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  • Changing rear end gears.

    I just got a new Summit catalog in the mail and Summit brand gears are $159.95. Isn't there a tag somewhere on my rearend that tells me the gears that are in it from the factory? It has a tall gear in it now but I'm not exactly sure which ones. I am leaning toward buying a 3.73 gear for it but need to know what carrier I have. Looks like I can get a 3.73 for either carrier. I was concerned with fuel mileage in a previous post and am not really looking for gears to improve that but don't want it to get much worse either. Are 3.73's good for a cammed 350 in a half ton 86C10 with a 350 and a 700R4 (stock convertor)? I can take the cover off and look or count teeth but I drive it to work every day for the next week. Also, besides gear lube and gasket maker, what else do I need to budget for? Thanks, Scott.

  • #2

    Re: Changing rear end gears.

    You need a dial indicator to set backlash. You'll need a shim kit too. You'll need a press (or access to one) and the right tool to pull the bearing off the pinion. You'll probably want new bearings too, unless you have a press and tools to remove pinion bearing with out damaging it (not that hard with the right tool).

    I've changed the rear gears in my car three times now since 2009. The first set was 3.70, then 3.08, and now 3.42.

    You'll want to remove the old bearing from the pinion, grind/sand the inside of the old one so you can install and remove it from the pinion relatively easily (unless you own a press), so you can use the old bearings on the new pinion to change out the shims easily until you find the sizes that give the best pattern on the gear. Once every looks good install the new bearings with a press (or length of pipe, block of wood and some violence). Make sure you are happy with the shims around the carrier bearings too before installing the pinion bearing. There are websites out there for showing best back lash spec's and for pattern on the gear teeth. I prefer trying to get the pattern near the inside of the tooth so when under stress it starts working it's way outwards.

    A local shop lets me show up with my pinion and use their press and tools to remove the bearing.
    Escaped on a technicality.

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    • #3

      Re: Changing rear end gears.

      Race gears will not hold up on a street driven car.....I got a set of Moser Gears and the pinion cracked, they are made of a softer metal to absorb the shock from launching a high HP car........Do yourself a favor and get the gears from GM, that's what I ended up doing, they were actually physically bigger in size than the Moser's were for the same 3.73 ratio........ I'm going out to diner now so I'm in a hurry, but I'll post pics of the pinion later........

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      • #4

        Re: Changing rear end gears.

        Budget for the installation kit, which should include a new crush collar, pinion bearings, shims, gasket, seal... I think that's it.

        3.73 would be great for a C10 with a 350 and a 700R4. With the overdrive ( .7:1 ) the final drive ratio would be a 2.61:1.

        I don't know about a tag to give you the original gear ratio, but if the gear ratio code isn't in the glove box (I don't know when they started doing that) then you can either pull the cover and count teeth (then do simple division: ring gear teeth divided by pinion gear teeth)

        Or you can turn the rear wheel and count how many times the drive shaft turns per 1 revolution of the wheel.
        If you don't have a posi or a locking differential, you jack one side of the rear end off the ground (and leave the other rear wheel on the ground), chock the vehicle so it can't roll, put the shifter in Neutral, then turn the tire, watching the mark you made on the driveshaft and rearend housing (that I'm only just now mentioning! Ha!) and count how many times the driveshaft turns.
        For example: Just under 3 revolutions, you have a 2.73 gear. Just over 3 revolutjions, you have a 3.08 gear. About 3.5 revolutions, you have a 3.42... etc.

        If the truck has a posi, jack the whole rearend off the ground to do the procedure.

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        • #5

          Re: Changing rear end gears.

          I will likely be getting 3.73's for the Chevelle some time this year, and I won't be attempting to set the pinion depth myself - but I would love to "help" the person I'm paying to do it, so I can learn. Setting the backlash is the easy part.

          Now about brands: I've heard (a lot) over the years that the Richmond gears tend to sing. I'm hesitant to buy house brand gears from Summit/jegs. I broke a set of Zoom gears... The Strange gears in it now whine badly, but they are set up on the tight side of all clearances. What brand of gears would you guys suggest I get for the Chevelle (and yes, street gears) - or are they all about the same as long as the installation is done right?

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          • #6

            Re: Changing rear end gears.

            if you only jack up one wheel you need to turn it twice....once for that side, and once for the other side (which is not turning). If you have posi you'll turn both wheels one revolution.
            My fabulous web page

            "If it don't go, chrome it!" --Stroker McGurk

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            • #7

              Re: Changing rear end gears.

              What brand of gears would you guys suggest I get for the Chevelle (and yes, street gears) - or are they all about the same as long as the installation is done right?
              OEM GM Gears are far more superior than anything you'll get in the aftermarket for a street driven car........

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              • #8

                Re: Changing rear end gears.

                my 3.73 richmond gears "sing" but all the wear/clearances seem ok, my last set were a little
                noisey but my car has no carpet or sound deadener
                COBEY..... franklin, kansas

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                • #9

                  Re: Changing rear end gears.

                  my 3.73 richmond gears "sing" but all the wear/clearances seem ok, my last set were a little
                  noisey but my car has no carpet or sound deadener
                  I think most aftermarket gears use a straight cut gear, which will make noise........

