|
|
Differential Addition - Get Some Traction ActionAdd a limited-slip diff to stop that one-wheel-peel From the October, 2011 issue of Modified Mustangs & Fords By Mark Houlahan Photography by Mark Houlahan
|
|
When we last visited our High School Hauler project, we had worked through much of the Mustang's electrical issues, beefed up the cooling system, and put a solid exhaust system under it so that we could actually hear ourselves think going down the road (that's where we do some of our best editorial project thinking actually). Along the way, we've been keeping tabs on the '70 coupe's performance gains (or losses) with the grand picture being a fun, streetable car that is ready for track action with the twist of a key. The owner is looking forward to hitting the dragstrip with each upgrade we bring to the table, and this month, we have a nice treat for when the '70 makes its next quarter-mile pass. As any Mustang fanatic worth his or her T-shirt collection will tell you, the majority of early small-block Mustangs were saddled with relatively lame axles for performance duty. The typical 8-inch rear saw mostly 2.79, 2.80, and 3.00 gears bolted around an open diff placed between narrow-shaft 28-spline axles. While Ford certainly kept costs down, this setup wasn't much help in the traction department or for turning a decent e.t. Sure, you could option a Traction-Lok and better gears, but it was a rare occurrence until you got into the later years and big-block engines. It's commonplace to see a 31-spline 9-inch with a Detroit Locker and 3.91 gears added to the option list when buying a 428ci Mach 1, but certainly not on a '70 coupe with a 302 and C4 automatic. Our previous exhaust system upgrade made the coupe much more livable as a driver, and the owner has been putting some miles on the car. Suffice it to say, the aged suspension and braking are the weakest links in the Mustang's chain of performance right now. The owner, like most of us, is itching for more power, too. We're looking at several upgrade paths for the near future, including a ôtop endö kit of some sort to wake up the small-block, and a freshening of the suspension with some sort of budget disc brake package up front. But more power and better handling aren't going to help a thing without an improvement in traction. The coupe's stock 8-inch rearend no doubt has stock gears in it, in the 2.80 to 3.00 range, and as we've already proven in our last story, the differential is a stock open diff directing the 302's power to the right rear tire under heavy acceleration. Sure, we could ring up a number of axle builders and spec out a pipe-hitting 9-inch with 35-spline axles, a locker, and 4.10 gears, but besides the hefty price tag, it's plain and simply overkill for this coupe, even once we put more power under the hood. Instead, we called upon the guys at Randy's Ring & Pinion and Yukon Gear to help bring our existing 8-inch back to life with an upgraded center section, including a performance differential, more appropriate gearing, and stronger 31-spline axles. Our previous best elapsed time at the quarter-mile drags was a 15.8 at 88 mph, with a 2.631 60-foot time. With the new Dura Grip diff spinning both wheels using the 3.80 cogs, we dropped that time to 15.38 seconds at 89.17 mph with a 2.22 60-foot time. Check out the swap in the photos and read on to see how we made it all happen.
| Part Used | Part Number | Cost |
| Randy's Ring & Pinion Third Member | REBF8-380SVO | $1,367.07 |
| Yukon Gear & Axle Cut-to-Length Axles | YA F8-31-32.87 | $160.99 each |
| Stifflers Bolt-In Driveshaft Safety Loop | DSL-M02 | $78 |
| Royal Purple Max-Gear 75W90 Gear Oil | 01300 | $17.99 each |
 1 In order to remove the...  1 In order to remove the 8-inch center section, the axles will need to be removed first. Each axle is retained by four T-bolts with locking nuts. These also retain the brake backing plate. Raise the rear of the car, remove the wheels, and using the access hole in the axle flange, remove the four lock nuts for each axle.  2 With the four lock nuts...  2 With the four lock nuts removed, the axle is usually free to slide out of the axle tube. A strategically placed prybar will sometimes help, but really stubborn axles (it’s never easy for us either) will most likely take a slide hammer to extricate. Don’t let the axle drag on the axle seal, which is located in the end of the axle housing tube, or you could damage the seal.  3 The driveshaft will need...  3 The driveshaft will need to be disconnected from the center section’s yoke next. Remove the four nuts retaining the two U-joint straps and then carefully push the driveshaft forward, into the rear of the transmission, enough to clear the yoke.  4a Before doing anything...  4a Before doing anything else, wrap the exposed U-joint with tape to retain the loose U-joint bearing caps...  4b ...If you have dual exhaust...  4b ...If you have dual exhaust on your Mustang or Ford, you should be able to “store” the driveshaft above the exhaust with a long screwdriver or a length of wood. This way you don’t have to worry about fluid from the transmission or tripping over the driveshaft.  5 This coupe had a nice layer...  5 This coupe had a nice layer of oil-laden Georgia clay hiding all of the fasteners (there are 10 studs/nuts by the way) and even the axle tag. Several minutes with a screwdriver, chipping away at the hardened clay, allowed access to the retaining nuts.  6 Remove all of the retaining...  6 Remove all of the retaining nuts except for one of the top most nuts. Depending upon if the center section has been removed before, you might find copper sealing washers at the base of the studs. These will need to be pried off of the studs as well. Oh, and if you can access the bottom two most studs with a socket, as shown, you indeed have an 8-inch rear and not a 9-inch. The 9-inch requires a box-end wrench for access to these two retaining nuts.  7 With all of the retaining...  7 With all of the retaining nuts removed in the previous caption, the top most nut can be backed off to the end of the stud. This will allow you to pry the center section away from the housing to drain the gear oil without fear of the center section coming completely off and landing on your gear-oil-soaked foot.  8 Once the gear oil has completely...  