brake stopping power?
Thread Starter
Cruising
Joined: Nov 2009
Posts: 10
Likes: 0
brake stopping power?
I've red all the threads on this topic but haven't seen my problem. I've bleed out my system with Dot 5 and over a few rest periods seems like clear fluid no bubbles.It's a 71' big block manual brakes.I've driven over 2000 miles since complete rebuild.The pedal is high but the effort to stop is also to high.I can't lock the wheels up, stops straight but in an emergency I might not stop in time.New stock rotors an Delco pads ,rebuilt calipers,.Any ideas? It's making me think of Hyro-boost. I should be able to lock up the wheels if every thing is in working order or did I miss somthing.Thanks Paul
Le Mans Master
Joined: Aug 2001
Posts: 7,804
Likes: 4
From: Standing still with all my might Texas
Cruise-In X Veteran
St. Jude Donor '09-'11
Are you sure you have the correct master cylinder for manual brakes installed?
The bore (and piston) size of the master cylinder for manual brakes is different than the one for power brakes.
The bore (and piston) size of the master cylinder for manual brakes is different than the one for power brakes.
Thread Starter
Cruising
Joined: Nov 2009
Posts: 10
Likes: 0
To be honest,It was on the car when I bought it.What is the correct piston diameter for a manual master?
Team Owner
Joined: Jan 2006
Posts: 37,637
Likes: 3,118
From: Crossville TN
If you have not changed the flex brake hoses [at each caliper] in several years (or ever...), I suspect that is your problem. The passage inside that flex line is very small; and the rubber deteriorates inside the line and can effectively plug that small passage. I suggest that you change those lines if they are many years old.
You could also have some mechanical issue with the proportioning valve. Or, someone [in the past] could have replaced the master cylinder with the wrong one. If a MC for power brakes was installed in your 'manual brake' vehicle, pedal effort would be substantially increased. I believe the casting numbers are the same, so you would have to disassemble the MC and measure the diameter of the valve to know if it is the wrong one or not.
Good luck on your search.
You could also have some mechanical issue with the proportioning valve. Or, someone [in the past] could have replaced the master cylinder with the wrong one. If a MC for power brakes was installed in your 'manual brake' vehicle, pedal effort would be substantially increased. I believe the casting numbers are the same, so you would have to disassemble the MC and measure the diameter of the valve to know if it is the wrong one or not.
Good luck on your search.
Le Mans Master
Joined: Aug 2001
Posts: 7,804
Likes: 4
From: Standing still with all my might Texas
Cruise-In X Veteran
St. Jude Donor '09-'11
Hopefully someone else will chime in and correct me if I am wrong.
Thread Starter
Cruising
Joined: Nov 2009
Posts: 10
Likes: 0
Thanks, When I built the car everything was changed including the hoses.The manual master has a 1" bore the power master has a 1 and an eighth" bore. If it were wrong how could that extra volume make it hard to press the pedal?
Le Mans Master
Joined: Aug 2001
Posts: 7,804
Likes: 4
From: Standing still with all my might Texas
Cruise-In X Veteran
St. Jude Donor '09-'11
Take a look at "Hydraulic multiplication"
http://science.howstuffworks.com/tra...hydraulic1.htm
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Race Director
Joined: Jul 2004
Posts: 12,706
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From: Scottsdale Arizona
You are correct, a manual brake master cylinder should have a 1" bore.
Take a look at "Hydraulic multiplication"
http://science.howstuffworks.com/tra...hydraulic1.htm
Take a look at "Hydraulic multiplication"
http://science.howstuffworks.com/tra...hydraulic1.htm
To the OP, obviously you need to sort out where/what the problem is. Many of us have experienced that sick feeling when you wonder if you're going to stop in time. Although many will disagree with me, I think Hydroboost will just mask your issues and not eliminate them. Probably a lot easier than converting to power brakes using a vucuum booster though.
Along with your master cylinder, make sure that your brake clevis pin is in the correct, top hole. If this is backwards it will increase the amount of force that you have to apply to the pedal.
Le Mans Master
Joined: May 2006
Posts: 9,993
Likes: 1,136
From: League City Tx
FWIW, my 71 is the same way with manual brakes. I have replaced EVERYTHING in the brake system as well as tried multiple master cylinders, bled the brakes every way possible (ended up pressure bleeding them with the pressure bleeder tool) and they are still lack luster at best. I have a firm pedal, under full hard braking the pedal is about 2-2.5" off of the floor. The car stops straight and smooth but this thing wouldn't lock the brakes up to save it's life. This scenario has been like this for 4-5 years. I re-bleed the brakes and flush the fluid every year....same ole same ole. It's liveable but I damn sure don't tail gate anyone.
