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SO! After having a pretty good pedal this summer I decided to check each caliper to see if they had any air left in them. I have been noticing the pedal getting a bit softer. I started with the left rear inner. With the rear wheels off and the rear of the car as low as I can get it (this makes the caliper at a better angle for bleeding) I hooked up a clear hose to the bleeder, made sure there was fluid already in the hose, cracked the bleeder just enough to start flow, wow, 6 large bubbles coming out, then clear. I finished bleeding the rest of the bleeders, 6 total. I was excited thinking I got the last bit of air from the system. BUT,,,,, now my pedal is **** again,,,,, soft, mushy, and goes to the floor. WTF! MC full,, only cracked the bleeders about 1/8th of a turn.
I cannot believe that starting on the left rear inner first rather than the right rear inner would make that much difference but some on this forum would. Unbelievable this has happened, I hope someone can come on and help as I would have done the same as you and been just as stunned and the results. Good luck...
I'm going to do the, push, hold, tight, release, on the rears today. But I don't understand, even if I use gravity and wait until no more bubbles come out, how does air get back into the caliper. With a solid clear tube on the bleeder, the only place air could get into the caliper is from the treads of the bleeder. But with constant positive flow out the tube, I don't get it.
Kansas123,,, I agree with you.
As Steve mentioned rotor runout.
Lifting the brake pedal before closing the bleeder. (don't touch the pedal)
Worn or damaged master cyl piston seals.
Caliper piston lip seals or "O' rings.
Caliper casting halves "O" ring.
How can it be runout when it wasn't driven? I drove it all summer and they were fine compared to how they were after I messed it up.
I know how to bleed brakes. The calipers and MC new or rebuilt, no leaks.
I still don't get it. Two person brake bleeding,,,,, The rear,,, left outer and right inner,,,, up down,,,, up down,,,, up down,,,, up down,,,, up down,,,,, bubbles, bubbles, bubbles, bubbles, bubbles, bubbles, bubbles, bubbles, over and over, ETC. Only opening the bleeder just until fluid starts coming out. Of course not having the bleeder open when the pedal is released. AND more bubbles....... gave up.
I wanted to figure out why the rears are so hard to manually bleed. I even have new bleeders.
I hooked up the motive bleeder,,, Just a few bubbles,,, then clear.
If air was getting past the threads when the pedal was pressed, why not when pressure was coming from the Motive? 15lbs
Yes,,, I am stubborn. BUT
I do have solid manual brakes now.
Your brake pedal exerts over 400 pounds of pressure when the system is closed or contained.
Your Motive should be around 12-15 lbs.
Why are you not starting at the right rear?
Why do you insist on using the brake pedal?
Every time the pedal comes back up to its normal position, it sucks air back in at the bleeder. The pedal stroke is way shorter than most vehicles being only a couple inches as opposed to 3,4,5". That is why the pedal method seldom works.
Use vacuum, pressure or gravity.
I can't stress this enough. Keep your foot off the pedal !
Just to answer your questions.
1. When the bleeder is open the pedal isn't exerting 400 PSI when pushed. It pushes down very easy.
2. The line to the rear brakes is a T fitting, it makes no difference whether you start on the rear left or right. For that matter it doesn't make any difference whether you do the front or rear first, they are completely, totally, two different systems, the fluid doesn't ever mix between the two systems. At least on the earlier C3's. Old wives tale.
3. I don't insist on using the brake pedal, that's why I have a Motive bleeder. I like so solve problems that I can't seem to figure out. I'm sure this will be good info for other C3 owners having the same question.
4. If the bleeder is closed when the pedal is released, it isn't sucking air into the system.
5. I did use gravity at first and it didn't work any better.
From: Some days your the dog and some days your the hydrant.
Royal Canadian Navy
Originally Posted by HeadsU.P.
Your brake pedal exerts over 400 pounds of pressure when the system is closed or contained.
Your Motive should be around 12-15 lbs.
Why are you not starting at the right rear?
Why do you insist on using the brake pedal?
Every time the pedal comes back up to its normal position, it sucks air back in at the bleeder. The pedal stroke is way shorter than most vehicles being only a couple inches as opposed to 3,4,5". That is why the pedal method seldom works.
Use vacuum, pressure or gravity.
I can't stress this enough. Keep your foot off the pedal !
