Muscle Mustangs & Fast FordsHow To Drivetrain
G-Forcing the issue
G-Force Racing Transmission does it again by releasing a complete line of T-5 and T56 gears and transmission upgrades.
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In a former life, one that I remember quite well, your faithful scribe was known as the T-5 Bandit. Imagine my photo plastered on dealership walls with a sign that read WANTED! I've bent, broken and, in some cases, demolished T-5 and T-45 transmissions; some were mine, some were not. In total, I've wiped out about 20 gearboxes, but who's counting? Besides, I'm not the only offender. I worked at a Ford dealership back in the late '80s, so I know many others have broken a T-5, T-45 or 3650. I'm quite sure many of you are shaking your head in agreement.
Thankfully, MM&FF has found a solution to this everlasting problem, one we think you'll like. With it comes the promise of long transmission life and much quicker shifting.
Enter G-Force Racing Transmissions of Annville, Pennsylvania, known as a giant in racing circles for its GF-5R five-speed, and most recently for the GF2000 clutchless five-speed, used by some Pro Stock racers. In addition, G-Force's G-101 four-speeds are used by a number drag racers and top circle track teams. But where does that leave the typical Mustang owner?
In good hands, that's where. G-Force recently released a complete line of upgrades for the popular Tremec T-5 and T56 trannys. Not only are the parts stronger, there is a variety of gear ratios to chose from and a new transmission case for the T-5. Amazingly, G-Force's top of the line T-5 is rated up to 600 hp, while the T56 is rated to withstand 900 stomping ponies. G-Force actually offers three versions of the T-5 and there are three gear ratio sets. The first T-5 kit was developed about one year ago as a stronger-than-stock replacement. It featured a fully syncronized gear set and a 2.94:1 low gear. But G-Force saw the potential of the market and took this T-5 thing a bit further. The once race-oriented transmission manufacturer now has a huge focus on street performance and offers a T-5 with the heart of the race unit. Internal upgrades include straight-cut gears and dog-ring engagement (which we'll explain later), along with a special helical/dog-ring combination that is legal for NMRA Real Street. In addition, there are three different ratio sets (see chart on next page) to meet the demands of drag racers, street enthusiasts and there's even a new close-ratio gear set that should be perfect for road racing.
"We knew the street market was huge and we also knew the trouble Mustang owners have with T-5 transmissions," stated Mike Long of G-Force Racing Transmissions, who owns a 560hp Roush Mustang. "The T-5 units were never designed for the type of abuse Mustang owners can dish out and those transmissions fail with regularity. The T-5 is often the weak link and breakage can come by way of hard usage, poor shifting practices or simple parts failure. So we developed a line of parts to make them work. In fact, I converted my Mustang back to a T-5 to test the parts. There's something nice about being able to use a part that bolts right into the stock location. It keeps the car stock and easy to work on," Long added.
Most know that the T-5 is a syncronized five-speed transmission that uses helical gears packed in an aluminum case. You may also know that the T-5 is lightweight and normally shifts smoothly, but they don't often last very long in high-horsepower applications or after many hard launches with slicks. "There are a few things that normally cause a failure in a T-5," stated Long. "One is the strength of the gears themselves, the second is shaft spreading, and the third is the high helical angle on the gears. You have to understand that the stock gears are pretty brittle when compared to gears used in a racing transmission. This is due mainly to cost and the fact that stock Mustangs only make about 225 hp.
"Gear spreading is a big problem in the T-5. When the transmission is under load the meshing teeth will try to push apart from each other. And the more power you make, the more the gears will spread. The stock mainshaft is relatively weak, and it can deflect causing the gears to spread away from each other leaving only the tips of the teeth in contact. And since the gears are much thinner at the tip they are more prone to breakage," explained Long. Mustang owners know it's common to break third gear and Long stated the reason is because third is the narrowest of all the gears and it's also the furthest gear from any bearing. Therefore, it lacks support and suffers the most from gear spreading. Additionally, there is a big drop in ratio from second to third, which increases the loading on the gear.
To limit shaft spreading, G-Force first developed T-5 internals using 9310 Alloy steel, including a new mainshaft that sells for $295. MM&FF did a story on this gearbox (Torque Hungry T-5, MM&FF September 2003). More recently though, G-Force introduced a stronger 4340-300M Thru Hard Premium Alloy mainshaft ($495) along with two more gear ratio combinations. Better still, is the complete line of dog-ring and synchronized internals and a newly designed T-5 case, which is much stronger than the stock unit. In addition, G-Force offers upgrade kits for the T56, with three available gear ratio combinations.
Call The Dogs
When it comes to manual transmissions there are two basic types of gear engagements, synchronized and dog-ring (also called face-tooth). All factory and some race-type transmissions use synchronizers because they allow for smooth, yet quiet gear engagement. "A synchronizer, or blocking ring as it can also be called, is used to slow the speed gear so that the slider can engage the gear when the gears are shifted," stated Long. "As the driver moves the shift lever he manipulates the shift forks and that moves the sliders. The sliders will start to force the syncronizer onto the tapered ramp that is attached to the speed gear. As the syncro rides up the taper it grabs the gear and slows the gear, or synchronizes the speed of the gear, so that the teeth can engage. When it comes to racing, the limiting factor with a synchronized transmission is often rpm, and that's because as rpm is increased it becomes more and more difficult for the synchronizer to slow the gear quick enough and allow the teeth to mesh. "Normally the limit is around 6,500-7,000 rpm, but a good clutch setup and a good driver may be able to go a little higher," added Long.
