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Project Vapor Trail Gear Swap - Gear DrivePVT Gains Ratio And Grip While Losing Reciprocating Mass From the November, 2010 issue of 5.0 Mustang & Super Fords By Steve Turner Photography by Steve Turner
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Most people know I'm a little... Most people know I'm a little nutty about Project Vapor Trail. I don't let just anyone touch her. After a recon run over to ProFab Performance in Thonotosassa, Florida, I felt more than comfortable letting Blue Oval expert Dave Piercey wrench on PVT. Dave has been swapping gears since before I had a driver's license, so he knows a thing or two about getting them spot-on. It's been popular to add gears to Mustangs since the dawn of time. Gears are usually one of the first performance modifications because they make an instant impact in the way the car feels. Sure the right gear makes the car quicker, but it's the seat of the pants that really makes the gear swap one of the most popular Mustang mods. I really don't know why I waited so long. I guess I had some vague, silly concerns about noise and gas mileage. Could a 700-rwhp GT500 really need gears? As it turns out, yes it does. Sure the car never had a problem getting out of its own way, but the addition of gears makes dealing with the GT500's naturally tricky clutch engagement much easier. Moreover, the 3.73s keep the car in the happy place of its powerband at all times, and the highway cruising speed is only up a couple hundred rpm. Ultimately, mileage seems to only have suffered marginally. Moreover, the car simply feels snappier and more responsive, and that's what it's all about. While PVT was under the knife, it was a good time to add some complementary hardware. I opted for a diff girdle from FRPP, a Torsen T2 differential from FRPP, an aluminum driveshaft from Axle Exchange, and a driveshaft safety loop from BMR. To make it all happen, I carted the parts over to ProFab Performance, where renowned gear setup expert Dave Piercey worked his magic with a perfect, noise-free install. Follow along with the captions to see how Dave brought PVT's driveline up to snuff with its other mods.  If you're going to swap gears,...  If you're going to swap gears, the stock Traction-Lok has to come out anyway, so it's a good time to consider swapping in a performance differential. To get the most performance from your ride, you need all the power applied to the pavement. Drag cars can simply connect both axles with a spool, but a street car like PVT needs torque biasing for all-around use. I opted for the Torsen T-2 diff (PN M-4204-T31; MSRP $589) from Ford Racing Performance Parts, which uses helical gears to constantly bias torque between the two rear axles. The Torsen is quiet enough for the street and durable enough for the FR500 race cars (in T2R form), so it's a good match for PVT.  As I mentioned, gear noise...  As I mentioned, gear noise was one threat that kept me from making the move sooner. Well, most people will tell you to go with FRPP gears if you want them quiet, and that's just what I did. I opted for the ever-popular 3.73 ratio (PN M-4209-F373N; MSRP $ $179.95). This set now benefits from a new Face Hob Process, which is said to deliver higher quality, strong gears. Combined with Dave's expert installation, mine are indeed library quiet.  When doing a gear or diff...  When doing a gear or diff swap, you might want to order this FRPP installation kit (PN M-4210-A; $162), as it includes all the necessary shims and bearings for the install, including the unique high-torque pinion bearing that is stock on Bullitts and GT500s.  A gear swap also presents...  A gear swap also presents a handy opportunity to add an axle girdle (PN M-4033-G2; MSRP $199) like this beauty from FRPP. It features a low-profile design just for S197 'Stangs, and is said to increase ring and pinion life by adding rigidity to the 8.8 rear. It also adds handy drain and fill plugs for servicing.  I warned Dave that PVT had...  I warned Dave that PVT had a few suspension upgrades that might complicate the gear and diff swap. If you are considering adding Steeda's sweet Watt's link like I did, you should definitely consider doing the gear swap beforehand. That said, its presence wasn't a big deal, it just added a bit of time to the job.  To get the party started,...  To get the party started, Dave removed the Steeda Watt's link, unbolted the factory diff cover, and popped it off with a prybar.  Next he unbolted the cumbersome...  Next he unbolted the cumbersome stock driveshaft. We did an unofficial weigh-in of the stock 'shaft and it tipped the scales at 38 pounds.  From the moment I saw the...  From the moment I saw the S197's two-piece driveshaft, I was scratching my head. It seemed like a lot of weight and complexity in the name of improving NVH. In fact, after adding the Steeda suspension to my car, the stock driveshaft actually made a tick-tock noise when I got on and off the throttle because of the innate slack of its two-piece design. Of course, weight is the enemy of performance; so dropping some reciprocating weight while adding durability is always a great idea. After doing some research, I discovered the one-piece aluminum shafts from Axle Exchange (PN MAMTCOBRAST; $739.95) have a great reputation. They are made in the USA with Alcoa 6061 T-6 aluminum, and benefit from Precison Schenck balancing.  Using this puller, Dave plucked...  Using this puller, Dave plucked off the stock pinion flange.  Time to gut the stock 8.8....  