Brake bleeding

[Russell Fulks]

Hello All,

I know there have been a ton of posts on bleeding the brake system, and I've read most of them. What I haven't ever seen is a detailed description of the gravity technique. I am replacing my calipers and want to get rid of all the old fluid as I'm sure the previous owner has never flushed it. If you all might be so kind as to tell me exactly how to remove the old fluid and fill the new calipers using the gravity method, I would really appreciate it.

Thanks in advance,
Russ Fulks

[Wayne W.]

Re: Brake bleeding

If you are replacing the calipers the lines will drain on their on. Just clean out the MC and add fluid to it. If you do this first, before you remove the calipers, the new fluid will drain through the lines, flushing the old out. Replace the calipers and refill the MC. You will have to get fluid back into the lines. If air is there the fluid will not drain by gravity. You can do this using the old method of operating the pedal while someone opens the bleeders. Once the lines are filled the fluid will drain on its on and will fill the calipers. It takes a while but is very effective in removing air. Let it sit for a while, and re-open the bleeders to release the rest of the air. You should have a good pedal.

[Wayne W.]

Re: Brake bleeding

If you are replacing the calipers the lines will drain on their on. Just clean out the MC and add fluid to it. If you do this first, before you remove the calipers, the new fluid will drain through the lines, flushing the old out. Replace the calipers and refill the MC. You will have to get fluid back into the lines. If air is there the fluid will not drain by gravity. You can do this using the old method of operating the pedal while someone opens the bleeders. Once the lines are filled the fluid will drain on its on and will fill the calipers. It takes a while but is very effective in removing air. Let it sit for a while, and re-open the bleeders to release the rest of the air. You should have a good pedal.

[Russell Fulks]

Re: Brake bleeding

Wayne,

Thanks for your response, however, I am a little bit confused. When you say the lines will drain on their own, all I have to do is clean out the master cylinder and refill with fluid, how would I do this? Should there be a bleeder valve on the master cylinder? After removing all brake fluid from the system, and installing new calipers, I refill the master cylinder and do the pump method to initially fill the lines and calipers, then the gravity bleed to get and leftover air out? If I completely drain the system will I have to bench bleed the master before bleeding the calipers?

Thanks

Russ Fulks

[Russell Fulks]

Re: Brake bleeding

Wayne,

Thanks for your response, however, I am a little bit confused. When you say the lines will drain on their own, all I have to do is clean out the master cylinder and refill with fluid, how would I do this? Should there be a bleeder valve on the master cylinder? After removing all brake fluid from the system, and installing new calipers, I refill the master cylinder and do the pump method to initially fill the lines and calipers, then the gravity bleed to get and leftover air out? If I completely drain the system will I have to bench bleed the master before bleeding the calipers?

Thanks

Russ Fulks

[Duke W.]

Re: Brake bleeding

Assuming you're just changing the fluid, I would not recommend the so-called gravity technique, but it is recommended by some if you need to fill a freshly installed rebuilt caliper.

If you just want to change the fluid, siphon all the old fluid out of the reservoir, then fill it about 3/4 full of fresh fluid and install the cap, but don't secure it. Pack clean rags below the m/c to catch any spillage. (The rags can be rinsed in water when you are done, and quickly flush any spilled fluid with water. Glycol fluid is water soluble, but it attacks most paints.) Use clear vinyl hoses on the bleeder valves and convenient containers. You will get some seepage past the valve threads, so if you have painted calipers, have a water spray bottle handy to flush it off when the valves are closed.

Now start bleeding at each corner. You'll need a helper to pump the pedal. As they push down you open the valve. When the pedal is to the floor the helper says "bottom" then you close the valve and give the command to let the pedal back up, then give the command to press down when you are ready.

It doesn't really make any difference where you start, but by bleeding the shortest path first the fluid between the m/c and junction block does not have to go all the way through the system. Do each corner six to twelve pumps, and be sure you get a handle on how many pumps you need before the reservoir is low. Running it dry will cause you to bleed a whole lot more to get the air out. Don't let that happen.

Go around the car two to three times until the exiting fluid is as clean as the fresh fluid, or at least a quart, which is about three times the system capacity.

