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    Changing the rear gears

    Junior Member
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    Changing the rear gears Empty Changing the rear gears

    Post  hugh.stone.rocket on Sat Jan 23, 2016 2:21 am

    I want to run 3.73's. Can I just change the ring, pinion and crush seal? Or do I need a posi locker assy too?

    She came form the factory with a 350 mated to a 200 metric trans, so I believe the gears are 2.73...

    Thanks in advance,
    Hugh G Rox
    Sweet Seventy9
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    Changing the rear gears Empty Re: Changing the rear gears

    Post  Sweet Seventy9 on Sat Jan 23, 2016 10:55 am

    Why would you go through all the work changing gears when you have an open carrier?  (non-posi)  It sort of doesn't make sense and defeats the purpose of installing a lower gear.

    Depending on the manufacturer of the gear set you purchase, you might have to replace the carrier anyway.  The thickness of the ring gear is much different between the 2.73 and 3.73.  Talk to the gear manufacturers reps, they should know all the little details like that.

    Beware! If you've never done a GM gear swap, it's not as easy as just swapping out parts.  I strongly urge you to get it professionally done or you might wind up breaking it.

    You're probably better off simply changing out the whole rear end.  It'll be bigger (8.5 inch), stronger, it's faster to change, easier to change, most likely will have disc brakes, and it removes any doubt to if you got the pinion depth set correctly.  1990s Caddys had as low as a 3.73 gear.  Someplace on here I have a list of what cars have which gears along with the RPO/SPID codes.  Stick with sedan rear ends.  Wagon rears won't interchange.

    1977 Impala Landau x1
    1977 Caprice Coupe x3, Sedan x3
    1978 Impala Landau x1, Sedan x2, Station Wagon x1
    1978 Caprice Landau x1, Caprice Coupe x2
    1979 Impala Coupe x2
    1979 Caprice Coupe x7, Landau x4, Estate Wagon x1
    1981 Impala Coupe x1
    1983 Impala Sedan x1
    1983 Caprice Sedan x1
    1984 Caprice Landau x1, Sedan x1
    1985 Caprice Coupe x1, Landau x3, Sedan x4
    1986 Caprice Coupe x1, Landau x1
    1987 Caprice Landau x1, Sedan x4
    1989 Caprice Sedan 9C1 x4
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    Changing the rear gears Empty Re: Changing the rear gears

    Post  GM B-Body Forum on Sat Jan 23, 2016 11:13 am

    Even if you just changed the gears you would still have to shim the pinion, more than likely the factory shims wont be correct, if your not changing the carrier then you can reuse the carrier shims. But you will have to check for backlash and ring and pinion marking engagement. Youll also have to purchase a beam style inch foot pounds torque "wrench" to measure the preload on the pinion bearing from crushing the crush sleeve. I know on the 8.5 its around 26 in lbs. Purchase a few extra crush sleeves, its sometimes hard to get it right the first time. If you purchase a master rebuild kit it will come with all the bearings, shims, crush sleeve and usually some marking compound. But as stated above, its alot of work if your just going to change gears on an open carrier, might as well change it while you are there.

    1979 Caprice Sport Coupe, 400hp Vortec 350, Th350, GM 8.5 w/disc brakes, 3.90 gears Detroit Truetrac, 2.5" stainless duals w/ x-pipe, Dynomax race bullets.
    1984 Caprice Sedan, 305 motor, 700r4
    1978 Caprice Sedan, 305 motor, th350
    1993 L99 Caprice, 4.3 v8, 4l60 trans
    1972 Ford F-100, 302 windsor, c4 trans
    2001 BMW E46 330i, 3.0L
    Changing the rear gears 20150410
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    Changing the rear gears Empty Re: Changing the rear gears

    Post  Kit1078 on Tue Feb 02, 2016 10:04 pm

    You have to pay careful attention to the carrier when you change gears in your rear end. Anything 2.73 and up should be a '3-series' carrier, below 2.73 and you'll have a '2-series' carrier. The difference is the mounting flange for the ring gear on the 2 series is moved further toward the bearing to clear the larger pinion gear. Most GM positractions are 3 series, from what I've seen.

    anyhow, yeah, if you haven't set up a ring an pinion before, you might want to take it to a shop, unless you know someone who has all the proper micrometers and feel like spending an entire weekend making sure it's right.

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