The trick is to get the car off the ground with 4 jack stands, one on the frame at each corner. For the tranny mount, remove the mount nut, put a bottle jack under the tranny, and lift slightly. Remove the 4 crossmember bolts and the 2 mounting bolts. Put on the new mount (1 plate, 1 mount, 2 bolts) and bolt up the crossmember. Lower the tranny and screw the new bolt into the mount to tighten.

The torque arm mount is more involved, but straight forward. You need to have the suspension at full travel since the two rear bolts holding the torque arm to the differential are very long and need to come out the top. Remove those 2 bolts and slide the torque arm out of bushing and out of way. Then go to work on the front bracket. Remove the entire bracket from the car (2 bolts with nuts, 1 nut, and 1 bolt). Then you need to grind/drill out 4 rivets. Using a grinder makes it fairly easy although time consuming (about 20-30 minutes). Then lube the new bushing, slide it into bracket, put bracket back on and tighten all the bolts except the one that tightens the 2-piece bracket together. This makes it a little easier to put the torque arm back in. Slide the torque arm into the bushing. Get the rear of the arm aligned and drop the two rear bolts back thru it. Then tighten the front bracket bolt and tighten the rear bolts. Finally, lower the car.

First, you'll need the following:

• 2 quarts of rear differential fluid (i.e. Mobil-1 75W-90, synthetic)
• 1 bottle (4 oz.) of GM Limited Slip Additive (available at any GM dealer)
• 1 rear differential gasket (also from any GM dealer or auto parts store)
• 1 tube of Permatex or Locktite NON-HARDENING adhesive/sealer
• 1 ratchet with 1/2" socket and open-end wrench of the same size
• Sharp razor blades (preferably with a handle/holder)
• Large oil pan to catch the old fluid

Wear old clothes as the old differential fluid stinks and the smell will never totally come out of your clothes. Back the car onto car ramps or jack it up under the rear differential and put jack stands on each side of the axle and lower the jack to rest the car (axle) on the jack stands (you could leave the jack under there, but it will only get in the way).

Place the oil pan under the differential housing (you may want to prop it up up on a box to get it as close as possible to prevent splashing). Remove all the differential bolts with the ratchet (the very bottom bolt will require the open-end wrench as the sway bar is in the way), but do not remove the very top bolt. Just loosen it. This will hold up the rear cover preventing it from splashing down into the pan w/ the fluid. Also note that the bolts at 10 and 2 o'clock are longer than the rest of the bolts to accommodate the brake line brackets. These bolts must go back into the same holes they came out of.

The seal on the cover should be tight enough that the cover won't break free after removing the bolts. So gently pry on the bottom of the cover with a screwdriver to loose it up (if necessary). Even though you left the top bolt slightly in to hold up the diff cover, pry slowly until the fluid starts to trickle down since pulling the cover open will cause a splash down of fluid and you won't smell pretty after that.

Once most of the fluid has drained, remove the top bolt and the cover and wipe out the inside of the cover with some rags. Try to especially get the metal shavings off the magnet inside. Scrape off all of the old gasket with a razor blade to ensure the new gasket will make a proper seal. Also check the edge of the differential housing under the car to scrape any old gasket off of there as well.

At this point, it's suggestible to lower the car off the jacks/ramps since the housing is at an angle and lowering it allows any additional fluid to drain. It also makes the housing level so when you put in the new fluid, you don't over/underfill it. Using a rag, wipe out any fluid sitting in the bottom of the housing.

The New Fluid:

Apply the non-hardening sealer/adhesive around the entire edge of the cover and firmly attach the new gasket (no sealer is needed on the housing side). Put the cover back onto the housing and tighten all of the bolts. Keep tightening all of the bolts around the differential in a circular pattern to ensure all are equally tight (30 N-m or 22 lb-ft if using a torque wrench).

On the right side of the housing (passenger side), there is a square-inset/ plug which the ratchet (without a socket) will fit perfectly into. This is the filler hole. Remove it with the ratchet and squeeze the bottle of GM Limited Slip Additive in first. Put in the new fluid (about 1.5 quarts) and keep filling until the fluid starts to come out of the filler hole down the side of the housing. Then it's full. You might want to pour the fluid through a small piece of rubber tube since the filler hole is on the side of the housing and at a weird angle to pour. Finally, replace and tighten the filler cap (35 N-m or 26 lb-ft).

While the following doesn't detail exact instruction for swapping rear gears on your own, it will describe the process and what's needed in order to do the swap on a 4th generation car with an automatic transmission where the speedometer has to be adjusted for the change.

