I converted the front drums on my 68 Chevelle to 1969 discs. Everything is rebuilt or new. I bought what is supposed to be the correct master cyl. and prop.valve. It is not a power brake car. The pedal has always felt spongy no matter how many times I bleed the system. I also have new rubber lines. The master cyl doesnt look much different than my drum brake unit. I looked at a buddy's car and his master cyl is larger than mine, but its a power brake car. The car stops better at hi speed but worse at low speeds than my drums did. The spongy pedal takes more travel so response time is slower and it takes more pedal effort now. Also harder to hold the car still in the staging beams. It seems to be getting worse and feels like air in the lines, but bleeding doesnt let any out. Any help would be very welcome.

you sure you got all the fittings tight ? If it feels worse and worse, you may be pulling more air into the system. Check for leaking brake fluid. Also, are the rears adjusted ?
I just went thru holy hell bleeding the brakes on my 70. New Wilwoods in the front and Wilwoods in the back. I did every method of bleeding. 2-man, vacuum, gravity, speed bleeders. The best way by far was a homemade power bleeder. I took an air regulator made a plate with a fitting on it and pressurized the master with about 12 psi. Used a c-clamp to hold it on and used the master's seal to seal it air tight. The pressure forces the fluid thru the lines and will empty the resovoir in about 10 seconds! I got quite a bit of air out that didnt come out the 2 man way. These Chevelles seem to p.i.t.a. to bleed.

Do you have the caliphers on the correct side. The bleed screw must be on top or you will never get all the air out.

Thanks Guys, yes the rears are adjusted properly, and there are no leaks. The system getting worse has taken over a year. I may try the homemade bleeder setup. And the calipers are on correctly too. I am wondering if I have an incorrect part somewhere?

You may want to try a different master cylinder if nothing else works. I went through this same thing when I rebuilt the brake system on my '69. Somehow the master cylinder was letting air into the system even though all fittings were tight. New master cylinder and the problem went away.:yes:

I may try that if power bleeding does not help. Thanks

ya, trying another master may be a good idea after your sure you got they system bled. I tried 2 Wilwoods masters after I bled the system, a 1 inch bore and a 1.125. Still had a crappy pedal. So I switched back to the stock Chevy master (for 4 wheel disc) and got a good pedal. Wilwood's lame tech dept. had no answers so I sent them back.

You mentioned that you have new rubber lines... Does that include the one in the rear? I have heard of these going bad (as any rubber hose can do) without any visible warning. They stretch under pressure and never quite deliver the volume of fluid that they should. Just a thought, as many folks tend to overlook that particular hose.

Patrick

Yes its new too....Thanks

Only thing I can think of is if you bench bled the master before installing it. But it sounds like you have a solid pedal when you press down hard but when you coast to a gentle stop, it goes down further to the floor.

No the pedal isnt that solid. That makes me think maybe I should re bench bleed the Master though.

Can you or did you bench bleed the master.
If you cant get the bubbles to stop comming out on the bench you will never get it right.
I have had new masters suck air in through the rear seal of the master cylinder itself.

I did bench bleed it, but maybe I inadvertantly reintroduced some air when I installed it. I will check it out. Thanks everyone.