FWIW - I'm not sure how many other members have setup the diff gearing themselves, so I'll give you my take on it. - It's very do-able yourself if you have the right tools, a very good clean workspace, and a shit ton of patience.
The following is a lot of stuff that's pretty hard to describe, but easier to demonstrate. My life is simply too busy right now to do a full tutorial video on how to do this.
The front is a lot harder than the rear. The pinion depth is by far the most difficult part of setting up any differential gear set. The pinion depth is 90% of the work to get a proper gear pattern. The ring gear is set to mesh at a specific distance relative to the pinion, so if the pinion is set correctly, the ring gear depth is just a matter of getting spacing correct.
Doing this DIY style usually means that you don't have the proper measuring tools for pinion depth. So you'll be doing by essentially the "guess and check" method. And that takes a lot more time than doing it with advanced measuring tools. Advanced tools allow you to simply measure the stock pinion (it has a depth measurement written on the end), new pinion will also have depth measurement that was measured by the manufacturer during the manufacturing process. This is a measurement to the surface of the end of the gear head. You cannot add or subtract the shims based on the two different measurements. The measurement is from the center of the carrier bearing (side bearings) center point to the head of the pinion. But it's offset laterally, so you can't just measure it directly. There are tools that do this, I just don't own one. Toyota almost certainly does it with sophisticated laser interference measurements. They don't guess. And they only assemble once for a perfect pattern every time. If I ever do a front setup again - I'll figure out how to either buy or build my own very high precision measuring setup. The guess and check method is pretty easy on a rear diff. It's not on the front. I'll try to explain why;
When setting up a diff, you're trying to match a gear pattern in 3 dimensions. The pinion moves in one axis - let's call it "in and out". The ring gear is then adjustable in another perpendicular axis we'll call "left and right". The backlash is essentially just the small space between the gears. They can't be setup completely pushed together. They need a little space. It's measured by the distance between contact of the teeth in one direction, and then again in the other direction. That's called backlash, but it really just means a way to measure how much extra space there is between them.
On a typical Toyota rear diff - the ring gear adjustment left and right is done with big adjuster rings that you move with a specialty wrench. So you can set the pinion depth to start with, then adjust the ring gear left or right to get the correct backlash. Then you check the paint pattern and see if the pinion needs to go in or out more. You take a guess at how far, and check again. Every time you have to adjust the pinion depth - you have to remove the ring gear and carrier assembly, then remove the pinion and remove the pinion bearings.
It's difficult to remove the pinion bearings without damaging them. This is why you really need a set of "setup bearings". I make my own. What that means is that you take a good used set of bearings and you take a die grinder and sand the inside so that they are a slip fit over the pinion shaft. That way you don't have to go press the bearings on and off each time. You can simply slip fit them. Final assembly you'll then use the real bearings that will require a press together fit. *so this is a one of the costs that you're probably not accounting for. If you're buying full rebuild kits with all new bearings - then you use your old bearings. If you're not replacing the bearings (honestly - even in the rear diff there's no need to unless you're probably 150k miles plus. Toyota uses very good quality stuff and they basically don't wear out - but still, you'll want a second set for setup bearings if at all possible. They make life so much easier. - the ones that IMO are kind of a must-have for an easy assembly is the main pinon bearing on the rear diff and both pinion bearings on the front diff.
What makes the front clamshell a huge PITA is that the backlash or ring gear left/right adjustment is also a guess and check situation and the shims you use go outside of the bearing races on the clamshell housing. So you set the pinion depth with the shim stack you think is correct. Then you have to put shims in the housing on both sides to guess what backlash will be and to do so you have to remove the bearing races on both side, add or remove shims on both sides, re-hammer in the bearing races, then put the carrier in and clamp the clamshell sides together and measure for backlash. If the backlash isn't correct - you can't take a paint pattern to see if the pinion depth is correct.
