5.0 Mustang & Super FordsHow To Drivetrain
Budget Mustang 8.8 Rearend Build - Baby Got Back
If You Want To Go Fast, Kick Your '99-'04 GT In The Rear
Horse Sense: The used car market is littered with '99-'04 Mustang GTs in excellent condition. While the aftermarket was only lukewarm when the cars debuted, it is now white hot with performance equipment that can transform one of these cars into a serious street machine. You can find a nice GT-like our test car used for this story-for under $12,000.
In our December '04 issue, we introduced you to Tim Stockwell and his insanely stock 10-second street 5.0 LX ("Stock Exchange," p. 64). Since then, Tim has helped us with a couple of technical articles and, most recently, he invited us to tag along as he transformed his newly acquired '99 GT into the next Stockwell project Mustang. In case you're wondering, the white LX coupe was sold to fund the purchase of an '03 Cobra, which was itself sold. So, Tim continues to update cars and move on to the next project. We are hoping to document a full-and trick-drag suspension on this '99, and perhaps put a turbo kit on the engine to see how a 4.6 Two-Valve likes a hairdryer. For our first dance with this GT, Tim suggested we check out his standard 8.8-inch rearend buildup. We couldn't resist.
The '99-'04 GT Mustangs are hot members of the Mustang universe right now. These low-mileage cars are being sold by their original or second owners. They have also survived the test of time better than the '87-'93 5.0 Mustangs, so you have a better starting point. They're super-solid, and the aftermarket industry has finally gotten a handle on the 4.6 twice-cammed V-8. While we dog the modular family for having fragile bottom ends (the obvious exception being the bulletproof '03-'04 Cobra motors), these things make upwards of 500 rwhp with a power adder and careful tuning.
With any street/strip car, make sure the supporting equipment (fuel system, exhaust, suspension, and such) is in place before you make outrageous power, or you'll be kidding yourself on the starting line. Tim's '99 GT came with a automatic transmission, a Bullitt intake, some exhaust pieces, and 4.10 gears. Surprisingly quick from the get-go, the yellow screamer ran 13.70s after he put his super tune to it. Tim has always been a big proponent of getting a car's stance and suspension right before pouring in the power, so he outlined a plan that would have the GT down in the weeds with a little more room under the quarter-panels for some bigger street tires. We'll detail the killer stance of this car-and how to build a drag suspension for your '99-'04 GT-in an upcoming issue. But, for now, we're going to start at the rear of the car to get it ready to handle a bit more oats from the small-block Ford up front.
Our pictures detail the transformation that took place once Tim wrestled the 8.8 from under the car. He wanted the rearend straightened, the axle tubes welded to the rearend, and each tube narrowed to accommodate a bigger tire. Through the development of the modular Mustangs, Ford continued to widen the rearend to increase the footprint and fill out the growing quarter-panels. This makes the Mustang a great-handling car, but it can be tough when a hot-rodder wants to install aftermarket rims because the required backspacing isn't available. Further complicating matters is the use of the ABS system. Again, this is a great feature on the Mustang, but it presents problems when you start building the rearend.
We wanted to install 15x10 Weld rims with 5.5-inch backspacing. The rim is big enough to run a 325/50 tire, but Tim prefers the 275/60 that's stretched a little on this rim, giving the look of a smaller tire but with a nice contact patch. To fit this tire on a '99-'04 GT, the axle tubes need to be cut 2.5 inches on each side. Any narrower, and you'll run into some serious work-such as replacing the brake system and backing plates hitting the inner fenders. At 2.5 inches, you'll remove the quad shock bracket, which isn't a big deal for most folks. In this application-because we are going to show you how to safely lower one of these cars-we removed the shock mounting bracket and positioned it down and inward on the axle tube to clear the emergency brake bracket. As it turns out, the shocks are arranged in a straight up-and-down pattern, which should allow them to perform better.
While Tim handled the removal of the rearend, disassembly of the housing, and reassembly of the 8.8, all of the welding and cutting was done by Pro Street Chassis (Norton, Ohio). Al Morgan, the owner, has been a certified welder since 1964, and he's no stranger to the hot-rod marketplace. As you'll see in our photos, Al has even built special jigs and fixtures for this type of work on the 8.8 Ford rear just to accommodate Tim and his work on the 8.8-inch rear-axle assemblies. If you weld the axle tubes to the center of the housing without a good jig bar and tight fixtures, the heat will warp the tubes, and these housings aren't usually straight from Ford. With the axle housing, you want everything perfectly straight and centered. If not, you'll have a nice-looking Mustang that goes down the street crooked and wears out bearings and other parts quickly.
As you have probably guessed, Tim likes to save money when he can. He gets more out of stock Mustangs than anyone else in the country (remember, he went 10.60s with a completely stock-motored 5.0), and he does it cheaply. We have tapped into that philosophy with this newest project car. From out of the car to back in, Tim has a narrowed, straightened, and completely rebuilt 8.8 rear for little money. In addition to the housing, you'll have to spend money on axles ($239), bearing/seals ($120), 31-spline centersection ($75 for a used Ford truck Traction-Lok), ABS ring ($40), ring and pinion ($189), rearend lubricant ($30), and labor for the housing modifications ($250).
