!993 C4 Brake Mystery??
03-19-2016, 01:11 PM
#1
!993 C4 Brake Mystery??
I've owned my 1993 C4 convertible all stock, 6 speed manual for a couple years. It has 60,000 miles on it. Brake pads are good. What is happening ever since I've owned it is.....When the engine isn't running, I have no brakes. Just a hard pedal with no braking and no emergency brake. It's a real problem when I happen to park on an incline (which I never do anymore) because as soon as I push in the clutch I start rolling with no brake til the engine starts. What could be the problem. I'm thinking brake booster (I've already tried the pedal test as recommended on here and it passes). What does the Power Brake Booster Vacuum Valve do? Could that be the problem? I need cheap, reliable help from my Corvette brothers.
03-19-2016, 05:33 PM
#2
The vacuum only works when the engine is running. Push your brake and set the emergency brake before you shut the car off. And start the car before you take it off.
Last edited by antfarmer2; 03-19-2016 at 05:35 PM.
03-19-2016, 05:42 PM
#3
I've never had a car that I've had to follow that procedure. I've owned plenty of manual transmission cars. Parking brake doesn't hold the car from rolling anyway. I don't know what the problem is.
03-19-2016, 05:52 PM
#4
Team Owner
Pro Mechanic
Two things;
1. You don't have "no brakes". It irritates me when people claim that when their power/boost system fails. It's a bit alarmist, dramatic...and it simply ain't true. You still have brakes, they still work. There is (obviously) no power assist, so in this particular case, you have to man up a little bit and step on the pedal...harder.
2. Brake booster should hold a vacuum (and thus, provide power braking) for at least 3 pedal strokes, after a vacuum source is removed (engine is shut off). It should hold this vacuum, for days. Maybe even weeks. You need a new brake booster OR the one way check valve in the vacuum line where it plugs into the booster.
You can easily test the valve by removing from the booster and the vacuum hose (or from the manifold, which ever is easier), and try blowing through it backward ("backward would be tryin to blow air through the valve/fitting toward the booster side/from the manifold side. If you can pass ANY air through it....it junk.
W/regard to your parking brake....what are the symptoms? Does the lever come all the way up w/no resistance? Does the lever effort get hard down low....but brakes aren't engaging?
.
1. You don't have "no brakes". It irritates me when people claim that when their power/boost system fails. It's a bit alarmist, dramatic...and it simply ain't true. You still have brakes, they still work. There is (obviously) no power assist, so in this particular case, you have to man up a little bit and step on the pedal...harder.
2. Brake booster should hold a vacuum (and thus, provide power braking) for at least 3 pedal strokes, after a vacuum source is removed (engine is shut off). It should hold this vacuum, for days. Maybe even weeks. You need a new brake booster OR the one way check valve in the vacuum line where it plugs into the booster.
You can easily test the valve by removing from the booster and the vacuum hose (or from the manifold, which ever is easier), and try blowing through it backward ("backward would be tryin to blow air through the valve/fitting toward the booster side/from the manifold side. If you can pass ANY air through it....it junk.
W/regard to your parking brake....what are the symptoms? Does the lever come all the way up w/no resistance? Does the lever effort get hard down low....but brakes aren't engaging?
.
Last edited by Tom400CFI; 03-19-2016 at 05:59 PM.
03-19-2016, 07:51 PM
#5
Drifting
Sounds as if your parking brakes either need adjustment or replacement.
When you shut your car off, the pedal will raise up and get hard. The booster will not hold your car in place. The car will be held in place with the parking brake, hence the word " parking" brake.
When you shut your car off, the pedal will raise up and get hard. The booster will not hold your car in place. The car will be held in place with the parking brake, hence the word " parking" brake.
03-19-2016, 10:48 PM
#6
Team Owner
Pro Mechanic
No...that is not right either. Only two things should deplete the vacuum stored in the booster;
1. pedal movement
2. a leak
If you depress your brake pedal to hold your car on a hill, shut the car off and maintain the same pedal pressure/position, the booster should maintain it's effectiveness (essentially) indefinitely. Unless it has a leak.
1. pedal movement
2. a leak
If you depress your brake pedal to hold your car on a hill, shut the car off and maintain the same pedal pressure/position, the booster should maintain it's effectiveness (essentially) indefinitely. Unless it has a leak.
03-19-2016, 10:55 PM
#7
Race Director
No...that is not right either. Only two things should deplete the vacuum stored in the booster;
1. pedal movement
2. a leak
If you depress your brake pedal to hold your car on a hill, shut the car off and maintain the same pedal pressure/position, the booster should maintain it's effectiveness (essentially) indefinitely. Unless it has a leak.
1. pedal movement
2. a leak
If you depress your brake pedal to hold your car on a hill, shut the car off and maintain the same pedal pressure/position, the booster should maintain it's effectiveness (essentially) indefinitely. Unless it has a leak.
03-20-2016, 10:14 AM
#8
No...that is not right either. Only two things should deplete the vacuum stored in the booster;
1. pedal movement
2. a leak
If you depress your brake pedal to hold your car on a hill, shut the car off and maintain the same pedal pressure/position, the booster should maintain it's effectiveness (essentially) indefinitely. Unless it has a leak.
1. pedal movement
2. a leak
If you depress your brake pedal to hold your car on a hill, shut the car off and maintain the same pedal pressure/position, the booster should maintain it's effectiveness (essentially) indefinitely. Unless it has a leak.
03-20-2016, 11:16 AM
#9
Team Owner
Pro Mechanic
You haven't shed any more light on your parking brake behavior, but with the limited information on that, and your inability to get the brakes to function w/no power assist, I wonder if the two issues are related?
Need more info....
03-20-2016, 11:27 AM
#10
Team Owner
Pro Mechanic
HOW IT WORKS: Brake boosters
03-20-2016, 01:12 PM
#11
Thank you, Tom. I'll give that a try. Rolling backwards down my Dad's driveway into traffic waiting for the engine to fire up, I was definitely stepping on the brake pedal as hard as I could. I'm no wimpy, little guy. It's just rock hard with no hydraulic action with the engine off.
