master cylinder bleed


Old 07-05-06, 03:26 PM
Thread Starter
Join Date: Jul 2006
Posts: 6
master cylinder bleed

On a '98 S10 truck, I let the resevoir run dry while bleeding the brakes. To bleed the master cylinder I'm
1.) loosening the brake line fittings
2.) pressing the brake pedal via my wife
3.) tightening the fittings
4.) releasing the brake pedal
with 10-15s intervals

When doing this repeatedly, the rear line (closest to the resevoir) bleeds fine after several attempts, but the front line never seems to bleed fluid. I've done this with both lines open ~10-15x and just with the front line open 15-20x. Is this a problem or normal? How can I remedy this?
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Old 07-05-06, 04:11 PM
Join Date: Jun 2006
Posts: 338
LOL I answered in your other post,You don't always have to bench bleed it, I have had it go dry before to on accident I just poured more in and bleed as normal.

But if you want to go this route you can undo the brake lines slip a small 1/4" vacuum hose or what ever fits in the holes and run it up to the reservoir all this does is push the air out the shortest way possible.

If there is bleeders on the master cyl you can put the vacuum hose over the bleeder and run it up to the resorivoir.

IF you are not concerned about using a big $3 bottle of brake fluid or a couple of small bottles you can just bleed it like you didn't run it dry, but bleed it a lot so you know that the air is out you will here the air come out.

Bench bleeding is not different than regular bleeding exept you don't waste as much brake fluid. and your not pushing the air through the lines to escape out the caliper bleeder.

You still need 2 people to bleed it and follow what I said before, the pedal should feel solid no spongy after your done with the final caliper and pump the pedal with out the engine running it should get rock hard.

I don't know why he told you to bench bleed its such a pain in you know what and a mess.
If you don't have vacuum hose which you probably don't disconnect the lines fill the resvoir pump it let spray all over after 2 or 3 pumps put the lines back on and bleed as before. Or crack the bleeders loose on the master if there is one

If I were you just bleed like normal brakes.

Last edited by hotrodder89; 07-05-06 at 04:33 PM.
Old 07-05-06, 04:28 PM
Join Date: Jun 2006
Posts: 338
what fitting no brake line fitting don't touch

the bleeder on the caliper/wheel cylinders touch that.

All you have to do is put fluid in the reservoir have your wife pump the pedal 5 times. Press down and hold,then you crack the bleeder loose a little, if fluid comes out close the bleeder BEFORE the stream goes back in. if just air comes out tell your wife to let you know when the pedal went all the way down, then you close the bleeder and tell her she can let up and pump it 5 more times, repeat till air/foam/sputters stops coming out

There is no time intervals do exactly as stated above

the rear lines are the farthest
Old 07-05-06, 06:40 PM
Thread Starter
Join Date: Jul 2006
Posts: 6
Thanks for the info. I bench bled the cylinder and got things moving again. Unfortunately, the rain started so I'll have to put the rest of the it off for a day or so.

Any preference for bleeding via vacuum hand pump vs. an assistant pedal pumper for the calipers/drums ?
Old 07-05-06, 06:55 PM
Join Date: Jun 2006
Posts: 338
I have never used a vacuum pump to bleed, but then again I haven't been as drunk in a while as I am right now. The only tools I have seen to aid in bleeding are typically called speedy bleed, which pressurize the reservoir in the master cylinder to push the fluid through so you don't need your wife to pump the pedal to push it through.

I still wouldn't bench bleed it waste of effort and time. Your still going to have to bleed the air out you put in the system by the master since you disconnected the brake lines from it.

Thats right the little brake fluid that came out of the line got replaced by air that can only be removed by the procedures I have stated above.
Old 07-05-06, 06:57 PM
davzack's Avatar
Join Date: Jun 2006
Posts: 304
I've found that using a helper pushing the pedal is better...personal preference maybe. I think your technique may be wrong if I read your post correctly. Here's how I do it...

Start at the farthest point away from the master cylinder...usually right rear. Have the person pumping press the pedal down 3 times (slowly) until pressure is built up. (Pressing slowing keeps air bubbles from forming in the fluid.)

On the final pedal pump have the person pumping hold pressure on the pedal while you open the bleeder screw. Just before the flow of brake fluid comes to a stop, close the bleeder screw. As you open the bleeder screw, the brake pedal will sink to the floor...just advise the pedal person to keep applying constant pressure the entire time. Keep this up until no air comes out of the bleeder screw.

Check your fluid level in the master cylinder before proceeding to the next wheel which should be the left rear. Then repeat for the front right and then finally the left front. Some vehicles' pedals will still feel crappy when you start the vehicle until you actually start driving.

PS. You could have tried bleeding the lines where they connect to the master cylinder in the same manner as described above in an attempt to bleed the master cylinder. Usually works for me but I have had vehicles where I actually had to pull the master cylinder and bench bleed it...some cars are just more of a pain in the butt than others.
Old 07-05-06, 07:00 PM
Join Date: Jun 2006
Posts: 338
If you read down a few post I stated that exact procedure to him, he already asked this before I think it was blazer

My car dumb gf says take it to a shop but I say you can do it yourself I have faith on you because she bleeds my brakes I taught her and she hates doing it.

If she can do it so can you.

Last edited by hotrodder89; 07-05-06 at 07:32 PM.

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