Copy and Photos by Jim Batie

Using factory parts from various models or model years to peform an upgrade on your Ford project car can be incredibly satisfying. First, factory part upgrades are usually cheap and can sometimes be achieved with inexpensive salvage yard components. Secondly, mixing and matching factory parts for increased performance requires careful research and knowledge that is sure to impress fellow hobbyists. As you will see in this tech article, converting front drum brakes to discs or upgrading from 11" to 12" rotors using factory parts demonstrates ingenuity that goes above bolting on an aftermarket kit. When comparing notes at a car show, others will easily conclude that this upgrade didn't come with step by step instructions and a ziploc bag with all the correct hardware.

Several years ago FordMuscle acquired a '77 Lincoln Continental primarily to keep the running 460 powerplant. While disassembling the Lincoln front end we discovered the brake rotors were almost and inch larger than those on 70's Ford intermediates. Interestingly, the calipers and backing plate were identical to what we've been accustomed to seeing on most 70's Rancheros, Gran Torinos, Montegos and some Cougars. The caliper mounting brackets were also similar to the intermediate's and share a common spacing on their mounting surfaces. We retained the Continental front spindles and related parts hoping they could be used to perform an OEM upgrade on our '73 Ranchero's 11" brakes up to 12" brakes. We knew if it could be done, early Galaxie owners would also be interested since many upgrade their drum brakes to disc, using the 11" intermediate spindles and rotors.

Unfortunately, the full size Continental rotors we salvaged had a 5 on 5" bolt pattern. Intermediates all have a 5 on 4 1/2" bolt pattern. Since maintaining a standard bolt pattern on all four corners is best, this presented a problem. A set of 5 on 5" aftermarket rear axles or perhaps a later set of OEM axles could be used giving us a 5 on 5" pattern all the way around. Better yet, what if Ford made a 12" rotor with a 5 on 4 1/2" bolt pattern? We researched the possibility. After numerous inquires, we found Jack Grice of Dubuque, IA. He is the technical advisor for the Fairlane Club of America for the years 1972-76. Jack compared data in an old interchange manual and looked to see what he could find and confirmed that a '72 Thunderbird used a 12" rotor with a 5 on 4 1/2" bolt pattern. He then looked up the bearings required to fit these rotors. They were the same as the 72/73 intermediates.

From left to right...
12" rotor full size Ford. Larger inner bearing and 5 on 5" bolt pattern.
B. 12" rotor from '72 Thunderbird. Smaller inner bearing and 5 on 4 1/2" bolt pattern.
C. 11" rotor from '73 Ranchero. Smaller inner bearing and 5 on 4 1/2" bolt pattern.
We compared the seats for the inner wheel bearings on both the 12" full size Ford rotor and 12" '72 Thunderbird rotor shown to the left. It's clear, the T-bird uses the smaller inner wheel bearing.

Close inspection shows a larger bolt pattern on the 12" full size Ford rotor shown to the right.



In This Article:
We demonstrate how to upgrade to 12" rotors on all 70's Ford intermediates and early Galaxies equipped with 11" intermediate front rotors and '72 -'73 spindles.

  This is a typical 11" front disc brake assembly found on 70's intermediates (Rancheros, Montegos, Gran Torinos, some Cougars, and some Thunderbirds). Fairly commonplace in wrecking yards, these have often been used for converting early Galaxies from a front drum to a front disc set-up. Notice how the 11" rotor does not completely cover the backing plate.

Using rotors from a '72 Thunderbird and caliper mounting brackets from a 70's full size Ford we were able to modify our '73 Ranchero from 11" front discs up to 12" front discs. Calipers, wheel bearings, and seals were all stock replacement parts for our '73 intermediate spindle.

Galaxie owners wishing to make this conversion possible should locate '72-'73 intermediate spindles. In '74 Ford standardized front wheel bearings for all Ford, Lincoln, and Mercury full size and intermediate passenger cars. If you have a '74 and up intermediate or a Galaxie running '74 and up intermediate spindles this means you could use the common full size ford 12" rotor, but you'd have to be content with a 5 on 5" bolt pattern up front. The spindle shown right is from a '72 intermediate. Note the smaller OD for the inner wheel bearing.
The 5 on 4 1/2" '72 Thunderbird 12" front rotor only works on the '72-'73 intermediate spindle. However, it is worth locating them if you are not already running them on your 70's intermediate or early Galaxie. Notice how the 12" rotor completely covers the backing plate.

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