76 Brake Issue
Thread Starter
Racer
Joined: Aug 2014
Posts: 479
Likes: 93
From: Tennessee
76 Brake Issue
I have been completely through my wife's 76 braking system and replaced every part except the hard lines but the problem still exists. I have also flushed and bled the system multiple times with my Motive Power Bleeder. First off, we've never had a great pedal but the problem we have is the pedal gets worse after driving and the brake light comes on. At this point I can pump the pedal to get the light out but it will be back on with continued driving and braking. There are no signs of leakage and no fluid loss whatsoever. I have noticed the master cylinder and booster are pretty warm (some would even say hot) after driving the car. The excessive heat is from the exhaust headers even though they are ceramic coated. I believe the fluid could be getting too hot I'm thinking of flushing the system of DOT 3 and refilling with DOT 5 and see if that helps . Do any of you have any ideas? If so, please post.. Thanks!!!
Melting Slicks
Joined: Jun 2011
Posts: 3,116
Likes: 598
I have been completely through my wife's 76 braking system and replaced every part except the hard lines but the problem still exists. I have also flushed and bled the system multiple times with my Motive Power Bleeder. First off, we've never had a great pedal but the problem we have is the pedal gets worse after driving and the brake light comes on. At this point I can pump the pedal to get the light out but it will be back on with continued driving and braking. There are no signs of leakage and no fluid loss whatsoever. I have noticed the master cylinder and booster are pretty warm (some would even say hot) after driving the car. The excessive heat is from the exhaust headers even though they are ceramic coated. I believe the fluid could be getting too hot I'm thinking of flushing the system of DOT 3 and refilling with DOT 5 and see if that helps . Do any of you have any ideas? If so, please post.. Thanks!!!
This is air in the lines problem period.
So lets start with the first place to make sure all the air is out. The Master cylinder. Start with a bench bleed of the MC to get most of the air out. Then proceed to bleed the MC while installed on the car.
Like this. https://www.corvetteforum.com/forums/c3-tech-performance/4000148-get-the-last-bit-of-air-out-from-the-brake-master-cylinder.html
Once you have no air in the MC then start at the calipers. First push all the caliper pistons in by shimming the brake pads. I use a vice grip to hold the pads in place. Then bleed the caliper.
The order you bleed the calipers doesn't matter if you don't care how much fluid you need. But to reduce the amount required start with the longest brake line to the shortest brake line.
Once you have completed the caliper pressurize the brake system and remove the shims / vice grips etc to make sure the caliper pistons move out freely and return the brake pads against the rotor again.
I bleed and pressurize the MC like this. I set my air compressor for 30 PSI.
I connect a clear plastic tube to the bleeder. The bleeder tube is about 7 feet in length and for me I can bleed the length of the tubing 3-4 times before I need to refill the MC with fluid.
Melting Slicks
Joined: Jun 2011
Posts: 3,116
Likes: 598
Thread Starter
Racer
Joined: Aug 2014
Posts: 479
Likes: 93
From: Tennessee
I have only bench bled the master cylinder so I will give the method of bleeding the master while on the car a try. I am unclear about shimming the pads and bleeding the calipers as you have mentioned. Are you wedging shims between each rotor and pad, removing a caliper, clamping the pads with vise grips to compress the pistons, bleed that particular caliper, reinstalling , pressurizing, continuing to next caliper? What do you use as shims?
Last edited by ykf7b0; Jul 22, 2018 at 12:55 AM. Reason: miswording
Melting Slicks
Joined: Jun 2011
Posts: 3,116
Likes: 598
I have only bench bled the master cylinder so I will give the method of bleeding the master while on the car a try. I am unclear about shimming the pads and bleeding the calipers as you have mentioned. Are you wedging shims between each rotor and pad, removing a caliper, clamping the pads with vise grips to compress the pistons, bleed that particular caliper, reinstalling , pressurizing, continuing to next caliper? What do you use as shims?
Make sure to press the pistons in evenly. That is why I leave the brake pad in place. If you press the pistons in without evenly applying pressure you could cause the seals to be damaged.
But before you re-bleed the calipers test after bleeding the MC while on the car.
Le Mans Master
Joined: Aug 2006
Posts: 7,427
Likes: 1,560
From: mount holly NC
2025 c3 ('74-'82) of the Year Finalist - Unmodified
2019 C3 of Year Finalist (appearance mods)
Rebleed the system and note the mileage, if the pedal goes down again then check the runout.
