I recently changed from power drums to power disc on my 71 BB Malibu. New Master Cylinder, Calipers, hoses and pads. Original rotors, disc porportion valve, lines etc. The car will stop but I would not trust it in traffic. I have bleed the brakes and I get good fluid at all points - but still have weak brakes. The pedal does not seem to travel has far as it did with drum brakes. Any help will be greatly appreciated.

Thanks,
Michael

Not an expert, but you may need a disc brake proportioning valve provided everything else is healthy. Good luck graemlins/waving.gif

If the pedal feels firm and not spongy, then I'd say you bled them ok and would turn my attention elsewhere. Do you have the rear drums adjusted properly? Are the rotors freshly machined? Did you break in the brake pads gently? What pads are you using?

And what do you mean by 'weak' brakes... that they simply don't stop good? Also, can you get them to lock up at all?

Bill C.

By "Weak" I mean they do stop the car at low speeds - I would be afraid to even try at higher speeds. The pedal does seem firm but it does not travel far at all. The pads are just new pads from Advance Auto Parts and the rotors have been turned. The Porportion valve is from a disc brake car. The rear drum brakes have all new hardware and have been adjusted.

Thanks,
Michael

I put the same post here a couple three months ago after swapping my drums for disc on my 71 Elky. After much research and about a hundred miles of driving my brakes are perfect. I guess its not uncommon for the disc to have to seat in before they are 100% effective. I was told the best way to do this is just to drive normally and avoid hard braking for about the first 100 miles. Got this info after it was too late for me to avoid hard braking but they still work great.

i had a simillar problem after installing 12" disc brake kit from SSBC ,the problem persisted after break in and took it to three different shop's trying to fix prob. noone could find anything ,so i then swapped new booster for one off my '66 then i had brakes(bad booster), i tore a lot of hair out before this hapend

Did you change to the other hole in the brake pedal arm? Have not done it myself but many guys have mentioned it. Where the booster rod connects to the pedal there are two holes, one for disc and one for drums I believe.

It definitely sounds like you are not generating enough pressure at the calipers. For a boosted syste, the rod should be on the lower hole in the pedal. Check your vacuum at idle. Make sure its sufficient to operate the booster. Also check for any vacuum leaks between the booster and the engine. If all that checks out, then I would suspect that you have a MC with a bore that is too large. I suspect this, because of your high, firm pedal.

Let us know what you find out.

Andrew

When you did the conversion did you put a correct disc prop valve? If not you need to. The drum and disc prop valves are different.