How do you gravity bleed the brakes?

[ladams]

Hi all,
I replaced all calipers, hoses and master cylinder on my '81 and cannot get fluid to the rear while bleeding. I have bled the master and there is fluid going to the fronts, but nothing to the rear. I read something about gravity bleeding for a while before two person bleeding.
Can someone go over the process? Should the car be running? Should the MC cap be off? Should the pedal be depressed?

Thanks

 

[chevy6673]

Hi all,
I replaced all calipers, hoses and master cylinder on my '81 and cannot get fluid to the rear while bleeding. I have bled the master and there is fluid going to the fronts, but nothing to the rear. I read something about gravity bleeding for a while before two person bleeding.
Can someone go over the process? Should the car be running? Should the MC cap be off? Should the pedal be depressed?

Thanks

keep master full at all times back first car not running fluid must come out study stream it worked on my 66 ss impala keep bleeders opened cap on or off it takes time

 

[wishuwerehere82]

Keep in mind that the rear calipers have 2 bleeders. One on each half of the caliper, inside and outside. The inside bleeders must be opened first to allow fluid to pass into the inner half of the calipers before the outer ones can be bled.
Personally, I think pressure bleeding will be quicker than gravity bleeding, because air pockets in the lines will stop the flow once the calipers start to fill.
Keep the cap loose (but on to prevent squirting) and to allow the level to be topped off often as you bleed the system.

Have someone help you by stepping on the pedal.
The pedal should move as soon as you open the bleeders. If it doesn't, you have an obstruction in the line.

The correct order to bleed the lines is to do the right rear inner and outer, then the left rear inner and outer. Then bleed the right front, and the left front.
You may have to repeat the process again after a short drive if the system doesn't seem firm enough.

 

[JohnZ]

Gravity bleeding can take FOREVER. Get a Motive Products power bleeder and it's a one-person ten-minute job, with one trip around the car, and you don't have to watch the master cylinder; best sixty bucks I ever spent on a tool. Makes stubborn Corvette disc brake bleeding a cakewalk.

 

[GerryLP]

Hey JohnZ,

I have wanted to check-out that product, and I am glad that you recommend it. Thanks for the product endorsement!

 

[White75]

Hey JohnZ,

I have wanted to check-out that product, and I am glad that you recommend it. Thanks for the product endorsement!

those pressure bleeders are great. you can also try speed bleeders. The basically replace the existing bleed screws and have a valve in them to let fluid out but keep the air from getting into the caliper when using standard pedal bleeding methods.
You can pick up generic ones at Autozone in the HELP section. Look for one-person bleed screws.

 

[red70vette]

I have not used the Motive Pressure bleeder but I have tried a Mity Vac with some success. My vote though is for the speed bleeders. I installed them several years ago and they work like a charm. They are especially good for a one man bleeding. Install them once and then just open them and step on the brake and bleed. I can think of nothing that is easier.

 

[DR.Jay]

If you are only getting brake fluid to the front you might want to check, and see if the perportioning valve isn't stuck. Did you bench bleed the master cyl. before installing on the car.

 

[ladams]

figured it out....

If you are only getting brake fluid to the front you might want to check, and see if the perportioning valve isn't stuck. Did you bench bleed the master cyl. before installing on the car.

I was talking to a friend and former GM mechanic at work and he mentioned the proportioning valve possibly being stuck also. He told me to try gravity bleeding and then stepping hard and quick on the pedal to "unstick" the p-valve. It worked. I now have all four calipers bled. By the way, I did bleed the master beforehand but obviously I did something else wrong.