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Changing out a 411 rear end

Discussion in 'Chevy Trucks' started by Wally3128, Jul 22, 2002.

  1. Wally3128

    Wally3128 Junior Member
    Messages: 28

    Just picked up a '85 Chevy 3/4 ton, 350 4bbl. Former owner says 411 rear end. I am not sure what that means, but... it sure has a lot more gitty-up, than the old '81 1/2ton, w/305.And at 6mpg and redlining the engine at 65 mph, I am sure it has to do somthing with the gearing. (dah!!!) I don't need all that pulling power. The most I would pull is a small boat trailer. I would hope to do better than 6 mph. I need a little more than 65 without blowing up that old 350!
    What type of gear can replace what is in there and can it be done with out too much trouble?
    Thank you
  2. karl klein

    karl klein Senior Member
    Messages: 557

    you should beable to replace it with a 3:73 and get about 11 mpg and 70mph.
  3. Wally3128

    Wally3128 Junior Member
    Messages: 28

    Thanks Karl

    Thanks Karl,
    Is is a big prosses to change it out? Is it better to get used parts or spend more now??
  4. 75

    75 PlowSite.com Addict
    Messages: 1,382

    "411" refers to the ratio betwen the rear end gears, and is more correctly stated as "4.11 : 1" (Did Chevy have 4.11 : 1 axles, or is it 4:10 : 1?) meaning that the driveshaft will turn 4.11 times for every time the rear wheels turn once. Lots of "grunt" for pulling but as you pointed out, the engine is turning pretty fast to go 65 mph.

    The 3.73 : 1 gears that Karl mentions will have the driveshaft turning 3.73 times for every time the rear wheels turn once, which will cut down a little bit of the pulling grunt but not enough to be a problem in your application.

    Your best bet, IMO, is to change the entire rear axle as a unit rather than get into swapping the gear sets. Look for an axle from a similar 3/4 ton truck (or a complete donor truck - sometimes it's cheaper to get the whole truck and gut it yourself) and it should be a straightforward bolt up conversion. Do yourself a favour and get "brand new everything" for hardware (U-bolts, nuts, washers etc) and don't waste time trying to undo the rusty old bolts: Hack 'em with a torch and toss 'em.
  5. karl klein

    karl klein Senior Member
    Messages: 557

    it is a big project and would not recommend change the guts yourself if you wan't to just replace the guts get it done at a axle shop.there is just to much complecation with doing it yourself. as 75 was saying it might just be cheaper to replace the hole thing