Quick master cylinder question
Race Director
Joined: May 2006
Posts: 16,528
Likes: 53
From: Dayton, Ohio
You could also still have air in the system,are you using the pump up and bleed method , gravity or a Motive type.
You know you might be better off going to Autozone and getting a 19.95 master and bleeding your system with it,if the pedal stays up you'll know the chrome master was at fault.
Where is your old master ?
Thread Starter
Racer
Joined: Mar 2005
Posts: 471
Likes: 1
From: Hometown The best
I did let the master sit for a day and a half with the plugs in it and still had the same rock hard pedal. I am using the pump and bleed method as I can't find a motive locally and have never had a problem with the pump and bleed method. I still have the old master cylinder so I will switch masters today and see what happens. This shouldn't be rocket science, there's only the master, booster, porportioning valve and calipers that move unless I'm missing something. I've bled the system so many times I don't see how I could possibly have enough air in the system to make the pedal go to the floor and not be able to pump the brakes up at all.
Thread Starter
Racer
Joined: Mar 2005
Posts: 471
Likes: 1
From: Hometown The best
I tried bench bleeding my old master cylinder but there was to much trash floating around and it was taking forever trying to flush it out so I decided to pick up the m/c rebuild kit that I ordered. I rebuilt my new chrome m/c, bench bled it , installed on the car, bled the lines at the m/c and proceeded to bleed the system. It was worst than before. Some fluid imeadiatly came out of the inner rr bleeder then stopped flowing. The rest of the bleeders on the rear were the same. Went to right front and a unusual amount of fluid came out. The left front was the same way. Bleed the whole system again and can hardly get any fluid out of the rear. So there the car sits. Im about at my wits end. Anybody got a very large caliper gun ....... no ,not for me .... the car. Where do I go from here? 
Race Director
Joined: Mar 2009
Posts: 19,777
Likes: 4,592
From: Canada's capital
2020 Corvette of the Year Finalist (appearance mods)
C1 of Year Finalist (appearance mods) 2019
Went through the exact same thing last year on a 68, and nothing worked. Turned out the calipers were sucking air on the upstroke, and not leaking fluid. New s/s calipers.....Fixt!
Burning Brakes
Joined: Jul 2010
Posts: 755
Likes: 8
From: delco pa
i agree,,, air is getting in some way, and the calipers are a good place to look,,, i have ss calipers on my 68, and find they still can get some rust and corrosion in them,,, teh springs and the bottoms of teh cylinders are either iron or steel, so, they corrode.... a little piece of rust will hold teh caliper seal open enough to suck air... i just went thru my calipers, and found some rust in them,,,, i'm using dot5, but the iron can still rust.....
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Thread Starter
Racer
Joined: Mar 2005
Posts: 471
Likes: 1
From: Hometown The best
I guess I'll spring for new calipers tomorrow. Hate to spend that much $$$ and not know that it will fix the problem but I built this car to drive and not be a boat anchor sitting in a garage. I'll look at the brake switch also. Just about the whole brake system will be new after I do this. Keep your fingers crossed.
Race Director
Joined: May 2006
Posts: 16,528
Likes: 53
From: Dayton, Ohio
If your calipers are sucking air , if you gravity bleed air should come out of the bad caliper almost immediately after you open the bleeder.
If air is being draw in at the master cyl bore,you should be able to get air at the line fittings.
If air is being draw in at the master cyl bore,you should be able to get air at the line fittings.
Race Director
Joined: Mar 2006
Posts: 14,112
Likes: 28
From: Florida
If you are getting lots of fluid out the fronts and a trickle out the back as you said in post #25, then your combo/proportioning/differential valve is tripped. It has to be recentered. That's at least half of your pedal travel right there.
If your master is truly as dirty as you said in post #25, then so is your combo valve. It would be wise to remove and clean it.
Before you buy new calipers, take them apart, they are likely already ss lined and can be rebuilt fairly cheaply with piston/seal kits. Check to see that they have the springs in them. This prevents them from sucking air with use of the master.
