Muscle Mustangs & Fast Fords
G-Force T5 Transmission - Rowing The Gears
Fixing Smog-Legal Killer's weak drivetrain with G-Force Racing Transmissions, a Ram clutch, and safety items from Quicktime and Lakewood.
Ask anyone who's owned a manual-transmission-equipped Fox-body and there's a good chance they have a story about grenading the stock T5 transmission. Some snap at the hit, others break on a good powershift, but most often they let go in the middle of a long Third-gear pull. Whether you've blown one or not, you fall into two categories: the ones who have blown a stock T5 and the ones who will blow a stock T5.
That's not to say the World Class T5 is a horrible transmission. Quite the contrary, as it's a lightweight, slick-shifting, synchronized five-speed box that can hold considerable power for its size. At stock(ish) power levels, the T5 is a great transmission, but bring the torque output above 350 lb-ft with sticky tires, and its days are numbered. Even the strongest of stock T5 boxes, the '93 Cobra spec units, were only rated for 310 lb-ft, so you can imagine our trepidation in feeding 530 lb-ft of torque at the wheels (that's roughly 600 lb-ft at the crank) through our stock T5.
The first few track outings with the stock components were anything but frustrating since forward progression was hindered by the worn differential and old T5. Any attempt at powershifting was met with protest, and forcing the issue would have ended in disaster. Instead, we launched soft and granny-shifted our way to some unimpressive e.t.'s. Miraculously, the stock T5 survived without spilling its guts, but a closer examination of the input shaft after it was removed revealed tons of free play. In other words, it was one good shift away from leaving the building.
One Bad Box
In search of an ever-elusive 10-second smog-legal timeslip, we decided another stock T5 just wasn't going to do. While thoughts of a six-speed box were tempting, we decided to save the additional 50-plus pounds and stick with the tried and true G-Force Racing Transmissions Street T5.
That's right, G-Force has been at it for over 20 years and builds transmissions for many top-level NASCAR and NHRA teams. Needless to say, they're damn good. Over a decade ago, G-Force saw the need for a reliable T5 transmission when Mustang owners began pushing their cars beyond the capabilities of the stock boxes. After tons of R&D, G-Force created the box before you, a fully built badass that's capable of 600-plus horsepower and 500-plus lb-ft in a 3,300-pound car launching on sticky tires.
Not one to leave anything to chance, G-Force redesigned the internals, and in turn, produced a T5 unlike any before it. In place of the wimpy stock components, G-Force uses high-nickel-content gears that are fabricated in-house, along with a heavy-duty, 26-spline input shaft and bronze/aluminum or steel shift forks.
The high-nickel-content gears are softer than the stock gears, but actually much stronger. The increased physical size of the gears gives them strength, while the softer material helps prevent failure from shearing compared to the stock units. Because of the material, G-Force recommends a special Syngear oil that protects the gears from undue damage. This special stuff can be purchased from Syngear directly or through G-Force.
As for the rest of the internals, the mainshaft is also beefed up from the stock 10-spline shaft to a hardy 26-spline unit forged from 9310 alloy steel. The burly unit helps resist deflection and adds more mating surfaces for the clutch disc.
According to G-Force, gear spreading is a big problem with the stock transmissions. When the gears are loaded, the meshing teeth attempt to push apart from each other—the greater the load, the more severe the problem. The stock mainshaft only exacerbates this problem as it deflects under load, leaving only the gear tips (the thinnest area of the gear) in contact, which ultimately leads to catastrophic failure. As for why Third gear is the weak spot on stock units, G-Force explained that the third cog is not only the thinnest of gears, but it's also farthest from any bearing, which means this lack of support leads to extreme gear spreading.
Along with a total overhaul of the components, G-Force took it several steps further by offering multiple ratios and even different types of gear engagements. Since the Smog-Legal Killer will predominantly be driven on the street, we opted for the synchronized gears (like the stock units) to aid in smooth shifts and quiet operation. If you're after the ultimate race box, G-Force also offers dog-ring, straight-cut, and NMRA-approved helical-cut dog-ring gears for lightning-fast upshifts at the strip. The only downsides on the street are gear whine (which can be cool) and some stubborn shifts at slow speeds that may need a little double-clutching, especially on downshifts. Although neither are a big deal, we wanted to preserve the street-car traits in this little coupe.
