Muscle Mustangs & Fast Fords
Ford Mustang Rear Axle Upgrade - Buns Of Steel - Tech
All the parts and pieces to strengthen your 8.8-inch rear.
Late-model Ford owners are a fortunate bunch. It's easy to make your Blue Oval machine stomp the competition with copious horsepower, and these days the transmissions aren't too bad, either. The last link to getting the power to the ground is what lies under the rear flanks of your Mustang or other fast Ford-in most cases, it's the tried-and-true 8.8-inch rear. Whether you start off by adding stronger axles or go the whole nine yards and order a complete, professionally built rear, making the 8.8 live behind your powerful Ford engine is key to going fast.
For some, making hellacious horsepower is their only concern. While dyno numbers are a surefire way to back up the smack talk about how fast your ride is, a timeslip will back up any dyno flog. But if your rear breaks or flexes, it can't supply all that power to the tires.
Getting down the dragstrip can be a demanding task, especially when it comes to the final link of the chain. While a factory rear can handle the output from a stock or mildly built powerplant, when the horsepower scales tip to the "heavy" side, the 8.8 can only stand so much before it goes on a permanent vacation.
Hooking too hard can also cause damage that may be unfixable if your rear is stock. We've seen axle tubes twist away from the centersection, and we encountered a housing that literally split in two. That's why we first recommend welding the axle tubes to the centersection to prevent them from spinning out of the vehicle. Then you can add a rear girdle, which adds strength over the stock cover and limits the movement of the differential when the power is on.
On launch, the differential tries to drive right out the back of the housing, but a properly installed girdle will help keep it in place by applying a small preload to the housing main caps. Also, consider aftermarket axles, which are inherently stronger than stock units. Next should come a strengthened differential that can handle the extra power.
To keep the rearend together no matter how much power your Stang is pumping out, check out the following parts and pieces that will help beef up your buns into buns of steel.
Strengthening the Housing
Throwing the strongest axles, gears, studs, and other parts into the 8.8 will help it live behind the power made by your engine, but making sure the housing lives is another thing. Adding a rear cover and rearend bracing will help keep the housing from failing. There are other things you can do to the housing, too (see "Weld It Up" sidebar).
According to Tim Frey of Strange Engineering, many times two of the best things you can do to upgrade the strength and reliability of the 8.8 housing are to add weld-on ends and weld the axle tubes to the pumpkin, or centersection, of the rear. "There is no determining factor or horsepower rating that I have seen to tell whether or not strengthening the housing is needed," Frey says. "It can't hurt, however."
One of the more common ways to strengthen the housing is by welding the axle tubes to the pumpkin. "This will aid in strengthening the housing," Frey says. You can remove the rear from the vehicle and have the rear set up in a jig, which holds the rear in a straight position while it is welded, or it can be done in the car. Using a jig is the preferred method. When welding the rear in the car, do only a small area at a time and allow the rear to cool, as this prevents the rear from warping. Another way to strengthen the housing is to add weld-on ends that utilize a 9-inch bearing instead of the standard 8.8-inch bearing. Obviously, running the larger bearings means less chance of bearing failure as the larger bearing will be able to absorb more punishment.
Different-ial Strokes For Different Folks
You have the axles, gears, studs, and everything else to put together your 8.8-inch rear. Now you need something to turn the axles, and that task is handled by the differential. There are numerous types from which to choose. You can go with a locker, a spool, a mini-spool, a limited-slip, or an open differential, however, for street-driven applications with higher-than-average horsepower numbers, there are a few that can be eliminated right away.
Let's look at the open differential first. Because it drives only one tire rather than both, if that tire spins, you'll be left sitting in your tracks. While the open differential is great for driving around town, for performance applications, it is, in a word, useless. It is commonly referred to as a peg-leg, or one-wheel wonder, for obvious reasons. Since the differential transfers power to just one wheel, trying to put all of the power your supercharged 4.6 Cobra motor makes to the ground is impossible.
