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700R4 OD vs Drive

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by BettyBurb, Feb 16, 2003.

  1. BettyBurb

    BettyBurb Registered Member

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    After getting various advice from various sources, my conclusion is not to tow in OD, and to use Drive unless actually on the highway. So I started using Drive instead of OD for everyday around town driving.

    I now notice that the downshift into 1st is very harsh compared to the downshift in OD. Is there a problem or is this normal ???

    If this is normal why the difference.

    I hope I am doing the right thing by using Drive instead of OD.
     
  2. Chevit

    Chevit 1/2 ton status

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    BIG NO NO TO TOW IN OD /forums/images/graemlins/eek.gif /forums/images/graemlins/eek.gif /forums/images/graemlins/eek.gif /forums/images/graemlins/eek.gifThe only time I use OD id when I am way out of town...
     
  3. R72K5

    R72K5 Banned

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    some info: staying out of 4th gearis highly reccommended if are towingor hauling weight, especially if are driving hilly terrain,

    driving in town willprobably never allow you to get going fast enough to even get to 4th gear upshift, noneed for that range unless are going fast enough anyways

    there is a cause for harsh return to first range, but i forget what it is, i read causeof that on thirdgen.org, but i cant remember what it is now.

    good luck
     
  4. Can Can

    Can Can Pusher Man Staff Member Super Moderator

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    The advantage of staying in D at city speeds is that your tranny won't gear hunt. Try doing this experiment:

    Get the truck up to about 40 in OD. Now let off the pedal slightly. You will feel the tranny drop into OD. Now gently apply pressure to the pedal. You should feel it pop back into D.

    If you're driving around town in OD, this up and down shifting could happen hundreds of times an hour. Every time you let off the pedal, the tranny will choose OD, and every time you give it a little gas, the tranny will go back into D.

    Everyone knows that excessive heat is bad for a tranny(especially a 700), and it is also common knowledge that shifting is a cause of heat buildup, so by forcing the tranny to gear hunt you're actually causing the tranny to run hotter than it normally would.

    There is a reason that 1-2 shifts are harsher in D, but I can't recall why. I'm sure somebody will come along and answer the question for you. FWIW, my 700 does it too.
     
  5. jc71355

    jc71355 1/2 ton status

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    Mine has done that since I got it rebuilt, I just assumed it was the shift kit /forums/images/graemlins/confused.gif

    I drive just about all the time in D, the only time I drive in OD is if I have a GOOD tail wind and I'm gonna be on the highway for a while. I actually get better gas mileage running in D with my present 3.42's. I'm looking forward to getting my 4.56's so I can run in OD more.
     
  6. sled_dog

    sled_dog 1 ton status

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    I always smack someone who is driving a 700R4 equiped vehicle and puts it in OD for normal driving. Then I explain the cheif reason that those trannies die so often is that people drive around in OD all the time and it gear hunts like that. They usually stare at me and don't get it then put it in D. Then the next time we get back in they put it in OD again and I just say fine its your money.
     
  7. DesertDueler

    DesertDueler 1/2 ton status

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    I tow in OD all the time. But the heaviest thing I tow in my racecar and trailer, and that is about 5200 lbs. It helps that I have a built motor, 4.56 gears, and 35s for towing (38.5s for wheeling). If I dont kick into OD, with the 4.56s, I cant go over 50 mph without winding the motor up to high. I tow in OD at about 2500 rpms. It is in the power band, so it doesnt lug down, and going uphill, mine doesnt downshift. But that is because the motor has enough power. (aprox 325 hp)

    Dan /forums/images/graemlins/burb.gif
     
  8. Can Can

    Can Can Pusher Man Staff Member Super Moderator

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    Your case is a lot different- a lot of these comments are directed towards stock rigs. On a stock rig, you'll only be turning about 1600-1800 RPMs in OD at 55-60 MPH. The torque output at 1800 RPM in OD isn't enough to keep it from downshifting to D on anything less than level ground.

    I know that YOU know this, but I thought I would clarify your point for others who may not understand the concept.
     
  9. sled_dog

    sled_dog 1 ton status

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    kind of jumping off topic but nice 69, have one sitting in the driveway as well(dad's /forums/images/graemlins/frown.gif). I want that car bad have since he got it.
     
