I thought it would be nice to cover what I did for the Shifter and the Rear in the 94 GT. Since they are both related to the drivetrain, I decided to keep them in the same blog rather than separate.
Shifter:
I bought some various parts off a friend that upgraded his mustang transmission to a Tremec T600. There was a steeda tri-ax shifter (in pieces), the stock T5 transmission and the stock T600 shifter. I re-sold the stock transmission for what I paid for everything. I also rebuilt the tri-ax after giving it a very thorough cleaning. I had a Pro-50 in the car at the time, and I wanted to try something else. I removed the pro-50 and installed the tri-ax along with the new shift knob. The installation is VERY easy. remove the shift knob, remove the boot (it just pulls up, attached to the trim). Disconnect the cig lighter connections. Remove the lower boot (4 small bolts) and remove the shifter (4 bolts to the trans). clean the surface of the trans where the shifter mounts, lay a bead of black RTV, and install the new shifter. The trick is to adjust the stops correctly. When in gear, you should BARELY see daylight between the stop and the shifter in second and third gears. The rest of the installation is reverse of the removal. I also sold the Pro-50 for a profit. I think I got about 100$ for it. So by the time it was all said and done, I had about 150 in profit, swapped shifters and had a nice leather shift knob. Not a bad deal!
I really like the Tri-ax shifter. It leaves the option of installing the shifter handle on the drivers side OR passenger side of the shifter shaft. I chose the drivers side. There are also two mounts for the hight of the handle. I chose the lower height since I'm not too tall. It shifts so well that I actually removed the MGW shifter from my 03 Cobra and also installed a Tri-Ax. Thats it for the shifter!
Rear:
I know I didn't say this in the title, but I also had an aluminum driveshaft in the car for a short while. I installed that after buying it for a great price! I took the stock driveshaft and replaced the U joints with some new ones. Then I swapped back to the stock one and made a good bit of money on the aluminum driveshaft.
After one of my very long road trips, I noticed that the rear in the car was starting to make some noise. It was also showing some signs of wear in the posi. At 145k on the clock, I knew it was time to give it some attention. My goal was to completely rebuild it, upgrade the posi a bit and possibly change the gears. The stock gears are 3:08. I didn't think that 3.27 would be enough of a change, and 3.55's were a bit too much for highway / daily driving. I needed something in the middle. The new S197 GTs sometimes came with 3.31 gears. I found someone selling a used set with very low miles on them and bought them. They are called 'take off'. Its what happens when someone buys a new car and takes it to a shop to customize it. These gears had about 5k miles on them when I got them. I bought the ford FMS-M-4210-C kit. It includes everything you would need to completely rebuild the rear and install new gears.
The nice part about having gear-heads for friends is that they usually have parts laying around. My buddy had a stock Traction Loc posi unit on his shelf. He told me I could have it so long as I replaced it with the one that was coming out of my car. I already had the 3.31 gears, so I decided to rebuild the unit. I could do all of this without removing anything from my car. I purchased the rebuild kit for the Posi (FMS-M-4700-B) which is the standard rebuild kit. There is also a carbon fiber rebuild kit which is a bit more money, but this is my daily driver. The carbon fiber kit also requires an upgraded, and subsequently more expensive, gear oil. The stock gear oil is about 12 dollars a quart and it will work perfectly with the standard rebuild kit. I also bought the upgraded S spring (they use these in the 03/04 cobras and F150s). The S spring pushes against the spider gears / clutch packs. Having a bigger S Spring in there should tighten up the rear a bit.
Before I begin, please understand that there are many write-ups on installing gears. I'm going to cover this from a high level and may leave out some details. This is not a job for the average mechanic, and requires some specialty tools that are pricey. I borrowed some of these specialty tools from a friend, bought some of my own, and even had to make some. I also did all of the work with the rear housing still in the car. Never again will I do that! It will always come out and live on some saw horses for the rebuild.
