Very Weak Brakes
Thread Starter
Burning Brakes
Joined: Mar 2005
Posts: 861
Likes: 0
From: WNY
Very Weak Brakes
Well I finally got to drive it last night after the re-build. It runs great but the brakes are VERY weak - almost not able to stop the car. I can push the pedal all the way down to the floor with very little force and its like I have barely applied the brakes at all.
The brakes have always been pretty soft, but never this bad. I did have to pull one brake line when putting in the rear spring (it was sitting right above the pilot hole and I couldnt get the bolt in or out with it right there). I went ahead and bled the brakes before testing it out, and I bled them again after noticing the pedal being so soft but that didnt seem to help any.
What are the normal causes of this? I have power brakes on it, so I checked to make sure there was no vacuum leak from the back of the carb to the booster. Everything looks to be hooked up and they do work, just badly. Any suggestions?
The brakes have always been pretty soft, but never this bad. I did have to pull one brake line when putting in the rear spring (it was sitting right above the pilot hole and I couldnt get the bolt in or out with it right there). I went ahead and bled the brakes before testing it out, and I bled them again after noticing the pedal being so soft but that didnt seem to help any.
What are the normal causes of this? I have power brakes on it, so I checked to make sure there was no vacuum leak from the back of the carb to the booster. Everything looks to be hooked up and they do work, just badly. Any suggestions?
Thread Starter
Burning Brakes
Joined: Mar 2005
Posts: 861
Likes: 0
From: WNY
I have not flushed all the fluid - I could probably do that this evening. No leaks that I can see. Master Cyl has been replaced or rebuilt at some point by the looks of it.
Team Owner
Joined: Jun 2000
Posts: 38,923
Likes: 1,481
From: Southbound
Cruise-In II Veteran
Boosters seldom fail and tend to get blamed for other brake problems. Sounds like you might have a master cylinder going bad or one or more calipers pulling air. Have you checked the run out on all four corners?
Team Owner
Joined: Jul 2008
Posts: 23,419
Likes: 22
From: In limbo
St. Jude Donor '13-'15, '17 thru '22
Usually when the booster fails, the pedal will feel very hard, and you will have to push on it real hard to stop the car. This does not sound like your problem.
As Easy Mike said, the only reasons I can think of for getting what you described is a small amount of air in the system, or a master cylinder going bad. I see ejpii's post on the lines, I have never experienced that but have heard stranger things. I think if it was me, I would bleed the brakes again all the way around and get a good look at all of your brake lines. Also look for brake fluid around your pistons, a caliper pulling air will usually be weeping a little fluid as well.
As Easy Mike said, the only reasons I can think of for getting what you described is a small amount of air in the system, or a master cylinder going bad. I see ejpii's post on the lines, I have never experienced that but have heard stranger things. I think if it was me, I would bleed the brakes again all the way around and get a good look at all of your brake lines. Also look for brake fluid around your pistons, a caliper pulling air will usually be weeping a little fluid as well.
Melting Slicks
Joined: Mar 2007
Posts: 2,100
Likes: 12
From: Frederick Maryland
As already said, it could be rubber lines collapsing internally. I know you've had the air bled, but there could well be air hiding in there. You could have a caliper piston seal not seating and it's sucking air in (happened to me).
Also...has anyone inadvertently mixed DOT 3 and DOT 5 silicone brake fluid? They're incompatible and will definitely make for a very soft brake pedal or no brakes at all.
If the rubber brake lines are original, then replacement is in order for safety's sake, followed by a complete flushing of the system.
Also...has anyone inadvertently mixed DOT 3 and DOT 5 silicone brake fluid? They're incompatible and will definitely make for a very soft brake pedal or no brakes at all.
If the rubber brake lines are original, then replacement is in order for safety's sake, followed by a complete flushing of the system.
Thread Starter
Burning Brakes
Joined: Mar 2005
Posts: 861
Likes: 0
From: WNY
As already said, it could be rubber lines collapsing internally. I know you've had the air bled, but there could well be air hiding in there. You could have a caliper piston seal not seating and it's sucking air in (happened to me).
Also...has anyone inadvertently mixed DOT 3 and DOT 5 silicone brake fluid? They're incompatible and will definitely make for a very soft brake pedal or no brakes at all.
If the rubber brake lines are original, then replacement is in order for safety's sake, followed by a complete flushing of the system.
Also...has anyone inadvertently mixed DOT 3 and DOT 5 silicone brake fluid? They're incompatible and will definitely make for a very soft brake pedal or no brakes at all.
If the rubber brake lines are original, then replacement is in order for safety's sake, followed by a complete flushing of the system.
Now that is something I did not think of - that could have happened at some point for sure.
I will flush the system tonight and re-fill. I will also inspect for any break fluid leaks. Thanks for the advice!
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Melting Slicks
Joined: Feb 2007
Posts: 2,136
Likes: 62
From: West Kingston RI
This is how mine was before I replaced the booster.
Le Mans Master
Joined: Jan 2007
Posts: 5,485
Likes: 7
From: Peekskill NY
My vote is the MC needs to be rebuilt or replaced. Does it improve at all if you pump the pedal to build up pressure before you try to stop?
Also, have someone pump the pedal while you look at the lines also to see if they are expanding.
Glenn
Also, have someone pump the pedal while you look at the lines also to see if they are expanding.
Glenn