The opposite of the open differential is a full locking differential, better known as a spool. The spool is great for getting all of the power to the pavement, but it drives both axles with no slip, so when it comes to street use, it is not recommended. For example, the spool and mini-spool are both great for drag racing because they allow both axles to get 100 percent of the engine's and drivetrain's potential. When it comes to going around corners or cruising on the street, however, instead of taking the corner nicely, the rearend of the car will hop and chirp. That's because it is necessary for the inside and outside tires to spin at different speeds when negotiating a corner. In a turn, the inside tires cover less ground than the outside tires, so they will turn slower. Without the ability of the rear to slip, the tires would go the same speed, and the inside rear tire will skip and break traction.
Therein lies the true advantage of the limited-slip or locker differential. More commonly referred to as the "posi unit," the limited-slip differential, or its upgraded, more sophisticated sibling, the locker, transfers all power to both rear wheels when going straight. In a corner, the unit senses an increase or decrease in wheel speed or torque on one side as opposed to the other, and it transfers or decreases the amount of power from side to side, thus allowing slip. It's the best of both worlds.
In addition to the gearsets, axles, and other parts offered by each respective manufacturer listed herein, we have also included the different types of differentials available. Keep in mind that choosing the correct differential and associated parts depends on the application and/or type of racing/driving you plan on doing.
Some of the different designs of a limited-slip differential are the worm gear, cone, and helical design. The worm gear design (Figure 1) has no clutches or disc packs, and the side gears are turned via planet gears.
The cone design (Figure 2) uses springs to differentiate torque to the wheels. The pinion gear and shaft are encased in a spring-loaded retainer in which the springs are preloaded. The side gears and cone clutch assembly activate when the set preload on the springs is reached. This type of unit is called the cone design because of the side gears' appearance. Finally, there's the helical design, which is seen in Detroit Locker's Truetrac. The design is based on parallel axis planetary helical gears, which interact directly with the side gears. This design eliminates the need for springs and clutch packs.
AMP Performance has a wide selection of items to keep your car's rearend in one piece. After perusing the catalog, a couple of items came to our attention that will help shine up the 8.8 and keep it in tip-top shape. For $21.95 you can grab AMP's chrome 8.8-rear differential cover. The chrome 10-bolt cover looks awesome under the rear of your Mustang and will replace the drab factory piece with class. If the Traction-Lok posi unit is starting to go and you catch it early enough, instead of popping for a new differential, you can rebuild the one you have using AMP's 8.8-inch Traction-Lok rebuild kit. The cost is $43.00 and includes a clutch pack, shims, a friction modifier, and an instruction sheet. So why not save a few beans and rebuild the posi?
Auburn offers two different posi-units, the High Performance Series limited-slip and the Pro Series limited-slip for the 8.8. Power is transferred to the wheels via the use of cone clutches coupled to beveled side gears. The cone design, along with the applied force, determines torque transfer capability. The High Performance unit is similar to the OEM differential from Ford, while the Pro Series is an upgrade that features more preload on the side gears for quicker activation. Contact Auburn Gear for pricing and application.
BB&T is a dealer for Moser Engineering, and two of the items offered for the 8.8-inch rear are the axle packages that come from Moser. The first package, priced at $549, includes Moser C-clip street axles, an Auburn heavy-duty differential, and Moser wheel studs. The second package prices out at $609 and comes with Moser NHRA race axles, C-clip eliminators, wheel studs, and a spool.
Without having the correct axles in your 8.8, all you'll do is just sit at the starting line. For those with an 8.8 in their Fox-bodies, the simplest way to beef up the rear is to replace the stock four-lug axles with a pair of 28-spline five-lug pieces from Brothers Performance. The induction-hardened axles are over 50 percent stronger than stock, and the kit includes the axles, axle seals, bearings, and studs. Retailing at $319.99, the kit is a cheap but surefire way to strengthen things under the rear flanks of your car. While you swap out the axles, spend the $119.99 for Brothers Superior Axle Overhaul kit. It has everything needed to reinstall the rear gears, including a new pinion seal, ring gear bolts, a crush collar, a pinion nut, shims, a pinion bearing, carrier bearings, a gear-marking com-pound, Loctite, and all gaskets.
