brake question
Thread Starter
Pro
Joined: Jun 2008
Posts: 680
Likes: 3
From: charlotte N.C
brake question
Here’s the dilemma. When I bought my 76 corvette I received a “new” master cylinder with it so when I did a full engine bay restoration I installed the “new” master cylinder. Well with this master cylinder the brakes were always being applied. It wasn’t enough to drag the wheels but it would prevent you from rolling on an incline. Not good, I know but I was anxious to start driving it. Well I had some free time the other day and decide to switch out the master cylinder with one I know is new from NAPA. Before installing it I benched bled it to get any air out. Once it was on the car I bleed the brake; maybe doing it 4 times to each wheal to make sure all the air was out. The problem now is the brakes are not firm at all. It does applied pleasure but not enough. I think the petal is hitting the mechanical stop. There are no leaks under the car. I am going crazy trying to think what it is. I have done brakes for years and never had any problems. Does anyone have any advice? 
Le Mans Master
Joined: Jan 2000
Posts: 8,918
Likes: 27
From: New Hill NC
Here’s the dilemma. When I bought my 76 corvette I received a “new” master cylinder with it so when I did a full engine bay restoration I installed the “new” master cylinder. Well with this master cylinder the brakes were always being applied. It wasn’t enough to drag the wheels but it would prevent you from rolling on an incline. Not good, I know but I was anxious to start driving it. Well I had some free time the other day and decide to switch out the master cylinder with one I know is new from NAPA. Before installing it I benched bled it to get any air out. Once it was on the car I bleed the brake; maybe doing it 4 times to each wheal to make sure all the air was out. The problem now is the brakes are not firm at all. It does applied pleasure but not enough. I think the petal is hitting the mechanical stop. There are no leaks under the car. I am going crazy trying to think what it is. I have done brakes for years and never had any problems. Does anyone have any advice?
Melting Slicks
Joined: Dec 2000
Posts: 3,407
Likes: 2
From: Carmichael CA
It sounds like you bought a car which has a brake system problem and the previous owner was not able to solve it. I think the best place to learn how to do brakes yourself is to purchase the Bureau of Automotive Repair (BAR) Brake Inspection and Repair manual which is published by your State.
You need to diagnose the problem and fix it...just replacing parts isn't going to get you anywhere except broke.
You need to diagnose the problem and fix it...just replacing parts isn't going to get you anywhere except broke.
Intermediate
Joined: Feb 2010
Posts: 36
Likes: 0
I think I may know what your problem is. If you have power brakes, the booster plunger that fits into the master cylinder to actuate it, has a screw thread with some sort of deformed locking collar on it so the length can be adjusted. Your dragging brakes problem followed by the loss of pedal sounds like someone "adjusted" this or it has come loose. It is easy to measure the depth of your old versus new master cylinder and compare the numbers. Also you can measure the distance the brake booster plunger sticks out and compare it to the depth of the master cylinders. I have a feeling there will be a difference between the master cylinders.
(the reason i know this is recently i replaced my leaking mc with an aluminum "hot rod" master cylinder. it turns out the hot rod guys use a lot of corvette parts (independent rear) and as a result the brake system also. they have knocked off the original steel mc with an exact duplicate, except with an aluminum body. the reason i did this was for weight. the mc weighs 1/2 of what the steel one weighs. before i made the swap i carefully measured all this stuff to make sure it would work properly. It did, it is an exact duplicate. and for the first time since i have owned the car (3 years!!) it finally has brakes.)
(the reason i know this is recently i replaced my leaking mc with an aluminum "hot rod" master cylinder. it turns out the hot rod guys use a lot of corvette parts (independent rear) and as a result the brake system also. they have knocked off the original steel mc with an exact duplicate, except with an aluminum body. the reason i did this was for weight. the mc weighs 1/2 of what the steel one weighs. before i made the swap i carefully measured all this stuff to make sure it would work properly. It did, it is an exact duplicate. and for the first time since i have owned the car (3 years!!) it finally has brakes.)
Thread Starter
Pro
Joined: Jun 2008
Posts: 680
Likes: 3
From: charlotte N.C
I believe the one the car now is the correct one but just won’t work.
How do I determine if my MC has a deep hole or a shallow hole?
I never messed with the push rode length. How do I know if it is the right length?
The car worked perfectly when I bought the car 2 years ago but once I did the engine bay restoration about 3 months ago I couldn't get them right.
Here is the one that was on the car when I bought it which worked perfectly. It looked like this so I decided to switch it out with a "new" one.
Here is the "new" one I got with the car when I bought it. With this one, the brakes were always being applied. This gave me great gas mileage as you can imagine.
The one on the car now is a new one that I believe is correct that I got from NAPA. I don't have a picture but here is a link.
http://www.napaonline.com/Search/Det...+50012+2012030
Brakes really shoudn't be this difficult. There isn't that much to it.
How do I determine if my MC has a deep hole or a shallow hole?
I never messed with the push rode length. How do I know if it is the right length?
The car worked perfectly when I bought the car 2 years ago but once I did the engine bay restoration about 3 months ago I couldn't get them right.
Here is the one that was on the car when I bought it which worked perfectly. It looked like this so I decided to switch it out with a "new" one.
Here is the "new" one I got with the car when I bought it. With this one, the brakes were always being applied. This gave me great gas mileage as you can imagine.
The one on the car now is a new one that I believe is correct that I got from NAPA. I don't have a picture but here is a link.
http://www.napaonline.com/Search/Det...+50012+2012030
Brakes really shoudn't be this difficult. There isn't that much to it.
Le Mans Master
Joined: Sep 2003
Posts: 8,812
Likes: 2,029
From: eastern NC
I would try to determine exactly which wheels are dragging. All or one, two or three...
One thing you haven't mentioned is the fabric lines that go from the hard lines to the calipers. These are notorious for deteriorating and acting like check valves by holding residual line pressure after the pedal has been released.
If you find that only some of the wheels are dragging, keeping in mind that disc brakes don't exactly spin freely when operating normally, you can isolate it to those corners of the brake system. If all drag uniformly, by all means look closely at the master cylinder.
Good luck... GUSTO
One thing you haven't mentioned is the fabric lines that go from the hard lines to the calipers. These are notorious for deteriorating and acting like check valves by holding residual line pressure after the pedal has been released.
If you find that only some of the wheels are dragging, keeping in mind that disc brakes don't exactly spin freely when operating normally, you can isolate it to those corners of the brake system. If all drag uniformly, by all means look closely at the master cylinder.
Good luck... GUSTO
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Intermediate
Joined: Feb 2010
Posts: 36
Likes: 0
oh... I don't think either of the master cylinders you have pictured are correct. The correct ones look like a pair of toilet bowls. The rusty one is certainly not right. The second one is close, but not right either. I will bet the napa one is correct, the link would not open BTW.
The previous owner adjusted the rod to work on the rusty mc. the next mc you installed, this resulted in the brakes dragging (partially actuated) and your new one is likely running out of actuation throw before building any pressure. This is my guess.
The previous owner adjusted the rod to work on the rusty mc. the next mc you installed, this resulted in the brakes dragging (partially actuated) and your new one is likely running out of actuation throw before building any pressure. This is my guess.
