completely new brake system = major problems

I had a similar problem as yours. I finally had to start with plugs at the master cylinder and plugging all the holes. With plugs in all the holes then you should have peddle if you don't then it is the Master Cylinder. If you have pedal then add the shortest line only the and bleed until you have a pedal if, no pedal then that line or wheel cylinder is the problem, keep doing this progressively going to the longer lines until you find the one that will not hold. I did this until I was able to pin point the brand new bad wheel cylinder that was cracked and I couldn't see the leak because it was squirting fluid into a pocket in the frame rail. Just a process of elimination. I had to do it like someelse pointed out here with a cool head and a freind.

 

There were only two '68 Vette master cyls:
1-1/8th" for power brakes
1" for manual brakes

The same actually 67-70.

 

did you buy this from "mbm brakes" or from "fatrodder" or similar on ebay?

 

Try taking a piece of newspaper or one of the blue cloth shop towels and wrap it around each fitting on the brake system. Either one will wick the brake fluid and show a small leak that you can’t see just by looking or wiping with cloth or regular household paper towel. If you are getting a good stream of fluid by bench bleeding the master it should be ok. Make sure the residual valves are installed in the correct flow direction for both the front and rear system. Also some of the corvette master cylinders have built in residual valves. If it does, remove them, this will cause the master cylinder to hold pressure on the system just like riding the brakes would. If you haven’t already you should check the items some of the others have suggested. Check the clearance on the internal rod on the booster; check the clearance on the rear brake shoes.
If you find any leaks correct them and try bleeding the system the following way. Get a piece of clear nylon hose that fits tightly over the bleeder and is long enough to reach down to the floor. Place the other end in a clear container filled with brake fluid. You can zip tie something heavy to the hose to help keep it in the container. You should be able to do this by yourself as long as you can move the pedal from under the car. With the clear hose and container you can tell how much fluid and air you are getting. Start at the furthest wheel away from the master cylinder and work your way around the vehicle. Check the master cylinder before moving to another brake. Make sure you pump the pedal slowly and allow the piston to fully return on each stroke. You should see results in 5 to 10 strokes on each brake if you don’t have any major leaks. After all four have been done one time you should check for leaks again and bleed one more time. Normally on a new system once the master cylinder has been bled this will take 15 to 30 minutes to do. Hope this helps.

 

well guys thanks for all the help i got the brakes working awesome. ended up noticing a bunch of leaks from my novice flares after we finally started to get some preasure in the system. so i bought a bunch of pre-flared lines in different lenghs and re-did every single line, not one leak!!!. also pulled the master out and re-bench bled it with good reason as there was some air in it. put it all back together and spent about 3 hours between the va***n bleeder and the neighboor pumping the pedal system. but it stops now and pretty damn well. rears dont lock up either so i'm guessing i can do without a prop valve?!?!

anyways i'm off to turkey run tmrw morning

thanks again!!!

 

Way to stick with it.......... thanks for posting the cure. Have fun!

 

awsome good to hear the fix was painless, well mostly..

 

Good job sticking with it, it's better to learn than to give up and take it to a shop. Next time you'll do the job twice as fast.

I was going to mention, never buy a rebuilt master cyl. 1/2 the time they are junk and just not worth it. Something to consider when things aren't working right.