I know this has been covered here in the past, but I just cannot seem to find my "air" issue with my brakes. Here is the story: Soft pedal when I purchased the car a few months ago. I bled the brakes(old fashioned method, with a 2nd person pushing the pedal after I cracked the bleeder, closing the bleeder prior to letting the pedal back up, and so forth. I used the correct sequence as well, seemed great for a few days. Then back to a spongy pedal.

So, I purchased 6 speed bleeders. Last evening, I installed all of the bleeders, and then proceeded to the left rear of the car to begin. No problems, got all of the air out, same with the left outer rear. Moved to the right inner rear, no issues, right outer rear, no issues. Got to the front and realized there was brake fluid all over the floor. Apparently the bleeder on the left front was not seating properly, as even when tightened down, it was spewing fluid. Just great! And of course the front half of the master cylinder was drained down, so now I had even more air in the system. I topped of the master cylinder, and started again at the left rear. Bled both halves of the caliper with no problem. Got to the right rear, and no matter how many times I tried, I kept getting a steady stream of bubbles from the outer bleeder. I was constantly checking the MC to ensure that it wasn't getting too low. I even went back to the original bleeder, and had a partner assist me again. So at this point I am thinking that I have a bad caliper, because air appears to be getting sucked back in on the return pedal movement.

I moved to the front left (the one that initially had the speed bleeder issue), and I had the same problem. Even using the original bleeder. Steady stream of air. So now my brakes are even worse than when I started, and my $40 worth of speed bleeders was a complete waste. But even with a pressure bleeder, I don't think I am going to be better off.

Does this sound like a bad caliper(s) issue? Possibly a bad MC? Not really sure where to start, but looking for some expert opinions and advice. I am thinking about starting with a new master cylinder, as they are pretty inexpensive. Bench bleed that, and then start over with the bleeding process. Any other suggestions would be greatly appreciated!!!

 

Suggestion, because I too have had what seems to be bubble but it's because the tube kind of sucks air in while bleeding.

Get a Motive Bleeder. Add a few cans of fluid and pressurize it. Make sure it holds so you know you have no leaks. Do a walk round and check every connection.

If all is good start in the rear and crack it. While it bleeds hit the caliper with a rubber mallet. If you are getting clean fluid close it off.

Do each caliper of course and you should have a really good bleed. Break the seal on the MC and dump the unused fluid.

 

+1 for the motive bleeder.....best money Ive spent on a tool in a LONG while. I don't know what it is about the C3, but on both my '68 and my current '69, nothing would get 100% of the air out of the system besides the pressure bleeder. I highly recommend using a few C clamps on the reservoir as opposed to the useless chain system they supply to keep the plate on the master cylinder.

 

It just seems as if air is entering back into the system. I guess the pressure bleeder would be the starting point, and if that doesn't cure the issue, then dig further...

 

if air is entering the system, the pressure bleeder will push fluid out the opening and you'll find the leak via puddle

 

I have never used one, so that makes sense. So, if I pressure bleed and have no air bubbles, no leaks, and then STILL have issues, what next? Master cylinder?

 

I had the same problems over several days/no fun........steady streams of air no matter what I did/bleeders were rusty and not sealing well after I broke them all aloose in preparing to bleed the brake calipers.

I bought all new bleeder screws and found tiny bits of "trash" using a bright light looking into the bleeder holes/cleaned-flushed the trash out of all the calipers and installed new seals and the new bleeders.

Then I removed the master cylinder/honed the bore and installed new seals/BENCHB-LED the master cylinder/re-installed it.

I did the two-person bleeding method.....it took an hour to bleed all the bleeders, but the pedal has been firm for a year now.

Next time I'll buy a Motive bleeder

 

You could save a lot of time by removing the master cylinder/honing it/install new seals/bench bleed it which could take up to 30 minutes in some cases to get a good spurt of clear fluid in both bowls.....

then re-install it and start fresh........trust me/been there for 3 days!

 

I think I may just replace the master cylinder regardless, and use that as my starting point. Which model # of motive bleeder did everyone here purchase, and where did you purchase it? Did it come with the aluminum MC adaptor, or did you have to purchase that separately? If so, was it the 1105 or the 1115? I am pricing these out, and they seem to cost a lot more than the $50 that everyone is saying, so maybe I am looking at the wrong model number...

 

I bought the 0115 Early American Rectangular Bleeder - Large

 

Hi 79C3
You have been given alot of good information here. For me I use the gravity method, with a rubber mallet to tap on the calipers to break any air bubbles lose. Another thing I have read here on the forum is to put some grease around the bleeder screws to keep air from getting into the system. Because some of the screws are a little lose where they screw in to the calipers. I have always had good luck with this method, and had a good pedal.
Good luck, hope you find the problem and fix it.
Larry

 

Ok, sounds like you have gone through a lot of time and brake fluid and I can relate to how frustrating brakes on a C3 can be.

First do you have the original calipers on the car? If you do, then ultimately your calipers will likely leak as the caliper seals are known to fail over time.

You can purchase rebuilt calipers from supporting vendors that have updated seals and sleeves that will solve the problem.

I went with Wilwood calipers as I wanted better overall technology and weight savings. I also purchased a new Wilwood Master Cylinder as I didn't want to deal with rebuilding the original.

Ultimately, I still purchased a pressure bleeder because even with brand new Wilwood components I still could not bleed the system successfully by using manual processes.

Hope that info. helps you to save some money,grief, and time.

 

** Update: Still having issues, and I noticed when bleeding the rears, there was a nice drip/puddle at the front left. It was coming from the rear of the Master Cylinder where it mounts to the booster. Finally I think I have found my problem. So I get a new MC, bench bleed it, then and then use the two person method and a large bottle and a half of brake fluid following the recommended sequence. I had ZERO air, and a steady stream of fluid at each bleeder. I also used Teflon tape on each bleeder as well. Still didn't have quite the rock hard pedal I thought I would have, so I let it sit for a few days, and went out to give it a test drive this evening. Pedal goes right to the floor. WTH??

With the engine off, if the pedal is pumped 4 times, it will stay about 1 1/2"-2" off the floor, but if I release it and then push it again, it slowly goes to the floor. With the engine running and the booster assisting, the pedal always goes to the floor. So I get under the hood and look, and there is some brake fluid under the MC on the steering linkage and frame rail. It appears as though there is still some leakage at the rear of the cylinder where it mounts to the booster. So I assume I have ANOTHER bad Master Cylinder? I am at the end of the rope with what should be so simple, and something I have done many times in the past with many vehicles. Feedback and suggestion would be appreciated!!


Thanks everyone!

 

Is it possible that brake fluid got into the booster and ruined it.....I hope not.

Check the booster to see if excess brake fluid is dripping out of it which could make you think the new master cylinder is leaking.

Vette brakes are monsters to bleed completely....I feel for ya"!

 

I agree with Doorgunner. If brake fluid was leading out the back of the old one, it has gone into the booster. Probably just a matter of time until it ruins the rubber diaphragm in the booster. This might be another "while you are at it" moment.