When we bought our '67 Ranchero, we got a pleasant surprise when we discovered that the original C4 transmission had been replaced with an AOD four-speed automatic overdrive. The seller never mentioned the presence of the overdrive-equipped transmission and we listen with great satisfaction each time the transmission plunks into fourth gear at about 50 mph. The overdrive is great and the engine is just loafing as the car goes down the freeway. However, our Fairlane Ranchero is in reality a pickup as well. It has a bed and a trailer hitch. It is used for everything from pulling a boat to helping our friends move their refrigerators.
After having driven the Ranchero for some time, we've discovered that while the gearing is great for freeway cruising, the new final drive ratio of 0.67:1 makes the 3.00 axle gearing too tall for any kind of serious towing. Another argument for a deeper gearset is the fact that the Ranchero isn't exactly a rocket ship coming away from the traffic light with its original 289 4V engine, even without a load. These considerations combined with the howling noise emanating from the rear of the vehicle meant that it was time for a visit to San Diego Gear and Axle of El Cajon, California.
SD Gear and Axle is a complete rear axle service center for any Ford car, and we were able to make an appointment, drive our vehicle into the shop, and leave a few hours later with a completely refurbished and re-geared 8-inch differential. We didn't know what to expect when the gearcase was opened, but we were hoping that we wouldn't have to replace the entire third member. We felt fairly certain that we'd need to replace the ring-and-pinion, and the shop had a good set of used 3.50 gears available-just the ratio we had in mind. A locking differential, while considered a must for high-performance use, isn't as important when simply hauling a load or towing. Hence, we decided to avoid the added expense of a locking differential setup and retained the open rearend. Join us at San Diego Gear and Axle and we'll see just what is wrong with our third member and what it's going to take to repair it.
Cost: $272
Included used gears, new bearings and seals, lubricants, environmental fees and taxesLabor additional
 We began by removing the four...  We began by removing the four axle-retaining T-bolts and then using a little gentle persuasion with a slide hammer to get the axles free of the housing. While some axles will slide right out, it takes more effort to remove others. |  Once the axles are free, the...  Once the axles are free, the driveshaft is disconnected at the pumpkin and moved aside. We left the other end in the transmission to avoid fluid leaks. It's advisable to mark the flanges before removal to avoid inducing possible vibration issues. After the centersection's retaining nuts are removed from the housing studs, the case is carefully pried away from the housing and drained. Once empty, the gearcase was taken over to the bench and set in a support fixture. |  On the bench, the first step...  On the bench, the first step was to check the ring-and-pinion mesh. As the gear marking compound shows here, the engagement pattern is almost all the way off the thrust side of the tooth. It was determined that these gears were too worn to reuse, so they were headed for the scrap recycling bin. |
 It's important to avoid getting...  It's important to avoid getting the main caps in a differential mixed up during disassembly. Here, they are marked with a punch to ensure replacement in the original position. |  With the man caps off, the...  With the man caps off, the differential is removed from the case. Although the bearings and races were heavily worn, no damage had occurred to the gearcase casting, which means we can reuse it. We can tell the axle has been worked on before because the cross-webbed casting is too new to be OE on a '67 Ranchero. Orange Permatex and an axlehousing that was very clean on the inside were other tip-offs that the axle had been opened before. |  Here, the pinion housing is...  Here, the pinion housing is removed from the gearcase. Notice the multiple shims in place between the pinion housing and the gearcase. Their thickness won't be recorded because a new adjustment will be required, but you'll want to note the shim pack thickness for general servicing. |
 Between the worn differential...  Between the worn differential bearings and these wiped-out pinion bearing races, it's easy to see where all of our noise was coming from. In this photo you can see how the race is worn and pitted. Outer axle bearings were good on both sides, so we knew the noise wasn't coming from there. |  On the differential itself,...  On the differential itself, the ring bolts are removed. Here, the ring gear is being separated from the differential with a mallet and drift punch. All of the small parts being reused are loaded into a basket along with the gearcase and are completely cleaned. |  Here is our replacement gearset....  Here is our replacement gearset. The 3.50 ratio will be perfect for improving our off-the-line performance and low-end grunt for towing ability. With a 25-inch-tall tire, these gears will yield an engine rpm of 2,300 at 70 mph, so our car will still have very reasonable freeway performance. The used ring-and-pinion set cost $150. |