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maintaining overdrive , what gears?

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by G-Force8, Jun 10, 2006.

  1. G-Force8

    G-Force8 1/2 ton status

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    hola compadres

    I am going to kick off the first phase of my 'Burb buildup (suspension wise) with 35" swamper TSL/SX's

    The truck, as of now, has the stock TBI350/700R4 combo. I will be keeping a 700R4 in this truck for a while and will modify/beef it to perform better and to handle higher torque loads, but, my concern right now with the suspension and tires being the area I am targeting first.....is what diff ratio would be ideal for maintaining cruiseability and a properly functioning overdrive?

    This truck will not be a daily driver any more very soon ,but will be driven on the street often. The truck will also see its share of hard wheelin'. The axles that I'm going to start off with will be geared @ 4.10:1. What kind of performance can I expect with 35" tires and 4.10's with a completely stock TBI350 ( full exhaust from headers back and injection mods coming soon tho)?

    Will the overdrive still work right?
     
  2. ryoken

    ryoken Puppy Fabricator Premium Member GMOTM Winner

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    Without looking at the calculators, you'll rarely be seeing od with the 4:10's.. It'll be drivable for sure, just a bit sluggish...

    I plan on 36's with my 700r4 and would like to be running 4.88's or 5.13's eventually. But I'll probably be in the same boat, running 4.10's in some 3/4 running gear till I go over em and regear...

    I figure I'll just run around in 3rd like I do now with my 32's and 3.73's except out on the highway... At some point I'd like to get 4th a little lower in the mph scale even running TBI...
     
  3. G-Force8

    G-Force8 1/2 ton status

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    I'm running 32's with 3.73's too. I just want the overdrive to work on the freeway. I'd love to spring for a pair of CUCV 1-tons for this truck and get 4.56-ready axles.....but @near 2 grand for the pair , I'll have to pass for a while. I've seen a pair of 3/4 tons re-geared to 4.56 with lockers for a starting price of 1k,but I could get a D60 for that.

    Bah, the 4.10's'll have to do for a while. A built 350 should take up the slack tho :P
     
  4. pauly383

    pauly383 Daddy383 Staff Member Moderator

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    It may drop down to 3rd on you occasionally on the highway over certain grades , but 4.10;s and 35's aren't that bad to start with . Most 35's measure lower anyway . I get by with 3.73's and 33's , and I leave in OD exclusively if there is no heavy trailer attached .

    Of course 4.56 would be better , if you can afford it , and like to keep the rpms in a simmilar mileage window :thumb:
     
  5. Hossbaby50

    Hossbaby50 3/4 ton status

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    IMHO the minimum for a good driveable truck with 35" swampers and OD is 4.56's. That is what I have in my truck. I was trying to decide whether I wanted to go to 4.10's or 4.56's on my gear swap. Alot of people talked me into 4.56's and I am glad I went there. 4.56's are ok in my opinion for 35's and OD. Personally if I had to do it all over again I would do 4.88's or if you don't go fast on the highway even 5.13's.

    If you want the best all around performance I would say 4.88's. If you don't need to pull 80mph on the highway and you tow alot then 5.13's for more grunt.

    My truck had 4" lift, 35" MTR's, TPI 350, built 700R4, 3/4 ton axles w/4.56's. It worked ok but I wish I had 4.88's. It would have given me better crawl ratio and better grunt for climbing the hills on the highway.

    Harley
     
  6. 4xcrazy

    4xcrazy 3/4 ton status

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    fixed
     
    Last edited: Jun 10, 2006
  7. ryoken

    ryoken Puppy Fabricator Premium Member GMOTM Winner

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    And your probably turning 1500 rpm's poking around town.... And if your "searching" at 75, you definitely don't have enough gear...

    And it certainly would "get out of it's own way" hella better with 4:56's or 4:88's...

    Don't get all butthurt, it's not the optimum gear for that tranny/tire combo, plain and simple...
     
  8. 4xcrazy

    4xcrazy 3/4 ton status

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    fixed
     
    Last edited: Jun 10, 2006
  9. ryoken

    ryoken Puppy Fabricator Premium Member GMOTM Winner

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    Well, towing puts a whole other consideration into it.. Your a burb, much more of a consideration, being most K5's aren't known to be the best for towing big loads...

    I can do 80 in the K5 and I'm barely over 2 g's... I'd rather get into the overdrive a bit sooner and more into the torque curve with my gears, even with the TBI.... If I was running a carbed sb, I'd definitely want 4:88's at least...
     
  10. Creek

    Creek Registered Member

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    Assuming tire diameters are true, to go from stock 31s with a 3.73 gear to 35s, the equivalent ratio would be 4.21. Since you're already running 32s with a 3.73, the equivalent ratio for 35s would be 4.05. You will not be able to tell the difference other than maybe on acceleration due to the increased inertia of the 35s. If you want to get into 4th sooner, you can change the springs and/ or weights of the governor.

    I'm running 32s with 3.42 gears and it goes into 4th at 45mph at light throttle. With the stock springs in the governor, it shifted at 40mph but it shifted from 1st to 2nd at 5000 rpm at full throttle. I tried a Corvette governor which made the 1-2 shift at 5800 rpm which was great but the 3-4 shift was at 55 mph. I went with the stock governor with lighter springs and the 1-2 shift is at 5400 rpm. I would love to get 6000 out of first so when it made that long jump into second it would be in the fat part of the torque curve.

    David
     
  11. sgarrison

    sgarrison 1/2 ton status

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    I'm running 4.88s with 35s and have no problems on the road. I have a torque converter lock up switch and leave the t.c. locked a lot of the time. If I had known how well this works I would have gone with 5.13s.
     
  12. tch777

    tch777 1/2 ton status

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    OUr Sub had 3.73 gears and 33 when we bought it.
    I could not hold OD unless we were going more than 90 mph on the freeway, otherwise on flat ground it would hunt.

    We re-geared to 4.56 and I am really glad we did. Around town it is snappy. And on the highway I can run OD over pretty much most hills. In the mountains I still run out of steam but we can maintain a reasonable speed much better.

    I think in my case all I need is a stouter 350 or a 383 and the Sub will be perfect.

    Tim
     
  13. loafer

    loafer 1/2 ton status

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    IMHO, 4.10s are minumum for 35's with OD, 4.56's would be a better all-around ratio though.
     
  14. desertrat67

    desertrat67 Hawk Driver

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