irish_Alley:
Irish_Alley:
BLEEDING THE BRAKE
HYDRAULIC SYSTEM
A bleeding operation is necessary if air has been introduced into the hydraulic brake system. It may be necessary to bleed the system at all four wheels if air has been introduced by a low fluid level condition in the master cylinder. Also if the brake pipes have been disconnected at either the master cylinder
or the combination valve. If a pipe is disconnected at one wheel, then only bleed that particular wheel. The time required to bleed the hydraulic system when the master cylinder is removed can be reduced if the master cylinder is filled with fluid and as much air as possible is bled from the cylinder before installing it
on the vehicle.
MANUAL BLEEDING
If the vehicle is equipped with power brakes, deplete the vacuum reserve by applying the brakes several times with the engine off. Use extreme care to prevent brake fluid from contacting any painted surface.
1. Fill the master cylinder reservoirs with brake fluid specified in MAINTENANCE AND LUBRICATION
(Sec. OB).
Maintain the fluid level in the reservoir during the bleeding operation.
2. If the master cylinder is suspected to have air in the bore, it must be bled before any wheel cylinder or caliper.
Remove the forward brake pipe connection at the master cylinder.
Allow brake fluid to flow from the connector port.
Connect the brake pipe but do not tighten.
3. Slowly depress the brake pedal allowing the air to bleed from the loose fitting.
Tighten the fitting before releasing the pedal.
Wait 15 seconds, and repeat this sequence, including the 15 second wait until all the air is purged from the bore.
4. After all the air has been removed from the forward connection disconnect the rear pipe.
Allow brake fluid to flow from the connector port.
Connect the brake pipe but do not tighten.
5. Slowly depress the brake pedal allowing the air to bleed from the loose fitting.
Tighten the fitting before releasing the pedal.
Wait 15 seconds, and repeat this sequence, including the 15 second wait until all the air is purged from the bore.
6. If it is known that the calipers and wheel cylinders do not contain any air, then it will not be necessary to continue. Otherwise bleed each wheel in the following sequences.
Right rear
Left rear
Right front.
Left front
7. Attach a hose to the wheel cylinder/caliper bleeder screw.
Immerse the opposite end of the hose into a container partially filled with clean brake fluid.
8. Slowly depress the brake pedal one time and hold.
Loosen the bleeder screw to purge the air from the wheel cylinder/caliper.
Tighten the bleeder screw and slowly release the pedal.
Wait 15 seconds, then repeat this sequence, including the 15 second wait until all the air is purged from the wheel cylinder/caliper.
9. Continue steps 7 and 8 at each wheel until the entire brake system has been bled.
10. Check the brake pedal for sponginess and the brake warning lamp for an indication of an unbalanced pressure. Repeat the entire bleeding procedure to correct either of these two conditions.
more brake tech
http://forum.73-87chevytrucks.com/smforum/index.php?topic=28592.msg238566#msg238566
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