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Overdrive Trans

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by 77JimmyMan, Apr 7, 2002.

  1. 77JimmyMan

    77JimmyMan Registered Member

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    Ive decided to go with 4.10's for my 77' Jimmy. Now to make it more highway friendly, Id like to put in a 700r4 in place of my current th350. My truck has a np203 transfercase. Will the 700r4 bolt up to my np203? I see that the 700r4 came out in 82' and was standard equipment in everything 86' and up. What would be the best year to get one out of? If any one out there has done this conversion before, lend a fellow K5er a hand. Any info you can offer or links would be great. Also while I have you attention: While looking at gears to buy, some are listd as "thick" and cost about 50 bucks more. I currently have 3.08's. Would the "standard" gears work or would i need the "thick" ones. Thanks in advance. ~Mark~
     
  2. Can Can

    Can Can Pusher Man Staff Member Super Moderator

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    The later the model year, the better the 700r4. Mine was rebuilt in 1993 with all the updates to that point. You could also consider having a reputable local tranny shop build you one, that way you can get exactly what you want!!!/forums/images/icons/smile.gif

    Sorry, I can't help with the gearing or 203 questions, although I would imagine that the thick gears would be tougher and perhaps worth the extra 50 bones...........

    I'm glad to hear you're gettin rid of the 3.08s. I can't believe GM ever put that crappy ratio into a truck....../forums/images/icons/tongue.gif
     
  3. shoeless

    shoeless Registered Member

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    The thick gears are for the higher geared(numerically lower) carriers, then thin are for the lowered geared carriers. I'm not sure of the case break right off hand(i'm at work and not really supposed to be on the internet), but if you have 3.07's you will either need to get the thck gears, or a carrier for the lower gears. I'm pretty about 90% sure of that without any references at right here at hand. HTH
     
  4. Blazinaire

    Blazinaire 1/2 ton status

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    Absolutely correct. With your 3.07's you will need the thick gears because of your carrier. No sense in getting a new carrier unless you are getting a detroit locker because the factory high and low carriers are roughly the same strenghth as each other, just designed to take different ratios. Your carrier has the ring gear mounting face pushed more to the side to make room for the larger pinion gear on numerically lower gears. The ''thick'' gear will simply move the ring gear closer to the smaller pinion gear without shimming the carrier over so much. Does this make sense? Sorry for the lack of more appropriate terminolgy.
     
  5. 4X4HIGH

    4X4HIGH 1 ton status Premium Member GMOTM Winner

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    Your 203 will bolt up to the 700R4 but you will need a different length output shaft from Advanced Adapters. You will simply have a shop install the A/A shaft into the 700R4 and then just bolt your current trans case adapter and trans case to the tranny. You want to make sure you get a 1988 and later 700R4 as those have had all the problems fixed by then. What size tire are you going to run? If you are going with 35" tires I would recommend going with 4.56 gears. I am currently running 4.10's and 35" tires with the 700R4 and the tranny wants to "search" between 3rd and O/D. That is not a good thing it will cause the tranny to go south on you fairly quick. I just purchased my 4.56 gears and am about to make the change myself. If you are going to keep your existing carrier then you will need the thick gears like other people have said. The carrier break on the 12 bolt is 2.73 & down, low 3.07-3.42, high 3.73-4.56
     

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