This drawing shows all of the components that we will be involved with during this install. You also have the option of replacing the pinion seal as necessary without too much additional effort. You can even replace the pinion bearings, but that process is a bit more complex than a simple differential install, so that will be out-of-scope. Basically, we'll be involved with the case & cover, the stub shafts, the side adjusters (listed as "bearing carriers"), and the differential.

Please note that this procedure covers the installation of an Eaton or Detroit LSD into a non-LSD 7.5" rear axle (such as the Merkur XR4Ti rear axle). If you have a Cosworth 7.5" axle with the viscous LSD, then the installation procedure is mostly the same. However, you will need to use your short stub shaft on the right (differential) side and your long stub shaft on the left (ring gear) side. The long stub shaft will need to have some material machined off of the end so that it does not contact the pinion shaft in the center of the Eaton differential. Also, you will not use the stub shaft spacer that is included in the differential install kit. If you are in Norway I can put you in touch with a shop that is familiar with this process - just send an e-mail to grayson@mc2racing.com.
Before you even remove your rear axle I recommend planning ahead and picking up a bearing carrier/side adjuster tool. In the past we would make tools out of oil filter cap wrenches, but times have certainly changed for the better. We're now able to use the tools produced by Company23 to spin the side adjusters, and they work well with no assembly required. These are available on the www.mc2racing.com website in the Driveline section.
Drain the gear oil by removing the fill hole bolt and sitting the rear axle on its cover over an oil container. Once empty, remove the nine cover bolts with a T50 Torx bit. Ensure that the Torx holes in the cover bolts are cleaned out so that you get good engagement between the bit and the fastener. My Torx bit had a rounded nose on it, and I actually ground the nose of the bit flat so that the splines of the bit would penetrate as deep as possible into the fastener. Smack the head of the Torx bolt with a hammer, and then carefully remove the cover bolts. Whatever you do, do everything you can to not round out the cover bolts.

I don't like Torx bits at all, and if you purchase our "full" differential install kit, you will receive replacement cover bolts with hex heads instead of Torx heads.
Now that the case is open, remove the C-clips from the ends of the stub shafts. There is a small hole in the middle of each C-clip that you might be able to use to pull the C-clip out. If you're not able to do that, you can use a pair of screwdrivers to push on each tip of the C-clip until is pops off. Don't get upset if this turns out to be a pain - sometimes these can be finnicky. Just take your time, and you'll eventually get them.
While you've got your T50 Torx bit out, remove the side adjuster lock plate bolts. Again, ensure that the fastener hole is clean, and give it a good whack with a hammer before trying to remove it. Don't round these bolts out either. Once you get the bolts out, pull off the lock plates and set them aside.

If you purchase our "full" differential install kit, you will receive replacement lock plate bolts with hex socket heads instead of Torx heads.
Use the side adjuster tool to remove the side adjusters. Both of these have normal right-hand threads (righty-tighty, lefty-loosey). I recommend placing the axle assembly on the ground, putting one foot on the case, and using a 2' long breaker bar to turn these. Do not put a shock on these side adjusters, or you will snap off one of the aluminum tabs! Apply smooth pressure to the wrench, ensure the tool is engaged well, and it will eventually loosen and you can rotate the side adjuster out.

One time the O-ring seemed to be binding when I was removing a side adjuster. If this happens to you, unscrew the adjuster until it gets tight, screw it back in a little, unscrew it some more, and keep doing that until it finally comes out. It was just like tapping threads into a hole, as if you had to clear the chips.

Your differential can now fall out of the case and break! Be very careful if you move the rear axle off of the floor at this point!