CJ Pony Parts
Breaking an axle and having it spin out of the rearend housing is an easy way to turn your beloved Mustang into the guardrail. In an effort to add strength and safety to your 8.8, consider ordering CJ Pony Parts' C-clip eliminator kit. The kit retains the axles externally, thus eliminating the C-clips in the housing. At $169.95, it's a great product for keeping your car-and yourself-a bit safer at the track. Keep in mind, however, this product is billed by CJ as a drag racing-specific product, as use of a C-clip is not recommended for road racing or for cars with rear disc brakes. Don't forget to add a little flash and Ford pride when replacing the rearend cover by picking up CJ's axle girdle complete with Ford Racing script. The girdle will set you back $164.95.
Detroit Locker offers a couple of posi units worth looking at. The first is a unit of the same name, the Detroit Locker. A spool-type piece on straight roads, yet it runs like a normal posi under cornering. The other posi from Detroit Locker is the Truetrac, which is designed around parallel-axis planetary helical gears, which means this unit has no clutches, friction plates, or cones. Instead, three sets of pinions, or helical gears mesh together to transfer power. The gears move quickly to transfer power away from the slipping wheel, gradually feeding it back in as wheel speed decreases. Both of the units are offered for the 8.8. Contact Detroit Locker for pricing.
Eaton offers a posi unit and a locker for the 8.8 that easily replaces the stock piece. The Eaton posi has carbon disc clutch packs preloaded by a central spring assembly located behind each side gear. When torque increases, so does the clamping load on the clutch pack. The Eaton locker operates in a different way than most limited-slip units. It is speed sensitive in that it has a flyweight governor that responds to changes in wheel speed. When one wheel speeds up, the governor flies open, pushing the flyweight onto a latching bracket. This bracket then starts the lock-up of the unit, allowing power to be transferred away from the slipping wheel. The process is pretty trick. Contact Eaton for details and pricing.
Ford Racing Performance Parts
FRPP offers a host of parts for the 8.8-which is made by Ford-so you know they'll fit and work without a problem. One of the items that caught our attention was the 8.8 ring-and-pinion gearset. The gears will fit the stock housing, and there are many different ratios from which to choose, depending on vehicle weight, horsepower, and application. The gears will empty your wallet $225, but they are a great way to spend a little cash to go a bit faster. If building a rear isn't your strong suit, then take a look at FRPP's 28-tooth Traction-Lok rear axle assembly. The assembly is nearly 35 percent stronger than the 7.5-inch assembly, and is fully assembled with the housing, gearset, and 28-tooth posi unit. The unit will fit in any Fox-body, comes with a choice of 3.55 or 3.73 gears, and will set you back $875. If a new S197 sits in your driveway, feel free to call FRPP and pick up the newly released rearend girdle for the '05-and-up Stangs.
Also, when it comes to differentials, check out Ford's Traction-Lok, which features plate-type clutches, meaning power is moved around through clutch-pack bias. As you lose traction, the clutches bind tighter together, transferring power away from the slipping wheel. Call FRPP for applications and pricing.
For ultimate protection and durability, pick up the appropriate amount of Royal Purple Synthetic gear oil from Holcomb Motorsports. Priced at $8.99 a quart, the 75W90 gear oil will last a long time, no matter what the circumstances.
Latemodel Restoration's catalog has pages upon pages of rearend parts for the 8.8. Two items of interest are the Super Shim Kit and the 28-spline Yukon-brand axles. The shim kit runs $24.95 and contains all of the shims you need to complete the rear gear change. Shimming the gears ensures proper operation and longevity in the rear and the gears themselves. Also adding longevity to the life of the rear are the Yukon 28-spline axles, which are 25 percent stronger than the stock items. The four-lug pieces sell with studs for $189.95.
When it comes to bulletproof driveline components, Mark Williams is at the top of the list. By far, the ring-and-pinion gears feel the most abuse when backing a high-horsepower Ford engine. Mark Williams offers 8.8 gearsets to not only help your Mustang get down the track quicker, but to build reliability as well. The gears are made from 8260-steel alloy, and can be used on the street, dragstrip, or oval track. The com-pany has many different ratios from which to choose, so specify which set you want before you plunk down the cash (prices vary).
