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700r4, 37" tires & 3.08s

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by 78Jimmyish, Aug 15, 2001.

  1. 78Jimmyish

    78Jimmyish 1/2 ton status

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    700r4, 37\" tires & 3.08s

    With the 700r4, I'm running 37" tires with what I'm pretty sure are 3.08's. I really can't afford a gear change or an aftermarket cooler right now. Is it safe to drive with this setup or am I killing my tranny quick. I'd say I'll be able to replace the gears in 6 months or so, but am I gonna kill the tranny before then? I'm just wondering how much extra heat is actually produced.
     
  2. 86K5TrailBlazer

    86K5TrailBlazer 1/2 ton status

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    Re: 700r4, 37\" tires & 3.08s

    yeah I'd say your gonna kill something if not yours self if anything someting is gonna give that a "tall" order for your current setup. I good tranny cooler is worth the $100 bucks that you can spend eaasy install and save you big bucks down the line. How is you rig performing now. Does it seem like it takes a lot to get going? I'm just happy with 4.56 and 36"
     
  3. 78Jimmyish

    78Jimmyish 1/2 ton status

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    Re: 700r4, 37\" tires & 3.08s

    I doesn't perform too badly. I've definately lost some power since I went from 31's to 37's, but that's to be expected. Is there a quick way to check my gear ratio without counting teeth? I'm assuming that they're stock, but I don't know for sure. I just don't want to fry my tranny.
     
  4. Mreetz

    Mreetz 1/2 ton status

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    Re: 700r4, 37\" tires & 3.08s

    Do you still have the original factory order sheet on the drivers side wheel well under the hood? I'm running 35s on 3.73s and have really like it so far.

    1984 K-5
    4" lift
    35x12.5 MTs
    buildin a 400 for it, any info greatly appreciated
     
  5. WakeBoard&4X4er

    WakeBoard&4X4er 1/2 ton status

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    Re: 700r4, 37\" tires & 3.08s

    If you are not doing any wheeling or pulling or long drives you should be OK. If you can add a temp guage to your trany and watch it all the time. I am running 33 and 3.42s , but i have a big as$ trannt cooler and water temps never get over 200, any more that is
     
  6. Leadfoot

    Leadfoot 1/2 ton status Premium Member

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    Re: 700r4, 37\" tires & 3.08s

    It's like a game of Roulette. Your tranny MAY last until your gear change, but the chances/odds are stacked against that. That combination can kill a 700 quick. If you do decide to drive it, try to drive sensibly (no towing or overloading). Give Jegs or Summit a call. They have a 24,000 GVW tranny cooler that takes an hour to install (including removing grill) for under $70 and could buy you alot more time on the tranny. Heat is the biggest killer of trannys, especially a 700.

    If you didn't build it yourself, how can you call it yours.......?
     
  7. 78Jimmyish

    78Jimmyish 1/2 ton status

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    Re: 700r4, 37\" tires & 3.08s

    No, the only thing on my drivers side wheel well is a sheet that tells me how to change my tires..great... Most of the time it's a daily driver (to and from work..still uninspected) but this fall I'm taking it to PA (from RI - about 6 hour drive) to go wheeling. Hopefully before I leave, I'll at least be able to afford the tranny temp gauge and cooler. Are the coolers pretty quick to install?
     
  8. 78Jimmyish

    78Jimmyish 1/2 ton status

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    Re: 700r4, 37\" tires & 3.08s

    Well, hell, I just looked at Jegs website, and the B&M tranny cooler is only $42.99 and says it's a quick install. The cooler was cheaper than the temp gauges! So that'll definately happen before I take my trip this fall. B&M tranny cooler 16000 GVW okay? Anyone know anything about brand reliability?
     
  9. Leadfoot

    Leadfoot 1/2 ton status Premium Member

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    Re: 700r4, 37\" tires & 3.08s

    B&M is one of the better coolers out there. 16,000 GVW is better than nothing, but call and ask about their 24,000 GVW "Super Cooler" as opposed to their regular coolers (not sure if that's the name but its the flat tube design which is more efficient). The 24,000 GVW "Super Cooler" is the largest one with an install kit).

    If you didn't build it yourself, how can you call it yours.......?
     