When the synchro can't slow the gear down fast enough to engage the gear, the result is grinding and that shreds the teeth on the synchro. Ultimately, the transmission will grind all the time and may pop out of gear. If these symptoms sound familiar it may be time to call in the dogs. The dog-ring gears, that is. A dog-ring (or face-tooth gear as it is called), is a system of gear engagement that essentially has no blocking ring, just big steel lugs (on the slider and on the speed gear) that engage and lock together to drive the transmission. "The lugs on a dog-ring setup are on the face of the gears as opposed to being on the inside diameter of the slider and the outside diameter of the speed gear. So the face of the gear and the slider engage, rather than the inside diameter and the outside diameter of the speed gear. And rather than having 35-40 little teeth that must mesh together, the lugs simply slam together and lock in. There are between three and eight lugs on most face-tooth gears and that allows them to interlock quite easily, with virtually no chance of grinding. The advantage to the face-tooth setup is unlimited shift rpm, quicker shifts and much fewer missed gears; however, you can expect additional noise from the transmission.
In addition to the dog-ring gear engagement, G-Force offers a straight-cut gear set to replace the helical-cut gears found in a stock transmission. Helical gears work well in stock applications because they run quiet, but the downside is that there is less material in contact when compared to a straight-cut gear. "Helical gears are generally used for noise reduction, and that's the only reason the factories use them," stated Long. "The straight cut gears are stronger, but noisier, sometimes much noisier. The strength in straight-cut gears comes from the fact that you have full contact across the whole tooth. With a helical cut gear you only have a small point of contact, so you're only loading a fraction of the tooth at any given time. But that's what makes them quiet. The additional noise found with straight-cut gears comes from the gears actually slapping together. If you could break the noise down it would sound like slapping, but the repetitiveness makes it comes off as a whine." G-Force also employs gears with a coarser pitch on the teeth, which equates to stronger teeth. Lastly, you can upgrade to stronger shift forks for $250. Aside form having greater resistance to breakage, the stronger shift forks reduce flexing and provide more precise shifting.
The T56 Upgrade
It's almost unbelievable to think that a daily-driven Mustang can make upwards of 600 to 700 hp, but it's true. The '03-04 Cobras are doing it with regularity and some are making close to 800 stomping ponies. And while the Tremec T56 is one tough unit, it has its limits. While half-shaft failures are more common than transmission failures, we've seen a few T56 units in the high-powered cars go south. It seems the limit on these transmissions can be found by jacking up the boost and having at it with some sticky tires and a stiff clutch.
Naturally, some Cobra owners have gone the automatic route, but those wishing to keep the six-speed should consider the G-Force T56 Upgrade Kit.
The basic kit, which sells for $2,195, includes first, second and third mainshaft gears, input shaft with input drive gear (fourth gear) and a complete cluster shaft with gears. Three ratio packages are available, along with G-Force overdrive gears and mainshafts, which are optional. The overdrive gears sell for $740 and there are two mainshafts, one made from 9310 Alloy steel ($475) and a second formed from 440-300M Thru Hard Premium Alloy ($690). As I mentioned earlier, a T56 with the full treatment, can handle up to 900 hp. "One of the biggest features of our T56 is the triple-cone synchronizers that make the transmissions shift really well," explained Long. The three-cone synchros act almost like a dual-disc or triple-disc clutch in that they provide lots of surface area for the synchros to grab on to. This allows the speed gear to be slowed rapidly and that allows the driver to make gear changes quick and smooth and at higher rpm. Currently, only a syncronized version is available, but with a rating of 900 hp, how much more do you need?
We had the opportunity to drive a Cobra with a G-Force-prepped T56 and the results were impressive. Jim D'Amore of JDM Engineering was kind enough to let us "borrow" his black '03 that has full-length headers, non-cat H-pipe, MagnaFlow cat-back, JDM cams, JDM throttle-body and inlet, JDM heat exchanger, QA-1 shocks, 3.73s, JDM chip and 55-pound injectors. In addition, an 8-pound lower and 3.10 upper pulley set combines to produce 21 psi of boost. The Mustang also sported skinnies and a set of Mickey Thompson E/T Streets.
On the track we made two passes and ran 11.20 at 128.40 and 11.04 at 129.63 mph. The first pass came with too much spin (1.86 60-foot) and on the second, with the track prepped, we bogged badly, with a 1.90 60-foot resulting. Despite the poor launches we threw six powershifts and the transmission worked like a dream. It was one of the cleanest transmissions I've shifted. Performance was outstanding, as the transmission shifted so smoothly you'd swear it was "Pro-Shifted," but Long promised that the smoothness is due to the triple-cone synchronizers. Unfortunately, on the third try the Cobra spit the independent rear out, ending our fun. With a good launch I believe the Cobra could have run mid-10s at about 131 mph.
After learning about the new line of T-5 and T56 equipment and getting to test the product, I'd say G-Force has its act together. For a fair price you get a great product and you can confidently get out there and bang off powershifts like a pro. And that's something we love. How about you?