We encourage you to try this at home, but if you want to ship your 8.8 housing and all the parts to Tim [www.5litermustang.com], he'll do the work, assemble everything, and send it back to you for under $1,000, depending on options like powdercoating, shock bracket install, etc. That price includes a welded, straightened, and shortened rearend.
Next time, we'll show you what Tim's car looks like with the narrowed rear end, a trick drag suspension, and dropped to the floor. After that, we'd like to add one of the trick new turbocharger systems on the market right now. If you have a better idea, write us a quick e-mail. We'll put Tim to work on it!
A professional welding job should look like this. Pretty good, Al-you're getting there.
The car was going to be so low that it would actually bottom out the shocks when we put it back on the ground. Knowing this beforehand gives you the opportunity to relocate the shock mounting bracket when the rear is out of the car-the first time. Al fabricated a mounting plate for our shocks, which put them an inch and a half lower to the ground. It also moved the shock inward an inch to clear the emergency-brake spring on the stock calipers. This gives the shock the compression it needs.
Once all of the cutting, straightening, and narrowing is complete, you should have something that looks like this. Tim had his rearend powdercoated (we wonder how Mrs. Stockwell feels about that). At this point, the rear housing is ready for reassembly.
This is everything you need to assemble the rearend: gears, bearings, races, bolts, shims, pinion spacer, pinion nut, and pinion flange. Just put it together with the Moser axles and add 75W-90 synthetic gear lube. It's that simple.
Use a piece of pipe or socket to install the seal (make sure it's straight).
Tim is installing the inner pinion bearing race. He likes to tap it in with a brass punch, then he positions an old race upside down and on topof the new race to avoid any damage while hetaps it in.
Here's a shot of how to assemble the six pieces to put the pinion in the rearend housing.
Use a small piece of pipe to install the pinion shim under the bearing. As a rule of thumb, use about a 0.030-inch shim. Most 8.8 rearends will call for 0.022- and 0.034-inch shim sizes for the correct pinion depth. Start with the 0.030-inch shim, and adjust accordingly.
These are the homemade tools Tim uses instead of an expensive ($300) depth gauge. You can swap gears at home with this inexpensive procedure. A 3-foot level and a piece of metal is used as an alignment tool (use as a reference source). Use RTV to glue the reference metal piece to the level. Lay the level across the housing at a repeatable reference point. Use calipers from the reference piece to measure from the head of the pinion gear in two or three places (take an average). Then, slide the level over and measure to the main-bearing mating surfaces. Subtract the two numbers to get the pinion depth (or checking distance), which is defined as the centerline of the axle to the top of the head of the pinion. Once you have this value, shim the pinion to the appropriate value.
The crush sleeve will crush at approximately 150 lb-ft. Crush it down until you are at zero slop, then a little more for preload-there is no backing off at any point. This step seems to bother most people, because if you go too far it ruins the crush sleeve-and creates too much drag on the pinion. You want between 14 and 20 in/lb with new bearings-slightly less with used pieces.
Now you're ready to set the differential into the housing. Measure for side-to-side backlash and preload at this time. Slide the carrier until there is zero backlash. Fill up both sides until it is snug and you are happy with your backlash setting, then add 0.003-0.004 to each side for preload. Ford likes 0.005-0.009-inch backlash-Tim sets his up at 0.009. Add 0.003-0.004 inches of shims to both sides once they are tight to preload both sides.
A dial indicator is used as the carrier is rocked back and forth to measure backlash. Torque main caps to 75 lb-ft-as you did with the bolts on the ring gear.
Moser has been building parts for 8.8-inch Fords for years. The axles in this build are 31-spline, five-lug units. Moser was our first choice to build an axle to our requirements-a stock replacement axle that contains provisions for the ABS equipment and a stock-type C-clip slot cut to our desired length. These axles cost $239, and there is no additional charge for the machine work (shortening).
This is how Tim puts the ABS rings on the Moser axles. Since he doesn't like to use a press on powdered-metal parts, he puts a set of tone rings in the oven at 450 degrees for 10 minutes. Then he uses a piece of pipe over the axle, and the ring taps right on. The rings go on both ways, so be sure they go on the right way. You don't want to take them off. Tim's oven technique can save you $40 for the install. Put some oil on the axle seals, and the axles should slide right in. Install the cross-shaft and tighten the bolt. At this point, you can put gear lube and friction modifier in the rearend. It's easier than installing everything in the car and squeezing it through the little hole in the rearend.
After installing the rearend cover, you are done. From start to finish, you have a fresh 8.8 rearend that's been straightened, narrowed, rebuilt, and, in this case, powdercoated for under $1,000.