The new 12"D disk brake is shown
in the top left picture compared to the original 10.5"D disk brake setup
in the top right picture. The tubular upper control arm, which made the
swap possible, is illustrated at the left.
I have installed 12"D disk brakes on my Grand
National. Much of the information, for the conversion, was collected
from the G-Body.org, GNTTYPE.org, and Global West sites. Other information
was taken from the GM 44W Parts Manual and an old copy of the Motor Crash
Estimating Guide. Basically, an aftermarket upper control arm, such as
Global West's or Hotchkis', is needed to adapt the taller spindle/12"D
disk brake assembly from the GM B-body (full size car, i.e. Caprice, etc.).
Although, the 12"D rotor to use is from the Camaro with the 1LE option.
The Camaro has the same 4.75" bolt circle diameter as the G-body, as opposed
to the B-body's 5" D bolt circle. The parts one needs for the conversion
are as follows
Global West upper control arms, no. CNR-88-CB, for turbo
Buick application w/brass bushing under downpipe & lower control arm
left front spindle, no. 18021052 (old no. 14012589)
right front spindle, no. 18016024 (old no. 14012590)
brake hose to caliper bolt, Motormite 13940 (same for G &
B body), qty. 2
pads for B-body w/12" brakes
brake pad spring clips, Carlson H5404-2
Russell steel braided hose kit, no. 9210/692100 (optional)
The spindles came on GM full size cars (B-body) with the 12" brake
option from approximately 1978 to 1992. Calipers were, at least, from 1982
to 1992. The G-body tie rods and lower ball joints will bolt up to the B-body
spindles. The G-body brake hoses and retaining bolt can be used.