12" Brake Conversion for GM G-Body

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G-Body Conversion to 12" Brakes


	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 bushings
left front spindle, no. 18021052 (old no. 14012589)
right front spindle, no. 18016024 (old no. 14012590)
1LE 12" rotors, no. 18027886 (old no. 18016035)
left dust shield, no. 344023
right dust shield, no. 344024
left caliper, no. 18015427
right caliper, no. 18015428
dustcap, no. 14003444, qty. 2
washer, no. 457707, qty. 2
nut, no. 378137, qty. 2
caliper retaining bolt, no. 18022601 (old no. 5463495), qty. 4
gasket between shield and spindle, no. 15699959, qty. 2. This is a rubber gasket that is 0.060" thick w/ ~1.97" ID & ~2.69" OD

Additionally, other parts that will be needed are

bolts for shield to spindle, 5/16"-18x3/4", qty. 6
inner wheel bearings, Timken Set 6, qty. 2
outer wheel bearings, Timken Set 3, qty. 2
bearing seal, Timken 8871, qty. 2
lower ball joint, Moog K6145T (stock G-body replacement, optional), qty. 2
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.