Master Power Brakes Disc Kit and 11" Rear Drums

[bwhitejr]

I installed a Master Power Brakes front disk kit on my 72 Duster and I am having disproblems getting the brake light to keep from coming on from resonable braking. The brake failure light comes on everytime the brakes are pressed. We have bled these brakes a million times and can't get the light to stop coming on. Here is some background: the master cylinder they shipped with the kit leaked, so got a rebuilt one for a 73. The piston size from the kit is a 1" the replacement one is a 1-1/32" the original drums in the rear were 9" and the 8-3/4 rear end on there now has 11x2.5's with 15/16" wheel cylinders were the originals were 13/16". Is it possible the mismatch is causing the problem and is there a solution?

bwhitejr

 

[Vs29H1B]

The brake light switch adjustment on your brake pedal needs to be looked at.

Do you have fade or sponginess in the brake pedal feel? If yes, did you properly bench-bleed the master cylinder BEFORE you installed?

If you did properly bench-bleed, check the master for internal leakage.

Also, invest in/borrow a power brake bleeder to rid the system of air.

 

[bwhitejr]

Yes, the master cylinder was bench bled. I think that this is the result of altering the system. The car originally had a SL6 with 10" drums up front and 9" drums in back. I installed a disk brake kit that changes the master and adds calipers and combination valve. The other change was the rearend. The SL6 had a 7 1/4" rear with 13/16" wheel cylinders. It now has an 8 3/4" rearend with 11x2.5 shoes and 15/16" wheel cylinders. I suspect the change in volume in the rear wheel cylinders is at least contributing to the problem. I figure there have been several people who have done this same brake mod and might could help with some insight into the problem.

The brake light comes on when the brakes are being applied firmly. If pushed really hard the combo valve locks off fluid from the rear and has to be reset.

Thanks for any suggestions.

bwhitejr

 

[ecw329]

anyone have any ideas, we are stumped a this point.....