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Dirvetrain Upgrade - 91 Sub V1500

Discussion in '1969-1972 K5 Blazer | Truck | Suburban' started by JungleBoy, Jun 18, 2001.

  1. JungleBoy

    JungleBoy 1/2 ton status

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    I know this a Gen1 Blazer forum, but a lot of gearheads post here, and I wanted to get your views on what I am planning with my 91 V1500 Suburban.
    I am taking the next steps to upgrade my V1500 (350,3.73 gears), which is in perfect mechanical shape, but does not have much "oomph". I have already lifted to truck 2" (ride considerations only), upgraded to hydroboost and installed a 28k GVW transmission cooler. The next steps, prior to engine upgrade are:

    1) Installation of 14 bolt FF rear and Dana 60 front axles with 4.10 ratios. I want rear disc brakes and Praise Dyno-Brake rotors and pads all around. I am considering running Michelin 265-16 LTX "E" LR M/S tires ,as well as keeping my 1/2 ton springs, to maintain a decent ride.

    2) Installation of TH400/Gear Vendors OD/NP205 setup to provide a strong, reliable transmission/transfer case combination.

    These are items I would like specific input on, and please advise if anything else occurs (unless you are going to question my sanity, that's already been done):

    1) Has anyone converted the rear drums on a 14 bolt FF to disc using GM parts from late model trucks? I would prefer this approach to the method using Cadillac rear calipers. Are the late model parts compatible with the earlier (mine's from an 86 1 ton). If so, part numbers?

    2) My 700R4/NP241C has an electronic speedometer output, while the TH400 is set up for a mechanical one. How can I get the TH400/NP205 to tell my speedo how fast I am going? Since I will be running about two tire sizes more and a gear size lower than stock, I will need re-calibration as well.

    3) Thoughts about the tire size/gear ratio combo for towing?

    Thanks in advance, as always.
    JB
     
  2. Rasberry

    Rasberry 1/2 ton status

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    Haven't had much experence with the 14 bolt, the 4:10 ratio would be a good cloice for those tires, but why are you replaceing the 700r4 with a 400. Both have a low first gear and the 700 has an overdrive,the 700 is just as stong as the 400. I don't see why you would make that swap.

    Rasberry 71' K/5 Blazer
    http://www.geocities.com/71blazer
     
  3. JungleBoy

    JungleBoy 1/2 ton status

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    Ras
    I think a 700R4 is just as strong as a TH350, IF you don't consider the weak link, the OD gearing. The TH400 with Gear Vendors OD is stronger than a 4L80E, according to my sources, drag racers here in Houston. I am going for durability.
    JB
     
  4. Triaged

    Triaged 1/2 ton status

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    I was going to ask why the th400 and gear vender O/D but you answered my question. On the spedo cable thing you would have to talk to gear vender on that because that is where your speed would be mesured from.

    '71 Blazer CST with alot of rust
     
  5. JungleBoy

    JungleBoy 1/2 ton status

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    ... you're right...
     
  6. Steve_Chin

    Steve_Chin 1/2 ton status

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    I think that all early GMs use a 2-pulse square wave output (not sure) for the speedo signal and the later ones use a 4-pulse sine wave output. In either case, Jaguars That Run in Livermore, CA has an adapter that will bolt onto the mechanical speedometer output of an earlier non-electronic transmission (M40, M38, SM465, etc.) and has a compatible output to your speedometer. All you will need to do from there is select and install the proper drive and driven gears for your transfer case and then screw the adapter onto them. If oyu can't find the proper gears, Stewart-Warner makes a device called a "drive ratio adapter" that you can use. I've got one on my Blazer that is a 1.2020:1 overdrive ratio because the gear setup in my transfer case is for a 3.73:1 truck. FWIW, GM also sells the drive ratio adapters (I bought a new one from GM less than a month ago for another car).
     

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