The FoxValley Technical College Firebird salt flats racer had reached 193 mph on its first run in the “2012 World of Speed” event at Bonneville and was ready to go faster on its second run. Then, the rear axle started making noise. It turned out to be a “spun” pinion bearing in the race car’s Ford 9-in. rear axle.
By necessity, the fix was carried out on the salt which meant the team needed to be quick, efficient and thorough. We began by removing the rear wheels and setting the axle on jack stands. Then the brakes were removed. The axle was rotated to line up the hole in the flange with one of the retaining bolts. The four bolts were then removed so the axle could be pulled partly out. The axles only need to come out about four inches to allow the center section to be removed, but you have to be careful not to damage the wheel seals in the housing.
The team inspected the wheel bearing race and found it be intact and the axle seals looked solid- no missing rubber and no leaks, so new seals weren’t needed. New bearings were not required either. Two team members cracked the gasket while pulling upward on the third member. Plastic tubs caught any fluid that leaked out. A screwdriver between the third member and housing allowed the fluid to drain for about five minutes.
The third member was removed and placed on a clean surface. The fluid was mopped from the bottom of the crankcase and a check for metal particles was made. The third member was set on blocks and checked for backlash
A large adjustable wrench made it possible to hold the pinion flange and remove the pinion nut, as well as the bolts holding the pinion, pinion bearings and retainer to the main casing. The smaller pinion bearing was replaced. The retaining ring was pried out. The retaining ring can usually be reused. The casing around the small pinion bearing was inspected to make sure it wasn’t cracked.
The Fox Valley Tech racing team installed the ring gear and differential assembly and the bearing caps, temporarily leaving the bolts loose. The side adjusters were screwed into the side of the main case and bearing caps. A dial indicator was set up. The adjuster opposite the ring gear teeth was turned until the ring gear was tight against the pinion gear. Then, the opposite adjuster was turned until it got tight. Each adjuster was loosened and tightened until all were tight and had .008 in. backlash. Then, the bearing cap bolts were snugged tight.
The Fox Valley Tech racing team installed the ring gear and differential assembly and the bearing caps, temporarily leaving the bolts loose. They screwed the side adjusters into the side of the main case and bearing caps. A dial indicator was set up. The adjuster opposite the ring gear teeth was turned until the ring gear was tight against the pinion gear. Then, the opposite adjuster was turned until it got tight. Each adjuster was loosened and tightened until all were tight and had .008 in. backlash. The bearing cap bolts were snugged tight.
Team members painted the ring gear teeth with gear marking compound. They put force on the ring gear in each direction and spun the pinion and flange 10-20 times, five or six teeth meshed with the pinion gear teeth. By releasing the pressure and rotating the ring gear, the pattern of previously meshed teeth could be seen and checked. The ring gear was then forced in the opposite direction and the pattern was rechecked. We were looking for meshing in the center of the teeth, rather than running off at the sides. We were careful to check different spots on the ring gear to ensure similar patterns over the entire ring gear, which means the ring gear is seated properly and runout on the ring gear is acceptable
If we had seen a pattern that wasn’t correct in all directions, a different shim would have been installed after removing the pinion. The idea is to add or subtract only .002 inches of shim on the first check. Thicker shims can be added on a second try, depending on how much the pattern changes.
When everything looked good, we called upon two team members—Jim and Bob Buchman—to re-install the side adjusters and redid the adjustment to set backlash at .008 inches again. This can take a long time to get right and doing so requires talent, patience, which Jim and Bob had—and sometimes luck.
The entire team finished the job up by applying Loktite to the main bearing cap bolts and tightening them to 75-85 Ft-lbs. The next step was to install the side adjuster retainers, again using Loktite on the small bolts before tightening them up. A check showed that the ring and pinion meshed smoothly all around the ring gear, so we started re-assrembling the axle.
We put the third member back in the housing and applied gasketmaker between the housing and third member. The brass washers were inspected, looked good and were put back on. We torqued the third member nuts to 30-40 lbs.-ft. using a criss-cross pattern. Then the axles were pushed all the way in and we torqued the four nuts to 50-75 lbs.-ft. After re-installing the brakes, we fired up the Firebird for a test drive. If the axle got hot again we would have still had problems, but it didn’t. We were ready for our third run down the salt.
As luck would have it, on the third run the axle worked perfectly, but the tranny bit the dust and, of course, took the engine with it. We had to be happy with our 193 mph first run, which was the best the car has done in three trips to Bonneville. Nevertheless, the 200 mph goal has not been reached and the Fox Vallety Tech “Beat the Heat” Firebird will be heading west again in Sept. 6-9, 2014 when the Utah Salt Flats Racing Assoc. (www.saltflats.com) holds its next “World of Speed” event.