Tools:
You need a dial indicator, a base, a press, a good impact gun, micrometer/caliper, time, patience, bearing splitter, bearing puller, pinion nut socket, brass punch(es), in. lb torque wrench, adapters for 1/4" all the way to 3/4" drive for in. lb torque wrench, ft lb torque wrench, and bearing race/seal installers.
Dependancies:
The largest dependancy, by far, is your education and research. Will your new gear set require a new carrier? If I need a new carrier, should I get a locker? Is that locker warrantied with those gears and tires? Will my new gearset require a change in speedo gear? Will my new gears put my RPMs too high on the highway?
Risks:
Screw it up badly enough, you may break other items in the housing, or the housing itself.
Not completing the installation and having to have the vehicle towed to a qualified shop to complete.
Something gets installed out-of-spec and damages the gears to the point where a shop has to repair it by installing new gears and bearings.
Almost all of these risks result in increase cost, potential vehicular damage, and potential vehicular downtime.
The Installation:
Step 1
When removing your old gears, be sure to mark the carrier bearing caps for orientation and direction. You need to install them in exactly the same way you found them, so what I usually do is take a sharp punch and make a mark on the top half of one, then a corresponding mark on the gasket surface next to it. Then I make two marks on the upper half of the other one, and another two marks respectively. This allows me to always know how to put them back. Sometimes there's a letter which has been stamped in the caps and the gasket surface that will tell you the same thing.
Step 2
You're going to have to be able to slide out and basically remove the axle shafts from the housing. On the front, this may also mean removing the tie-rods. Check your manual for all this.
Step 3
The first basic step when installing new gears is to measure the shims as you take them out of the housing. The shims on a typical Dana 44 will be in 3 places as follows:
To remove the pinion head bearing race, take the long brass punch and punch it out from the opening for the pinion. Once it starts to seperate a little, make sure you push the shims back where you're going to be punching and get them out of the way.
Once you have them all catalogued and totalled, you can almost not mess this up. Why? Because if you get in too far, or over your head, you can put the old gears back in with the original shims and be nearly back to where you are now. That being said, this is not a great idea if you can avoid it. Putting new bearings on may throw these values off, but at least you'll be able to drive onto the wrecker to get towed to a shop. ;)
These measurements are also the best place to start for installing the new gears. Generally, people will tell you not to use the new bearings until everything is setup and ready to go. I'm going to say almost the opposite. Use the new bearings on the pinion head and on the carrier, but not for the (outer) pinion bearing. Reason being is because when you're setting pinion preload, this bearing can get crunched a little too easily, IMO.
Step 4
For starters, what I like to do is get the new parts together. Get the new bearing pressed onto the pinion head, get the new pinion head bearing race installed, get the new bearings on the carrier, etc. This provides you a nice starting point at which there is no return. This is where the bearing splitter and bearing puller come in. You need to be able to use the press to get the old bearings off, and using the splitter and puller, or a combination of both, may be the only way to do this. The pinion head bearing may not even need to be removed if you have a new bearing (recommended!) and a new pinion. The same goes for the carrier, but you'll need to get those bearings off to measure the shims as in Step 3.
Checking The Settings
Step 5
After getting the ring gear on the carrier or locker, I like to set the pinion preload to something average and run a quick pattern. By using the original shims and old bearing, you should be able to crank down on the pinion nut and you should be able to turn it by hand, but it should also have some tension. Trying to get a backlash reading with no backlash is frustrating and you won't get a good reading.
Step 6
If by some amazing stroke of good luck, your pattern is acceptable or close to acceptable, now's a good time to measure backlash. If backlash is not in spec, you have to try and get it within spec...here's where the fun begins. Backlash and pinion depth (indicated by the pattern in Step 3) feed off of one another. By changing the backlash, you're changing how the pinion gear meshes with the ring gear. It's critical to compromise these two until you have an acceptable pattern AND acceptable back lash. By changing the pinion depth, by the way, you're also changing the pinion bearing preload. It's important to keep an eye on how you're affecting the pinion bearing preload so it doesn't get too low or two high accordingly.
Settings
The end result of a good installation is having 4 distinct qualities measured to be within predetermined specifications.
Pinion Bearing Preload
On Dana 44s, for instance, the pinion bearing preload is set by using a shim pack - no crush sleeve. By cranking down on the pinion nut with at least 250 ft lbs of torque, you're basically pinching the bearing in against the housing, but you can change how far into the housing the bearing can go. More shim equals less preload. Checking pinion bearing preload is done by measuring how much effort it takes to spin the pinion gear without the carrier and axles installed. Basically, it requires turning the pinion with the in. lb torque wrench and getting a reading.
Backlash
Backlash is measured by setting up the dial indicator so that the point is on the drive side of one of the ring gear teeth. What you essentially need to measure is how much back and forth movement the ring gear has without the pinion actually moving. In other words, you should be able to rock the ring gear back and forth and measure the distance it moves before the pinion will also move. Backlash is adjusted by adjusting the shims between the carrier and the carrier bearings. Shifting the ring gear away from the pinion equals more backlash.
Gear Pattern
In order to see how well (or how badly) the pinion gear contacts the ring gear, marking compound must be used to indicate 'a pattern'. This is done by 'painting' a few teeth on the ring gear with gear marking compound and then turning the pinion so the painted area goes by the pinion. It's best to do this by placing some friction on the ring gear so that it makes a good pattern. Letting the ring gear spin freely makes for a difficult pattern to read. Reading the pattern really tells you how far 'into' the ring gear the pinion is. By adjusting the Word of advice: Summit sells gear marking compound for ~$3. Buy extra now. There must be gold or something in the paint because they only give you a tiny dab in that 1" container in the install/rebuild kit. As a novice, you'll go through this very quickly. This spec is the hardest to set mostly because there's no way to quantitatively measure the contact, you do it by eye. This is where experience comes into play.
Carrier Bearing Preload
When inserting and removing the carrier from the housing, you'll notice that it may be a tight fit. This 'tightness' is what carrier bearing preload is. Essentially, it's how hard the bearings are being forced sideways <--> into their respective races. To be honest, I don't consider myself capable of measuring this, but while I don't leave carrier floating around in the housing, I make sure it's not too tight to remove by hand, or at least with a wrench on the ring gear bolts/turning the pinion trick.
Disclaimer: This webpage is for informational purposes only. What you do with your own hands and eyes is your responsibility.
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