While replacing the gears, consider installing Mark Williams' Street/Strip C-clip eliminator kit. The kit is for MW or Masterline axles, and is billed as the best C-clip eliminator kit for street usage. The price is $259. Speaking of axles, if you want to beef up your rear in one shot, then think about picking up MW's Ford axle kit. It comes with Hi-Torque axles, the C-clip eliminator kit, weld-on end or retainer kit, spool, drive studs, and wheel bearing. Contact MW for specifications and pricing.
If you're still planning on cruising the streets and terrorizing the masses with your Mustang, then maybe that spool you're thinking of isn't the way to go. The next best thing is the posi unit, better known as a limited-slip differential. Maximum Motorsports has you covered with its Torsen-supplied line of posi units. The differentials come in either 28- or 31-spline versions, and are recommended for street, auto crossing, or road racing usage.
Moser is another company that makes driveline components able to take a beating. Case in point is the company's new C-clip axles for the S197 cars. The axles are made from the same alloy as its custom pieces, and they're said to be 25-30 percent stronger than the OEM pieces. The axles come either as 28-spline units for V-6 cars or 31-spline pieces for the GT, and retail for $167.50. Making sure the driveshaft spins the ring-and-pinion gears is a task handed off to the 1350-series yoke for the 8.8. Every Moser yoke comes with the necessary hardware to bolt it on, including U-bolts, nuts, and lock washers. The price for the 1350-series yoke is $130.
If you'd rather rebuild your differential than buy a new one, then Motive Gear has a rebuild kit for both the open and posi units. Known for its ring-and-pinion gears, the kits are a great complement to an upgrade in that department. The open differential kit includes side gears, side washers, pinion gears, pinion washers, a pinion shaft, and lock bolt or roll pin. The kit for the posi unit contains the same, in addition to clutches or posi plates and retainers where applicable. Contact Motive Gear for pricing.
National Drivetrain, a dealer for Detroit Locker, has a wide selection of Detroit Locker posi units, among the other pieces the company offers for the 8.8. For '83-'86 8.8s, you have a choice of a 28- or 31-spline posi, while the '87-and-up folks have one choice-the 31-spline unit. National Drivetrain also sells Motive Gear ring-and-pinions. Both the 3.90 and 4.30 ratio gearsets come with a mini installation kit and will set you back $189.95.
Powertrax has a neat item in that it guts the internals of the open differential and replaces them with locker-type pieces. This item is called the Lock-Right, and as stated, it is made to fit in the case of the open differential, replacing the unit with spider pinions, a thrust washer, and side gears. The unit will carry between 850 and 875 lb-ft of torque, which is more than the factory axles hold. This means you'll break something else before the Powertrax. In addition, the Powertrax eliminates the clicking and ratcheting sound when differentiating power between both tires. Contact Powertrax for info and pricing.
Known mostly for its shifters, Pro-5.0 also offers items for the 8.8, including a wide variety of ring-and-pinion sets. The gearsets sell for $199.99 in the following gear ratios: 3.31, 3.55, 3.73, 3.90, 4.10, 4.30, 4.56, 4.88, and 5.14. The gear ratio you choose is dependent upon the application and powerplant of your car, so contact Pro-5.0 for advice in choosing the correct gearset.
Randy's Ring & Pinion
A dealer of Yukon products, Randy's Ring & Pinion offers a wide variety of Yukon gearsets with ratios ranging from an economically friendly 2.73 to a valvetrain-murdering 7.33. The Yukon gears are designed to run quietly and last longer than other gearsets. Randy's also offers Yukon axles, which are replacements for the stock pieces but designed to last much longer. Also available are easy-to-order install kits to make swapping axles a breeze. Contact Randy's for applications and pricing.
Reider Racing has a host of parts for the 8.8-inch rear, including its Precision Gear line of ring-and-pinion gears. With ratios ranging from 3.08 to 5.13, these ring-and-pinion sets offer more durability with reduced noise. Call Reider Racing for pricing and advice in choosing the right gearset for your Mustang.
