Quote:
Originally Posted by jeffahart
For sure not correct. I did have trouble when I moved to front disc on this truck with the newer master and prop.I ran the drum/drum with yanked RPV for a few months. I finally got around to installing the correct master setup. I was dissatisfied, and it left me scratching my head for weeks. It drug its hind end and I hated the feel of the pedal. I went back to the original drum/drum distribution block and master with the yanked RPV. The brakes worked great... go figure. I only have so much brake bleeding in me. I got sick of dickering with the brakes. And I refused to put an adjustable on the rear, call me stubborn. When I upgraded the booster I decided to give the Hydro a whirl. It seemed like a cheap easy upgrade... it was. I am delighted.
If you read any of my posts, you will always see me advocating for a working baseline. Once you start mixing and matching components you can really start chasing our tail.
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Jeff, as I mentioned in my first sentence - using a drum/drum mc on a disk/drum mod'ed vehicle will indeed work. The point is that the internal fluid passages of a disk/drum mc and a drum/drum mc are different for a reason. The factory distro block on drum/drum systems was only that - distribution and a place to mount the warning switch for the brake circuit isolation valve - any front-to-back biasing was done internally in the mc circuitry, not the distrib block. Anyway, the delta of using a drum/drum mc in a disk/drum setup can certainly be adjusted out and tinkered with via an adjustable proportioning valve until it feel about right - or it may work just fine as your example highlights, but that doesn't mean it's optimized. The drum/drum mc was still accomplishing its internal biasing - yet you had a disk/drum setup, so it wasn't the factory designed biasing for a disk drum system - even though it still function fine overall. That's really my only point in this discussion.
I agree completely with having a baseline from which to deviate, but in my experience, the best working baseline has been the factory setup - that's why I advocated starting there for the OP, especially if it's only $20-30 to have a brand new disk/drum master cylinder, and then deviating to one's taste/preference to modify the system.
A dragging rear brake system when the only change made was the installation of a disk/drum mc doesn't mean that using a disk/drum mc on a disk/drum system is a bad idea (the factory did it on every truck they produced from 71 forward)- it means there was some problem within the system, perhaps even a defective new mc. Anyway, just wanted to clarify. There is a reason GM didn't just continue using the same mc from pre-71 when they changed to a disk/drum system in 71.