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overdrive/underdrive switch

Discussion in 'Chevy Trucks' started by home rescue, Jan 15, 2005.

  1. home rescue

    home rescue Member
    from wv
    Messages: 94

    Looking at a 1990 3500 4x4 454 with turbo 400 tranny, anyway in the dash looks like an after market switch that says overdrive/underdrive. Owner doesn't know what its for or if it works off the tranny or transfer case, anybody know what this switch is for or is it any good to have on truck. I have never seen this before.
     
  2. wfd44

    wfd44 Senior Member
    from Maine
    Messages: 369

    Assuming it is actually a turbo 400 (they were still available in 1990), there is no factory overdrive on this truck. It could have a gear vendors (or other) aftermarket overdrive box installed behind the transmission to make up for the lack of overdrive in a turbo 400 or the trans could have been changed and someone came up with this as a way to access O/D in a truck originally equipped with a 3 speed. Only way to know is to crawl under and see if the TH400 is till at home and/or if an aftermarket overdrive has been installed. If it has an overdrive (of either type) this will benefit you with improved fuel economy.
     
  3. home rescue

    home rescue Member
    from wv
    Messages: 94

    Actually now that you mention gear vendor I pretty sure that was the name on the switch, so this is a good set up, right.
     
  4. wfd44

    wfd44 Senior Member
    from Maine
    Messages: 369

    Yes, Gear Vendors O/D unit is a top shelf unit. You can actually use it as a splitter giving you 6 forward gears with a TH 400. Pretty much a bulletproof way to have O/D in a pre-4L80E one ton.
     
  5. derekbroerse

    derekbroerse 2000 Club Member
    Messages: 2,377

    Have a peek at:

    http://www.gearvendors.com/

    The only thing I don't like about the gear vendor's design is that you cannot use overdrive in 4wd as it is bolted on behind the transfer case. This, for me, would be a PITA running up the highway to the cottage where road conditions change ie: some stretches of hwy require 4wd, others are plowed and salted but you don't drop your speed enough to shift the transfercase...

    Other than that, it is brutally strong and a very effective unit. It's worth about $2500US+ if memory serves...
     
  6. home rescue

    home rescue Member
    from wv
    Messages: 94

    thanks for the help, quess it makes the truck worth a few more bucks then.
     
  7. home rescue

    home rescue Member
    from wv
    Messages: 94

    Got the truck :redbounce suppose to pick it up evening of 1-20
     
  8. derekbroerse

    derekbroerse 2000 Club Member
    Messages: 2,377

    Excellent. I hope it works out for you. Be sure to post us some photos once you've gotten it home!
     
  9. PackRat

    PackRat Member
    from Kansas
    Messages: 47

    Devil's Advocate

    Before you cut him a check, stick your head under it, and make sure it's there. I'd be mad as a wet hen, to get on the road, and find that it's just a switch, left for looks.
    Might just net you a few bux, toward future improvements.
     
  10. derekbroerse

    derekbroerse 2000 Club Member
    Messages: 2,377

    Very good point!

    I just made the assumption that he did that, and preferably tested the unit!
     
  11. home rescue

    home rescue Member
    from wv
    Messages: 94

    I think the truck was probably a steal anyway with out it though, hate to say it but only paid 3500 and it is excellent shape. Flat bed doesn't even have a scratch, the guy had it set up to pull a gooseneck type trailer, but thanks for metioning the tip.