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  1. #11
    stephan's Avatar
    Join Date
    Sep 2010
    Far West, Oregon USA,
    Blog Entries


    At 3,000 RPMs @ 55 mph with 29 1/2 inch diameter tires that would compute to 4:75 gears, but I doubt your tires are that short. Go measure the dia of one of them & post back here with exact RPMs @ 60 mph & with your tire dia & I can give you a more exact ratio..
    1988 Chevy C-3500 2wd (no pic)
    350 c.i. 5.7 L Stock Block, 4 Bolt Mains
    L-31 Vortec Heads, Edelbrock Cam & Intake,
    Holley 650, Flowtech Headers, Magnaflow exh.
    Jet Trans 700R4, B&M Ratchet, 4:10 gears,
    3" susp. lift kit "shadetree"
    No rev limiter, No speed limiter lol

  2. #12
    Sr. Apprentice
    Join Date
    Dec 2010
    25 Mi. E. of Kingman, AZ.


    I found some RPO codes that might help. GK9=4.63, GS6=4.56, HF8=4.83. I don't know if these were all available in pickups. My 1990 C2500 was built as a camper special and came with a 4.10 & a TH400 3 speed. Also if you check your speedo accuracy with a GPS or a measured mile and it's correct the truck probably came with those gears. It's a pretty good project to recalibrate those early electronic speedos.

    Good luck with your project.
    Last edited by Taddpole; 01-24-2011 at 02:21 PM.

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