If you're having us rebuild your side adjusters for you, now is the time to send these off to us. Don't send them to us with a signature requirement in case we don't hear the delivery guy over the noisy machines. Also, unless you want your new o-rings, seals, and bearing races to come back to you dirty, don't send your side adjusters to us dirty.
You can now remove the differential and ring gear assembly. Be careful! This assembly is heavy, and if you drop it you can chip a gear tooth. If you drop it on the pinion you can chip multiple gear teeth at once. You have to angle the assembly just right to get it out. Just grab it with both hands and carefully move it until it's out of the axle case.
Remove the ring gear cover bolts. If you can put the differential into a vise as shown, this step will be very easy.
Now you can punch the ring gear off of the differential. The image shows a brass drift being used. The reason they're using brass is because the drift will get knicked up before the gear will. Use whatever you need, but try not to damage the gear in any way. Now, if you have the assembly situated like the one in the image, the ring gear is going to fall down onto the bench, which could lead to a chipped gear tooth. I'd recommend placing some towels under the ring gear so that it has a soft landing once it breaks free of the differential.
You do not need to complete this step if you purchase both your differential and an install kit from us.

You now have a decision to make. You can install your differential without clearancing the rear axle case with a grinder, but that is only possible if you press the bearing cones on the differential after you install the differential in the case. This allows for a fast and simple installation without grinding, but removing the differential in the future will be difficult since the bearing cones will have to be removed first. If you wish to perform the installation without grinding, skip this step.

If you wish to clearance the case with a grinder, making it possible to install and remove the differential with the bearing cones installed, then press the bearing cones on to the Eaton differential now.
You do not need to complete this step if you sent your side adjusters to us to be rebuilt.

Punch or press the stub shaft seals out of the side adjusters. Be careful not to gouge the side adjuster.
You do not need to complete this step if you sent your side adjusters to us to be rebuilt.

Press the bearing cups out of the side adjusters. There really isn't enough meat to punch these out by hand, so a press and a properly-sized slug is required for this step. Be careful not to gouge the side adjuster.

Thoroughly clean the bearing cup bores in the side adjusters.
You do not need to complete this step if you sent your side adjusters to us to be rebuilt.

There are two methods for installing an Eaton/Detroit differential. The preferred method is to use offset outer bearing races, and the other method is to use stock-size outer bearing races and a ring gear spacer. If you're using the offset outer races, install the thin race in the right (differential side) side adjuster, and the thick race in the left (ring gear side) side adjuster. If you're using a ring gear spacer, the races are the same on both sides, so simply press them in. Make sure that the races go in perfectly straight.
You do not need to complete this step if you sent your side adjusters to us to be rebuilt.

Thoroughly clean the stub shaft seal bores in the side adjusters, then press the stub shaft seals into the side adjusters. Make sure that they go in perfectly straight. The left (ring gear side) side seal should be pressed into the side adjuster until the seal face you're pressing against is 11mm below the top of the seal bore. The right (differential side) side seal should be pressed into the side adjuster until the seal face is 4mm below the top of the seal bore.

Cosworth owners - If you are upgrading from a Cosworth viscous LSD, press both of your seals in 11mm.

Note that if you did not purchase our full differential install kit, and you're looking to install new stub shaft seals, pretty much every auto parts store is recommending an incorrect 42mm stub shaft seal. Be sure to only install the proper 43mm seal or else you'll experience premature seal failure.
You do not need to complete this step if you sent your side adjusters to us to be rebuilt.

Remove the old O-ring from each side adjuster and replace with a new O-ring. Try to stretch the O-ring as little as possible while pulling it over the outside of the side adjuster. The guy in the image is definitely stretching the O-ring way more than he needs to.
Slip the 0.250" (6.35mm) spacer over the right-side stub shaft, as shown in the picture.

Cosworth owners - If you are upgrading from a Cosworth viscous LSD, do not use the stub shaft spacer.

Next, carefully apply the stainless steel shim tape to each stub shaft as shown. Each strip of shim tape comes cut to length, and you should use all of it. You'll want to ensure that the surface is very clean so that the tape can adhere properly. As you wrap the tape around the stub shaft, press the tape as flat as possible, and definitely avoid bubbles or wrinkles.

Now push each stub shaft into the appropriate side of the differential. The purpose of this is to ensure that the application of the shim tape went well. It will take a surprising amount of force to install each stub shaft into the differential. Just be careful that the shim tape does not wrinkle or slide as you are pushing. If you are able to push each stub shaft in until it bottoms out, you can remove them and set them aside for later. When you go to install the stub shafts in the final steps of this procedure, you should find that they slide in well.

