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I need shorter gears and was wondering if I can just change out ring and pinion gears without having to do much more work inside the pumpkin? or is there more to it than just that?
Yes, you could actually change only the ring and pinion and nothing else. Is it a good idea? Probably not unless the unit has very low mileage. Unless you are absolutely limited in funds, and because it is a pain to remove the rear gear unit, I would at least change the carrier and pinion bearings and the yoke and pinion seals. You also should check the cross shaft in the carrier for wear and also check the yoke ends for wear. Hope this helps. Good luck.
While seemingly simple, wouldn't do this unless experienced at it. Lot's of proper close tolerance set up involved here, and may not last very long if done wrong. Can see the temptation of doing this yourself, as very expensive at a shop. Or at least seem's to be at the beginning.
When you change the R & P you may also have to change the shims on both side of the carrier and pinion to make sure you get a good pattern and the proper backlash.
IMHO if you are going to swap the R&P, you should spend a little extra time and do a total rebuild. If you have the tools and some basic fabrication skills you can make the fixtures you will need to set up the diff correctly. For tools, besides the basics you will need a press, a bearing splitter, dial indicator & magnetic base, micrometer, a good 2-jaw puller, 90 deg snap ring pliers and an inch-lb torque wrench (this last I had to buy, and they are $$$).
A decent rebuild kit is under $150 bucks. If you don't already have one get a cheap engine stand from Harbor Freight (use one of their 20% off coupons from Chevey Hi-Perf, Car Craft, Hot Rod etc.)
Do a forum search, there have been some excellent write-ups on this in recent years...GTR1999 and Stinger12 come to mind.
I went from a 3.08 to a 3.73 in my 1968 SB and love it...
First, changing a ring & pinion is not as simple as, for example, R&Ring a rocker arm, pivot ball and adjusting nut. In my opinion, it's the most technically difficult procedure you can do to your Vette. Remember, you cannot easily install a 4 series R&P on a 3 series carrier; just won't fit. 3.08, 3.36, 3.55, 3.70 are the OEM ratios that fit a 3 series carrier.
For the record, a perfectly useful pinion preload torque wrench can be had for ~$40.
KD Tools 2955 Beam Torque Wrench (0-60-Inch/Pound)