  10. 78Jimmyish

    78Jimmyish 1/2 ton status

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    Re: 700r4, 37\" tires & 3.08s

    Cool, actually the one that I looked at is the supercooler. They've got the 16000GVW for $42.99 and the 24000GVW for $49.99. Should I just spend the extra 8 bucks and get the bigger one? Or is that overkill?
     
  11. 6.2Blazer

    6.2Blazer 1/2 ton status

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    Re: 700r4, 37\" tires & 3.08s

    I would recommend always driving with the tranny shifted into Drive with the 3.08 gear/37" tire combo. As has already been said, heat buildup is what kills and automatic transmission. When the gears and tire size are mismatched like yours, then the tranny would have to shift into and out of overdrive all of the time in order to maintain speed, and this constant shifting generates a lot of heat. Also when taking off from a stop the torque converter has to slip more in order to get the vehicle moving, and that really generates the heat.

    Definitely spend the $50 or so and buy a tranny cooler. It will save you a lot more in the long run.
     
  12. 78Jimmyish

    78Jimmyish 1/2 ton status

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    Re: 700r4, 37\" tires & 3.08s

    Yeah, I never drive in overdrive with it. It's still uninspected, so I don't take it out on the highway at all. Only in town speeds, but it's the takeoffs from a stop that I was worried about. I'm ordering the tranny cooler pretty soon, I guess I'll just keep my fingers crossed and go easy on the throttle till it gets here. The nice thing is, I only drive it about 10 mins to work, it sits for 8-10 hours, then I drive it 10 mins home, and that's as far as it goes for right now. So I don't imagine the tranny gets too much chance to get hot.

    As a side note, I must say, I've gotten more useful advice since I joined this forum and started reading everything I could than I did the whole time I've owned the truck before this. Thanks for the help guys.
     
  13. rampage

    rampage 1/2 ton status

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    Re: 700r4, 37\" tires & 3.08s

    The easiest way to determine your ratio without removing the diff cover and counting teeth is to raise the rear and rotate a tire one revolution and count how many times the driveshaft turns. Put a mark on the driveshaft with a piece of chalk so it's easier to determine how many times it rotates (plus the partial revolution). I'm not sure if you need to have one wheel immobile or not, maybe someone else can clear that up.
     
  14. CaptCrunch

    CaptCrunch 1/2 ton status

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    Re: 700r4, 37\" tires & 3.08s

    Well considering my experience w/ 700's... so you don't have money for a cooler, how the heck are you gonna afford a 700R4 tranny? You are asking for MAJOR trouble... I personally wouldn't even drive it... I have 4.10's w/ 35's and have worries w/ the tranny so moving up to 4.56's. If you have to drive it get the biggest cooler you can get and keep it in 3rd... OD will fry quicker then anything else. Then go axle hunting... or change gears... bust pout the credit if you have to or you will probably shell out more for a tranny. 3.08's and 31" tires doesn't even tend to live very long. That's my $.02

    -Mikey
    1987 Chevy K5 Blazer- 350 TBI
    <a target="_blank" href=http://www.geocities.com/milnerlives_2000/blazer.htm>http://www.geocities.com/milnerlives_2000/blazer.htm</a>
     
  15. 84_Chevy_K10

    84_Chevy_K10 Banned

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    Re: 700r4, 37\" tires & 3.08s

    I wouldn't even shift out of 2nd gear. I drove my truck with that combo about two weeks, and I'd never do it again.

    I suggest you go to the junkyard and find a K20 and swap axles in NOW. You're going to destroy your tranny in short order if you don't. It's already almost as old as I am and halfway worn out.

    I have the 24,000 lb. cooler. There's no such thing as too much tranny cooler. If I wasn't swapping my 700R4 out for an SM 465, I'd get TWO of them.

    I would really like to tell you that everything's going to be great, but that gear setup and tire size is killing your tranny and working your engine to death. If you can't afford to have a big 4x4 and everything that comes with it, I regret to tell you that you got into the wrong ball game when you lifted your truck and installed those tires.

    And when I had those gears if I'd have taken my truck off-road, 4 high would be totally useless. Gears aren't just for the road, they're for the trail too, and you don't have gears that are good for either trail or road. In fact, even the 31" tires on there were too big for 3.08 gears.

    Tim
    '84 Chevy K10, lifted, loud, fast, and 3/4 ton axles
     
  16. loudandproud

    loudandproud 1/2 ton status

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    Re: 700r4, 37\" tires & 3.08s

    What axels and gears does a K20 have on it???