Ok, back to rebuilding the posi. I removed the bolts that hold the ring gear to the posi, and removed the ring gear. I used a dead blow hammer and the ring gear did NOT come off easily. I used a puller to remove the carrier bearings (this is a loaded statement, there's a LOT to this). I removed the S Spring, and subsequently the clutch packs for the spider gears. I made sure I kept the cutch packs IN ORDER so I could match with the new packs. I took the friction disks for the new clutch packs and soaked them in gear oil / friction modifier. Then I installed the new clutch packs and the spider gears, and the upgraded S spring. I really had to get creative to compress the S spring / pry it in there. This is a lesson in hand strength. I've done it twice, and its a challenge each time. I then put the posi unit in the freezer, boiled some water and put the new 3.31 ring gear in the boiling water. after a few minutes I removed the ring gear, took the posi out of the freezer and the ring gear slid right onto the posi. I was able to line up a few bolt holes before I couldnt move the ring gear any more because the temperatures equalized. I installed all the bolts for the ring gear along with some thread locker, and torqued them to spec. I also installed the carrier bearings using a seal driver. The posi was ready. I had more than a few hours into this rebuild already. But since I was able to rebuild the posi without first tearing into my car, I definitely saved some time.
Next I put the car up on jack stands, under the frame, and dropped the rear down. I removed the rear cover, carefully, because the fluid will come pouring out. The way I did it was to remove all the bolts except the bottom one, then loosen that only a few turns, then pry the cover. This method allows the fluid to drain in a controlled manner, and keeps the cover still bolted to the car. While that was happening, I remove the rear wheels, brake rotors and calipers. I removed the rear cover completely, and removed the 5/15 retaining nut for the pinion shaft. I removed the pinion shaft, pushed the axels inward and remove the C clips. The axels now come out. I used a puller to remove the outer axel bearings and seals. Then I removed the bolts for carrier and noted the orientation and which side each cap came off of. The carrier will now come out. I moved to the front of the housing and removed the driveshaft, and the pinion nut. I also used a brass punch to remove the pinion gear. It needed some 'help' but eventually popped out. I used a slide hammer to remove the pinion races, and a seal driver to install the new ones. I also used a seal driver to install the outer axel bearings and seals.
Now comes the tricky part. I needed to check the pinion depth. There is measuring involved, using precision tools. I may add more detail to this section later. I also used an old bearing that had been 'modified' so that it just slides on and off the 3.31 pinion gear. This helped because I did not have to press the bearing on and off each time I needed to make a shim adjustment. Eventually I got the correct shim pack under the pinion bearing, and pressed on the new bearing. I installed the pinion gear, crush collar, oil slinger, outer pinion bearing and seal, and drive shaft flange. I also installed the pinion nut. This gets tightened not to a torque spec, but to a drag. The drag is measured by using a dial torque wrench on the pinion nut and measuring how much it takes to spin the pinion gear. When you get the right amount of pre-load, the drag will be in spec.
I moved on to the carrier. The carrier races and shims get installed together on each side, which is why it was important to keep the shim packs and caps on their respective sides. I used that as a starting point. I installed them with the carrier, and the caps and torqued to spec. Next step is to measure the backlash, or space between the gears. The shims are adjusted until the desired backlash is met. Again, this is a loaded statement. Once the posi is installed, I installed the axels and C clips. The challenge here is that the anti-lock sensor prevents the axels from sliding all the way in to install the C clips. with a little help from a friend (he pushes the axel in while the other person installs the clips) it goes easier. Once the clips were installed, I installed the pinion shaft and pinion shaft retaining bolt, and torqued that to spec. I needed to adjust the S spring a bit here for clearance.
I installed the rear cover and removed the vent fitting on the passenger side, and filled the fluid there. I also removed the stock fill hole. I mixed the friction modifier with one of the quarts of fluid and filled the rear through that vent hole until the fluid drained out of the fill hole. I put some thread sealer on the fill hole plug and installed the plug.
The last steps were to install the driveshaft and rear brakes, then then wheels. Lower the car down off the jack stands.
The test drive was great! There was a noticeable change in the seat of the pants feel. It had a little more pickup off the line, and the RPMs at 75 mph were just over 2000. Perfect! The rear also felt 'tighter', meaning the posi traction is working, and there is very limited slip in the differential. This is what I wanted.
There were some lessons learned here. I did NOT use paint to determine how the gears were meshing. I also installed used gears. Because of this, there was some whining on the coast side of the gears. Most likely a pinion depth issue and not an issue with the gears. Also, the axel seal on the passenger side did not seat correctly and subsequently leaked. I had to replace that seal, which means pulling the axel out again.
I would definitely be confident doing this upgrade again in the future! And other than those lessons learned, I think this was a great upgrade.
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