Steeda offers two interesting products for helping the 8.8 in your Mustang live behind that powerful pushrod or mod engine. For the '05-and-up Mustang, Steeda's adjustable upper third link kit is a great way to set the pinion angle of the 8.8 and keep wheelhop from occurring. Priced at $179.95, the kit uses a three-piece urethane bushing to eliminate wheelhop associated with the factory bushing. Its adjustability also allows you to set the pinion angle easily and effectively. For those of you with an 8.8 in your Fox-body, an easy way to strengthen the rear and add longevity is by picking up Steeda's five-lug conversion kit. The kit comes with slotted five-lug disc brake rotors for the front, and, more importantly, five-lug axles and accompanying drums out back. The kit will set you back $469.95.
Strange Engineering has long since been the leader in drivetrain components, and the company's 8.8 aluminum support covers and ring-and-pinion gears complement its bulletproof axles and other rearend components. The aluminum cover features two load bolts that provide main cap support, which reduces ring gear deflection, stabilizes gear backlash, and decreases the possibility of the cap breaking or distorting. The cover is also stylish with its aluminum finish, and retails for $148.50. Increase the longevity and power-producing potential of the 8.8 with a new ring-and-pinion gearset from Strange. With ratios ranging from 3.08 to 4.30, this is a great way to utilize all the power your engine is making, while adding strength to the rear. Prices for the ring-and-pinion sets range from $158 to $169, and when ordering the gears, don't forget to grab the correct installation kit. You can choose from either the basic installation kit or the master installation one. At $34 the basic kit includes pinion shims, a crush sleeve, a pinion seal, a pinion nut, carrier shims, ring gear bolts, and a cover gasket. The master install kit includes all of that in addition to Timken cups and cones for the pinion and carrier. The master kit runs $94.
While on the topic of kits, replacing the axles when you change the gears would be easy since the rear would be basically empty. The top-of-the-line axle kit from Strange is the Pro Race axle package. The package comes with two Pro Race axles, either 31- or 33-spline, set up for drum brakes. The package also comes with a C-clip eliminator kit and 11/42-inch wheel studs for $489.50, though upgrading to a package with 51/48-inch studs is available for $543.50. The S/S axle package contains the same items as the Pro Race package, except the S/S package features Strange's Street 31- or 33-spline axles. The S/S package with 11/42-inch studs runs $398.70, while the 51/48-inch stud version will set you back $452.70.
Strange also has the Super Strength limited-slip unit. The Super Strength is a one-piece unit that is preloaded heavier and has additional clutches when compared to the factory posi. The Super Strength also utilizes specially machined clutches and aircraft-quality steel side gears for durability. Contact Strange for info and pricing.
T/A Performance's rearend girdle is an easy way to add support to the 8.8 housing and the internals of the rearend. The TA girdle is made from 3560 aircraft-grade aluminum and is heat-treated to T6 specs. Each cover has a fill and drain port for easy service, and it comes with two load bolts with swivel feet for bearing cap support. The girdles have shown a decrease in operating temperature of up to 15 degrees, which will definitely help in adding life to the rear. The girdle runs for $159.
Torsen offers the T-1 and T-2 differentials for the 8.8-inch rear. Both items are based on torque sensing and biasing systems, though the T-1 utilizes Torsen's patented INVEX system, while the T-2 has the patented EQUVEX system. Both differentials are parallel axis gear configurations, which provide better gear mesh for lower noise and less backlash. The T-2 also has longer side gears for more flexibility in regards to axle spline location. Contact Torsen for pricing and application.
Known mostly for its appearance-enhancing products, UPR offers an 8.8 rearend stud girdle kit for $129.99. While the girdle is great for drag racing and road racing applications, it is made with the street enthusiast in mind. Designed to handle higher-than-stock horsepower levels, the girdle comes with all necessary gaskets and hardware.
Weld It Up
As previously mentioned, there are a couple of easy ways to strengthen the housing of the 8.8 rear itself. While on the surface it may seem expansive and unnecessary, insurance never hurts. Check out what Drive Train Specialists did for this 8.8-inch housing.