Time to gut the stock 8.8. Dave removes the pinion-shaft bolt, pulls out the shaft, removes the C-clips, and slides out the axles enough to clear the differential. Next he removes the bearing caps, and pulls out the stock diff and ring gear.  Be sure to set the bearing...  Be sure to set the bearing caps aside in the same way they came out. They need to go back on just the way they came off.  After unbolting and removing...  After unbolting and removing the pinion gear, Dave taps out the pinion bearing and flushes the pumpkin with brake cleaner.  Dave says this pinion depth...  Dave says this pinion depth gauge is critical to properly setting up a gear. This tool allows you to mock-up the new bearings in the housing and check for the proper shims before you install the differential for real.  The FRPP install kit includes...  The FRPP install kit includes numerous shims. Depending on your setup, you might need to stack two to achieve the proper measurement. Dave prefers to use a single shim, and had the proper shim in his cache of shims collected from years of setting up 8.8s.  Dave finds a good use for...  Dave finds a good use for old bearing races as buffers for pressing on new bearings. This practice is seen here as he pressed the new FRPP carrier bearings onto the fresh Torsen T-2. Once again having the proper tools, like a press, really expedites the job.  When it comes to someone working...  When it comes to someone working on your 'Stang, you want a systematic, detail-oriented type. Dave fits that bill. He has a routine that helps him make sure that he doesn't forget a crucial step. Here Dave is bolting the ring gear to the Torsen in a star pattern before torquing them into place at 85 lb-ft.  After pressing on the new...  After pressing on the new bearings, Dave installs the pinion gear and the new pinion flange from Axle Exchange. The new flange is required to install the AE driveshaft, and it looks far more robust than the stocker. It takes a long wrench or wrench with a prybar to torque the pinion-bearing crush sleeve, but do it in small increments to get it just right.  After torquing the pinion...  After torquing the pinion into place, Dave checks the preload on the pinion. It should be 30 in-lb. Since many aftermarket S197 driveshafts require a new pinion flange, swapping a driveshaft and gears at the same time dovetails nicely. Dave says it's really tricky to get this preload correct when you just swap the flange.  After bolting in the Torsen...  After bolting in the Torsen and torquing the bearing caps to 75 lb-ft, Dave checks the backlash with a dial indicator. The proper range is between 0.008 and 0.015 inch. Thanks to Dave fastidiously selecting the proper pinion shims with the depth gauge, PVT's new FRPP 3.73s came in right in the sweet spot of 0.012 inch.  FRPP's install kit includes...  FRPP's install kit includes the white lithium grease to test the pattern of the newly installed gears. I knew it must have been a good install when Dave exclaimed, "Wow!"  He then proceeded to show...  He then proceeded to show me an ancient Ford document that showed a pattern just like the one on PVT. These gears are set up right!  The T2 is a perfect fit for...  The T2 is a perfect fit for the GT500, as it is compatible with 31-spline C-clip axles.  After Dave pops in the C-clips,...  After Dave pops in the C-clips, he bolts the thrust plate in to wrap up the Torsen portion of the install.  After liberally coating the...  After liberally coating the mating surface of the FRPP girdle with high-temp sealant, Dave bolts on the cover. He torqued the cover-retention bolts to 25 lb-ft, and then he installed the drain plug and load bolts. To provide extra room for a socket, Dave replaces the standard load bolt nuts with smaller fasteners for increased clearance. The load bolts only are only torqued in the 5 to 10 lb-ft range. Too much torque is not a good thing. Once they are within spec, the nuts lock them in place. With the cover installed, Dave filled the rear with some inexpensive 75W-90 conventional gear lube for break-in. He recommended that I drain it out after 1,000-2,000 miles before making the move to synthetic gear lube.  If you ever plan to drive...  If you ever plan to drive your car in anger, it's a good idea to install a driveshaft safety loop. I expect trouble-free service from the Axle Exchange 'shaft, but the loop provides peace of mind. It also keeps you on the good side of officials at the racetrack. This simple, elegant solution from BMR Fabrication bolts to the transmission crossmember. The BMR front driveshaft loop (PN DSL010; $109.95) is slotted so you can easily center it up before permanently installing it. With stock two-piece driveshaft you'd need a loop out back too; BMR has those as well.  With the BMR front driveshaft...  With the BMR front driveshaft loop loosely installed, Dave installed the Axle Exchange one-piece aluminum driveshaft. This driveshaft is a thing of beauty, with gorgeous welds and quality hardware, and it's proven to be vibration free. It also eliminated that tell-tale tick-tock noise that the stock shaft exhibited after PVT's suspension upgrade. We weighed the AE shaft and it was about 18 pounds, or about 20 pounds lighter than our stocker. You could definitely feel the difference in heft.  With the installation wrapped...  With the installation wrapped up, Dave carefully reinstalled PVT's Steeda Watt's link without disturbing any of its settings. While it did require a strategic installation plan, the Watt's does clear the FRPP girdle. Whew!
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