COLORADO REAR END (swap) INFORMATION (pics added 1/3/16)

Discussion in '1947-1954' started by 52wasp, Dec 3, 2015.

  1. 52wasp

    52wasp Member

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    For those of you who are considering doing away with the torque tube and converting to an open driveline, the Colorado/Canyon/Isuzu "I" trucks gives us a rear-axle swap option in a 6-lug (6 on 5.50"), drum-brake-only package.

    There are different 3 different gear ratios offered, the Gear Ratio RPO codes are:
    3.42/1 code GU6
    3.73/1 code GT4
    4.10/1 code GT5

    All variants have a Hub Diameter of 3.960"(100.5mm) which is larger than the hub of the AD.
    Spring perches will need to be replaced for proper spacing and pinion angle.

    There are 2 different Ring Gear SIZES available as well:
    ___________________________________________________________________
    The AAM800 has an 8.0" ring gear, and 28 spline axles. ALL 4- and 5-cylinder trucks 2004-12 have this rear end, the rear cover looks like this:
    8.0inch.JPG
    The 8.0" has a relatively relatively straight plane from ring-gear bump to the right side, mine (an '04) has no fill-plug.

    VIN 8th digit 8 (2.8L L4) RPO LK5 2004-2006
    VIN 8th digit 9 (2.9L L4) RPO LLV 2007-2012
    VIN 8th digit 6 (3.5L L5) RPO L52 2004-2006
    VIN 8th digit E (3.7L L5) RPO LLR 2007-2012

    A 2WD, Z85 optioned rear has a WMS to WMS width of 60-3/4" (verified 12/09/15)
    I do not yet have a width for the 4WD.
    ___________________________________________________________________

    The AAM860 has an 8.6" ring gear, and 30 spline axles. Only V8 trucks 2009-12 have this rear, the rear cover looks like this:
    8.6inch.JPG
    The 8.6" ('09 shown) has a noticeable bump to clear the ring gear and curves back to flat on the right side, and a fill-plug.

    VIN 8th digit L (5.3L V8) code LH8 2009-2012
    A 2WD (they call it 4X2), Z71 optioned rear has a WMS to WMS width of 63-1/8" (verified 1/3/2016)

    From what I can gather, 2WD V8 trucks were only available in 3.73/1. 4WD V8 trucks appear to have all of the ratios available.

    Differential types
    G80 is a Gov-Lok (a type of positraction) (look it up for more info)
    if G80 is not mentioned, it is likely an open-differential.

    In a stock I6 AD, the VERY plentiful 8.0" should be fine. If you are planning an V8 swap, and a Colorado rear end, the 8.6" may be a better choice. As a bonus there is much more aftermarket support for the 8.6".

    All that VIN code/engine info and RPO code info listed above is to help you at the junkyard (or www.car-part.com for an online junkyard search).

    For reference, a car-part search today 12/3/15 showed only 5 8.6" rear ends, NATIONWIDE (rare until more V8 trucks make it to the salvage yard), but literally hundreds of 8.0"

    If you have added a Colorado rear to your AD, and it was a 4WD donor, please PM me the width, and I will add it to this post. Thank you.
     
    Last edited: Jan 3, 2016
  2. 1946AK

    1946AK Member

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    Sep 27, 2016
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    52,

    From all the research I have been able to do, the 2WD Z71 off-road option and the 4WD Rear axle assemblies are the same width. I haven't been able to verify 100% that this is so though.

    I have also been told that the Z71 2WD option also had the 8.6 inch ring gear. I'd love to verify this, but haven't been able to yet.


    FWIW, I'm looking to put an 8.6 into a '46 AK truck that has the engine, transmission, and torque tube rear axle from a '54 AD truck in it already. 5-Speed GM tremec and front disk upgrade planned as well.
     
  3. coilover

    coilover Member

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    I saw in person the Colorado/Canyon rear in Zig's truck and it look like it came from the factory. Eight inch rears regardless of the brand are dimensionally very close to each other and we have used 8" Ford rears in very large cars with fairly powerful V8's with no problems. Have not checked out a disc brake rear but if the bolt count is the same then it is very easy to drill a new pattern with the right bolt circle and use the right size lugs. A lot of the metric lug bolts used are too big to fit the factory wheels with the 7/16 lug bolt size. I really like the available 4.10 gear option as this is still the best with an overdrive. With a Borgwarner you get a 2.88:1 in OD, a 700R4 gives a 2.87, and the T5 has several OD ratios but the one we like is from the V8 Mustangs since most are the World Class units with a 33% OD giving a 2.75 final. With a track width in the 61-63" range I'd bet this rear swap is going to get very popular.
     
  4. Zig

    Zig Member

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    Thanks, Evan! I am mighty happy with the way it turned out, and if I ever did want to put stock wheels on it, I could. Doubt that will ever happen now, however.
     
  5. coilover

    coilover Member

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    Shop truck is a 2004 drum brake Colorado 4wd and it measures very close to 61 inches WMF to WMF. Has 400,000 miles and rear end has never been touched.
     

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  6. Zig

    Zig Member

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    Still loving the heck out of this rear end! Great swap!
     

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