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Why does my tranny feel like it is hunting for gears?

Discussion in 'The Garage' started by Lance, Aug 4, 2003.

  1. Lance

    Lance 1/2 ton status

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    Ok, ok the subject in another post concerning RPM's / tire size encouraged me to insert my information to have a look-see about my RPM's. I was surprised to see my RPM's in OD at 70 MPH running the stock 3.42 gears and 31" tires were actually slightly less (1816) than the RPM's my current 4.10's and 36" tires appear to net (1875). I've entered this info on various calculator's and they all give similar results.

    Sooo.... my question is why does my brand new tranny feel like it is lugging out a highway speeds (45-55) with the tranny in OD. It also hunts for the right gear at any speed under 65-70 mph. I am certain the tranny pressures/temps are good and within normal operating ranges. I am also certain the TV cable is installed/operating correctly because this was all part of my tranny warranty activation. I also replaced the torque converter and flywheel at the time of the tranny replacement if that help. What could be the problem? The tranny shouldn't be hunting for gears if the truck is within a few dozen RPM's of the stock configuration, should it? I never did a comparison before and I always just assumed that the gears were too tall for the tires, so I kept the tranny in D for most of my on-street driving. I need some insight! /forums/images/graemlins/1zhelp.gif


    Thanks in advance for the replies,

    Lance
     
  2. Lance

    Lance 1/2 ton status

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    Anyone?
     
  3. Thunder

    Thunder 3/4 ton status

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    My 700 with 3.73 and 33" tires acts about the same way.
    I usually keep it in drive until I get up to 55. Then if I drop it to OD the convertor locks and unlocks when I give it a little gas till I get over 60 or so. I dont normally drive 55 /forums/images/graemlins/tongue.gif I usually cruise at 75+ it works good at that speed. /forums/images/graemlins/thumb.gif
    The 700 in my 89 is orginal and never been rebuilt. The pan is always clean when I pull it so it must not be hurting it.
    In my opinion you are still a little under geared. with 36 inch tires you should be running 4.56+ with a 700r4. With the 4.10s, even though the RPM is similar to your old set up. Your tranny is working a lot harder to push those big tires and more unsprung weight down the road. So it will hunt gears at lower highway speeds. Running big tires is almost like towing a small trailer. More air resistance, more weight, more rolling resistance, all = more work for the tranny.

    I hope you have a good tranny cooler also.
     
  4. Lance

    Lance 1/2 ton status

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    Thanks for the input! I always leave the truck in D when I am around town. I always just assumed my gears were too tall for my tranny and never bothered researching it because I had planned on a gear swap from the start. But when I read all those posts yesterday regarding tire sizes/gears and RPM's got me to thinking (which is dangerous) and I was shocked to see that I appeared to still be in the opotimum power band for my engine.

    I assumed that the additional unsprung weight of new axles/rims/tires and the associated rolling resistance were the cause of my tranny issues, which you confirmed. But I just wasn't sure yesterday and I immediately assumed the worst (bad tranny).

    Thanks again for the input and BTW I am running a 28,000GVW cooler for my tranny. It is the biggest available for passenger vehicles (at least at the time) and my tranny temps never get above 160 degrees.

    I'm just going to continue to drive in D until I can again afford a a lower gear swap.

    Lance
     

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