First of all, thanks to all the contributors here most especially speedygonzales. As others have noted the brakes on my '88 k1500 have always been a source of worry in any hard stopping situation and knew it could be better. Had already replaced front pads/rotors/calipers, rear shoes/cylinders/drums, flushed and bled system to little improvement in the braking ability of this truck. Did this mod about a month ago and wanted to report my experience.
I found the Fenco master cylinder locally at Autozone along with the AGS #BLF-26C adapter. Removed OBS master, bench bled and installed NBS master with line adaptor. Had to carefully bend lines and was afraid they might snap but there is enough "slack" to allow the realignment to the NBS master. Bled system and found firm pedal but less braking power. No good!
I suspected my booster might be bad, did the various tests which it passed. In the process I looked up a new one and found 3 different ones listed for my truck; a single diaphram 10.75" (standard brakes) stamped "AB", dual diaphram 9", and a dual diaphram 10.5" both stamped "HR". My truck had the single diaphram 10.75" "AB" booster from factory which I assume was standard equipment for the cheapest brake setup from factory. I looked up the 2002 Silverado that my NBS master cylinder was originally designed for and found that the booster from this truck was an 11" dual diaphram. I figured the new master was designed to require the additional boost from a dual diaphram booster so I went and bought the 10.75" dual diaphram booster that came on some versions of my truck. For my truck, that was the key to good brakes. Firm pedal and much much better stopping power.
Bottom line, for those of you with original equipment single diaphram brake boosters: install the dual diaphram 10.5" along with the rest of this mod. You won't regret it!
Parts list:
Fenco NM3089 Master Cylinder (Autozone) $85.99
AGS BLF-26c line adaptor (Autozone) $2.49
Brake Best 54-71046 brake booster (Oreillys) $104.99