Here's how:
https://www.youtube.com/watch?v=SSxC...ature=youtu.be
Here's how:
https://www.youtube.com/watch?v=SSxC...ature=youtu.be
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Le Mans Master
Joined: Aug 2006
Posts: 7,427
Likes: 1,560
From: mount holly NC
2025 c3 ('74-'82) of the Year Finalist - Unmodified
2019 C3 of Year Finalist (appearance mods)
You have done a good job replacing most parts so what's left?
Are the rotors parallel on both sides, could one be warped on the inside?
Next check the bearings. If you bleed the system again and note which caliper expells the most air it might give you a clue to the problem.
On the rear calipers are you bleeding the inner first then the outer?
Are the rotors parallel on both sides, could one be warped on the inside?
Next check the bearings. If you bleed the system again and note which caliper expells the most air it might give you a clue to the problem.
On the rear calipers are you bleeding the inner first then the outer?
Last edited by Peterbuilt; Oct 10, 2018 at 02:26 PM.
Thread Starter
Racer
Joined: Aug 2014
Posts: 479
Likes: 93
From: Tennessee
You have done a good job replacing most parts so what's left?
Are the rotors parallel on both sides, could one be warped on the inside?
Next check the bearings. If you bleed the system again and note which caliper expells the most air it might give you a clue to the problem.
On the rear calipers are you bleeding the inner first then the outer?
Are the rotors parallel on both sides, could one be warped on the inside?
Next check the bearings. If you bleed the system again and note which caliper expells the most air it might give you a clue to the problem.
On the rear calipers are you bleeding the inner first then the outer?
Rotors are true and bearing are great.
On the rear I'm bleeding the outer first.
Le Mans Master
Joined: Aug 2006
Posts: 7,427
Likes: 1,560
From: mount holly NC
2025 c3 ('74-'82) of the Year Finalist - Unmodified
2019 C3 of Year Finalist (appearance mods)
Thread Starter
Racer
Joined: Aug 2014
Posts: 479
Likes: 93
From: Tennessee
Melting Slicks
Joined: Jun 2011
Posts: 3,116
Likes: 598
So you need to start at the Master Cylinder. This is the first place you will get a soft pedal.
So bleed the master cylinder while on the car. Don't disconnect any lines to do this.
Follow this procedure.
https://www.corvetteforum.com/forums...-cylinder.html
This may take a few attempts to get all the air out. Make sure as you press the brake pedal you get no air and only fluid from the bleed holes in the master cylinder.
Next pick a caliper and press the a brake pad into the caliper (hold with a vise grip to hold the pad in place) so the piston are pushed in as far as they can go. Then apply pressure at the MC ( I use 30 PSI) open only the bleed screw to the half you pushed the pad in. Then with pressure still applied release the vise grip and watch the pad push back into place. Then do the next pad and repeat.
As a test you can also bleed the front driver caliper and have a hose connected from one of the bleed screws and have the fluid cycle back into the MC. Use brake pedal pumping. This way you don't need to add fluid. Also lift the back of the car like in the procedure to bleed the MC while on the car. This will also make sure there is no air in the MC.
Thread Starter
Racer
Joined: Aug 2014
Posts: 479
Likes: 93
From: Tennessee
This braking problem keeps returning to me. I bleed and the brakes are ok for a while then I again get the long travel pedal and a brake light. I'm now almost certain I have a runout issue. I don't have the tools to properly check and fix the issue and I'm thinking about getting a new set of rotors and calipers. What are my chances of eliminating the runout issue with new quality rotors from a respected brake rotor manufacturer such as Brembo or Wilwood? I should add the fact that I've never had what I would call a great pedal even after bleeding.
Le Mans Master
Joined: Aug 2006
Posts: 7,427
Likes: 1,560
From: mount holly NC
2025 c3 ('74-'82) of the Year Finalist - Unmodified
2019 C3 of Year Finalist (appearance mods)
Both manufacturers claim that their rotors are flat and parallel but still recommend to check the runout because of bearing problems or bent spindles.
Harbor Freight has a 'clamping dial indicator' #63656
Thread Starter
Racer
Joined: Aug 2014
Posts: 479
Likes: 93
From: Tennessee
The rotors are factory originals still riveted on. If I do get new ones does everyone recommend drilled/slotted or are they more prone to warpage? Also, my calipers are rebuilt AutoZone's so would you guys suggest getting new matching brand calipers?
Thread Starter
Racer
Joined: Aug 2014
Posts: 479
Likes: 93
From: Tennessee
Anyway, I have ordered and received new Wilwood cross drilled rotors and I will be installing them in a few days. I also bought a clamp on dial indicator as suggested by Peterbuilt,( Thank you very much!) and will get a runout reading on each as I go.