DOT 3 fluid is okay, DOT 4 is better as it is more resistant to moisture contamination and has higher wet and dry boiling points. Fluid should be flushed every one to three years, with the frequent end for damp climates and the less frequent end for dry climates.

Duk

[Duke W.]

Re: Brake bleeding

Assuming you're just changing the fluid, I would not recommend the so-called gravity technique, but it is recommended by some if you need to fill a freshly installed rebuilt caliper.

If you just want to change the fluid, siphon all the old fluid out of the reservoir, then fill it about 3/4 full of fresh fluid and install the cap, but don't secure it. Pack clean rags below the m/c to catch any spillage. (The rags can be rinsed in water when you are done, and quickly flush any spilled fluid with water. Glycol fluid is water soluble, but it attacks most paints.) Use clear vinyl hoses on the bleeder valves and convenient containers. You will get some seepage past the valve threads, so if you have painted calipers, have a water spray bottle handy to flush it off when the valves are closed.

Now start bleeding at each corner. You'll need a helper to pump the pedal. As they push down you open the valve. When the pedal is to the floor the helper says "bottom" then you close the valve and give the command to let the pedal back up, then give the command to press down when you are ready.

It doesn't really make any difference where you start, but by bleeding the shortest path first the fluid between the m/c and junction block does not have to go all the way through the system. Do each corner six to twelve pumps, and be sure you get a handle on how many pumps you need before the reservoir is low. Running it dry will cause you to bleed a whole lot more to get the air out. Don't let that happen.

Go around the car two to three times until the exiting fluid is as clean as the fresh fluid, or at least a quart, which is about three times the system capacity.

DOT 3 fluid is okay, DOT 4 is better as it is more resistant to moisture contamination and has higher wet and dry boiling points. Fluid should be flushed every one to three years, with the frequent end for damp climates and the less frequent end for dry climates.

Duk

[Russell Fulks]

Re: Brake bleeding

Duke,

I am actually installing 4 newly rebuilt calipers and was under the impression that the gravity technique was "the best" for this procedure. I guess me biggest concern is whether I should let all of the fluid out of the system before installing the new calipers. I had planned on removing all the old calipers and letting the fluid drain itself from the MC and all the lines. Once the system was empty, I planned on installing the new calipers, trailing arm lines, and hoses, then refilling the MC and bleeding the system. I was also aware that I might have to bench bleed the MC if I completely drained the system.

Do you instead suggest that I install the new calipers, trailing arm lines, and hoses with the MC full of old brake fluid and then "pump" bleed the system with new fluid to flush out the old?

Your comments are greatly appreciated.

[Russell Fulks]

Re: Brake bleeding

Duke,

I am actually installing 4 newly rebuilt calipers and was under the impression that the gravity technique was "the best" for this procedure. I guess me biggest concern is whether I should let all of the fluid out of the system before installing the new calipers. I had planned on removing all the old calipers and letting the fluid drain itself from the MC and all the lines. Once the system was empty, I planned on installing the new calipers, trailing arm lines, and hoses, then refilling the MC and bleeding the system. I was also aware that I might have to bench bleed the MC if I completely drained the system.

Do you instead suggest that I install the new calipers, trailing arm lines, and hoses with the MC full of old brake fluid and then "pump" bleed the system with new fluid to flush out the old?

Your comments are greatly appreciated.

[Duke W.]

Re: Brake bleeding

I should defer this question to those with disk brakes, but if you install new calipers and then leave the bleed valves open with some hoses attached and supported so their openings are a bit below the m/c then gravity should allow the fluid to drain down and displace most of the air.

BTW, if you're replacing all four calipers, you should remove the m/c for teardown, inspection, and rebuild, and replace all the hoses. Then if you flush all the steel lines with denatured alcohol you can use silicone fluid, but you'll also have to insure that silicone was used to assemble the calipers and m/c. If not, you can disassemble them, clean with alcohol and reassemble them with silicone fluid. Flush the new hoses with alcohol too just to be sure.

