Brake bleeding problems

[Wile E]

Here's what I posted on gbodyforum:
aaaggghh! Swaped the 8.5"GN rear out of my 78 Elky and bolted up the 9" we had been saving for my Malibu. All the brake hardware on the rear is NEW, including the wheel cylinders. I had to bend some new lines and make a support bracket for the rear distribution block/brake hose. I figured I'd have to bleed the brakes, but nothing works. No visible leaks and the resevoir stays full (unless I'm bleeding them) The peddle is nice and firm until I start the car, then the peddle is mush. I've bled the brakes like normal 3-4 times (two poeple), gravity bled them, used speed bleeders, and tonight used a vacuum pump . Nada, Zip, Zero, Zilch...same thing, nice firm peddle until I fire it up. Then...mush. The brakes worked fine until the rear swap. Proportioning valve? Could I have mucked up a fitting/line where air gets in but does not leak fluid? Don't want to start replacing parts if it's just something simple I'm missing

 

[bracketchev1221]

Someone told me that you need to put a clamp on the stock prop valve while bleeding to prevent turning on the brake warning light and potentially breaking the valve. I don't know if this is true. But it may be worth looking into.

 

[melloelky]

sounds vaccum related?booster?

 

[83StreetMachine]

Did you bleed the fronts as well??

 

[t5montecarlo]

a little unrelated, but it is not a good idea to put the brake lines on the front of any part of the car. Along top and behind is safer.

 

[abigda]

I had a very similar problem on mine when installing my 9" rear with ISC brakes, it was a bad master. Took me weeks to figure It out

 

[Wile E]

a little unrelated, but it is not a good idea to put the brake lines on the front of any part of the car. Along top and behind is safer.

Yes, good point,..I agree.
.
Bled the fronts also. Gone thru the whole routine 3-4 times,

Trying a new proportioning valve this weekend. I had replaced the master cylinder last year, thats next if the prop valve doesn't resolve this.