This is on my 77, sitting here with this stay at home order decided to replace a rt rear caliper that was leaking. As with most things with this car one issue is never enough and it turned into a lt frt leaking also as well as the m/c, rough winter I guess. Anyway I’ve bench bled the m/c twice and have bled the brakes more times than I can count, I’ve gone thru over 3 quarts of fluid get zero bubbles out of any line I bleed(gravity bleeding) and yet still can’t get the brake light on the dash to go out and the pedal goes nearly to the floor when the car is started. The pedal pumps up nice and firm when the car is off. I’ve searched the forum and read countless brake issue posts and here I am a week later and still same issue. All hoses and lines are new, m/c was new not rebuilt. I’ve been bleeding rt rear inner then outer, lt rear inner then outer, rt frt then lt frt. I’ve replaced lines, hoses, calipers, etc before and never had this issue. Any thoughts or ideas would be greatly appreciated as I’m at the end of my rope.

 

Well I will tell you how I deal with this. First I bleed the brake system after every track day, usually 8-12 times a year. Replaced many calipers due to leaks , rear suspension parts (trailing arms) requiring rear calipers to be removed.

Also I have bleed the calipers allowing the MC to go dry (mistake on judgement). So now what.

To not waste fluid on a opened system I return captured fluid back to the MC. Once I am happy with the brakes I do a final bleed.

So
Step 1 fill the MC and blench bleed as best as you can. Don't worry if its not perfect.
Step 2 fill the brake system by bleeding each caliper bleed screw. Starting with the longest to the shortest. Doesn't need to be perfect.

I use pressure at the MC to bleed the system. My DIY setup, but Motive Bleeders etc will also do the same job.



Connected to the bleeder screw is a clear plastic tubing about 6 ft in length. I apply about 30 PSI at the MC and bleed about 2-3 full length of the clear tubing of fluid before refilling the MC.

Once you have the brake system full of fluid (doesn't need to be perfect)
Here is the most important step (my view)

YOU NEED TO BLEED THE MC WHILE ON THE CAR. Blench bleeding helps prepare for this step.
Here is how this step looks. I usually let the car sit for 30-60 minutes and try again after the initial bleed.
https://www.corvetteforum.com/forums...-cylinder.html

This step may take as many as 3 -4 attempts between days before you get all of the air out of the MC. With a opened system I repeat this step with 1 day between attempts until I get no more air from the MC.

Now bleeding the calipers I apply vise grips to the brake pads to force the pistons into the calipers to force any trapped air in the piston into the brake lines.

This is a very slow process if you want the last bit of air removed. And you will notice better brake feel as each step completes.

 

Thanks for the reply, I had read your post a few days ago and then couldn’t find it again.

 

I recommend a Motive Power Bleeder as well as the procedure described by cagotzmann. I followed through with his procedure with great results but later learned I was having a runout issue on the right rear after driving some. I bit the bullet and bought a Wilwood system and have been enjoying the car for a change.

 

Stab the pedal hard a few times to get light off assuming your e brake isnt on..so your issue is the light correct?
it may take a few times works for me stab hard..resets proportion valve or whatever it’s called

 

I have been using a "Phoenix Reverse Bleeder" and it works great on brakes as instead of pushing down you are pushing the fluid in at the bottom and having it push the bubbles up and out the top. This system works on later Corvettes with their hydraulic Clutches and their brakes. It was the only method I could find to get the air out of my Wife's old Chevy Pickup truck clutch.

Several years ago I tried Silicone Brake Fluid in my C3 (BIG mistake) and in the process I had to flush the system several times. This reverse bleeder makes my 1968 C3 easy to flush all the fluid in less than 1/2 hour. I use it on my RV with it's long brake lines to prevent any corrosion from water absorbed into the brake fluid. I have since used it on my Cessna 172, my motorcycle and numerous vehicles so the tool has long since paid for itself in time saved. The Phoenix Reverse Bleeders really do work well!

 

Part of the issue is the light, already checked the ebrake and it’s off. The big issue is the pedal is soft. I’m thinking there is air somewhere but not sure where. I have been gravity bleeding and I get a steady drip approx 1 drip per second at each wheel so not sure.

 

you may need one of these...but I'd try the pressure bleeder first. Mine (home built from garden sprayer) works like a dream and I don't do anything special.

https://www.performanceonline.com/GM...Tool-AC-Delco/

 

So I just quickly looked up that tool, if I’m reading it correctly it appears as simple as pumping fluid from each caliper backwards to the master cylinder and forcing the air out there, is that all there is to it?

 

When you bench bled; How far did you push your screwdriver / MC piston in? More than 1 3/8"? If so, you rolled over the piston seals (rings) and damaged them. Plus you voided any warranty on the MC. If the piston seal, either front or back is damaged, you will never get the air out of the MC.
Check out my profile, photo album, bleeding MC.

 

 

Thanks for the link. I looked up a motive pressure bleeder and my only question is what did you use for the master cylinder lid? The one I saw has a thread on cap for a different style reservoir.

 

No, I actually had found your profile album before I dove into this so I was at least semi prepared

 

Yea I tried this and found it also pushed air (sucked) in at the bleed screw threads (need to be careful with some loose / older bleed screws, I found the motive bleed method (pressure at the MC) just doesn't have a way to introduce air. But since air rises to the top it make sense this should work as well. I still always bleed the MC while on the car. Best way to make sure no air in the MC. Those holes in the MC where put there for a reason so I use them to my advantage.

 

If you do go the Motive tank route you will need to make your own MC lid. Which is also in my photo album. I think I have $20 into it.

As a last resort, there is always gravity bleeding. Get four clear hoses, four empty water bottles, open the four rear bleeders and walk away. Then do the fronts. Don't touch the pedal. Check-in on the rez once in a while.

 

I’ve done the gravity deal more times than I can count now, I have brakes but just not a firm pedal. In my head I think there has got to be air trapped somewhere. Time to look into a bleeder of some sort before I go nuts.

 

https://www.corvetteforum.com/forums...post1599103205

See post #9. That's how I bled the master, bled the car, then got rid of the light. Before going through all this, make sure that the wire is actually plugged into the top of the distribution/proportioning valve. If not the dash light will always be on.

 

I used an aluminum plate about 1/4" thick. I notched the underside so that both the forward cavity and the aft cavity of the master cylinder get pressurized. You can see mine in this picture below. You really only need one hole, I made the second one to experiment and now have it plugged.
Get a couple of air compressor fittings, some tygon tubing, a pressure gauge, a piece of rubber to place between the plate and the master cylinder (I used inner tube rubber), and large c-clamp.
Those garden sprayers are cheap. I made it because I didn't want to wait and now I've had it over a decade. Works like a dream. You'll love it.
I've used on my other cars and friend's cars (Toyota, Nissans, Mustangs.... even on the plastic type reservoirs--just have to be careful, I have different inner tube rubber cutouts in the storage box -- for/from the different reservors that I have helped bleed).

Here is a link for other folks ideas:
https://www.corvetteforum.com/forums...post1581454605

 

The old fashioned, Plews "bleeder ball", circa 1985......





I know that these items look a little "shop worn", but as stated, they're well over 30 years old.....

 

Mine came with the flat type that is needed for C3 Corvettes. I also bought the kit containing all other types of master cylinder lid sizes.