I just put disc brakes from a 69 chevelle onto my 68 chevelle to replace the drum brakes i had. Everything went well during installation; lines are bled, no leaks, and looks sharp... But i took it for a test drive and brakes are soft! The first initial push of the brake pedal goes all the way to the floor, then i let up and pushed again and the pressure was there (felt nice and stopped well, but the first pump gets no response).

I re-bled the brakes again and it still is doing it. I have searched the web for any tech articles but cant find anything to help solve my problem. Does anyone know how to fix? Proportional valve? Please advise this new member..

Thanks
Bubba graemlins/beers.gif

You may need to adjust the rod on the brake pedal. I had a similar problem. Went to the floor, then was OK, then after noy using pressure bled off. I lenghted the rod a little and it ia working fine now. If you try this make small adjustments to the rod. if you make large adjustments, the pedal may feel good, but after driving anf using brakes you will fing that they are not releasing.

make sure your rear brakes are adjusted up tight against the drums. If they are loose, you will get that problem. ;)

I had the same problem, mine slid to the rear and wasnt getting any pressure to the rear brakes, but had alot of pressure to the front and the pedal felt weak. what I did was opened the two front bleeders and had some one hit them 2 or 3 times real hard and hold them while I tighten them back up. then repeated the same thing. this popped the valve back into place. then I re bleed the rear brakes. The one way you can tell is when you bleed em is when the person holds the pedal to the floor and u loosen the bleeders and the pedal doesnt go to floor thats a sign that its blocked by the valve. but after I did what I explained earlier and repositioned the valve the pedal went to the floor. after that I had real good pedal and the pedal felt good. hope this helps.

I dont think i mentioned that i had all drum brakes before, and then put disc brakes on the front. So disc in the front, and drums in the back. I tried repadjusting the pedal but it didnt fix the problem. I 'think' that the problem may be that when it was all four drum brakes, each brake would recieve the same amount of fluid. now that the discs are on the front and drums on the rear, the discs might require more fluid to activate them (thats why it take one full pump before the fronts actually engage...)

Just a thought on trouble shooting my problem...

Any ideas? Thoughts?

Thanks,

Bubba

Did you change the master cyl?

no i did not replace the master cylinder. is that my problem? what kind do i need if that is the problem?

Bubba

Originally posted by bubba68ss:
no i did not replace the master cylinder. is that my problem? what kind do i need if that is the problem?

Bubba You need to ask for a master cylinder for a 69 Chevelle with power disc brakes.
The Raybestos part number is MC39018. Also, did you install the proportioning valve?

You also need the metering valve that bolts to the MC too.

Or else some other proportioning valve.

69 Chevelle Master Cylinder is same as Corvette MC

{EDIT} sorry Jerry I didn't read all your post redface.gif

Just went through the same set up on my '69.... (provided you had power drum set up like mine).

Just purchase a '72 Monty Carlo master (with internal residual valve) and dump it on (make sure the shaft is the same length between the master and booster). Benchbleed the master (as per the units particular instructions), Bleed all lines again starting from the pass rear, then drivers rear, pass front, then drivers front.

All should be good to go.

-Greg