The article featured on this page is from the December 2010 issue of Auto Enthusiast Magazine.
Plates and splines to beef up your S197 Mustang’s 3650 five-speed.
STORY Dan Sanchez
Many S197 Mustang owners have found that bolting on a supercharger can lead to big horsepower gains. But the factory drivetrain isn’t necessarily designed to handle the extra stress coming from a 450-500 rear wheel horsepower engine.
This is especially so for Mustang owners whose vehicles are equipped with the Ford 3650 five-speed manual transmission. With this kind of power, they quickly discover that the factory clutch slips, and the fear of breaking the transmission’s input shaft or other components becomes a harsh reality every time they stomp on the throttle.
New Twist On A Twin-Disc: Only recently did clutch manufacturers such as Centerforce come up with some solutions for the growing number of late-model car enthusiasts using superchargers to make big horsepower and torque. Utilizing patent-pending technology, the company’s new DYAD DS Twin clutch provides enough clamping force to handle up to 1,300 lbs-ft of torque. Yet, the clutch material does not have to be as aggressive as that used on full-race style clutches, making clutch engagement much more pleasant during normal driving conditions.
According to Will Baty of Centerforce, the DYAD DS Twin system works differently than twin-disc clutch systems of the past. Instead of both clutches being driven off of the input shaft, this new design has only the first clutch disc, closest to the engine, driven off of the transmission’s input shaft. The second clutch is driven off of six drive lugs that are riveted to the face of the first disc. This technique provides full dampening of both clutches and makes for extremely smooth operation, while maximizing clamping force and improving the strength of the clutch to handle big power.
Putting It All Together: We wanted to see how well these modifications would work and opted to make them on one of our Mustangs, an ’07 GT outfitted with a Kenne Bell, 2.6L twin-screw supercharger. This car was the perfect candidate for this upgrade, as the 4.6 liter 3V is putting out slightly over 500 rear wheel horsepower and the five-speed transmission uses a racing style Centerforce DFX clutch. Upgrading the input shaft and installing the new Centerforce DYAD DS Twin clutch would smooth out the engagement and take the abuse of a high-powered street engine.
On the road, the Centerforce DYAD DS Twin clutch operates smoothly, and with its added holding capacity, it can take more power than this Mustang will ever want to produce. Baty at Centerforce mentioned the system once made a slight noise when the clutch pedal was depressed, but they have since eliminated that problem. The clutch noise was similar to but not as loud as the factory twin-disc system on the GT500. In fact, the Centerforce DYAD DS Twin clutch is actually quieter and has less pedal effort when you compare the two.
After a short break-in period, it was easy to power-shift our 3650 transmission through the gears. Most importantly, low-speed shifting on the street (especially on hills) was smooth, and there’s no clutch chatter like we experienced on the DFX clutch. The cost of a job like this, especially if you remove the transmission yourself, is definitely much less than a full TR6060 six-speed replacement and offers some added insurance that your five-speed can take some added abuse.
For any dual-purpose street and strip-type Mustang that makes some impressive horsepower, there’s no doubt that the Centerforce DYAD DS Twin clutch and the Liberty’s Gears 26-spline input shaft conversion are a great way to get the power to the pavement in a reliable fashion.
1 The DYAD clutch system uses an SFI-approved billet aluminum flywheel, two clutches and a center spacer plate. The first clutch is driven off of the input shaft and uses heavy-duty lugs to drive the second clutch.
2 This upgrade began by taking our ’07 Mustang GT over to GTR High Performance, where Ricardo Topete put the vehicle on a lift and unplugged the O2 and transmission sensors, the wiring harness, then removed the negative battery cable and unbolted the starter motor.
3 Unbolting the exhaust from the manifolds and loosening the clamps allowed the removal of the aftermarket H-pipe. Only the H-pipe needs to be removed.
4 Removing the driveshaft bolts allowed Topete to gain easier access to unbolt the performance short shifter. Then, with the transmission properly supported with a trans jack, Topete unbolted the crossmember from the frame.
5 While some of the bellhousing bolts are easy to access, the top bolts require a very long extension to remove. Once the transmission was free from the engine, it was lowered and pushed back to clear the input shaft from the clutch. It took some maneuvering to get it out, but eventually it broke free.
6 The last step before removing the transmission is to detach the hydraulic line from the master cylinder. Centerforce includes a plug in all its clutch kits to keep the fluid from pouring out of the reservoir.
7 The shift lever detents are removed, and the bellhousing can be unbolted to reveal the input shaft. The rear synchro hub hits the countershaft gear so that it can’t simply slide out without further disassembly.
8 At the rear, the driveshaft flange must be removed from the output shaft with a puller. Then, the rear case cover can then be unbolted and removed.
9 The reverse gear synchronizer assembly is at the back of the countershaft. It must also be removed. First, the fork-pin is pushed out from the internal shift lever.
10 Then a C-clip is removed from the shaft.
11 One of the top forks must also be removed from the internal shift lever. Finally using two pull bars, the reverse gear synchronizer assembly can be persuaded out from the countershaft.
12 Here, you can see the seal and race that holds the countershaft in position. Removing this gives the shaft enough play to move it out of the way and pull out the input shaft from the front.
13 They lubricated the input shaft synchros and put them in place by simply lifting the counter gear up to insert them. The same was done when installing the new input shaft. They lifted up the counter gear and slid the shaft into position. You can see how the new 26-spline input shaft fits into position with the countershaft. For reference, the transmission is upside down, so the countershaft doesn’t fall down towards the bottom of the case.
14 All the original bearings were reinstalled onto the transmission’s bellhousing. With some new sealant, the bellhousing was reinstalled back onto the case.
15 The reverse synchronizer assembly and fork were kept together and were reinserted into the countershaft along with the seal, race and C-clip. The top and bottom shift forks were then reinstalled using the expansion pins that hold them in place.
16 With the bellhousing on, the three shift arm detents are reinserted. A spring puts pressure on the detents like lifters on a camshaft, and the covers are screwed back onto the housing to hold them in place.
17 Back at GTR High Performance, Topete had bolted on the new Centerforce SFI-approved flywheel using new ARP bolts that were torqued between 65-70 lbs-ft. Then the first clutch disc is installed using Centerforce’s alignment tool. Note the six lugs that will drive the second clutch disc.
18 After the first clutch disc, a spacer plate is inserted. Then, the second clutch disc is put into position. You can see how the lugs drive the center portion of the disc, which help dampen the assembly.
19 Using the alignment tool, the pressure plate is installed. The ARP bolts are torqued between 35-40 lbs-ft.
20 Before reinstalling our modified 3650 trans, we poured in three quarts of Royal Purple Synchromax fluid. The transmission was bolted back into position, along with the crossmember, exhaust, shifter, driveshaft and wiring harness. Our Mustang’s five-speed can now handle some serious horsepower and torque.