World Class T-5 Transmission Upgrade

Once I decided to upgrade the World Class T-5 transmission, I investigated the companies that provide the gears, and chose G-Force, which resulted in a very pleasurable experience. They were more than willing to work me on information exchange as well as ensuring that I was happy with their product (enough of the promotion).

Background first. The original WC T-5 worked flawlessly behind the 289. 289 was not a torque monster, but it was a 390 HP motor. The new 383 (stroked 351W) will provide a lot more torque, and I did NOT want to disassemble this car again (for a transmission failure) simply for a shortcut in not upgrading the transmission. Therefore, I needed to either go with a new TKO, a T-56, or an upgraded T-5.

Option 1: The T-56 would have added another 50 lbs to the weight of the car (which I try to avoid this kind of situation like the plague), plus the needed changes to the transmission tunnel, bellhousing, and anything else I was not seeing. The torque rating on this transmission is better than the T-5, but not as good as the TKO, or an upgraded T-5, BUT, it did have an extra overdrive gear (thumbs up for 6 speeds).
Option 2: The TKO required a change in driveshaft yoke, bellhousing, and tunnel mods as well. It was only 25 lbs heavier than the T-5, which was better than the T56’s 50 lbs, but I still wanted to avoid the external changes and additional weight as much as was possible.

Option 3: The upgraded T-5 was my final choice and the one I went with. It cost almost as much as the TKO, but it should be very close in strength. The main advantage is that once this internal modification is completed, nothing more than a new clutch disc (from 10 spline to 26 spline) was needed to install the upgraded transmission back into the car. The upgraded T-5 included a stronger G-force mainshaft, input shaft, gear set (including the overdrive gear), and the cluster gear. Basically every gear and shaft in the case was swapped. The two photos below show the vast difference between the OEM overdrive (5th gear) verses the G-force gear (the OEM gear has the smaller teeth and greater cut angle).

T-5 G-force overdrive gear and OEM 5th GearT-5 Transmission 5th gear verses OEM overdrive

During the disassembly, the OEM 5th gear (overdrive) was impossible to remove from the shaft and I was forced to grind the teeth off the gear in order to remove the mainshaft from the transmission case with the gear attached. This may have eventually been a good thing because this gear (the 5th gear) is NOT designed for high torque applications. In the left photo below, you can see why I had to grind the teeth down on the gear. This transmission had a close ratio set-up, and with a .80 fifth gear, the gear was larger than the bearing race. Because I couldn’t remove the gear even after removing the retaining clip, I had to grind the teeth down to the point that the gear would pass through the bearing race, thus allowing me to remove the main shaft out of the case.

T-5 Overdrive gear distroyed

T-5 5th gear removal

Destruction of that gear required me to consider the purchase of a new gear, and in particular the G-force gear. The G-force gear is of the same basic design as the first 4 gears, so it can be used during a hard pull just as the first 4 gears are. The G-force gear assembly went smoothly with no problems.

One of the best bits of knowledge that I came away with from this project was the importance of proper clearancing for the cluster gear bearings and the need for the “billet” cluster gear rear bearing support that G-force provides in their kit. The WC T-5 transmission has conical gears, which means any dimensional changes along the axis of that gear will result in bearing clearance changes. A T-5 case is aluminum, and the gears are steel. Aluminum has a greater expansion coefficient (Wikipedia link about Thermal Expansion) than steel with temperature changes.

What all this means is that as the case and gears get warm, the case expands more than the cluster gear lengthens, which means clearances start opening up, which means the cluster gear now starts moving away from the drive gears due to the helical cut under torque. Now you’ve got a problem with a warm transmission and high torque.

To fix that issue,

  1. G-force gears are cut with less angle (in fact, the overdrive gear is almost a straight cut, and consequently a little noisier than the OEM gear, but a lot, lot stronger), and
  2. G-force recommends an interference fit (negative bearing clearance) for the cluster gear bearings. In other words, instead of the factory .000″ to .001” clearance on the cluster gear bearings (accomplished by using shims behind the rear conical bearing), G-force recommended a -.005” to -.008” clearance, which means a thicker shim, and a tighter “cold” bearing assembly. What this also means is that when the transmission is cold, shifting must be taken deliberately and without hurry until the transmission warms up to temperature. But once the case is warmed up, this upgrade shifts better and faster than the previous OEM T-5 did at any time or temperature.

Introducing a new blogger, BlueovalZ. If you haven’t already stumbled onto his garage, do it. He’s an excellent fabricator of metal and fiberglass with an awesome eye for style too. I found his Ford powered Z a long time ago and since then, he’s been an awesome supporter of Make sure to let him know if you’ve learned something from his blog. Thanks!!

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