So you have your dream car and are working on it just about weekly. You plan to do some autocross and take it out to the dragstrip on Thursday nights for some grudge matches in the quarter- or eighth-mile. You spent your money where it counts: in the engine and trans. So once on the highway, you are absolutely flying, but stop sign to stop sign your ride is a bit sluggish off the line. Well, son, that peg leg 10-bolt has gotta go.
The right rearend gear and a tight converter can really wake up your car. If you’ve been driving around with the same 3.08 gears that your mom enjoyed back in the 1960s, it’s time to make a change. It’s just no fun unless you get your excitement driving on long road trips or boring rides to the local market for some pop. Face it, that’s not who we are. As performance enthusiasts, we live a little more on the edge and want a whole lot more out of our hot rods.
Our friend Joel Rode owns a 1969 Nova (the same car we did some recent bodywork articles on) that needs a little waking up, so he went to Oceanside Driveline (Oceanside, California), and talked to Paul Headrick who clued him in on what it would take to make Joel’s powerhouse stick to the road and make two black streaks instead of one without breaking the bank.
Joel and Paul came to the decision that it needed a limited-slip differential from Auburn Gear, a 4.10 ring-and-pinion from Richmond, and a slight girdle for the main caps. This would provide Joel with all new parts for worry-free driving.
The limited-slip, as you probably know, is a great run-around that offers the freedom to run in the rain to the store, yet clean up at the dragstrip. A full locker is really race stuff, but Joel plans to use his ride for the street and autocross as well.
So on we went to put this thing together. The idea of tackling this job might be a little intimidating, but Oceanside Driveline made it simple for all of us to understand.
01. So on we went to put this thing together. The idea of tackling this job might be a little intimidating, but Oceanside Driveline made it simple for all of us to understand.
02. Cleanliness matters when you’re dealing with the internal workings of your car. Make sure all the old seals, glues, grease, and grime are scraped away and cleaned. After the initial cleaning, hit the internals with some brake cleaner and wipe everything down. This goes for the axletubes as well as your housing.
03. The first step is to remove the main bearing off of the pinion and pull the shim. The main bearing comes off with very little effort using a pinion bearing remover and an impact gun. Once it’s off, you will find this shim. Ours was OEM and a bit worn. Usually they will have a stamp showing the size. Ours didn’t so we had to pull out the micrometer to find out ours was worn to 0.0030 inch.
04. With the housing completely clean, we installed the pinion bearing races with our bearing race tool.
05. Paul Headrick, who regularly rebuilds diffs, showed us this trick. He used a “tool bearing,” which is an extra bearing that has been machined a few thousandths over on the inside diameter. In all other ways it is an exact match to the bearing we will be pressing on later. This gives us the opportunity to install and remove the pinion bearing to change shim size in order to get the correct backlash. Like before, our starting point on the shim under the bearing was 0.0030 inch. It was finalized at 0.0032 inch. If we had pressed on the bearing we wanted to use and taken it off a couple of times, it would have trashed the bearing. Some say to use the old bearing to get this adjustment, but that bearing has tons of hours and miles on it, so it will give an incorrect reading when assembled for test and assembly.
06. With our 4.10 ring gear installed to the limited-slip, our end bearings can be pressed on and races can be held in place. The shims sit between the bearing race and the housing, sandwiched by two hardened washers. You’ll take a measurement off of the ones that came out and start there with new shims. Be patient since you’ll need to install the differential more than once, taking measurements each time, to end up with 0.0010-inch backlash.
07. After getting to the 0.0010-inch backlash, the paint-wear pattern on the gears looked very uniform. It was then time to install the new bearing that came in our kit and put the “tool bearing” on the shelf for the next time. A thin coating of antiseize is used on the surface of the pinion where we will be installing bearings. This gives it just enough slip not to mar the bearing or the surface. Our 0.0032-inch shim was installed and off to the press we went.
08. With the new bearing and shim pressed in place, the new crush washer is installed on the pinion.
09. Our housing surface had a few burrs and nicks in it so Paul used a fine file to knock them down since they could mar the cast-aluminum cover we’re using. If you were using the original tin cover it wouldn’t matter as much as you would be using the gasket and a lot of RTV sealant.
10. On all bearing seals we used a coating of grease on the inside of the seal to keep the spring in place. This was a great trick for us as those springs, upon install, can come off and go bouncing around inside and make a real mess.
11. It was determined that the yoke was worn out so we needed a new one. This one used U-bolts instead of the stock straps for the U-joint. It’s recommended before installation to lightly coat the yoke splines with RTV sealant to deter leaks.
12. The pinion bolt and washer both should get a liberal amount of antiseize on the mating surface, while the threads on the lock nut get thread locker.
13. Once the pinion is installed and all the bearings are seated, drive the yoke on with an impact gun. This will crush the bearing on the front to the crush washer. Don’t go overly tight since the goal is to crush the washer so there’s a 15 ft-lb drag on the pinion.
14. When we felt the washer was crushed, we measured the drag. Looking close you can see we were at 13 ft-lb (orange pointer), which is close to our target of 15 ft-lb, so one more crack with the impact put us right where we needed to be.
15. With the main caps and bolts clean, we applied thread locker and torqued to the manufacturer’s specs.
16. As you can see, the mating surface of the ring to pinion is a clean wipe in the middle of the ring gear. If it was heavy on one side or the other, we would have made an adjustment by adding or subtracting shims.
17-18. We are at 0.0010 inch of backlash, so the hard work and shimming is over.
19. As you can see, the passenger-side axle has some severe wear and pitting. Paul recommended replacing both axles to lessen wear on the newly installed axle bearings and seals. It’s common for the passenger side to get most of the wear as it is the spinner and warms up over time.
