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gears and trannies ?

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by riz, Jul 23, 2001.

  1. riz

    riz 3/4 ton status

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    <font color=purple> I currently have a 700R4 tranny and will be stepping up to 35" tires as soon as I get some other things done but want to be prepared............ Would it make a difference what gears to run by the type of tranny ? Say the difference between a 700R4 and a 350 turbo ?? If I installed 4:56's with the tranny I have now and later swap out for a 350 tranny would it be better or worse ???

    L8r,
    . Riz . <a target="_blank" href=http://www.geocities.com/rizmonkey>www.geocities.com/rizmonkey</a>
     
  2. Leadfoot

    Leadfoot 1/2 ton status Premium Member

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    Riz, you will notice a difference. To see approximately what the difference will be. Ride down the highway in OD and check RPM's (or listen to the motor), then manually shift to Drive, and check RPM's (or listen to the motor). The TH350 does not have OD so this is what you will be running on highway. You will also notice a slight drop in acceleration if you swap to a TH350 because the 700 has a lower (higher numerically) first gear. This is all assuming the same gear ratios. You can change gears to compensate, but you will be comprimising low speed or high speed RPM's. <a target="_blank" href=http://randysringandpinion.com>randysringandpinion.com</a> had a good RPM/Gear Ratio/Tire diameter calculator where you can get an idea of what different changes will do to RPM's.

    If you didn't build it yourself, how can you call it yours.......?
     
  3. txbartman

    txbartman 1/2 ton status

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    With a 700, 3.42 gears, and 35s, I definitely think you'll need a gear change. I have a 700, 3.73s, and newly installed 35s. I am definitely having to go with taller gears. Of course, I also have a fairly tired 305. I am going with 4.56 gears. But, if you are swapping to a TH350 (without OD), that may be gear swap enough. Driving in D (at a 1:1) versus OD (at .7:1) is the same as going from 3.42s to 4.88s in your highest gear! (doesn't impact your other gears the same)

    I know OD in the 700 is .7:1 ratio. I think the TH350 is 1:1 in D (but I could definitely be wrong. This means that if you are currently running 2000 RPM in your 700, you will be running about 2850 RPM at the same speed with a TH350 with all the same running gear (gears, tires, etc.). This is the same as running in D (3rd gear) on your 700 now.

    If you are definitely going to swap in a TH350, I would use the charts you can find on many websites (like the one on Randy's mentioned above) and detrmine your current RPM with your 700. Figure out what it will be after you install your new tires. Then convert that to what it would be without OD. See if that is the RPM you would desire at whatever speed you are most concerned with using your engine's power band. Then decide if a gear swap is right for you.

    Just my pennies...

    Brian
    Click to see <a target="_blank" href=http://tx85gmcguy.alloffroad.com> My 85 Jimmy </a>
     
  4. CaptCrunch

    CaptCrunch 1/2 ton status

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    Riz- I would go w/ a 4.10 gears. This way w/ 35's you will have good take off w/ the 700R4 and good milage and rpm at freeway speeds... maybe even a bit low, but also what will be nice is if you decide to go to a TH350 the rpms will still be bearable on the freeway. I like the 4.10's and 35's i have... good setup, but might be looking to go steeper... Not sure if I'm gonna go bigger tires in the futre or not.

    -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>
     
  5. riz

    riz 3/4 ton status

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    <font color=purple> I don't know if I'm going to swap trannies now, just was wondering if I did .......... I was thinking it wold be beneficial to do so ............. I'll more than likely stick with the 700 and go to 4:56's .

    L8r,
    . Riz . <a target="_blank" href=http://www.geocities.com/rizmonkey>www.geocities.com/rizmonkey</a>
     
  6. One more thing to consider is unless you get a t350 with a lock up converter its not just a 1.1 ratio you need to add about 200 rpm's to the figure so in d you'll be turning 2950 to 3050 at the same speed.
     
  7. 84_Chevy_K10

    84_Chevy_K10 Banned

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    But a TH 350C has a lockup converter, so if he got one of those, then that would help somewhat.

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

    CaptCrunch 1/2 ton status

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    Haha Riz! Your gonna have to fight me for them [​IMG] LOL [​IMG]. I have really like the idea of more gear... especially when some trimming is done and the true 36's or 37's go on. Unfortunetly it looks like to fill that bill though it will call for 3/4 ton axles... But I'm still not positve... gonna watch my rpm's more carefully w/ my 4.10 and 35 set up and decide. But I'll keep an eye out for ya too Kev.

    -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>
     
  9. riz

    riz 3/4 ton status

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    <font color=purple> Thanks, Mikey !

    L8r,
    . Riz . <a target="_blank" href=http://www.geocities.com/rizmonkey>www.geocities.com/rizmonkey</a>
     

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