Dismiss Notice

Welcome To CK5!

Registering is free and easy! Hope to see you on the forums soon.

Score a FREE t-shirt and membership sticker when you sign up for a Premium Membership and choose the recurring plan.

overdrive problem

Discussion in '1969-1972 K5 Blazer | Truck | Suburban' started by Chip, Aug 24, 2001.

  1. Chip

    Chip Registered Member

    Joined:
    Aug 24, 2001
    Posts:
    5
    Likes Received:
    0
    I need help...I have a 71 Jimmy with 350 tbi (factory computer) and 700r4 transmission...33in. tires and 3.73 rear gears. All new drive shafts and output shaft from Advanced Adapters. My problem is when I am doing about 35mph my transmission keeps going into overdrive and then down shifting and then going back to overdrive then down shifting and so on. Someone told me I may need a new computer chip since the 93 Sub it came out of was not setup with 33s and 3.73 gears..can anyone help??
     
  2. Triaged

    Triaged 1/2 ton status

    Joined:
    Feb 21, 2001
    Posts:
    3,808
    Likes Received:
    0
    Location:
    CA (LA/OC area)
    With those gears you should hardly ever need OD. The easy thing to do would be to drive with the trans in D insted of OD unless on the freeway. I believe in those years the 700r4 was not controled by the computer (except for T/C lockup) so a shift kit would make it shift into OD later (my s-10 w/ 700r4 shifted into OD at 35 now it shifts into OD at 45 if I take my foot off the gas). The other thing you might want to look into is changing to 4.10 gears (maby even 4.56) to make better use of the available gears in the tranny

    '71 Blazer CST w/ a 400sbc, 4" lift, 36" Supper Swampers, and alot of rust
    <a target="_blank" href=http://community.webshots.com/user/triaged>See it Here </a>
     
  3. BobK

    BobK 1/2 ton status

    Joined:
    Oct 5, 2000
    Posts:
    1,604
    Likes Received:
    0
    Location:
    Petrolia,Ontario,Canada but working in Port Huron,
    If the TBI system was complete and you just placed it in your truck the computer still thinks it's in the same truck it was orig. placed in.It's configured to those stock parameters(tire size and gearing).You can get a reprogrammer that will allow you to change shift points in a computer controlled tranny as well as some other parameters.
    Check out this link.I have no expirience with these scanners so I personnally don't know how well they work.

    <a target="_blank" href=http://www.jegs.com/cgi-bin/ncommerce3/ProductDisplay?prrfnbr=26971&amp;prmenbr=76>http://www.jegs.com/cgi-bin/ncommerce3/ProductDisplay?prrfnbr=26971&amp;prmenbr=76</a>

    hope this helps.

    <font color=green>BobK<font color=green>
     
  4. Steve_Chin

    Steve_Chin 1/2 ton status

    Joined:
    Mar 6, 2001
    Posts:
    1,126
    Likes Received:
    0
    Location:
    Foster City, CA, USA
    Depending on how the transducer gets its signal, there are a couple of ways to fix this. If it drives off of the speedometer driven gear output, all you need to do is put the correct ratio adapter between the driven gear and the transducer. If it is driven directly off of the output of the transmission (all electronic speedometer system), the reprogramming kit mentioned above is the way to go.
     

Share This Page