Brake bleeding
Thread Starter
Heel & Toe
Joined: Sep 2013
Posts: 20
Likes: 0
Brake bleeding
I know there is tons written on bleeding brakes and the headaches that are common. Anyway, on my 66, a year ago I replaced my single manual master cylinder with a double and power brake booster. Also replaced some lines. Never had great breaks, good but not great. Excessive pedal travel recently caused me to revisit the bleeding process. I have a power bleeder and when bleeding the rear brakes, if I tap on the pads or move them with a screwdriver I get lots of air. It eventually stopped and I now have great breaks. My question is, by tapping the pads am I introducing air that I see when I am bleeding or is this just air I never got out from a year ago?
Tom
Tom
Safety Car
Joined: May 2004
Posts: 4,469
Likes: 275
From: Naples FL
I've used a rawhide mallet for the same purpose. The little air bubbles like to hide out in the caliper. The hammer scares them. Ok, dislodges them.
The real question is how this air got into the calipers.
Richard Newton
Car Tech Stuff
The real question is how this air got into the calipers.
Richard Newton
Car Tech Stuff
Le Mans Master
Joined: Oct 2000
Posts: 8,897
Likes: 1,357
From: Santa Ana CA
I've used a rawhide mallet for the same purpose. The little air bubbles like to hide out in the caliper. The hammer scares them. Ok, dislodges them.
The real question is how this air got into the calipers.
Richard Newton
Car Tech Stuff
The real question is how this air got into the calipers.
Richard Newton
Car Tech Stuff
Drifting
Joined: Mar 2011
Posts: 1,402
Likes: 214
From: Iowa
When you are tapping the pads you are also bouncing the pads off the caliper pistons...and while I have never heard of your technique of tapping the pads while bleeding the brakes, it sounds as though it may have helped remove some trapped air in the caliper. Therefore, since you indicate the pedal has firmed up, I don't think by tapping the pads that you were introducing more air that you were seeing while doing the bleeding. The only way to know is drive it a bit and see what happens...the original non stainless/non HD o-ring calipers are known to draw in air around the piston...the redesign has proven to be much better and reliable.
I use a Motive bleeder and it works ok...even with the pressure bleeder it can be a challenge to get all the air out. I usually bleed each caliper before I try focus on the lines.
Sounds like you may have got it figured.
Cheers,
Frank
I use a Motive bleeder and it works ok...even with the pressure bleeder it can be a challenge to get all the air out. I usually bleed each caliper before I try focus on the lines.
Sounds like you may have got it figured.
Cheers,
Frank
Le Mans Master
Joined: Oct 2000
Posts: 8,897
Likes: 1,357
From: Santa Ana CA
You should check your rotor run-out to determine if air pumping is a possible cause.
I lost my brakes on the freeway due to air pumping and I had to use the rear emergency brake (still has '64 rear drums) to stop when coming off the ramp. A long drive on the freeway is the worst thing you can do and probably the best test.
Very hairy, especially for my wife
! We had to have the car towed home. My calipers were exchanged for a later design with stainless pistons right after that.
Air pumping can cost you both your car and your life.
I lost my brakes on the freeway due to air pumping and I had to use the rear emergency brake (still has '64 rear drums) to stop when coming off the ramp. A long drive on the freeway is the worst thing you can do and probably the best test.
Very hairy, especially for my wife
! We had to have the car towed home. My calipers were exchanged for a later design with stainless pistons right after that.Air pumping can cost you both your car and your life.
Last edited by toddalin; Nov 21, 2014 at 08:06 PM.
Thread Starter
Heel & Toe
Joined: Sep 2013
Posts: 20
Likes: 0
I've used a rawhide mallet for the same purpose. The little air bubbles like to hide out in the caliper. The hammer scares them. Ok, dislodges them.
The real question is how this air got into the calipers.
Richard Newton
Car Tech Stuff
The real question is how this air got into the calipers.
Richard Newton
Car Tech Stuff
I will check the run-out on the rotors and drive it and see if the pedal stays firm. I have a dual master and so I don't think I will ever suddenly lose my brakes.
Le Mans Master
Joined: Oct 2000
Posts: 8,897
Likes: 1,357
From: Santa Ana CA
