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Transmission Options

Discussion in '1969-1972 K5 Blazer | Truck | Suburban' started by 72lowblazer, Jun 27, 2001.

  1. 72lowblazer

    72lowblazer Registered Member

    Mar 8, 2001
    Likes Received:
    Annville, PA
    Hi all,

    I am thinking about fixing up my one 72 k5 instead of selling it. It has a 307 and 3spd. I would like to know what options are available in automatic and manual. I am not sure wich route I want to go right now. If I go with auto, I am going to put in a B&M shifter. Any help would be appreciated. I am not sure right now if I am going to upgrade the engine or not.

    Thanks Jerr

    72 k5 Blazer 307/3pd on tree, posi rear (one of my projects
    69 Chevy Pickup currently being put together
  2. Rasberry

    Rasberry 1/2 ton status

    Mar 30, 2001
    Likes Received:
    Orlando, Fl
    I haven't dipped into many manual tranny's. But as far as automatics go. Your looking a about three different upgrades.

    The Th350 which was used for the 69-72 blazer, is pretty sturdy but if you run big tires and a lot of horse I wouldn't recommend it but seems perfect for your case.

    Then there's the Th400 which has a lower first gear than the 350 and is stronger. Its a few inchs longer than the th350 so you'll have to move some mounts. Either engine or t-case crossmember.

    Your next bet would be the 700r4 w/ over drive. Has a low first gear and is strong as the 400 as long as you get a newer model. The early model 700's had a few flaws they worked out over the years.

    As far as money and time goes your easiest automatic upgrade would be to the TH350. Get a nice tranny cooler and it should last you a long time.

    Rasberry 71' K/5 Blazer
    <A target="_blank" HREF=http://www.geocities.com/71blazer>http://www.geocities.com/71blazer</A>
  3. Steve_Chin

    Steve_Chin 1/2 ton status

    Mar 6, 2001
    Likes Received:
    Foster City, CA, USA
    Manual transmission options (I am assuming your Blazer is a 4x4):

    New Venture 5600 - 6 speed, ultra-tough, shifts like greased lightning, VERY expensive and you have to fabricate everything to mount the thing up to the transfer case. Not a good option unless your fabrication skills are way above average. I won't post much more about this since it isn't a true bolt-on.

    New Venture 4500 - 5 speed transmission. Early GM models had a really screw-ball gearset in them, but the rock crawlers love that version because the first gear is very low. '95-'99 GM versions of the transmission have the same gear ratios as the Dodge versions and a non-synchronized reverse gear (can be modified to put in a Dodge synchronized reverse gear). Late GM versions ('00-present) include the synchronized reverse gear. Kind of expensive (plan on about $3200 for the conversion parts including the transmission, plus about $140 in special lubricant). It requires a special synthetic lubricant that is from Castrol (SynTorq - do not confuse with Syntec, because they are wildly different in formulation). Available only from GM and Chrysler dealers at a cost of about $20-$40 per quart. Supply is currently a little constrained. You must modify the transmission cover (aka dog house) by moving the shifter openings back toward the console.

    Muncie SM465 - The manual transmission of choice for decades because it's tough as nails (the NV4500 is just as tough if not tougher). Fairly plentiful in the J-yards and all of the parts to mount the thing are factory parts (no aftermarket conversion parts needed). No synchronizer in first or reverse gears. Shifting is vague at best compared to the New Venture boxes, even on a well rebuilt box. Ultra-low 6.43:1 first gear ratio that makes it the darling of the rock-crawler crowd. Cast iron case and top plate that make it heavier than all get-out.

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