If you look closely at the picture, you can see that the stub shaft on the left side of the image has been pushed into the differential already, and the one on the right side of the image has not.

The Eaton differential and the Detroit differential require different lengths of shim tape. If you purchase a full differential install kit we'll match the length of tape to your application. It should also be mentioned that you may machine a bushing to install over the stub shafts rather than using shim tape, if desired.
If you have chosen to use stock-size outer bearing races in your side adjusters and a ring gear spacer (rather than offset outer bearing races and no spacer), install the ring gear spacer against the differential ring gear flange. Our spacer is made with a very tight tolerance, and you have to carefully tap it down over the ring gear pilot with a rubber mallet. Once the spacer is seated flat against the ring gear flange, you'll be able to spin it to align the bolt holes.

Next, align the ring gear on the differential pilot and install the ring gear bolts. If you need to use the bolts to pull the ring gear onto the differential, do so one-quarter turn at a time, and use a torquing pattern like you're installing a wheel and tire on your car.

If you are using a ring gear spacer, we recommend using longer ring gear bolts during your installation. You'll need ten. ARP part number 206-2803 comes in an 8-pack and will give you 1.5 more turns, which pretty much makes up for the thickness of the spacer. ARP part number 151-2801 comes in a 6-pack, but are way too long to use. However, they are relatively inexpensive, and they can be ground to the length of your choice, allowing you to engage as many threads in the ring gear as you'd like. Obviously if you are not using a ring gear spacer, you don't need to worry about replacing your bolts.
If you have chosen to install your differential without grinding the rear axle case, skip this step.

Before the differential and ring gear assembly can be installed in the rear axle case, it is necessary to clearance the case. Generally grinding with an air grinder (or electric drill) and carbide burr is selected to accomplish this task. The clearancing takes place in a very thick area of the case, so strength is not much of a concern. The picture shows how the case should look after the grinding process is complete. Note that the only area that is clearanced is the "rear" portion of the left side stub shaft opening.

Do whatever you can to prevent chips from falling into the pinion area when you are grinding. Clean the case really well and cover the pinion area with a few cloth towels. When you're done grinding, vacuum up the chips with a shop vac, then carefully remove the towels one at a time. Usually there is only a chip or two that makes it past, and those are easily swept up with the tip of my finger. Normally I try to remove the absolute bare minimum amount of material from the axle case, so I find myself grinding, trying to install the diff, grinding a bit more, trying the install again, and so on. This is a little annoying since I'm constantly replacing the towels, but I know that after I'm done, I have the strongest case possible and I'll never have to grind this case ever again.
Carefully install the differential and ring gear assembly into the axle case. Be careful not to drop it on the pinion, or else you may chip a gear tooth on the ring and/or the pinion.

If you have chosen to install your differential without grinding the rear axle case, press your bearing cones on the differential inside the case now.
Now it is time to reinstall your side adjusters. The adjuster with the seal pushed in 11mm goes on the left side, and the adjuster with the seal pushed in 4mm goes on the right side. Simply twist in each side adjuster until it contacts the differential bearing cones. Seat the side adjusters good and snug - about as hard as you can twist them by hand without a tool.
We're getting to the point where you'll need to set your backlash. In order to do this, you'll need to prevent the pinion from rotating. In the picture you can see that I bolted a block of steel to the driveshaft flange. To rotate the pinion now would require a relatively large amount of force at the ring gear.
Now you need to setup a dial indicator and magnetic base to measure the backlash. You can purchase these two items at any decent hardware store. You want the dial indicator to be positioned 90° from the face of a gear tooth. The picture shows a good indicator position. Note how the indicator is not touching the tooth above the one we're measuring.

