Master cylinder bleeding
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7th Gear
Joined: Jul 2008
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Master cylinder bleeding
I am replacing the master cylinder on a 66 as part of a complete brake restoring. Every part from the rod to the bearings. The new cylinder has an instruction note that states: "Due the type of seals used, do not bench bleed this cylinder. Vacuum or power bleed only." I'm not familiar with either when it comes to a master cylinder. What's the deal? FYI Cylinder is single - no proportioning valve, no power booster.
Thanks, Ron
Thanks, Ron
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From: Close to DC
C2 of the Year Finalist - Modified 2020
Vacuum bleeding is when you attach a hand held vac pump (Mity Vac) to each bleader on each caliper. You have the top off of the master cyl. with fluid in it. As you open each bleeder it will draw down on the fluid. You don't want to let it get empty, otherwise you'll have to start over. Power bleed should refers to attaching a canister to the top of the master cyl. It would contain brake fluid under pressure so that as you open each bleeder that pressure would force the air/fluid out until it ran clear. In each case make sure you follow the manufacturer's instruction. Others here on the CF may add to this. 
Dennis
Dennis
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From: Washington Michigan
Heel & Toe
Joined: Mar 2008
Posts: 15
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From: Woodinville WA
I replaced my master clyinder last winter, bench bled, then bled
each caliper. All was good, good pedal, stopped fine and straight.
Last weekend on the way to a show I had to do hard stop at a light
to avoid loosing the other two cars behind me.
When I left the show at the end of the day, I had little or no brakes.
Pedal was almost on the floor. Limped it home, master cylinder was
full.
I have less than five hundred miles on it.
I ordered a new one from the partsladi, it came with the warning
label,
"Warning due to the oem seal design on this cylinder, you should not attempt to bench bleed prior to installation. This item should be pressure bled or vacuum bled only."
each caliper. All was good, good pedal, stopped fine and straight.
Last weekend on the way to a show I had to do hard stop at a light
to avoid loosing the other two cars behind me.
When I left the show at the end of the day, I had little or no brakes.
Pedal was almost on the floor. Limped it home, master cylinder was
full.
I have less than five hundred miles on it.
I ordered a new one from the partsladi, it came with the warning
label,
"Warning due to the oem seal design on this cylinder, you should not attempt to bench bleed prior to installation. This item should be pressure bled or vacuum bled only."
Last edited by Kent S; Sep 6, 2009 at 03:40 PM.
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I've tried all the ways to bleed my '65 brakes and the BEST results are from the 2 person method. One sits in the car and pushes down on the pedal and the other person bleeds the calipers and keeps the master cylinder full.
Your mileage may vary.
Your mileage may vary.
Team Owner
Joined: Mar 2003
Posts: 26,118
Likes: 1,874
From: Greenville, Indiana
I saw this on a cylinder instruction sheet somewhere in the last year. I don't remember what vehicle it was for or other details but knowing me, it wasn't a new cylinder but rebuilt and not a GM.
I ignored the instruction and bench bled it anyway as I don't have a pressure bleeder and I don't care for the vacuum bleed method. No problem here but I don't know what the negative consequeces of bench bleeding might have been but I did it anyway.
I ignored the instruction and bench bled it anyway as I don't have a pressure bleeder and I don't care for the vacuum bleed method. No problem here but I don't know what the negative consequeces of bench bleeding might have been but I did it anyway.
Last edited by MikeM; Sep 6, 2009 at 04:42 PM.
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Joined: Feb 2005
Posts: 12,458
Likes: 27
I saw this on a cylinder instruction sheet somewhere in the last year. I don't remember what vehicle it was for or other details but knowing me, it wasn't a new cylinder but rebuilt and not a GM.
I ignored the instruction and bench bled it anyway as I don't have a pressure bleeder and I don't care for the vacuum bleed method. No problem here but I don't know what the negative consequeces of bench bleeding might have been.
I ignored the instruction and bench bled it anyway as I don't have a pressure bleeder and I don't care for the vacuum bleed method. No problem here but I don't know what the negative consequeces of bench bleeding might have been.