You have to adjust backlash by separating the clamshell and adding or removing shims. So each adjustment requires separating the clamshell, pressing out both bearing races in each half of the clamshell, trying new shim sets, then pressing back in the races. then re-assembling, checking backlash, then if you get it right - you can test the pinion depth via paint pattern. To adjust the pinion depth once you see the pattern, you then get to do the entire thing all over again (and yeah - you have to adjust the backlash shims again with every new pinion depth change). So it takes for fawking ever unless you guess pretty close on the first one. Or you have the correct measuring tools. If you add to this process having to use a press to press on and off the pinion bearing every time - it'll really take forever. Having a set of setup bearings makes this go a whole lot easier.
When I did mine - I bought a spare front complete diff so I could set it up before I got started with the rest. It was much easier and less stressful to do that way. I didn't start the rest until I had the front diff ready to go. I also bought a spare rear diff as well.
The rear is pretty quick and easy. I think I could do a complete rear diff gear swap in about 2 hours once the diff is out. The removal and install takes me something like 5 hours IIRC. If I had a vehicle lift, I'd cut that in half.
On older Toyota setups without the clamshell front - I'd say DIY without much hesitation. I could probably swap gearing in my FJ40 in an afternoon. The newer setups are just a lot more time consuming.
I ended up short on time and was trail guiding a moab event, so I went to a local shop to setup my rear diff - it went poorly. They botched it in a few ways, then promptly closed the shop a week later. FML. They had a good reputation among the jeep crews, had been around for 20 years, etc. They didn't get the pinion crush sleeve fully crushed and I could tell from day 1 that something was wrong. Pattern was WAY off. And preload was also not even close. So I had to pull the diff back out and re-build it anyway. Complete waste of time and money on that. I replaced all the bearings too when I did it because I didn't trust their work after seeing what kind of shit job they did. It was a shop called Orion in SLC, UT. They did some really fawking shitty stuff - like filled the pinion splines where the flange goes on with RTV. WTF?? They used red loctite on some of the diff housing nuts, but not all of them??? Just all around terrible job. So I basically just threw away the money on that one.
The point here - if you do have a local shop do the setup be very careful who you let touch your diffs. Sadly this skill is getting less and less common. It's really not that hard. But, it's done so infrequently that most shops don't have anyone who's good at it. Hate to say it - but 4wheel parts probably does more than almost anyone around here. At a minimum make them keep track of all the specs for you so you know they've checked them and you can verify if you need to - pinion preload, combined preload, and backlash, plus a picture of the final paint pattern.
In retrospect for mine - I think the ECGS swap is probably a good solution for most people. It's still going to take a full day to get them swapped in. But you get diff setup by pros who do a ton of them. And the cost is probably the same or less than what a local shop would charge to do the setup. Even if you have a local shop swap the diffs out - I'd still go for an ECGS or similar setup unless you know for absolute certain that your local shop is really good.
Hope that sorta helps explain some of the pitfalls of doing it yourself. Yes, you absolutely can DIY this if you have:
a hydraulic shop press
A GOOD QUALITY bearing separator. This is important. - cheap ones are soft metal and will not work. You will ruin parts if you try to use a cheap one. This is teh one I have.
Amazon.com: ABN Bearing Puller with 1/2in to 4-5/8in Jaw – Splitter Tool for Wheel Hub, Gear Pinion, Bearing Separator: Automotive I also have a cheap HF one - it's trash. The metalurgy is very weak on the cheap HF one and it would just deform and ruin the bearing if you tried to use it for this. You need a good one. This ABN one is totally different. It's very hard high quality steel. And works great. You need to use it in combination with your shop press to remove the pinion bearings without damaging them.
a decent set of bearing race press discs
a dial indicator on a magnetic base,
spare bearings for setup bearings (could probably buy some really cheap ones and keep the originals for final assembly)
torque wrenches - one full size, and one inch lb for bearing preload,
A long breaker bar for crushing the sleeve - it takes a lot of force,
A bench vice is really handy to have also,
some ability to fabricate tools to use for doing paint pattern test on the clamshell - it's not easy
ability to make a tool or a spanner wrench for the side bearing preload on the rear diff.
A clean bench top to work on
All the tools and space to remove and install your diffs in the vehicle - this means you'll also need to be able to clean the rear diff mounting face and bleed the rear brakes.
Also - boiling the ring gear as per the FSM really does work just right.
I think that covers most of it.
Hope that helps a bit. Good luck.
