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Gearing Problems?

Discussion in 'The Garage' started by wed68, May 20, 2005.

  1. wed68

    wed68 Registered Member

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    I have an 84 K5 with a fresh 350 and 700r4. It does not seem to have the power it should. Here are the specs that I am looking at, I believe that I need to regear, what do yall think?

    350 ci engine newly rebuilt and running well
    700r4 rebuilt and running well
    3.08 factory axles
    33 inch buckshots

    @ 75 mph I am turning 1500 rpm in od
    @ 70 mph I am turning 2200 rpm in 3rd

    When I go through the gears from a stop the rpms do not get above 2500 or so before the transmission shifts out.

    I think I need to go to 4.11 gears.

    Can I do this myself, I rebuilt the engine and am decent with a wrench?

    Thanks
    Bill
     
  2. dhcomp

    dhcomp 3/4 ton status Premium Member

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    yah, its a gearing problem. 3.08's are designed for like 27 or 28" tires i think ....or somethign like that


    In terms of regearing yourself, unlesss you have someone that has done it before to walk you through it, i'd say don't do it.

    But lets see what others have to say.....
     
  3. southernspeed

    southernspeed 1/2 ton status GMOTM Winner

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    If the trans is shifting at 2500 I'd suggest setting your t/v cable first. If the gearing was way too low(numerically) which it's not (but it is a bit), it would just hold the gear and not rev any higher, like when your going up a steep grade or towing and the trans is just holding a gear 'cause it can't make it's shift point.
    Set you r t/v cable and see what happens. If you don't know how to do it or why you should (critical on 700r4's) read the t/v 101 article at www.tvmadeez.com
     
  4. mountain4x4

    mountain4x4 Registered Member

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    If youre at full throttle it should be shifting higher in the RPM range. If you installed the tranny yourself, read up on TV function, you need to understand this to install a 700R4 properly.

    I just built a 14 bsf axle for my '90 Burban. I went with 4.56 gears to turn 33s, and its great. I live in the mountains of CO, if you drove on the flats all the time 4.11s would be better, but on my truck, 4.56 gearing worked out very well for all roads, although a good cruise speed on the highway seems to be no more than 75 mph or so, which is fine with me. The old 3.73s were pathetic with the weak tbi 350 motor.

    Diffs are easy work, just get the proper tools, and be patient with getting the setup right. Just like motors, attention to detail, measuring and doublechecking your clearances and torque specs, and youre good to go. My gear wholesaler sells me Yukon gears, they come with pretty good setup instructions and all the torque specs you need.
     
  5. Jonny-K5

    Jonny-K5 1/2 ton status

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    id go with 4.56, not 4.11 i had 4.56/700r4 with 33's, it was perfect.

    you shouldnt be in OD under 2000 rpm, it'll burn up the lockup clutch it the TQ. with your current combo, you probly have to wait til after 80mph to put it in OD.
     
  6. gone huntin

    gone huntin 1/2 ton status Premium Member

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    I just swapped to 4:10's from 3:73's due to 33's. Mine was kicking in and out of overdrive too much on the highway. I use my truck to tow a 16' trailer loaded with atvs alot and with the 4:10's it pulls it fine in O.D.
     
  7. u2slow

    u2slow 1/2 ton status

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    A pair of decent 3/4-ton axles with 3.73 or 4.10 gears is going to cost less than having it re-geared at a shop. As a bonus you get stronger parts and bigger brakes.

    Just my 2 cents.

    EDIT: A gree with the TV cable adjustment. IMO, if you hammer it from a stop, you should be able to pull 3000rpm before it shifts.
     
  8. Mad-Dog

    Mad-Dog 1/2 ton status

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    yah, thats a little lame for off roading, 4.11 gears will give you 2343 rpm at 70 mph.
    The SBC runs well between 1800 and 2800 at 70 mph depending on your cam choice
     
  9. wed68

    wed68 Registered Member

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    Thanks for all the replies I think I am going to go with 4.56 gearing, I am going to do a little more research before I install myself.

    Bill
     
  10. mountain4x4

    mountain4x4 Registered Member

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    Don't put $ into 1/2 ton rear axles. At least get a 6 lug 14 bsf. My 10 bolt started having problems with only very light offroad use, no abuse at all. With a little looking you can get a 14 bolt axle for about $100. I used an 8 lug axle, and got 8 lug front hubs, rotors and caliper mounting plates from the junkyard. Bigger brakes and a wider stance, but its tough if you just got new 15" 6 lug wheels and tires, in which case a hub conversion on the 14 bff, or a 6 lug 14 bsf might be the way to go.
     
  11. bigbadchev84

    bigbadchev84 1/2 ton status

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    i used to have the 305/700r4/208 3.08s and 33s, got some 3/4ton w/4.56s and some new 35s and did it wake up the motor it was tired but it never hesitated to smoke the tires
     

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