20. New axles were installed and the horseshoe clip keepers for the axles were put in place. The main set pin was pushed into place and the set screw, after getting some thread locker, was replaced.
21. A new seal was placed onto the aluminum cover with no sealant. It is a machine fit, so it will not leak. The cover was installed and the ARP bolts were torqued to 25 ft-lb per the instructions.
22. The two main cap support studs were ran in until they touched the main caps then pulled out 1/2-inch, and lightly coated with RTV sealant.
23. Once they were coated, the support studs were ran back in and torqued to 10 ft-lb. The RTV helps keep a seal in the threads so the gear oil won’t escape.
24. The same torque specs apply for the lock nuts.
25. With the driveshaft back in place, we tightened down the new U-bolts to secure it.
26. There you have it. Our new limited-slip diff and 4.10 gears are bolted up and ready to help improve the Nova’s 60-foot times and lower e.t.’s. But before we hit the strip, Paul suggested we do a 500-mile break-in or there’s a good chance we’ll be repeating this dance sooner rather than later.
27. Friction Modifier is absolutely needed for limited-slip diffs. If you don’t use it, you’ll burn it up and waste every bit of your hard-earned dollars. Oceanside Driveline has been at this for a long time and has found that Motorcraft friction modifier has the best properties for a limited-slip diff. They add two 4oz bottles in the service port of the rearend and top it off with 85W-140 gear oil.
The Starting Point
Looking for some cheap, easy power for his newly acquired 1969 Nova, Joel Rode dug up an old “boat anchor” Chevy 350 Vortec he had living under one of the benches at his boat repair shop. A visit to JMS Racing Engines in El Monte, California, got the engine a simple rings and bearing refresh and the addition of a Comp Cams X4270HR hydraulic roller cam (220/224-degree duration at 0.050, 0.474/0.474-inch lift). Joel added a PerTronix electronic distributor, Holley 800 double-pumper, and a set of Doug’s headers. Joel also modified the tunnel of his Nova and installed a TCI Auto Outlaw shifter to change gears in the 700-R4 trans that came with the car. Out back was a peg-leg 10-bolt rearend with 3.08 gears.
Curious to see what he was working with, Joel hauled the Nova over to GTR High Performance in Rancho Cucamonga, California, where he put the car on their DynoJet chassis dyno. Not expecting much, the car spun the rollers to a best of 254 hp and 290 lb-ft at 5,200 rpm.
Next up was to get the car some quarter-mile numbers, so Joel took the Nova over to Auto Club Dragway in Fontana, California, for some drag testing. After spinning the street radials like the car was on an ice rink, the first two passes ended at half-track when the car ran out of fuel on the top end, sputtering uncontrollably with the car barely breaking the 16-second e.t. barrier. An ill-planned fuel system and loose ground wire on the electric pump proved to be the culprits.
With a re-plumbed and simplified fuel system, Joel ventured back out to Auto Club Dragway. While still not hooking up, Joel throttled the Nova to a best 60-foot time of 2.407, with quarter-mile numbers of 15.643 seconds at 87.69 mph. Even with only 250 hp at the rear wheels, it was obvious nothing was going to be accomplished without some traction.
Small Steps to Improved Performance
Out came Joel’s checkbook for a new set of Mickey Thompson ET Street S/S drag radials (size 255/60R15). Another trip to Auto Club Dragway yielded a best 60-foot time of 2.212 and a quarter-mile of 14.619 at 93.19 mph. The MT’s did their job, as Joel was able to flash the converter to 2,000 rpm and leave the line with no noticeable tire spin.
The next step was to add some gear. Since the car was equipped with an overdrive trans, Joel wasn’t afraid to get a little aggressive and step up to a 4.10:1 rearend ratio. A short day with Paul Headrick at Oceanside Driveline in Oceanside, California, left the Nova’s rearend packed with a pile of goodies from Summit Racing, including an Auburn Gear High Performance series posi-traction differential, Richmond Gear ring-and-pinion set, Summit Racing cast-aluminum differential support cover, and a Motive Gear bearing kit.
Joel’s next visit to Auto Club Dragway with the new, shorter (numerically higher) gears and limited-slip helped to get the Nova down the quarter-mile almost 0.5 seconds quicker. The car’s best run of the day netted a 60-foot time of 2.118 and quarter-mile e.t. of 14.17 at 95.48 mph. With the 4.10s and the 27.3-inch tall rear tires, the Nova went through the lights at 5,000 rpm. An unexpected result of the added gear multiplication was a 300-rpm reduction in stall speed.
A call to TCI Automotive and Sales Tech Manager Will Vance gave us a quick education on a gear ratio’s effect on stall speed. Will told us that “stall is essentially slippage and it all comes down to making the car move. Just like a heavy car will gain more stall out of a given converter than a lighter weight car, more gear moves the car easier, so there is less load against the converter, which equals less stall.” What this told Joel was that the car now needed a smaller/higher stall converter to get the Nova to leave harder.
So it looks like Joel has a little work cut out in order to get the Nova to the next level. Stay tuned as we’ll follow the install of the TCI Auto 10-inch Street Fighter converter and share the results from the dragstrip.
Testing By The Numbers
Falken ZIEX ZE950 AS street radials
60-ft time: 2.407 seconds
Quarter-mile: 15.643 @ 87.69 mph
4,500 rpm through the lights
Mickey Thompson ET Street S/S drag radials (255/60R15)
60-ft time: 2.212 seconds
Quarter-mile: 14.619 @ 93.19 mph
4,500 rpm through the lights
Installed 4.10 gears with posi
60-ft time: 2.118 seconds
Quarter-mile: 14.17 @ 95.48 mph
5,000 rpm through the lights