If that's not enough, G-Force also offers the boxes in different gear ratios with several different Overdrives to suit anyone's fancy. We opted for a taller 2.95 first (stock is 3.35) with a deep 0.63 Overdrive. The taller first is welcomed on the street and strip, where more vehicle speed can be achieved in First, thus prolonging the shift to Second until the car is well under way. The tall overdrive also comes in handy on the super-slab, where the tach sits below 2,000 rpm at cruising speeds.
G-Force offers several different First-gear ratios, and even has close-ratio boxes with ultra-shallow Overdrives for road-racing, or drag applications where Fifth gear is needed as another cog for acceleration, not as an overdrive.
Although there are other five-speeds on the market like the TKO-500/600, and six-speed units like the almighty T56, the lightweight G-Force T5 still undercuts the other transmissions by nearly 50 pounds and is more than up to the task at our power levels. As for the installation process, it's a simple remove-and-replace since it's still a T5 case.
A solid transmission is nothing without a stout clutch so to feed the power to the pavement we opted for a Ram Powergrip clutch, pressure plate, and throwout bearing kit. The Powergrip clutch is an affordable single-disc unit that blends performance and price into one great street/strip package. These units increase clamping loads without significantly changing pedal pressure by utilizing a special pressure plate and dual-friction 900/300 series disc that's good for over 550 lb-ft of torque in standard applications and 650 lb-ft in HD applications. Truthfully, we might be pushing the standard Powergrip to its limits with our motor setup, but instead of stepping up to a multi-disc unit, we'll report how it fares against our high-torque motor.
Since our G-Force has a 26-spline input shaft, we had Ram spec us the appropriate disc and also opted for its 14-pound billet-aluminum flywheel. This bad boy comes fully machined, surface-ground, and balanced from the factory, and features a 0.250-inch-thick riveted steel insert that helps the clutch dissipate heat without distorting. These SFI-approved units have the steel inserts riveted in place before the flywheel is surface ground for a precision construction. The result? A quick-revving motor without the clutch-chatter.
With power comes responsibility; and now that we've upped the ante it was time to address the serious safety concerns all stick-equipped drag racing cars should face, the addition of a quality scattershield and driveshaft safety loop.
Sure the odds might be in your favor, but it only takes a slight mishap for a flywheel to break free and come buzz-sawing through the floorboards and possibly your legs. We'll save the horror movie details, but protecting yourself and your car from a clutch/flywheel explosion with a quality scattershield is a wise investment—not to mention it's needed to remain legal at our e.t. level.
When it came time to select a proper shield, we turned to none other than Quicktime. These quality scattershields are not only SFI- approved, but also much lighter than the competition. Another key feature is the compact design, which leaves plenty of clearance for the starter and headers to snake into place.
Quicktime units are made from machined steel, not stamped, making them “truer” than other scattershields. The straighter the 'shield, the easier it is to dial-in to the center of the crank, thus preventing additional load on the motor or transmission. In order to make sure our unit would dial-in, we took it to one of the best machine shops on the West Coast, Rankin Performance Machine, where owner John Rankin found the Quicktime unit to be nearly true. Rankin ultimately CNC'd some powdercoat at either mating surface to square it up. But if you know scattershields, then you know removing some extra powdercoat to achieve a flat mating surface is not a big deal.
The last bit of safety equipment was a driveshaft safety loop from Lakewood Industries that will help contain the driveshaft in the event it breaks free on either end. At minimum a broken driveshaft can beat up the floorpan of your car, but in some cases, it will not only tear through the floor and potentially harm you, it can actually launch the car should the transmission side of the driveshaft fall and bite into the ground. To prevent such carnage, we opted for the affordable bolt-in Lakewood unit made from hardy zinc-plated steel; it's both NHRA- and IHRA-legal.
While it might seem a little excessive, safety pieces like a quality driveshaft safety loop and a scattershield are crucial to keeping safe and enjoying the sport of drag racing for years to come.
Before really enjoying our newfound drivetrain components, we not only needed to put the necessary break-in miles on the clutch (Ram recommends 500 miles), but we also needed to break in the new G-Force transmission. After a thorough running-in, both the clutch and transmission operated flawlessly. Clutch take-up is smooth and easy, and rev-matching with the lightweight flywheel is amazing.
As for the transmission, it shifts like glass whether on the street or banging gears at the track, andFirst gear is now tall enough we can dig into a solid 60-foot without a quick 1-2 shift like the stock box. Lets also not forget the deep overdrive that lets us run down the highway without taching out.
We'll leave you here for now, but follow along with the installation process below and stay tuned for the next installments as we put the finishing touches on the car and hit the track in search of a smog-legal 10-second e.t.