I'm converting to vacuum brakes this weekend, and I realized that the last time I've had to do any brake work was several years ago when I was living at home. I can do the master cylinder portion just fine, and everything else. My only question is, how do I bleed this beast? Last time I did it, I barely had my liscense and my Dad helped me bleed my OLD El Camino. Anyone offer a refresher course?
Bleeding Vacuum Brakes
- Thread starter Shane
- Start date
- Joined
- May 26, 2001
You should NOT have to bleed your brakes when doing a vac conversion. If the master cyl is bench bled first, then when installed, leave the top off and both lines loose for 5-10 minutes after they start to drip fluid.
Have someone then push the pedal down and tighten the fitting before release. Do it again to be sure all air is removed from master. Make sure the reservoir is never out of fluid.
Done this many, many times and never had to bleed the wheel cyls to get a good pedal. Good idea to bleed the cyls after this procedure to get fresh fluid into the wheel cyls.
Have someone then push the pedal down and tighten the fitting before release. Do it again to be sure all air is removed from master. Make sure the reservoir is never out of fluid.
Done this many, many times and never had to bleed the wheel cyls to get a good pedal. Good idea to bleed the cyls after this procedure to get fresh fluid into the wheel cyls.
Robert Dean
Member
- Joined
- Jul 13, 2015
I just did the vacuum brake conversion on my 87 gn. Bench bled the master cylinder. Had to replace both rear wheel cyclinders because one was leaking. Then I bled each individual wheel while following the sequence that my repair manual instructed. Had a friend operate the brake pedal while I bled each wheel, making sure to not release the pedal until i had the bleeder oriface tightened up. I felt like it went well, got some air out of the back as i expected, after installing the new rear wheel cylinders. I thought maybe a little bit of air came out of the front but I'm not to sure. Went for a spin after and it doesn't seem to feel right. I'm getting alot of pedal travel and I'm having to stomp the hell out of the pedal to get any serious braking power. Have i just not bled to brakes enough? Do i have a proportioning valve issue? Whats going on. Any suggestions?
Shane, like Nick stated, you shouldn't have to bleed the brakes. I went from manual brakes to vacuum recently and all I did was make sure the MC was bled VERY thoroughly and made the brake line connections the very last thing to do. Basically, unhooked/unbolted everything on the old MC and when it was time to swap the new unit and booster in, I swapped them as quickly and carefully as possible. Is there a chance I got one or two small air bubbles in there? I guess....but perfect pedal for me. No bleeding required.
Robert Dean: Start your own thread so that you're not hijacking someone else's thread. But, based on your description, you probably need to bleed again. I suggest re-bench bleeding the MC. The step bore MCs can have a surprising amount of air still left in them, even when you're sure you've gotten it all out.
Robert Dean: Start your own thread so that you're not hijacking someone else's thread. But, based on your description, you probably need to bleed again. I suggest re-bench bleeding the MC. The step bore MCs can have a surprising amount of air still left in them, even when you're sure you've gotten it all out.
- Joined
- May 26, 2001
The suggestion above is a good one, as this 14 year old thread is not really applicable to your situation?
Since your rear cylinders were replaced, my procedure would have done them AFTER the MC was bled.
At that point I would have replaced the wheel cylinders and then let them gravity bleed 10 minutes, or however long for them to have expelled a lot of fluid.
Tighten the rear cylinder bleeders, then have someone pump the pedal and bleed the rears, then bleed the front calipers.
No need to mess with the prop valve during this process.
The good thing for you in this mess, you will have a clean hydraulic system with all fresh fluid!
Since your rear cylinders were replaced, my procedure would have done them AFTER the MC was bled.
At that point I would have replaced the wheel cylinders and then let them gravity bleed 10 minutes, or however long for them to have expelled a lot of fluid.
Tighten the rear cylinder bleeders, then have someone pump the pedal and bleed the rears, then bleed the front calipers.
No need to mess with the prop valve during this process.
The good thing for you in this mess, you will have a clean hydraulic system with all fresh fluid!
14 years? Where did the time go? Brakes still work great, thanks Nick.
Robert, I'm with Nick. Bleed, bleed, bleed. Good luck.
Robert Dean
Member
- Joined
- Jul 13, 2015
So I did alot more bleeding to the front and back. I did the gravity bleed thing and it seemed to work well.
I didn't mess around either, bled all for wheels at the same time. I just took the cap off the master cylinder, made sure it was right full of fluid and opened all four bleeder screws and let it drain for a while. I made up some plastic lines that I plugged onto the bleeder screws so I could see the fluid and any air coming out. I just kept topping up the MC as to not suck air into the lines from there. I poured a full can and then some of brake fluid through the system. If there was any air there I'm confident I got it all. After that I re-adjusted my back brakes, made sure there was a little drag equally on both sides. Put everything back together and took her for a spin. I definitely have brakes now!! The vacuum brakes feel different than the powermaster system did, I think its just something i'll have to get used to. Has anyone else experienced a different brake feel after switching to vacuum brakes? Is that normal?
I didn't mess around either, bled all for wheels at the same time. I just took the cap off the master cylinder, made sure it was right full of fluid and opened all four bleeder screws and let it drain for a while. I made up some plastic lines that I plugged onto the bleeder screws so I could see the fluid and any air coming out. I just kept topping up the MC as to not suck air into the lines from there. I poured a full can and then some of brake fluid through the system. If there was any air there I'm confident I got it all. After that I re-adjusted my back brakes, made sure there was a little drag equally on both sides. Put everything back together and took her for a spin. I definitely have brakes now!! The vacuum brakes feel different than the powermaster system did, I think its just something i'll have to get used to. Has anyone else experienced a different brake feel after switching to vacuum brakes? Is that normal?
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