8 Once the gear oil has completely drained, you can remove the last retaining nut and then pull the center section free. Remember, this sucker is just north of 70 pounds, so be ready for it or get a helper to lend a hand. Use a shop rag to remove the remaining gear oil and years of accumulated crud in the housing.  9 Since we’re going to be...  9 Since we’re going to be adding a clutch-based differential, it’s imperative that a friction modifier be added to the axle fluid. Ford offers friction modifier in an easy-to-use, single-use bottle that you add to your differential when adding oil. In our case, we simply poured it directly into the housing before bolting up our center section.  10 Our differential of choice...  10 Our differential of choice for the High School Hauler project is this Yukon Gear & Axle Dura-Grip. The Dura Grip is designed similar to the Ford Traction-Lok, but uses a nodular iron case half filled with forged internals, composite clutches for superior life, a high-bias spring, and a billet steel side hat. Available in 28- and 31-spline versions, we opted for the 31-spline version. Randy’s Ring & Pinion can build your center section with several options; just call to discuss your needs.  11 Wrapped around our Yukon...  11 Wrapped around our Yukon Dura Grip is a set of Yukon’s 3.80 gears. Made from quality steel for strength, and machined for quiet and cool operation, we felt the 3.80 ratio would be a great fit for the Hauler with its AOD transmission.  12 With a bead of skinned...  12 With a bead of skinned silicone sealer on the sealing surface of our housing, the custom-built center section from Randy’s Ring & Pinion is guided into place. We’ve had equal success using paper gaskets versus silicone, so the choice is yours how you wish to seal the mating surface.  13 Another personal point...  13 Another personal point of preference is whether to use the copper sealing washers over the mounting studs. Some people do and some don’t. Because we’re using silicone for a gasket sealer, including around the base of the studs, we simply reinstalled the retaining nuts without any washers. If you choose to use the washers (or a housing gasket), you can get them from Randy’s Ring & Pinion.  14 Our driveshaft bolted...  14 Our driveshaft bolted right up to our fresh center section from Randy’s Ring & Pinion with no issues. Anytime you’re doing axle work, or under car work of any kind, it’s the perfect time to check your driveshaft for damage, worn joints, and so forth before putting any power through it.  15 Since we knew our Mustang...  15 Since we knew our Mustang was going to see more track time, we felt the time spent on the lift would be a perfect opportunity to add a safety loop for our stock driveshaft. Something new to market is the Stifflers bolt-in safety loop. We heard good things about this product from our late-model Mustang friends and Stifflers says it will fit many early Fords as well, so we’re giving it a try here.  16 The Stifflers safety loop...  16 The Stifflers safety loop exceeds NHRA specs for a safety loop and requires no drilling or welding. It simply bolts into your chassis, sandwiched between your transmission and transmission mount using its own hardware.  17 After the main loop bracket...  17 After the main loop bracket is mounted the hoop is assembled with its included hardware. While we had plenty of room for our stock driveshaft, the Stifflers loop is designed to accept larger aluminum driveshafts as well without rubbing.  18 The finished safety loop...  18 The finished safety loop install is solid and gives us peace of mind, plus it will make the track officials happy when we start getting into those lower track times where a loop is required.  19 To complete our 8-inch...  19 To complete our 8-inch upgrade, a set of Yukon’s new cut-to-length, 31-spline axles were sourced through Randy’s Ring & Pinion as well. These axles feature 1541 alloy steel construction and extra length splines to allow a finished-cut axle length between 25.5-inches and 32.9-inches.  20 After measuring our stock...  20 After measuring our stock axles to determine stock length, we used a low-speed horizontal bandsaw to cut our axles to the correct length. You can also use a chop saw or even a handheld cut-off wheel, just be sure to keep the temperature down so that you don’t affect the axle’s hardening.  21 After cutting your new...  21 After cutting your new axles to length, take a minute to bevel the edge of the splines as you see here. This will reduce sharp edges where cracking/chipping can occur and will help the splines mesh with the differential more easily.  22 The only parts you’ll...  22 The only parts you’ll need off of your old axles are the axle retaining plates. You can purchase new ones if you want to keep your old axles 100-percent intact (or if you just like to use all new parts). To remove these plates, you’ll need to remove the axle bearings and retaining rings using a press.  23 Remember to install the...  23 Remember to install the retaining plates over the axle shaft before your axle bearing and retaining ring (sort of like sliding the tube fitting over a brake line before flaring it). Press the new axle’s bearings and retaining rings onto the axles as shown.  24 Don’t forget fresh wheel...  24 Don’t forget fresh wheel studs too. We kept stock length studs for our upgrade, but you can always add long studs to your build if you prefer, or if they are required by a particular racing sanction.  25 Our axle seals were in...  25 Our axle seals were in great shape, so we didn’t touch them, but if yours are hard, torn, or leaking, then now is the best time to replace them. Otherwise, carefully install your axles, supporting the weight of the axle with your hand to prevent damaging the seal as the axle passes through it. If need be, seat the axle with a few hits from a plastic-faced, dead-blow hammer, then secure the axles with the original retaining hardware.  26 We let our differential...  26 We let our differential sit overnight for our gasket to fully cure and then filled the housing with Royal Purple 75W90 gear oil until it was level with the filler opening. After following Randy’s Ring & Pinion’s break in procedure, we’re ready to hit the track.
|
|
|