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                  • #10

                    Re: Changing rear end gears.

                    OEM GM Gears are far more superior than anything you'll get in the aftermarket for a street driven car........
                    Are OE GM gears for a 12 bolt still available? I was just looking on Tom's Differentials website, and they don't carry gm gears, only some imported brand called "hoosier", US Gear (Strange), and Richmond.

                    Comment


                    • #11

                      Re: Changing rear end gears.

                      what size tire?

                      I have 4:10s in my truck, and love them because it's not like I'm setting land speed records with it; and for pulling a hill (loaded) the gear ratio is perfect for staying at 60 over most highway grades. Of course I also have approximately a 33" tire.
                      Last edited by SuperBuickGuy; April 13th, 2012, 10:00 PM.
                      It only takes one aweshit to erase a dozen attaboys

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                      • #12

                        Re: Changing rear end gears.

                        My tires are 235/75 r15.

                        Comment


                        • #13

                          Re: Changing rear end gears.

                          This is what I'm talking about how race gears don't hold up to street driving.......

                          Comment


                          • #14

                            Re: Changing rear end gears.

                            The best way to figure gear ratio is to do math. Your tire is roughly 28" in diameter.
                            You don't have to pull the cover to figure out the gear ratio. There are a couple methods to figure ratio - 1st, pick the rear tires off the ground (presuming open diff), put the transmission in neutral, and rotate a tire once counting the revolutions of the driveshaft... of course, that doesn't always work; If you have a tachometer - drive put your truck in "3", not overdrive, drive on the highway and observe the rpms. Without doing the math - 2.73 gears will be about 1600 at 60 mph, 3.08 is roughly 1900, 3.73 would be 2800 rpm.

                            In my experience, the best fuel economy with a carb'd motor driving mostly highway is (again, presuming stock electronic q-jet), 3.08 or 2.73. However, if you pull a trailer, carry large loads, do a lot of stop and go driving 3.73 is probably a better choice - and with overdrive you may not see any drop in mpg. If you mostly tow 4.10 is the better ratio. There are other benefits of the higher numeric gear is you have better accelleration, and you save your 700r4 (they have weak overdrive clutches - meaning they burn up under load without gear swap).

                            Anyway, back to math. Find the target mph you'll drive - in other words, city or highway - do the math to find what RPM you want to drive at (to a point, the lowest the rpm that you can drive at without moving the throttle for most of your driving). Figure out where you motor develops its power - then match the gear ratio to that "best" rpm.

                            A couple calculators
                            gear ratio calculators
                            http://www.rocky-road.com/calculator.html

                            free desktop dyno software

                            http://www.virtualengine2000.com/Products.htm
                            Last edited by SuperBuickGuy; April 14th, 2012, 07:47 AM.
                            It only takes one aweshit to erase a dozen attaboys

                            Comment


                            • #15

                              Re: Changing rear end gears.

                              This is what I'm talking about how race gears don't hold up to street driving.......


                              I've seen that happen on several sets of OEM GM gears. I think race gears usually are softer so they won't fatigue crack like that, but they will wear faster on the surfaces of the teeth.
                              My fabulous web page

                              "If it don't go, chrome it!" --Stroker McGurk

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                              • #16

                                Re: Changing rear end gears.

                                Back when a lot of cars I worked on had the old 9 1/2" rear, the pinion would crack just like that. Every week I was putting togather a new center section. The race gears have a higher nickel content that makes them softer, and in the catalogs they are usually labled. Driving them on the street for a long perriod of time will cause them to get hot and the lash will change. Lots of gear manufactures make street gears which hold up fine.
                                also boost will make the cam act smaller

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                                • #17

                                  Re: Changing rear end gears.

                                  I've seen that happen on several sets of OEM GM gears. I think race gears usually are softer so they won't fatigue crack like that, but they will wear faster on the surfaces of the teeth.
                                  The pinion there is a Moser unit which is made by US Gear and they are race gears....... I think the difference is the OEM gears that do that have 10's of thousands of miles on them, where these Moser gears only made it 10-15 thousand miles......

                                  Comment


                                  • #18

                                    Re: Changing rear end gears.

                                    Back when a lot of cars I worked on had the old 9 1/2" rear, the pinion would crack just like that. Every week I was putting togather a new center section. The race gears have a higher nickel content that makes them softer, and in the catalogs they are usually labled. Driving them on the street for a long perriod of time will cause them to get hot and the lash will change. Lots of gear manufactures make street gears which hold up fine.
                                    The thing that got me was that for the same gear ratio(3.73) the GM gears were physically bigger in size than the Moser gears where...... Put it this way the guy at the shop that redid the rear actually called the dealer to make sure they sent him the right gears because the size difference was so extreme.........

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