As long as you don't move the axle case during this procedure, you can put the dial indicator base on another surface. For example, I set an iron plate on the same table as my axle case, then put the magnetic dial indictator base on the plate. If I move the axle case or the plate at any time while I'm measuring my backlash, I'll have to start over. However, moving the heavy axle case or the heavy iron plate is not likely.
This step requires some patience. If you don't set the backlash correctly your rear axle will whine in an annoying manner, so take your time and be precise. Begin by rocking your ring gear "up" and note the reading on your dial indicator. Next, rotate the ring gear "down" and note the new reading. The difference between the two readings is your backlash. You want to adjust the side carriers until your backlash is 0.0004", or about a half a thousandth. You don't have to be perfect here. If you've got a backlash of 0.001", you've got too much, and if you've got no backlash at all, then you've got too little. Don't feel like you need to be accurate to the ten-thousandth though. Now, if your backlash is too high, you need to back off your right side adjuster a bit, which will allow you to turn your left side adjuster in, bringing the ring gear closer to the pinion gear. This reduces your backlash. If you need to increase your backlash, which is unlikely, then you do the opposite - back off your left side adjuster and turn in your right side adjuster. Just do what you gotta do until you get a backlash of 0.0004".

At this point, pull your dial indicator away and whack the axle case a few times with a rubber mallet. Also spin the ring gear a few revolutions both ways. This will ensure your bearings seat well. Now set up your indicator again and see if your 0.0004" backlash is still set right. Readjust as necessary.

Now you need to preload the bearings. To do this, you turn the right side adjuster in another 4 teeth. Do not adjust the left side adjuster. You're basically smashing the diff between the adjusters during this operation (preloading the bearings), and you're increasing your backlash a little. Now remeasure your backlash. The backlash should be 0.004"-0.006". If you have too little backlash, turn your right side adjuster in one more tooth (for a total of 5). If you still have too little backlash, you need to loosen your right side adjuster, back out the left side adjuster a little, re-seat the right side adjuster, turn the right side adjuster in another 4 teeth to preload, and remeasure your backlash. If you have too much backlash, you need to loosen your right side adjuster, turn your left side adjuster in another tooth, seat your right side adjuster, turn the right side adjuster in another 4 teeth to preload, and remeasure your backlash. It takes a lot of words to describe this process, but none of this is hard. You just need to keep following this trial-and-error process until you have a backlash between 0.004" and 0.006" after everything is preloaded. I try to get a backlash of 0.005" exactly when I set up differentials.

After you've got your backlash set, pound the case a few times with the rubber mallet again and rotate the diff a few times. Recheck your backlash. If you're still 0.004" to 0.006" after that, you should be safe to move on.
Once your backlash is set, you definitely don't want your side adjusters to move, right? Install the locking plates at this time as shown.
Install the stub shafts. The design of the Eaton and Detroit differentials make it difficult to reinstall the C-clips. It is acceptable to not reinstall the C-clips, but if you insist on retaining the stub shafts, I recommend trying out a pair of external snap rings. McMaster-Carr item #98585A124 appears to be a good candidate.

https://www.mcmaster.com

I've had more than one customer machine some steel cylinders that they attached to the end of the stub shafts. These cylinders had snap ring grooves machined into them so that the C-clips or some snap rings could be easily installed.
Install your rear axle cover and bolt it down. I recommend using a bead of RTV between the cover and the case. Also, while you're installing the bolts, try to use a sensible torque pattern.
Your rear axle is now ready to be installed in your vehicle. If you're using an Eaton clutch-type differential, purchase a 4-ounce bottle of friction modifier, which can definitely be purchased from GM, and probably from a significant number of other sources. Add the friction modifier to the rear axle before adding the gear oil. If you're using a Detroit helical differential, you do not need to add friction modifier. Fill the rear axle with 80W-90, 85W-90, or SAE 90 GL-4 (or better) petroleum-based gear oil. Eaton does not recommend using a synthetic fluid, and I also don't recommend using synthetic unless you're running a rear axle oil cooler and you're still struggling to keep rear axle oil temperatures under control.

As far as I can tell Eaton (who owns Detroit, by the way) does not make a big deal about break-in these days. If you want to follow a break-in procedure, try to not run the vehicle for more than 30 minutes at a time during the first few hundred miles. Allow about 45 minutes to pass before heading out again. After a few hundred miles, drain the rear axle fluid and refill with new gear oil (and friction modifier if you installed an Eaton clutch-type differential).