    <font color=red>_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _</font color=red>
    <font color=blue>'90 Jimmy</font color=blue>

    <a target="_blank" href=http://geocities.com/moose_53_99>geocities.com/moose_53_99</a>
     
  17. 78Jimmyish

    78Jimmyish 1/2 ton status

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    Re: 700r4, 37\" tires & 3.08s

    Whew..where to begin.
    First, thanks for all the tips 'n' tactics.
    Second. I guess the first thing I need to do tomorrow is throw the thing up on a forklift and find out exactly what my gear ratio is. I was hoping for something simple like that. See, I have a 700r4 tranny (was on the truck when I bought it.), a D44 front and a 12 bolt rear. From what I've read, I didn't think that the 700r4 was stock in 1978 (my Jimmy's year) Since the tranny's been changed, and I couldn't find a tag on the diffs, I wasn't sure what the gear ratio was - whether it was stock or not. But anywho, I'll find that out for sure tomorrow.
    So that leads me to my next question, if I spend the $50 on a tranny cooler, will that solve the problem of tranny damage due to sh*tty gear ratio? I know it won't overheat with the cooler but is there another way that the gear ratio could hurt the tranny besides overheating? If not, then I should be able to get by, right? If I can avoid spending the $800 or so dollars for a gear change right now, I'd like to put it off for six months or so. But at the same time, I do need the truck (I use it for work.) so...
    Let me know, because if driving my truck without changing the gears (even if I put in a cooler) is going to do daamge to it, then I'll have to suck $$ out of the savings acct. and do it.
    Thx again.
     
  18. CaptCrunch

    CaptCrunch 1/2 ton status

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    Re: 700r4, 37\" tires & 3.08s

    First thing forget the forklift man... just pull off the cover (yeah I know it is a smelly stinky job but hey it is cheap (rtv and 3 qt's of 80/90) and is the best way to find out). Count the teeth on the pinion and on the ring... mark them w/ some paint if you need to to keep track. then divide. It will give you the ratio. I would really say find a cheap axle to swap in... a 14B or even a 12B w/ 4.10 would be much better... then at least your tranny should be safe WITH a cooler. The man problem comes from the torque converter not locking up because the rpms are too low... even w/ 4.10's you may want to keep it in D all the time except over 70 or so. A cooler won't cool it enough if the rpms are lugging plus you'll eat gas like a mofo. So that alone will cost you big bucks... One note, you will have to wait to get matching gears or front and rear axles before you can use 4wd. 4.56's or 4.88's is probably what you will want w/ that combo IMO. Good luck [​IMG]

    -Mikey
    1987 Chevy K5 Blazer- 350 TBI
    <a target="_blank" href=http://www.geocities.com/milnerlives_2000/blazer.htm>http://www.geocities.com/milnerlives_2000/blazer.htm</a>
     
  19. RESTORE89

    RESTORE89 1/2 ton status

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    Re: 700r4, 37\" tires & 3.08s

    [​IMG] i agree way to much tire
    try to find a cheap used rear axle from a boneyard, and in about 2 hours you can change it out in the driveway. when i first bought the rear end was bad and i bought a used 10 bolt and it had 308's and 33-12.50's and you could not even use od at 75 on the highway, and i swapped to 411's.
    also you do not have to do both diffs at the same time, but like was said you just cant use 4 wheel drive
    i would definetly suggest doing something fast, cause i just had a 700 rebuilt and it was $1k

    It needs a bigger motor.
    what's in it now?
    doen't matter it NEEDS A BIGGER MOTOR
    89 350tbi/700r4h/np208/4.11's
     
  20. 78Jimmyish

    78Jimmyish 1/2 ton status

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    Re: 700r4, 37\" tires & 3.08s

    What comes stock in a 3/4 ton. My buddy's got an 87 k20 that he wants to get rid of. I know it's got a 14bolt in the back, dunno what's in the front. But what gears come stock in it? That might be an option for me. I'lll ask him if he'll part it out instead of selling it.
    So you're saying that even with a 24000 GVW cooler, it's still gonna get too hot? Even just on a ten minute drive to work, or should I just not take it off-road or highway? I'm gonna have to talk to the wife now about changing the gears (shiver).
     

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