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GM B-Body Forum, 77-79 Caprice/Impala Forum

A forum for all the owners and enthusiasts of General Motors B-Bodies from 1965-1996, but dedicated to the owners of 1977-1979 Impalas and Caprices. Join up now!


    rear diff interchange

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    driver4274
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    Posts : 1
    Join date : 2014-05-25

    rear diff interchange

    Post  driver4274 on Fri Jun 06, 2014 10:37 pm

    what rear diffs physically interchange with my 79 caprice 2dr?  i've heard stories of people swapping out rears from 68 to 77 chevelles and montes--there is a slight difference in width but they bolt in and work--or so i'm told. i also have heard the same about monte ss rears.---what gives, can anybody help me decide before i buy a used rear i can't use?  my 79 has a 350 4bbl th350 trans and not sure what rear is in it.if it helps,the car is fully loaded except for pwr seats.---thanks in advance.-------by the way, great website--i just found it and registered.
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    Sweet Seventy9
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    Posts : 952
    Join date : 2013-11-03
    Location : Upstate NY

    Re: rear diff interchange

    Post  Sweet Seventy9 on Fri Jun 06, 2014 11:08 pm

    Welcome to the forum!

    With some cutting and welding, any rear can be made to fit.  The only direct bolt ins besides ones from other box B-bodies I'm aware of are from bubbles.  Here's what to look for:

    Axle Ratio     RPO Code Ring/Pinion Teeth Application
    2.56     GM8        41/16                Std. Roadmaster LT1
    2.73     GU2        41/15                Std. Caprice L99 (exc. 9C1)
    2.93     GW9/GU3 41/14                Std. Caprice LT1 (exc. 9C1), Opt. Roadmaster LT1
    3.08     GU4        40/13                Std. Caprice 9C1/LT1 (Police), Std. Impala SS
    3.23     GU5        42/13                Opt. Caprice L99, Std. Caprice 9C1/L99 (Police)
    3.42     GU6        41/12                Std. 91-93 Caprice 9C1/L05, Std. 94+ Fleetwood w/V4P
    3.73     GT4        41/11                Std. 91-92 Fleetwood Brougham w/V4P

    *V4P = 7,000 lb. trailer towing package... look for a hitch.

    Those all have posi rears and are direct bolt in.  They're 1" wider than what you have now and have the large GM bolt pattern, 5x5", so different wheels are required.

    I hope this helps.


    _________________
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    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
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    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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    solo79
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    Posts : 457
    Join date : 2013-02-06
    Location : Kentucky

    Re: rear diff interchange

    Post  solo79 on Sat Jun 07, 2014 9:49 am

    Awesome!! Another '79 2-door owner! Welcome aboard!

    Post pictures of your ride in the "Share with Us" section. We love pictures!


    _________________
    1979 Caprice Classic Carmine Metallic 2-door 350/TH350 -under slow frame off restoration!
    1982 Pontiac Trans Am Black T-Top 327/TH350 -Knight Rider KITT replica
    1989 Pontiac Firebird Black T-Top 305/700R4 -nice sunny day daily driver
    1997 Chevrolet Silverado Ext. Cab 3rd Door White Vortec 350/4L60E

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