If your car came from the factory with the standard Good Year 235/R55/16 Eagle GAs tires (which are non Z-rated), then it most likely has a computer controlled speed limiter that cuts off the fuel pump at about 108 MPH. Getting rid of the speed limiter is going to be part of the desired effect. If, on the other hand, your came from the factory with Z-rated Good Year 245/ZR50/16 Eagle GSCs or RSAs, then you shouldn't have a speed limiter. Only wind resistance prevents your cars going over 160 MPH.

There are advantages and disadvantages to swapping gears. The assumption here is that you are swapping to a shorter gear (numerically higher - i.e. from 2.73 to 3.23 gears). The only real disadvantage of swapping is going to be gas mileage. If you don't want to experience a significant change, especially highway gas mileage, forget about a gear swap. Also, a slight loss in theoretical top-speed will result depending on how short of a gear you use. The main advantage is better acceleration. The lower ratio will get the tires turning much faster.

As for the ratio, you have a number of choices. The 4th gens have a GM 10 bolt 7 5/8 inch rear end. This is a different rear end than goes into the Corvette and other GM vehicles. Therefore, the 3.08 rear axle ratio will not fit. Unless you change to an entirely different rear axle, housing and all, your ratio choices are limited to 3.23, 3.42, 3.73, or 4.10. However, 4.10 gears with an automatic are a bad choice as the engine will just rev too high at highway speeds.

Your rear axle has a ring and pinion, and it has a positraction (Auburn limited slip differential) carrier. There is also something called an ABS reluctor gear. If you go to a gear shop, and they install U.S. Strange or Richmond gears, the positraction carrier doesn't have to be replaced. While opinions differ on this, it's recommended that you stick with factory GM gears. They are reliable and quiet. However, if you have currently have 2.73s and plan on going to GM gears of 3.23 or shorter, you're going to have to replace your stock 2 series carrier with a 3 series carrier.

Additionally, there is an ABS sensor located on the top of the axle housing and an ABS reluctor gear that is attached to the carrier. The ABS sensor reads the reluctor gear as it turns around inside the axle. On a car with a 2 series carrier (stock 2.73), this gear is only about 1/4 inch wide. If you change to a 3 series carrier, you need a new reluctor gear which is 1/2 inch wide. If you use the old reluctor gear, your ABS INOP warning light will come on because the ABS sensor cannot read the reluctor. It's well worth the $18 cost for the new reluctor gear.

Have the work done by reputable gear shop that knows what they are doing. Forget the dealer unless they promise you, in writing, an iron clad price with a warranty prior to beginning the work. A new Auburn 3.xx limited slip posi is going to cost about $300-$350. The entire job is going to cost you about $950 including installation, new factory GM gears, and a new carrier. About $150 of that cost is for labor. It is a 2-3 hour job. There is also a 200 mile break in period required for the new gears.

After the swap, you need to reprogram your on-board computer (ECM) adjusted so the speedometer and odometer get recalibrated to the new gears. This is entirely a computer controlled issue. Assuming you have an automatic 4L60E (electronic) transmission, the ECM thinks that the car has the old gears. The Power Programmer from Hypertech (901-382-8888), will reprogram the ECM to properly adjust the speedometer and odometer, in addition to removing the speed limiter. The programmer also adjusts the wide open throttle shift points. However, one thing that it doesn't do is alter your part throttle shift points. For this, you need to send your computer to Hypertech (or one of many other ECM companies) so they can reprogram all the part throttle shift points to match your new gears. Because after a gear swap, your part throttle shifts will be out of synch. Since shorter gears rev higher, the stock ECM will still be shifting at its preset points. So the engine may hit 3000 or 4000 RPM before shifting (whereas before it should shift at 2000 RPM under partial throttle). You may be tolerable of this, but the ideal thing to do is have the part throttle shifts reprogrammed.

Cyberdyne sells a box which can recalibrate your speedometer. You can get one from JEGS, Summit, or a local speed shops for around $65, There are 5 wires coming out of the box: red (to ign switched +12v source), black (ground), white (incoming speedo signal), blue (outgoing corrected speedo signal), and blue/black striped (don't know - leave it unconnected).

The black wire can be tapped off a shifter cable mounting bolt, and red wire can be tapped off a radio circuit line behind the reciever. For a hot lead, you should probably run one from the fuse box. The grommet for the the shifter cable should be deteriorated enough to poke two wires through to meet up with the speed sender. At the very back of the tranny tailshaft (on the driver side) is the sender with two wires: one yellow (the signal) and one purple (ground). Cut the yellow wire, solder the connections and cover them extensively with electrical tape.

Go for a test drive (with the box dangling) before permanently attaching it. The cyberdyne box has two small adjusters, one coarse and one fine. You'll probably have to mess around with the adjusters (especially the coarse one) to get a reasonable reading. The cyberdyne box nestles nicely between the wiring harness bundle and the brake interlock cable and shouldn't need to be fastened down.