Respectfully disagree. I've always used the brake pedal method (40+ years) and not just on my vette. It has never failed to bleed out the air. The brakes lock up all 4's. Something is either amiss in the bleeding method or a faulty part.
resdoggie: Thank you. Have you ever had air that keep burping from a bleeder when trying to bleed your brakes? I had large 1/2 inch bubbles that kept coming out of two different bleeders, maybe 20 times before I gave up. I'm using a clear bleeder hose at the nipple. The only thing I can think of, is air from the bleeder threads. Like I said, when I used the Motive to pressurize the MC, air stopped coming out in two seconds, and had a nice hard pedal. Just doesn't make sense.
From: Some days your the dog and some days your the hydrant.
Royal Canadian Navy
Air can't get in from the bleeder threads if the pedal method is done correctly because the brake pressure is greater than atmospheric pressure. And I've never seen an air bubble go down in a liquid!!! I've had to cycle through "pump pedal-hold pedal down-open/close bleeder-repeat" as many as 15 times or more sometimes to get the air out. I run a clear tube from the bleeder down into a jar half-filled with brake fluid. If there is anything being sucked back, its fluid from the jar, not air. Also, gravity bleeding needs to be followed up with bleeding to ensure all the air is expelled. Anyway, you never said if you had a helper i.e. someone else pumping the pedal while you crack the bleeder. Curious, why not just use your motive bleeder?
Yes,,, clear tube running into a bottle, both filled with fluid. My wife would start with slight pressure on the pedal,, I would crack the bleeder and watch her foot go down slowly, just before the pedal would bottom out, I closed the bleeder, then she lets up on the pedal. Over and over. I did state two person brake bleeding. I originally started a quick bleed of the calipers to make sure there wasn't any air in them after 6 months of driving. I thought it would be quick and easy. I was wrong. I still don't know why air keeps burping out when I use the pedal.
What is baffling,,, Before I started, the pedal was pretty solid. Just by bleeding the rears this way, they went to crap. Now they are good again.
From: Some days your the dog and some days your the hydrant.
Royal Canadian Navy
My method. Using FIRM pressure, pump pedal several times. The pedal should become hard and then while firmly keeping pedal down, crack bleeder 1/4 turn and retighten. Then, have helper release brake pedal. Repeat until no more air comes out.
2020 Corvette of the Year Finalist (performance mods)
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When you crack the bleeders use a shorter duration. If yo let the person punching on the pedal bottom it out and then you close it you hit equilibrium and air will go in around the threads. If you open it and close it about a half a second earlier, the pedal wont bottom out.... And you said that you lowered the caliper to its lowest point, you should raise the end you are bleeding, if its possible so the air in he system seeks out the highest point which is the caliper. And if yo want a reliable and efficient way that is the easiest, get or make a pressure bleeder like the motive, you could make a bug sprayer into a pressure bleeder if you like to fiddle with things. It would create a constant pressure that is limited only by the fluid volume in the pressure bleeder, this way you con almost fluch your entire system while you are bleeding it, which is why going to the furthest point away, you would force any water all the way out, in theory.
From: Some days your the dog and some days your the hydrant.
Royal Canadian Navy
You don't need to raise the ends of the car up. It serves no purpose. The denser brake fluid will push out the far less dense air out of the lines/calipers without the need to raise the vehicle.
I'm not sure I get what you are talking about. I never said anything about raising the car. I did say, I lowered the rear of the car as much as I could. When bleeding the rear calipers, this will angle the front of the calipers upwards (bleeders) so air is more likely to raise up to the bleeders
Brake bleeding
SO! After having a pretty good pedal this summer I decided to check each caliper to see if they had any air left in them. I have been noticing the pedal getting a bit softer. I started with the left rear inner. With the rear wheels off and the rear of the car as low as I can get it (this makes the caliper at a better angle for bleeding) I hooked up a clear hose to the bleeder, made sure there was fluid already in the hose, cracked the bleeder just enough to start flow, wow, 6 large bubbles coming out, then clear. I finished bleeding the rest of the bleeders, 6 total. I was excited thinking I got the last bit of air from the system. BUT,,,,, now my pedal is **** again,,,,, soft, mushy, and goes to the floor. WTF! MC full,, only cracked the bleeders about 1/8th of a turn.
