[Green Hornet]

Just installed a fresh (bench bled) master......and am ready to bleed the calipers.

Will they gravity bleed themselves if I crack the bleeders?

Other that starting with furthest away caliper....any other tips ...or tricks?

Thanks

[Warren Seale]

You will get quicker results if you pump the fluid through the lines using the brake pedal. Or use a Mighty Vac and draw it through the lines.

[Sirrotica]

Yes, you can gravity bleed them, and it makes no difference which side you do. I usually open both and close up the one that starts running first.

Gravity bleeding needs no sequence ,and you can do the whole system by opening all 4 bleeders at the same time. It's not any faster if you consider you're bleeding 4 points at once, as opposed to one at a time.

After opening the bleeder use a few very short strokes at the top of the pedal travel to start the siphon, roughly an inch at the pedal. You've now started 4 bleeding processes at once, by yourself, no extra equipment required, and no second person required.

I usually place my finger over the end of the bleeder, and restrict it so I can watch the flow to check to see if all the air is out of the fluid. When the bubble cease, you just tighten the bleeder, your done with that wheel.

Gravity also does a better job of purging the system of air in my 50 years of experience in automotive repair. You will also have air rising to the master cylinder reservoir and you may observe bubbles in the reservoir. You are bleeding the fluid column from both ends, which isn't done with pressure bleeding.

Someone may tell you different, but I'm fairly certain that my process is just as fast, and produces better results in the end product.

[Green Hornet]

Thanks...for posting...I'll give it a whirl....

I've read ..in a service manual....that there is a button...on the prop valve....that should be depressed...while bleeding.....

How does this enter into the equation?

[Sirrotica]

If the brake warning light is on, the spool between front and rear systems needs centered. It is centered by manually pushing the spool to center, and is behind rubber boots located on the valve.

If the spool isn't centered it will block half the system, effectively shutting it off from bleeding. It's a failsafe system to shut fluid flow off from whichever half (front, or rear) is leaking. It stays centered when both sides of the system have equal pressure. When one side has pressure it will shift towards the side with no pressure, and block that side.

[4dblnkldude]

Literally just did this 3 weeks ago. Like Scirrotica said. I did the rears and then the fronts. After all was gravity bled I did still get some one to pump for an hour with me. I did get some bubbles after that. I do take it for a rip after and drive it a few more times, leave it sit and check it again.

[78w72]

question for the gravity bleed guys... are you using a short tube on the bleeders to direct the fluid into a container or just letting it run down the backing plates or calipers into a pan underneath? i have a life long mechanic friend that likes to gravity bleed brakes too but after watching him do it a few times i decided i would never do that on a clean or painted/restored car. brake fluid is nasty stuff & will eat paint off any part it touches!

so if you care about fluid getting on parts i much prefer to do it manually with a clear hose into a container & then you can watch the fluid for bubbles to know when its good. ive done so many brake bleeds manually over the years & it goes very fast & is nice & clean.

[Sirrotica]

I have zero restored cars, stuff I work on are daily drivers that have no paint on the backing plates/calipers anyway. I just recently posted on replacing a LF hard line on my 1995 C 3500 HD box truck with a mere 246,000 miles on it. As you can see I live in Ohio, rust is not affected by brake fluid.........

On a restored car clear piece of tubing draining into a pan would work just fine if I was working on something that I was worried about stripping the finish off of the backing plate or caliper area. Since you watch the bleeder for air bubbles you wouldn't even need a clear hose, a piece of vacuum hose would be sufficient to observe the fluid as it runs out. As I said I put the end of my finger over the bleeder to restrict it so I can watch a solid stream of fluid to see if the bubbles have ceased, when you have no bubbles in the fluid, you're done.

Some people seem to think you have to let the stream run for 10 minutes to bleed the system, ending up with a puddle of fluid on the floor. That's not the case, just watching the bleed screw for the bubble to cease usually is done in a minute. I usually just take a rag and wipe the floor up so no one slips on the fluid, someone would be me, since 99 out of 100 times I'm working by myself. The reason I like gravity bleeding to start with, no person to pump the pedal is present, no extra equipment to take out and put away, gravity is present everywhere I work. A container of brake fluid, and a wrench to open and close the bleeder, is all that's required.

Not agitating the fluid by pressuring it, keeps it from getting bubbles in it to start with. Think about doing your average pressure bleed of pump and hold. You have a column of fluid with air at the base of it, you're pushing fluid in from the top, and as naturally occurs, the air rises to the top of that fluid. Your air it trying to go back towards the master cylinder, but you're pushing it back down with pressure. All that fluid is being aerated.

You only need to think of filling a bottle from a faucet to see that a forceful stream at pressure is aerating the water. Fill the bottle slowly and it rises to the top with zero bubbles in it, same principle. Brake fluid has a higher viscosity than water does and tends to trap the air more easily. Not aerating the fluid is why gravity bleeding works well. You don't have to push all the aerated fluid through the system to get the system bled. You actually use less fluid by not aerating it, and get a better quality job by not having to try bleeding again, after the air starts separating in the system. Many times with pressure bleeding, if you try it again after after a minute or two, you'll get more air out of a bleeder. That's the aerated fluid separating inside of the system.

