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Also New 87 K5 has 3.08 / How about highway..

Discussion in 'The Garage' started by stano, Feb 11, 2005.

  1. stano

    stano 1/2 ton status

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    We just got this truck, 1987 K5 and it does not have tags on it yet, so we have only drove it off the trailer and into the drive way. (4 wheeled through the ditch). We live in Iowa where it is flat but there is rolling hills. This truck was bought with the Idea of taking it back to Colorado moutains.

    New K5 has 3.08 gears and 700R4 at 55 miles an hour that is 1300 Rpms and at 65 that is 1500 Rpms. Using the calculator.

    The tires on the truck now are 31" and they measure 1" taller than the original spare in the back that measures 30"

    It seems to me that the Rpm may be to low for highway driving, but then I am used to the old K10 with 3.73 gears.

    Any info on how well the new 87 with 3.08s and overdrive works.

    Our 96 Suburban has 3.73 and 4L60E (I like that set up with vortex) This seems to work good for us.
     
  2. rjfguitar

    rjfguitar 3/4 ton status GMOTM Winner

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    You'll find the 3.08's to be sluggish. 1500 RPM's is not enough for it to work effeciently. 3.73's with 31's is not bad at all. I would see how you like it when you get it going but I imagine you will want to stay out of overdrive through the rockies out in Colorado. A gear swap to 4.10's would really be nice.
     
  3. stano

    stano 1/2 ton status

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    I love that feeling you get when the engine just seems like it is running on air and has power down the road.... For me that is about 2000 - 2100 in there some where. Does that hold true for the 350 V8 TBI of the 1987.


    If so I will look for that gearing.

    What gear would you recomend for using the overdrive. On flat ground. And what gear in the mountains.

    Yes I guess i could just stay out of overdrive in the moutains????? And use overdrive on flat ground.

    Any info on this.
     
  4. stano

    stano 1/2 ton status

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    I realize I need to drive this truck before I do anything with the gearing. I am just trying to get ideas, because swap meet season is coming up and I will keep my eyes open.

    This truck has a 10 bolt and will series 3 of the 3.08 carrier exchange to a 3.73 ring gear and pinion? Or even a 3.42
     
  5. HarryH3

    HarryH3 1 ton status Author

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    3.73's are farily easy to find. While 3.73's will fit onto your 3.08 carriers, it is usually less expensive to just swap out the entire axle. And it is certainly less hassle. But if you want to do the gear swap, I've got one 3.73 gear set that I'd part with for $25 plus shipping (heavy little buggers!) 3.73's are great with 31's, but if you plan to go with bigger tires later, then seriously consider going with even lower aftermarket gears. 4.10's are nice with 33's and the 700R4, while 4.56's or even 4.88's seem to be the sweet spot with 35's.

    Alot also depends on how you plan to use the truck. If it will just be a highway cruiser, then those 10-bolt axles will last quite a while. But if you plan serious off road use, with 35's or larger, then save yourself a lot of money and headaches by just swapping in a set of 3/4-ton axles now. :cool1: They're pretty easy to find with 4.10's from the factory and some even came with 4.56's. :)
     
  6. K5Jimmy

    K5Jimmy 1/2 ton status

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    My 89 had 3.08's when I got it and I had trouble with it not locking in OD. Wanted to downshift a lot....and the cruise wouldn't work at all in OD. That was with 235/75r15 (as in Bone stock)

    I actually drove it to Colorado like that to the Pikes Peak hill climb. It was a struggle to get it to do anything in OD.

    Then I swapped in 4.10's and 33's...works great! Road tripped back to the Race to the Clouds, and it was totally different. OD works like it should, cruise works.

    Been to Talledega (6 times), Richmond, Bristol (4 times), Darlington (4 times), Martinsville (twice), Dover with nary a whimper.

    I tow my boat all over creation, and hit muddy trails occasionally.

    BFG AT's on 8" Rally's for everyday....and BFG Muds on 10" Rally's for play or if I know I'm gonna have to rough the boat into someplace.
     
  7. sandawgk5

    sandawgk5 3/4 ton status

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    I have the exact setup that you do and everybody is right 3.08 suck. I actually get better fuel mileage in drive rather than OD because the engine is lugging so much in OD. It sounds wierd but it is true. Then again I live in East County in San Diego and there is not very much "flat" land here.:D
     

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