.
If Bambi ran out in front of me, I would be having deer meat chili for dinner as I cry about my car.
. If Bambi ran out in front of me, I would be having deer meat chili for dinner as I cry about my car.
Thread Starter
Cruising
Joined: Nov 2009
Posts: 10
Likes: 0
You are correct, a manual brake master cylinder should have a 1" bore.
Take a look at "Hydraulic multiplication"
http://science.howstuffworks.com/tra...hydraulic1.htm
Take a look at "Hydraulic multiplication"
http://science.howstuffworks.com/tra...hydraulic1.htm
Thread Starter
Cruising
Joined: Nov 2009
Posts: 10
Likes: 0
Cool link!
To the OP, obviously you need to sort out where/what the problem is. Many of us have experienced that sick feeling when you wonder if you're going to stop in time. Although many will disagree with me, I think Hydroboost will just mask your issues and not eliminate them. Probably a lot easier than converting to power brakes using a vucuum booster though.
Along with your master cylinder, make sure that your brake clevis pin is in the correct, top hole. If this is backwards it will increase the amount of force that you have to apply to the pedal.
To the OP, obviously you need to sort out where/what the problem is. Many of us have experienced that sick feeling when you wonder if you're going to stop in time. Although many will disagree with me, I think Hydroboost will just mask your issues and not eliminate them. Probably a lot easier than converting to power brakes using a vucuum booster though.
Along with your master cylinder, make sure that your brake clevis pin is in the correct, top hole. If this is backwards it will increase the amount of force that you have to apply to the pedal.
Thread Starter
Cruising
Joined: Nov 2009
Posts: 10
Likes: 0
FWIW, my 71 is the same way with manual brakes. I have replaced EVERYTHING in the brake system as well as tried multiple master cylinders, bled the brakes every way possible (ended up pressure bleeding them with the pressure bleeder tool) and they are still lack luster at best. I have a firm pedal, under full hard braking the pedal is about 2-2.5" off of the floor. The car stops straight and smooth but this thing wouldn't lock the brakes up to save it's life. This scenario has been like this for 4-5 years. I re-bleed the brakes and flush the fluid every year....same ole same ole. It's liveable but I damn sure don't tail gate anyone..
If Bambi ran out in front of me, I would be having deer meat chili for dinner as I cry about my car.
. If Bambi ran out in front of me, I would be having deer meat chili for dinner as I cry about my car.
Racer
Joined: Mar 2008
Posts: 315
Likes: 0
From: KY
I have the same problem with my 71 manual brakes it just doesnt seem like it is going to stop.
I looked into geting a vac booster but it is a super PITA to install the vac booster.
My car also doesnt have power steering so no hydra boost so I got one of these
http://www.abspowerbrake.com/ehpm.html
We pretty much finished up installing it last weekend hopefully we will bleed the system this weekend and go for a test drive.
I looked into geting a vac booster but it is a super PITA to install the vac booster.
My car also doesnt have power steering so no hydra boost so I got one of these
http://www.abspowerbrake.com/ehpm.html
We pretty much finished up installing it last weekend hopefully we will bleed the system this weekend and go for a test drive.
Last edited by ZZ71S; Mar 3, 2011 at 06:18 PM.
Instructor
Joined: Oct 2007
Posts: 154
Likes: 1
From: Hanover Maryland
I have the same problem with my 71 manual brakes it just doesnt seem like it is going to stop.
I looked into geting a vac booster but it is a super PITA to install the vac booster.
My car also doesnt have power steering so no hydra boost so I got one of these
http://www.abspowerbrake.com/ehpm.html
We pretty much finished up installing it last weekend hopefully we will bleed the system this weekend and go for a test drive.
I looked into geting a vac booster but it is a super PITA to install the vac booster.
My car also doesnt have power steering so no hydra boost so I got one of these
http://www.abspowerbrake.com/ehpm.html
We pretty much finished up installing it last weekend hopefully we will bleed the system this weekend and go for a test drive.
Racer
Joined: Mar 2008
Posts: 315
Likes: 0
From: KY
Its not cheap but after looking at what it takes to install that vac booster and than haveing that vac booster in the way or setting up for hydra boost which would have mint power steering probaly one of those rack kits the price startes to look a little better.