Internally, when the brake pedal is released, the pistons return causing slight neg pressure in the system and to prevent any wheel cylinders from sucking air, the pressure seals in the master have small orifaces behind them to allow fluid into the low pressure area and also top off the volume in front of the seal.
Any air entering the rear of the master should escape thru the inlet port into the rear reservoir.
Le Mans Master
Joined: Aug 2006
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From: mount holly NC
2025 c3 ('74-'82) of the Year Finalist - Unmodified
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Are you sure all the seals in the M/C are facing the correct way?
See post 11 by Duke94
http://forums.corvetteforum.com/c3-t...-cylinder.html
See post 11 by Duke94
http://forums.corvetteforum.com/c3-t...-cylinder.html
Thread Starter
Racer
Joined: Mar 2005
Posts: 471
Likes: 1
From: Hometown The best
I took all 4 calipers off and found one piston in right rear completely stuck, pulled the seal and found major corroison . Some of the pistons in two of the fronts were not releasing fully so I bought 4 new calipers to make sure there is not any problem with the calipers and will be installing them the rest of the day. Hope this fixes the problem.
Burning Brakes
Joined: Jul 2010
Posts: 755
Likes: 8
From: delco pa
I took all 4 calipers off and found one piston in right rear completely stuck, pulled the seal and found major corroison . Some of the pistons in two of the fronts were not releasing fully so I bought 4 new calipers to make sure there is not any problem with the calipers and will be installing them the rest of the day. Hope this fixes the problem.
Thread Starter
Racer
Joined: Mar 2005
Posts: 471
Likes: 1
From: Hometown The best
I installed the 4 new calipers yesterday and tried bleeding the brakes this morning. I have the same freekin' problem. Pedal to the floor and it will not pump up even enough to bleed the calipers no matter how many times I go around the car from wheel to wheel. I took the master cylinder off and bench bled it again. Put it back on the car and same thing.This just makes no since at all. I called several repir shops and they can't understand it either. I was going to start loosening the brake line connection to try to find the stopage but with no pedal I can't apply pressure. I think I will order a motive from Summit and see if that will pressureize the lines.The brake light on the dash is not lit and I get hardly any fluid from any caliper. Any more ideas. The porportioning valve is the ony thing I have not replaced. NAPA said they didn't carry them. 
Burning Brakes
Joined: Jul 2010
Posts: 755
Likes: 8
From: delco pa
I installed the 4 new calipers yesterday and tried bleeding the brakes this morning. I have the same freekin' problem. Pedal to the floor and it will not pump up even enough to bleed the calipers no matter how many times I go around the car from wheel to wheel. I took the master cylinder off and bench bled it again. Put it back on the car and same thing.This just makes no since at all. I called several repir shops and they can't understand it either. I was going to start loosening the brake line connection to try to find the stopage but with no pedal I can't apply pressure. I think I will order a motive from Summit and see if that will pressureize the lines.The brake light on the dash is not lit and I get hardly any fluid from any caliper. Any more ideas. The porportioning valve is the ony thing I have not replaced. NAPA said they didn't carry them.
do you new calipers have one bleed valve or two?,,, if two, you have to bleed them both, as far as i know....
Thread Starter
Racer
Joined: Mar 2005
Posts: 471
Likes: 1
From: Hometown The best
Does the prop valve come apart or do you mean remove the brake lines from the valve and clean it out? If it was the prop valve wouldn't I be getting pressure to the front and not the rear or pressure to the rear and not the front, depending on which way the valve was stuck. I can try that in the morning though. I didn't blow the lines out because I was getting plenty of fluid flow through the lines before I started replacing parts, If the lines were stoped up wouldn't I have some pedal pressure? Remember I did crack the lines at the master and bleed some fluid out each time I reinstalled the master so I don;t think there would be much air left in the lines before getting to the calipers. I just found out that Advance Auto Parts has a pump up power bleeder as one of their loaner tools. I will borrow that in the morning rather than ordering a motive. If anything was stopped up or valves closed ,etc., in other words anything preventing flow, why wouldn't I have some pedal pressure . It would be the same as putting plugs in the m/c ports to stop the flow and I had a rock hard full pedal when I did that. There is just more to this than I understand.