question to people who installed their own gears

i have read before that if you get the same brand gears, the shims "should" be the same. for example, if i were to buy some ford racing 4.10 gears, (which is going to happen) they should be basically a drop in install if i have stock gears. we all know you still have to make sure the gear is laying right, but i was just wondering of there is any truth to this, or not?

Ok....you're on a slippery slope here.

First off, YES, you can technically install the same thickness shim on the new pinion gear then install everything without checking clearances, but, if you don't know how to "set" the carrier/pinion depth then you're going to have a noisy rear-end.

When I did the 4.10's in my 5.0, I went that route and it worked out good, didn't run the "pattern" or anything and just tightened the crush sleeve until there was little to no play, but I don't recommend any of this.

If you don't know how to "build" a diff, I would take it to someone who does and do it right the first time. You can save money by tearing it down and prepping it, but let a builder set it up and run the pattern to make sure its on the money.

The reason that in some cases you can run with the same spacers is that the manufacturer cuts the gears on the same machine and maintains the same setup from gear ratio to gear ratio (where he locates the part in relation to the bearing shoulders). But, as with all thing that is a generality, and that all gear sets should be inspected after assembly for optimum performance (back lash, & pattern), as there is cutter wear, heat treat distortion, and grinding errors that all go into the total packadge. Gears are a very technical subject an I am not going to get into it just wanted to give you a little as to why you should check out the gear set after assembly. Note ometimes all will fall in spec by keeping all same shims, just depends on a few thing coming out right.

Also keep in mind that a little over a year ago, Ford Racing gears were outsourced to Motive Gear. They are no longer made in house at Ford and IMO don't go in a nicely as the old style Ford Racing gears of year past. Like J, I too have taken Ford Racing gears and just thrown them into Mustangs with no shim changes and had good luck, but I tried a Ford Racing gear here about a year ago in my 96 GT and had nothing but problems. After numerous tries at shimming the carrier and pinion at home I gave up and left it a touch noisy. Otherwise it would have needed to go to a professional with the right tools to set the pinion depth, side shims and gear pattern.

Chris

oh wow, so there is actually some merit to the theory. i have people like my dad and my boss that have done MANY gear swaps and can help/guide me along the way. i was just wondering if there was any truth in that idea.

Not really an idea or theory, more a "style" or "way" of doing a gear swap.