After you think you have the system bled, you let it sit a minute or two and hit the pedal, only to find it's gotten mushy, then do the sequence again after the fluid lets the air out. You don't normally get that with gravity bleeding, once you close the bleeder, it's done, because it didn't get aerated.

The operation is simple as it gets, yet some people try to make it complicated, it's far from complicated.

[78w72]

ok just asking how some do it & pointing out that it can get messy if you dont use a tube to get it past the backing plates or calipers. & most on here have nice or restored cars so fluid on parts is an issue to consider.

not knocking gravity bleeding as a process, & it is a good way if youre by yourself. but i have always preferred to do it manually & ive never had a mushy pedal or air in the lines from pushing fluid with the pedal. even with new empty lines doing it manually is pretty quick & easy & after doing it that way for so long.

[Green Hornet]

Thanks....for everybodys input....

Todays job...is to put the TA on stands.......

It's a driver survivor.......and the master cylinder I just replaced....appears to be the original.....so the odds are pretty good...that bleeders may have never been opened before......

It's not a rust bucket......but not a winter virgin either......Wish me luck...

[Green Hornet]

And the WINNER is......gravitational bleeding....

Only one broken bleeder (RF)....but got decent flow...by loosening the banjo bolt.

However....we have another issue....and I think I ran into this about 35 years ago...as well.....NO back brakes.....and had fluid flow to BOTH rear calipers....

I think the rear caliper pistons need to be adjusted out.......with the e-brake pedal possibly.....?

Just about ready to drive....but really should have back brakes working...

[Sirrotica]

Yes, takes a special socket to screw the pistons to adjust them

[ta6point6]

You can try and adjust with emergency brake if ratcheting system in caliper is working correctly. Over time these get locked up and need to be fully articulated to free up. Do not use a standard caliper tool on these 4 wheel disc cars, to screw piston in. The piston is indexed one way and needs to stay that way so the notch in brake pad stays seated correctly. The way you adjust these rear calipers is at emergency brake lever. Also I would stick with bleeding the brakes the original way, one person pumping pedal and another cracking open the bleeder. The rear caliper is different then your standard front piston. The rears have a cover over piston that could hold air. I just did these about a month ago, look a couple posts down. I changed calipers and rotors on the rear. Here is a NAPA bulletin that helps with adjusting if the ratcheting system is working correctly. Also check that emergency brake cables move freely after 40 years of road grim they are gummed up just like mine were

[Grand73Am]

Originally Posted by ta6point6

You can try and adjust with emergency brake if ratcheting system in caliper is working correctly. Over time these get locked up and need to be fully articulated to free up. Do not use a standard caliper tool on these 4 wheel disc cars, to screw piston in. The piston is indexed one way and needs to stay that way so the notch in brake pad stays seated correctly. The way you adjust these rear calipers is at emergency brake lever. Also I would stick with bleeding the brakes the original way, one person pumping pedal and another cracking open the bleeder. The rear caliper is different then your standard front piston. The rears have a cover over piston that could hold air. I just did these about a month ago, look a couple posts down. I changed calipers and rotors on the rear. Here is a NAPA bulletin that helps with adjusting if the ratcheting system is working correctly. Also check that emergency brake cables move freely after 40 years of road grim they are gummed up just like mine were

I agree. These 79-81 rear calipers don't use a piston tool. Here's the page from the Pontiac service manual for removing and installing the rear caliper.

Untitled by grand73am, on Flickr

[4dblnkldude]

Originally Posted by 78w72

question for the gravity bleed guys... are you using a short tube on the bleeders to direct the fluid into a container or just letting it run down the backing plates or calipers into a pan underneath? i have a life long mechanic friend that likes to gravity bleed brakes too but after watching him do it a few times i decided i would never do that on a clean or painted/restored car. brake fluid is nasty stuff & will eat paint off any part it touches!

so if you care about fluid getting on parts i much prefer to do it manually with a clear hose into a container & then you can watch the fluid for bubbles to know when its good. ive done so many brake bleeds manually over the years & it goes very fast & is nice & clean.

I drilled holes in gatorade plastic bottle caps, inserted tubing, poked a little relief hole near the top, and put a little zip tie around the bleeder. Crack it and roll.

[Green Hornet]

Great info guys....Thanks

Hope to be back on it tomorrow....

[Green Hornet]

Ok.........looks like a seized right rear E-brake cable....was the reason for no brake action on that wheel.

I pulled the caliper to inspect/test....

The top of the piston looks pretty clean....

Will check it out on Saturday...when I install the new cable...

Another question......How do you tell which caliper is right....and left?

I've been eyeballing a pair of cores I have....and they look pretty much the same...

[Grand73Am]

The face of the end of the screw that the lever bolts to should have an L or an R stamped on it. That's how you tell, since otherwise they look the same.

[Green Hornet]

Originally Posted by Grand73Am

The face of the end of the screw that the lever bolts to should have an L or an R stamped on it. That's how you tell, since otherwise they look the same.

Thanks for the tip..

.Good to know

[Green Hornet]

Originally Posted by Grand73Am

The face of the end of the screw that the lever bolts to should have an L or an R stamped on it. That's how you tell, since otherwise they look the same.

Found a couple of core rear calipers....and it appears they are stamped with directional curved arrow.... not R or L....

I'm guessing the may be OE....and not reman?