Bleeding the Brakes
Thread Starter
Instructor
Joined: Jul 2005
Posts: 160
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From: Sacramento CA
Bleeding the Brakes
I am helping a friend with his brakes on a 71 convertible. We started off by replacing both front brake calipers since they were both leaking. We were unable to keep a firm brake pedal after bleeding the brakes numerous times.
Since there were no brake leaks, we ended up replacing the master cylinder. The brakes would feel firm for 10 seconds, then go to the floor.
We bled the brakes the traditional way, used a vacuum bleeder and a pressure bleeder. We used a mallet on the brake calipers hoping to break free any air that was trapped but with no help.
The car was taken to a local ASE mechanic who was also unable to bleed the brakes and they do not know why the pedal will loose pressure. The mechanic also suggested we replace the proportioning valve, but with no leaks in the system, I find it had to believe it is the proportioning valve.
Does anyone have any ideas?
Thanks in Advance!!!
Since there were no brake leaks, we ended up replacing the master cylinder. The brakes would feel firm for 10 seconds, then go to the floor.
We bled the brakes the traditional way, used a vacuum bleeder and a pressure bleeder. We used a mallet on the brake calipers hoping to break free any air that was trapped but with no help.
The car was taken to a local ASE mechanic who was also unable to bleed the brakes and they do not know why the pedal will loose pressure. The mechanic also suggested we replace the proportioning valve, but with no leaks in the system, I find it had to believe it is the proportioning valve.
Does anyone have any ideas?
Thanks in Advance!!!
Le Mans Master
Joined: Jan 2001
Posts: 6,753
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Express
Search for "pressure bleeder" here in the c3 forum. Then go get a pressure bleeder....Or make a pressure bleeder from a garden sprayer, a tygon tube, a pressure gauge, a metal plate (1/4" aluminum is good enough), and a big enough c-clamp to go around it and the master cylinder. You can use a air fitting after you drill the metal plate. Ensure that you make a gouge on the underside such that both the forward and aft volumes get pressurized. You can make a rubber gasket out on old inner tube and it will seal well enough not to leak at all.
I made a pressure bleeder because I did not want to wait for shipping. Figured I'd order one later. It works so well that I never did order a fabricated one.
I'll go find a picture.
Search for "pressure bleeder" here in the c3 forum. Then go get a pressure bleeder....Or make a pressure bleeder from a garden sprayer, a tygon tube, a pressure gauge, a metal plate (1/4" aluminum is good enough), and a big enough c-clamp to go around it and the master cylinder. You can use a air fitting after you drill the metal plate. Ensure that you make a gouge on the underside such that both the forward and aft volumes get pressurized. You can make a rubber gasket out on old inner tube and it will seal well enough not to leak at all.
I made a pressure bleeder because I did not want to wait for shipping. Figured I'd order one later. It works so well that I never did order a fabricated one.
I'll go find a picture.
Le Mans Master
Joined: Jan 2001
Posts: 6,753
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Instructor
Joined: May 2024
Posts: 144
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From: Mid TN
I fought the same thing over and over. It ended up being air trapped in the master cylinder. I bench bled it multiple times I until all the air was removed. It took tilting it all around an tapping it with a piece of metal bar to finally get the air out of it. If you watch when you bench bleed it, with clear tubing returning the fluid, you will see it suck the air bubbles back in. I held the piston in util the bubbles rose in the tubing far enough not to suck back into the master cylinder. When I reconnected it I had someone hold the pedal, then opened the left rear then the left front without lifting the pedal between. After that I bled like normal. I just wanted to get the air away from the master from hooking the lines back to it.
Le Mans Master
Joined: Aug 2017
Posts: 8,336
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From: Cool Northern Michigan
O.P. says: Used a pressure bleeder.
I assume you poured a couple bottles of DOT3 into the pressure tank,
and not just use it like a compressed air tank.
Where did the new master come from? Good odds it is not the correct unit.
Or was bench bled improperly.
Proportioning Valves seldom faulter.
Click on my avatar and look for brake bleeding photo album for tips.
Last edited by HeadsU.P.; Jul 20, 2024 at 07:17 PM.
Le Mans Master
Joined: Jan 2001
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Express
If you have not done yet, then, if they're more than a few years old, I would replace the brake hoses at all 4 corners.
After changing the brake pads I removed the caliper on another vehicle and THEN I could not get those brakes to feel not spongy. And I even bled them with my Vette pressure bleeder. They worked fine before I disconnected the caliper. A friend told me to replace the hoses but I did NOT believe him because they worked fine before I went to do that pad change.
I finally gave in (months later being hardheaded) and replaced the hoses. HOLY COW. That's all it was. I *guess* that on my old brake hoses that once I drained that line, the hose swelled internally and then I could not get it to "un swell?" even with pressure bleeding. I was surprised.
I suggest the DOT braided SS hoses. Why not?
If you have not done yet, then, if they're more than a few years old, I would replace the brake hoses at all 4 corners.
After changing the brake pads I removed the caliper on another vehicle and THEN I could not get those brakes to feel not spongy. And I even bled them with my Vette pressure bleeder. They worked fine before I disconnected the caliper. A friend told me to replace the hoses but I did NOT believe him because they worked fine before I went to do that pad change.
I finally gave in (months later being hardheaded) and replaced the hoses. HOLY COW. That's all it was. I *guess* that on my old brake hoses that once I drained that line, the hose swelled internally and then I could not get it to "un swell?" even with pressure bleeding. I was surprised.
