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Old 02-09-2006, 01:25 PM
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Gravity bleeding of brakes.

Someone on here a couple of weeks ago posted about gravity bleeding of brakes, by opening the bleeders and letting the fluid drain for an hour.

Now I have bleed many of brakes in my lifetime and thought you were nuts.

Well the vette, I replace every piece of the brake system and had my wife pumping for who knows how long and 3 bottles of Dot5 later have great pedal until you start the car and then no brakes.

First, sorry I thought you were nuts as it turns out the two lines or calipers the had air you could tell witch ones they were as soon as you opened the
bleeder fitting by the flow.

Worked like a charm and wish I had learned this 30 years ago!
I was just about to give up and buy a power bleeder.

Who ever you were thanks as I could not find the post.

Thanks again
Barry

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Old 02-09-2006, 01:55 PM
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Thats about the only way you can bleed most Corvettes. Its the only way I can get all of the air out of my streetrod too.
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Old 02-09-2006, 01:56 PM
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only way to do it...unless your m/c is mounted below the level of the calipers / wheel cyl. Then it's under the vehicle with a vacuum pump
Works but what a PITA !
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Old 02-09-2006, 02:50 PM
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Intriguing, all my years I have never heard of this proceedure. My 34 is real PITA to bleed as it has a master below the floor and four wheel Wilwood cailipers. These calipers each have four bleed screws, two on top and two on bottom. Do I just open the bottom bleeders, or all of them?

Vince
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Old 02-09-2006, 03:08 PM
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I would think just the top ones as the air is going to go to the top.
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Old 02-09-2006, 03:20 PM
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Quote:
Originally Posted by 302/Z28
Intriguing, all my years I have never heard of this proceedure. My 34 is real PITA to bleed as it has a master below the floor and four wheel Wilwood cailipers. These calipers each have four bleed screws, two on top and two on bottom. Do I just open the bottom bleeders, or all of them?

Vince
If the master cylinder is below the level of the brake calipers, this procedure will not work. If not you would need to open the top bleeders.

Steve
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Old 02-09-2006, 07:36 PM
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Quote:
Originally Posted by 1931 steve
If the master cylinder is below the level of the brake calipers, this procedure will not work. If not you would need to open the top bleeders.

Steve
Master is below the floor, but is almost at the level of the calipers,so it probably will not work.

ince
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Old 02-11-2006, 08:05 PM
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the only thing better than gravity bleeding is pressure bleeding.

I used a 1/4" plate with a schrader valve ( like a tire valve) in the middle and a Schwinn tire pump, it has a pressure gauge. I pump it up to about 15 psi and bleed away!

Fast too!

Wifey is happy to loose that job!
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Old 02-12-2006, 01:27 AM
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I have found it works best with a dry system.

After doing major work and all the brake lines are dry I just fill up the res., open the bleeders, and go get a snack and a drink. I check the res. every 15min or so to make sure it doesn't go empty. I normally don't do it that way just because of how long it takes (I vacuum bleed normally)
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Old 02-12-2006, 01:33 AM
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Here is a twist on bleeding brakes: vacuum / pressure. I would have trouble alot of times with under the floor M/C cars even with the pressure bleeder and one day after I charged up a new AC system, I thought why not do brakes the same. I put an extra line on my pressure bleeder adapter plate with an inline valve. I purge all of the fluid out of the system. hook a vacuum pump and vacuum jar to the extra line. Evacuate the system down to 20 to 25" vacuum. shut the vacuum valve. The pressure bleeder is hooked to the standard fitting on the adapter plate. I open the pressure bleeder valve slowly and fluid is drawn in to the system, filling the vacuum. I pump the pedal once or twice to seat the pads and I'm done. I don't even open the bleeders. Works great, doesn't waste any fluid if you are doing a brand new system and that pedal is harder than chinese algebra the first time. An added benefit is that you don't take the chance of getting fluid all over a newly painted caliper or suspension part. I have done a few 4 wheel disc cars but no disc/ drum setups yet. I'm not sure that the wheel cylinder seals will seal when I put the vacuum to them. If anyone has any opinion about this, let me know. thanks for reading this,mikey
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Old 02-12-2006, 09:47 AM
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I did brake and front end work in tire stores and dealerships for years, taught Mechanics at the high school level for 13 years and Like 302/Z28 have never heard of "gravity bleeding brakes" or seen it performed.
Admittedly the old tried and true "pump and hold it" method doesn't work well on some systems.
Pressure bleeding will work most of the time and I have had good luck with the hand vacuum pump system although it is a bit slow.
I'm not saying that it won't work in some applications but I can't see it working in the majority of rigs.
If you pressure bleed a system I think 25# is the max pressure for most bleeder tanks. If you used the tire valve on a spare mc cap be carefull that you don't run out of fluid or you would be pushing air back into the system.
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Old 02-12-2006, 11:38 AM
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I was taught gravity bleeding when first starting out about 20yrs ago. Sometimes it's just about the only thing to get things working when you have no pressure bleeder, esp if your pedal pumper is an idiot. Vacuum bleeders never worked well for me.
Gravity bleeding and vacuum bleeding will not work well with residual valves in the system. I've seen it recommended in old shop manuals for disc brakes as early as 1970, or possibly earlier.
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Old 02-12-2006, 01:39 PM
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It also helps to tap on the calipers and wheel cylinders when bleeding
a system for the first time. It releases the tiny air bubbles that stick
to the insides!
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Old 02-13-2006, 04:28 PM
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I've Owned 7 Older Corvettes...

2-13-06

Only Thing I Can Add After Reading All Great Posts:

Older Corvettes Are Famous For Trapping Air At (Between) Dual Master Master Cylinder & Metering Block (Rarely Goes Bad) Causes (Adds To) Problem_

I Ended Up Replace (Metering Block My 1968 Corvette) And Use All Stainless Steel Calipers & Master Cylinders------BUT: Dual Master Cylinder Must Have Dual Bleeders_

I Follow Procedure Bleed Right Rear,Left Rear ,Right Front, Left Front Calipers-- Then Bleed Dual Bleeders Rear 1st, Front 2nd--Making Sure Master Cylinder Fluid Is At Level _

Colder Weather Adds To Above Problems- Corvettes- Calipers Originally Had Plastic Pistons In Them,i.e. Let Air In (Expansion & Contraction) Biggest Reason To Go All Stainless_

Due To and Of EPA Bullsh*t Even Todays Brake Fluids Are Diluted (Made Cheaper) Other Additives,etc.Only Adds To Continuing Problems...

Vincent Auto
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Old 02-13-2006, 07:09 PM
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One time I asked an old-timer I knew to help me bleed the drums in my 67 Tempest.... he agreed and showed up... I already had the car on stands.... I asked him to get in and pump 'em up and he just laughed.... he opened the bleeders, filled the master to the brim and said "lets's go get a beer".... we came back three hours later, he closed the bleeders and turned the adjusters in about 1/8 of a turn each.... best pedal feel I ever had in that thing.....
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