  10. georgiared84

    georgiared84 1/2 ton status

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    Mine shifts harder between 1st and second when it's in Drive versus overdrive too. It's newly rebuilt with all performance parts and upgrades. Anyone know why this is?
     
  11. DesertDueler

    DesertDueler 1/2 ton status

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    I agree, thats why I put in there that I have gears, and a built motor. In stock form it is a toss up on towing in OD. It is a big no if you put bigger tires on, and have stock gears.

    BTW thanks Alan, I am the second, and last owner of my firebird /forums/images/graemlins/grin.gif

    Dan /forums/images/graemlins/burb.gif
     
  12. caryhenry

    caryhenry Registered Member

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    I'm going to cali this summer, and I'm gonna be towing a 300lb trailer with a 500lb motorcycle. Would it be ok to tow this setup in OD with 31's and 3.08 gears at around 70mph?
     
  13. dyeager535

    dyeager535 1 ton status Premium Member

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    I know on some transmissions, there is more line pressure when certain gears are selected, (like more pressure to 1-2 with the shifter in D than OD as a made up example) so that may be what you are experiencing.
     
  14. Blazer1970

    Blazer1970 1/2 ton status

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    The tranny runs a different routine for torque converter lockup when in D than it does in OD. In D, it keeps the converter locked through the downshifts. You will notice that you get a lot more engine braking when you run in D than you do in OD. This is nice, because it saves wear on your service brakes. When they are in OD, they are set up to try to provide maximum fuel economy. One of the ways they do this is to make the truck coast when you take your foot off the gas. In OD, as soon as you let off the gas, the converter unlocks immediately.
     
  15. Lonnie

    Lonnie 1/2 ton status

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    A few clarifications.....

    The transmission does increase line pressure in drive, thereby making it shift harder than in OD. This is normal.
    Another reason to tow in drive.... less chance of slippage with higher line pressure.

    The transmission shifter position does not change the converter lockup action in a 700r4 transmission. The computer controls the lockup & the transmission has absolutely no feedback to the computer based on which gear it is in. The later 4L60E transmission (approx 94 & newer trucks) has feedback to the computer & will have an effect on operation.
     
  16. caryhenry

    caryhenry Registered Member

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    does this harsh downshifting in D hurt the tranny in any way?
     
  17. imiceman44

    imiceman44 1 ton status

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    The harsh downshifting will not hurt the tranny, it could hurt the driveline if anything but I don't think it's that hard.
    And by the way guys, his first question started with saying he now knows that towing on OD is not recomended and his question was about the hard downshift.
    /forums/images/graemlins/thumb.gif
     
  18. Dunc03

    Dunc03 1/2 ton status

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    if you really want to know how the tranny is working, read this article from bowtie overdrive. It explains how the converter works and why the transmissions overheat. The main source of heat is in the torque converter. IF you are driving in 3rd in a 700r4, the converter is unlocked and creating excess heat, However, if you are in 4th the converter automatically locks which reduces heat. I'm not sure about the issue on gear hunting. It makes since that it would cause wear and heat if it were hunting between gears at 40. My tranny normally doesnt shift into 4th until 45 or 50. I'm not sure exactly when it goes in cause I friedthe speedo cable. Anyways that article explains all you will ever need to know about the 700.
     
  19. Marshall

    Marshall 1/2 ton status

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    Im somewhat confused. At what speed should I use over drive.
     
  20. 3car

    3car 1/2 ton status

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    ok,here goes my opinion.i have had a 91's-10 blazer,bought new,traded it with 212,000 miles on it,an 88'k-1500 with over 200,000 on it,and my current truck,a 91' k-5 with over 100,000,all 700 r4's,never had tranny problems.i drive in o/d except when towing.all have done there share of towing and playing.heat kills auto trannies.bottom line.if you have 35's and 3.08 gears its gonna buy the farm.improper gearing stresses the entire driveline.if the truck is geared properly,it will shift into o/d when it should,and there wont be excess heat.a deep aluminum pan and a big cooler are also good ideas.my 91'has 3.08's and 31's.i run it in drive unless im on the interstate(freeway to all of you from cali)until i get the 14bolt installed.35's and 4.56's are the plan.its simple.dont tow in o/d,and properly gear the axles.700's are good trannys,but for them to live,you gotta'play by the rules. /forums/images/graemlins/k5.gif
     

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