now is the time to "upgrade' to a dual master cyl. set up for safety!!!! Think a 68 to 70 chevelle with drum brakes would be the ticket, a proportioning valve off same car & run a new lines!!! Much safer than a single.

usually a sign that the master needs replacement

dualquadpete wrote:

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had this problem with my Avanti, was a internal "leak' in M/Cyl.!!! Changed the Master, & had a firm pedal!!! It; used to slowly sink to the floor at a stop light, quick pump brought it back firm but would sink again!!! hardest part was figuring out what M/cyl. to order, turned out to be a 68/69 "FORD" Torino ????

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 thats exactly what mine is doing intermittently.

 

I really want to take the czr to the last show of the yer wit my dad but too afraid it might just let go..............................................

 

Your master cylinder is bypassing...(very common deal on 70's GM tandem masters...)

It may ALSO be pushing brake fluid into your brake booster.....which is NOT a happy thing....

Prolly BEST to replace BOTH..master AND booster....a tandem master is really NOT needed....as long as your emergency brake is functioning properly...

If you feel the need to add a tandem master....why not go the full route and put in some airbags...and maybe ABS?...

And how about some shoulder belts....and a roll cage...while you are at it...

Best to throw that master cylinder in the garbage. Take the booster and get it checked, a lot of times the diaphragm is damaged. The last brake system I changed up was on my convert and it was a mid to late 60's dual master I bought and I got a proportioning valve from the same era WITH ALL THE FITTINGS as they are different from standard fittings both on the master and valve. You also have to get the right bore, there is a shallow and deeper bore on the cylinders to match up with the push rod on the booster. You may have to adjust or change the rod on the booster for the cylinder. From the master two lines go down to the valve which you mount on the frame and three come out, one to the front left, one to the front right and the other to the back rear end. IF the brake lines are good on the car run a short new line to the front left, a new line over to the front right and a new larger line over to the passenger side and use a connector to tie into the line to the back. If you can find someone with a hydraulic brake flare tool trust me you will not be redoing the lines over and over to get them to seal. I bought a 25' coil of the easy bend brake lines, got both ends flared and then cut the lines to lengths and took then back and had them flared until I had them all done - no leaks. I gravity bled the system and I have power brakes that stop dead. This is the least expensive way to get a great brake system on an older Pontiac or Chev. A lot of guys go with the disc brake setup but a good dual master cylinder with drums works great. Also the disc brakes actually move the wheel outward which could be a problem on your project.