With silicone you only need to flush the system every five to ten years, and since silicone fluid does not absorb moisture, you'll have a lot less corrosion and the hydraulic system will last a lot longer.

Duke

[Duke W.]

Re: Brake bleeding

I should defer this question to those with disk brakes, but if you install new calipers and then leave the bleed valves open with some hoses attached and supported so their openings are a bit below the m/c then gravity should allow the fluid to drain down and displace most of the air.

BTW, if you're replacing all four calipers, you should remove the m/c for teardown, inspection, and rebuild, and replace all the hoses. Then if you flush all the steel lines with denatured alcohol you can use silicone fluid, but you'll also have to insure that silicone was used to assemble the calipers and m/c. If not, you can disassemble them, clean with alcohol and reassemble them with silicone fluid. Flush the new hoses with alcohol too just to be sure.

With silicone you only need to flush the system every five to ten years, and since silicone fluid does not absorb moisture, you'll have a lot less corrosion and the hydraulic system will last a lot longer.

Duke

[Russell Fulks]

Re: Brake bleeding

Thanks for your comments Duke.
I thought about silicone but decided not yet. I was not planning on taking the MC apart as I have not had any problems with air in the system. The only reason I am replacing the calipers is because they were so badly damaged by Just Brakes in Houston. The car was braking fine, I simply wanted Just Brakes to look at and adjust my parking brake because I couldn't seem to find the adjuster through the rotor. When I went to get my car back they told me that all four calipers were leaking and that they had just enough time to replace them ( at the tune of $1,000). I said no thanks and drove home. They so damaged the calipers and lines that the brakes literally started smoking on the way home. I was lucky the car didn't catch fire. Anyhow, $400 later with a new caliper set I am anxious to get back on the road as it has been great weather for some topless motoring and my baby has been stuck in the garage waiting for some new shoes! Maybe sometime in the future I'll have the MC rebuilt and flush the system with alcohol and make the swap to silicone, but not quite yet.

[Russell Fulks]

Re: Brake bleeding

Thanks for your comments Duke.
I thought about silicone but decided not yet. I was not planning on taking the MC apart as I have not had any problems with air in the system. The only reason I am replacing the calipers is because they were so badly damaged by Just Brakes in Houston. The car was braking fine, I simply wanted Just Brakes to look at and adjust my parking brake because I couldn't seem to find the adjuster through the rotor. When I went to get my car back they told me that all four calipers were leaking and that they had just enough time to replace them ( at the tune of $1,000). I said no thanks and drove home. They so damaged the calipers and lines that the brakes literally started smoking on the way home. I was lucky the car didn't catch fire. Anyhow, $400 later with a new caliper set I am anxious to get back on the road as it has been great weather for some topless motoring and my baby has been stuck in the garage waiting for some new shoes! Maybe sometime in the future I'll have the MC rebuilt and flush the system with alcohol and make the swap to silicone, but not quite yet.

[Wayne K.]

Re: Brake bleeding

Russell,

It sounds like you still have a closed system and unless you know you have air in it I wouldn't do anything that would introduce air into it. The old calipers still in place siphon the old fluid out of the master cylinder. Fill it 3/4 full of new fluid. Disconnect the first caliper to be replaced and the fluid should start to drain from the line. Once it comes clean connect your line to the new caliper and mount it on the car. Then open the bleeder and watch for the fluid to come through. Always remember to make sure that the master cylinder never goes dry during any of this. If you repeat this with all four calipers you should end up with a working system that may still require some pressure bleeding if you need to firm up the pedal.

[Wayne K.]

Re: Brake bleeding

Russell,

It sounds like you still have a closed system and unless you know you have air in it I wouldn't do anything that would introduce air into it. The old calipers still in place siphon the old fluid out of the master cylinder. Fill it 3/4 full of new fluid. Disconnect the first caliper to be replaced and the fluid should start to drain from the line. Once it comes clean connect your line to the new caliper and mount it on the car. Then open the bleeder and watch for the fluid to come through. Always remember to make sure that the master cylinder never goes dry during any of this. If you repeat this with all four calipers you should end up with a working system that may still require some pressure bleeding if you need to firm up the pedal.