I suggest the DOT braided SS hoses. Why not?
Le Mans Master
Joined: Aug 2005
Posts: 6,553
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From: Temple Terrace Florida
I recently purchased a Phoenix reverse brake bleeder. It works very well and is a one person job. It can easily reverse bleed the calipers and master. It can also reverse flush the entire system of fluid.I punched the mid-level system. Jerry
Le Mans Master
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From: melbourne florida
2023 C3 of the Year Finalist - Modified
Take four old t-shirts remove the wheels put the t-shirts under the bleeder open all the bleeders take the cap off the master cylinder keep adding fluid until everything runs clear then close the bleeders one at a time as they have full flow that should do it.
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Le Mans Master
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From: Cool Northern Michigan
Or, 6 pieces of clear hose tubbing, 6 clear water bottles.
Pull up a stool next to the master cylinder.
Bottle of DOT3 in one hand, bottle of brew in the other. (don't get the two bottles mixed up)
Enjoy a car magazine. It's a slow process but works.
Pull up a stool next to the master cylinder.
Bottle of DOT3 in one hand, bottle of brew in the other. (don't get the two bottles mixed up)
Enjoy a car magazine. It's a slow process but works.
Melting Slicks
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After you figure out the pressure problem. Every 2 weeks , if you haven't driven the car , start it up and work the brakes a few times. This will prevent future leaks from the calipers.
Safety Car
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Melting Slicks
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Once I have eliminated air in the MC and rubber brake line issues, I have had the best results with the Motive Pressure Bleeder.
Heel & Toe
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no need to do anything like press the pedal? Just wait for all the calipers to drip?
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Gravity bleeding works great once you get them started. But you said in another post your getting nothing out of the rear bleeders. So it just won't work. And yes after a Gravity bleed you generally still need to do a two man bleed to get them tight,
Or,
You can get a reverse bleeder and get it done. As in really tight brakes.
Have fun!
Or,
You can get a reverse bleeder and get it done. As in really tight brakes.
Have fun!
Heel & Toe
Joined: Apr 2025
Posts: 16
Likes: 3
Gravity bleeding works great once you get them started. But you said in another post your getting nothing out of the rear bleeders. So it just won't work. And yes after a Gravity bleed you generally still need to do a two man bleed to get them tight,
Or,
You can get a reverse bleeder and get it done. As in really tight brakes.
Have fun!
Or,
You can get a reverse bleeder and get it done. As in really tight brakes.
Have fun!
Last edited by Satoru; May 11, 2025 at 09:42 AM.
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If you pushed fluid backwards, with the master level. And your certain your prop valve is centered.
Yes it is possible you have a issue with your master cylinder.
I generally reverse bleed. Then give each caliper a couple pulls using the 2 man method just to be sure no air is trapped in the calipers themselves. Then put the wheels back on.
I've done this many times over the years with complete success.
So, could you have a defective part? Of course it's possible.
As per the missing vacuum line at the manifold T that someone else pointed out. That's certainly not good in operation. Your booster isn't going to work properly with a massive vacuum leak. Generally the brake booster should be on its very own vacuum source. Generally at the base of the carb.
That will not give you issues bleeding the brakes however.
But get all those vacuum leaks sorted or your booster won't work properly and you still won't have any brakes.
Yes it is possible you have a issue with your master cylinder.
I generally reverse bleed. Then give each caliper a couple pulls using the 2 man method just to be sure no air is trapped in the calipers themselves. Then put the wheels back on.
I've done this many times over the years with complete success.
So, could you have a defective part? Of course it's possible.
As per the missing vacuum line at the manifold T that someone else pointed out. That's certainly not good in operation. Your booster isn't going to work properly with a massive vacuum leak. Generally the brake booster should be on its very own vacuum source. Generally at the base of the carb.
That will not give you issues bleeding the brakes however.
But get all those vacuum leaks sorted or your booster won't work properly and you still won't have any brakes.
Racer
Joined: Dec 2022
Posts: 304
Likes: 87
I am helping a friend with his brakes on a 71 convertible. We started off by replacing both front brake calipers since they were both leaking. We were unable to keep a firm brake pedal after bleeding the brakes numerous times.
Since there were no brake leaks, we ended up replacing the master cylinder. The brakes would feel firm for 10 seconds, then go to the floor.
We bled the brakes the traditional way, used a vacuum bleeder and a pressure bleeder. We used a mallet on the brake calipers hoping to break free any air that was trapped but with no help.
The car was taken to a local ASE mechanic who was also unable to bleed the brakes and they do not know why the pedal will loose pressure. The mechanic also suggested we replace the proportioning valve, but with no leaks in the system, I find it had to believe it is the proportioning valve.
Does anyone have any ideas?
Thanks in Advance!!!
Since there were no brake leaks, we ended up replacing the master cylinder. The brakes would feel firm for 10 seconds, then go to the floor.
We bled the brakes the traditional way, used a vacuum bleeder and a pressure bleeder. We used a mallet on the brake calipers hoping to break free any air that was trapped but with no help.
The car was taken to a local ASE mechanic who was also unable to bleed the brakes and they do not know why the pedal will loose pressure. The mechanic also suggested we replace the proportioning valve, but with no leaks in the system, I find it had to believe it is the proportioning valve.
Does anyone have any ideas?
Thanks in Advance!!!