GTR's Chris Balster sprays...
GTR's Chris Balster sprays a blast of parts wash through our '02 GT's 8.8 rearend housing. Thoroughly cleaning the housing is a mandatory prep move for differential and gear swaps, as any debris in the housing could potentially damage a new differential or, if big enough, become lodged in the gears. Using fine-grit sandpaper and solvent to remove metal particles from seal surfaces is also a good idea.
While a 'Stangbanger's ultimate dream to have a super-modified car that remains absolutely perfect and free of bad noises forever, the truth is, horsepower and torque have a unique ability of finding the weak link in a Mustang. There's always a chance that a bad-noise-emitting problem could arise at some point, especially as more performance modifications are made.
Noises go hand-in-hand with the Mustang hobby. There are beautiful noises, such as the sounds that come from fine-tuned 'Stang engines at full scream on the chassis dyno or dragstrip. Then there are funny noises, like belt squeals, chassis creaks, dash rattles, and such. Finally, there are bad noises that are usually signs of serious problems with a Pony's engine or drivetrain, brought about by a lack of maintenance or an abundance of power.
Now before we go further with this report, we're not saying this to scare you or deter you from making moves that will put your Pony on the next plateau of performance. Rather, we encourage you to make those moves. As many of you know, making big steam is a favorite pastime for your tech editor and the crew at 5.0 Mustang & Super Fords. However, each time we increase the power output of the Ponies we work with, we're doing so with the understanding that we're taking the cars beyond the safe haven of stock.
Notice the aftermarket differential...
Notice the aftermarket differential cover that Chris is removing from the 'Stang's rear? The cover topped off an installation of 3.90 gears and a Detroit Truetrac limited-slip differential, which was done in 2008.
A loud clunking noise is our...
A loud clunking noise is our reason for taking this new look inside the rear.
Here is the carnage-two broken...
Here is the carnage-two broken teeth on the 3.90's ring gear. Without performing ultra-scientific metallurgic tests on the gearset, and without being aware of any abnormal stresses or loads being put on the rearend, it's difficult to place blame on anything for this particular type of failure. Sometimes the saying "it is what it is" works well when it comes to problems we encounter. This is one of those times.
With that said, bad noises are inevitable when you push closer and closer to the edge of the high-performance envelope. We've heard the sounds of catastrophic failure a few times now. We also understand that when parts do fail and you start hearing bad noises, sometimes you just have to charge the bad fortune to the game, identify the problem, make necessary repairs, and move on.
That's what we're doing with this tech effort-getting to the bottom of a disturbing hollow-sounding, clunk-type noise that's coming from the 8.8 rearend in our '02 Mustang GT. We first encountered the racket immediately after making our final pass at a dragstrip test session. Clunking and a severe vibration in the drivetrain (that increased and decreased with wheel speed) made their presence known during our drive back to our pit.
With the problem properly...
With the problem properly diagnosed, we decided to step up the GT's rearend game a bit and install a set of Ford Racing Performance Parts 4.30 gears (PN M-4209-G430M; $199.99), foregoing the Truetrac for a full-on, 31-spline Detroit Locker unit (PN 187C-145A DL FORD 8.8; 649.95). While 3.90s definitely are ideal from a best-of-both-worlds standpoint-and served our supercharged Pony well on the street, freeway/Mojave Mile and dragstrip-the lower ratio will bring about a tremendous improvement in the car's First-through-Fifth-gear acceleration. Royal Purple's Max-Gear 75W-140 gear oil rounds out the simple collection of parts.
Here is the FRPP ring-and-pinion...
Here is the FRPP ring-and-pinion install kit (PN M-4210-B; $90) that is needed for this type of project. The kit includes pinion and carrier shims, a crush sleeve, pinion seal and nut, new ring-gear bolts, carrier bearings, a pinion-gear bearing and a fresh gasket for the diff cover.
A rearend upgrade can be performed...
A rearend upgrade can be performed by do-it-yourselfers who have patience, good attention to details and are confident in their ability to take precise measurements. A robust work area also is helpful, as such tools a hydraulic press, dial indicator, digital micrometer, lb-ft torque wrenches, and in-lb torque wrenches are required. For anyone taking on this challenge, we strongly suggest you test fit axles in a limited-slip differential, locker, or spool before going any further with the job, to ensure that splines on both are a perfect match.
Right away, checks were made to isolate where the noise originated. After securing the 'Stang on four jackstands, we inspected the undercarriage to see if the noise actually was the result of the driveshaft making contact with the floorpan, torque arm or exhaust. After confirming that the shaft was OK, we checked out the differential (by engaging the transmission in First gear and turning the drivetrain) and found the noise was clearly coming from inside the 8.8.
As a general rule, if axles aren't broken and you're experiencing a bad noise from inside the 'Stang's rearend (but the car is still driveable, like ours), a broken ring or pinion gear, or a broken component in the differential usually is the source of the noise. With the malady requiring a more extensive investigation, we delivered the Mustang to GTR High Performance in Rancho Cucamonga, California, where technician Chris Balster found the source of our distressed diff's problem and performed the surgery that will make things right.
Photos of the search-and-rebuild process are telling, so we suggest you stay with this one and see what we've done to ward off future situations for our supercharged 'Stang's rearend.
New bearings are pressed on...
New bearings are pressed on each end of the locker, before Chris trial fits the unit in the 8.8 housing. A press facilitates this task, as does using one of the old bearings (between the new one and the press), to serve as a buffer and prevent any damage from happening to the new bearings.
The pinion-bearing race is...
The pinion-bearing race is a simple part, but it requires the correct tool and lots of care for proper installation. You don't want to damage this piece and banging it in with a hammer can prevent the race from bonding with the bore. Depending on their diameter, depth shims for the pinion gear are placed either below the race or on the pinion shaft itself (under the bearing).
is secured to the ring gear,...
is secured to the ring gear, to ensure the gear remains tight on the locker when it's go time.