79 L48 Brakes
Thread Starter
5th Gear
Joined: Jun 2008
Posts: 4
Likes: 0
79 L48 Brakes
Please help I'm stumped. I've bled the brakes. I've installed a new master cylinder and bleed the brakes a second time. Each time getting a good pedal. After driving a few miles and without warning the pedal goes to the floor and light comes on. NO BRAKES. No sign of caliper leak. Any ideas?
Race Director
Joined: May 2006
Posts: 18,734
Likes: 2,582
1. Did you bench bleed the master?
2. Are you bleeding in the sequence RR both bleed screws, LR both bleed screws, RF, and LF?
3. Are you tapping the calipers with a hammer to dislodge air bubbles when bleeding?
4. Have you looked at all piston seals on all calipers for signs of a leak?
2. Are you bleeding in the sequence RR both bleed screws, LR both bleed screws, RF, and LF?
3. Are you tapping the calipers with a hammer to dislodge air bubbles when bleeding?
4. Have you looked at all piston seals on all calipers for signs of a leak?
Team Owner
Joined: Apr 2002
Posts: 26,563
Likes: 29
From: Northridge California
St. Jude Donor '14
My first thought was if you bench bled the Master Cylinder, as suggested by the above poster...
Those lip seal calipers are a pain in the butt, after going through a few commercially rebuilt ones, I ordered the O-Ring units from Van Steel. NO. MORE. PROBLEMS.
Those lip seal calipers are a pain in the butt, after going through a few commercially rebuilt ones, I ordered the O-Ring units from Van Steel. NO. MORE. PROBLEMS.
Last edited by Chinaski; Mar 25, 2017 at 11:24 AM.
Melting Slicks
Joined: Jun 2011
Posts: 3,116
Likes: 598
Please help I'm stumped. I've bled the brakes. I've installed a new master cylinder and bleed the brakes a second time. Each time getting a good pedal. After driving a few miles and without warning the pedal goes to the floor and light comes on. NO BRAKES. No sign of caliper leak. Any ideas?
First test with engine off.
Remove the master cylinder cover. Then slowly press down on your brakes. You should see a steady flow of fluid in the master cylinder reservoir. You may need a second person to make this easier. Also the pedal should return when you lift off. If you see air bubbles then re-bleed the master cylinder.
Next put the cover back on and see how long you can apply brake pedal pressure without the pedal moving down. If it slowly moves down then the master cylinder will be the problem / or you have a leak somewhere.
Next repeat the steps with the engine running.
Also make sure you cover any areas of the car to prevent brake fluid splashing on paint etc.
With the engine running in step 2 you will be applying boosted pressure to the master cylinder.
Thread Starter
5th Gear
Joined: Jun 2008
Posts: 4
Likes: 0
1. Did you bench bleed the master?
2. Are you bleeding in the sequence RR both bleed screws, LR both bleed screws, RF, and LF?
3. Are you tapping the calipers with a hammer to dislodge air bubbles when bleeding?
4. Have you looked at all piston seals on all calipers for signs of a leak?
2. Are you bleeding in the sequence RR both bleed screws, LR both bleed screws, RF, and LF?
3. Are you tapping the calipers with a hammer to dislodge air bubbles when bleeding?
4. Have you looked at all piston seals on all calipers for signs of a leak?
Thread Starter
5th Gear
Joined: Jun 2008
Posts: 4
Likes: 0
Once you get the car back in the garage do you have good pedal at some point ? If not try the following.
First test with engine off.
Remove the master cylinder cover. Then slowly press down on your brakes. You should see a steady flow of fluid in the master cylinder reservoir. You may need a second person to make this easier. Also the pedal should return when you lift off. If you see air bubbles then re-bleed the master cylinder.
Next put the cover back on and see how long you can apply brake pedal pressure without the pedal moving down. If it slowly moves down then the master cylinder will be the problem / or you have a leak somewhere.
Next repeat the steps with the engine running.
Also make sure you cover any areas of the car to prevent brake fluid splashing on paint etc.
With the engine running in step 2 you will be applying boosted pressure to the master cylinder.
First test with engine off.
Remove the master cylinder cover. Then slowly press down on your brakes. You should see a steady flow of fluid in the master cylinder reservoir. You may need a second person to make this easier. Also the pedal should return when you lift off. If you see air bubbles then re-bleed the master cylinder.
Next put the cover back on and see how long you can apply brake pedal pressure without the pedal moving down. If it slowly moves down then the master cylinder will be the problem / or you have a leak somewhere.
Next repeat the steps with the engine running.
Also make sure you cover any areas of the car to prevent brake fluid splashing on paint etc.
With the engine running in step 2 you will be applying boosted pressure to the master cylinder.
Thread Starter
5th Gear
Joined: Jun 2008
Posts: 4
Likes: 0
Thanks. Appreciate the input. A guy I work with said the same thing.
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Melting Slicks
Joined: Dec 2009
Posts: 3,233
Likes: 657
From: Thunder Bay
Most likely cause of the symptoms you are describing is excessive runout at the rotors. Factory spec is not more than .002". common Corvette problem.
Melting Slicks
Joined: Jun 2011
Posts: 3,116
Likes: 598
even at 0.01 run out it will take many many miles of driving to add enough air into the brake lines to cause complete failure. You will notice over time the brakes getting softer and softer, not complete failure at one time.