Can I drop 3.08 gears in a 1998 2wd Suburban-3.4 gears?

Discussion in 'GM Powertrain' started by phoebeisis, Dec 12, 2007.

  1. phoebeisis

    phoebeisis Epic Member 5+ Years 1000 Posts

    I have a 1998 2wd 1500 Suburban-bought it about 6 months ago-195000 miles-and it runs,drives great-I'm impressed-lotta vehicle for $2950 and the mpg isn't as bad as I was lead to believe(maybe 12 pure city,15.5 mixed city-maybe 17-18 pure hy).This is about what my lighter, much more modern motor2004 Titan,and 2001 Tundra -both V-8s got.It is 1000 lbs heavier than the Tundra,and 500 more than the Titan.
    I noticed that older Suburbans,and some more recent 1500 pickups(maybe 6 cyl-not sure) have 3.08 ring gears.Any chance these would be drop in for my 3.4 gears?
    I plan a lot of hy driving,and wouldn't mine getting a mpg or so more.
    I'm guessing my ECM might have some problems??
  2. MrShorty

    MrShorty Epic Member 5+ Years 1000 Posts

    Yes you can put 3.08 gears in there.

    ECM shouldn't have any problems, especially if you reprogram it for the new gear ratio.

    Will you see any improvement in gas mileage? I don't know. I've got 3.73's in my '98 K1500 (K=4wd where yours is C1500 C=2wd) and I'm getting about the same gas mileage. If you spend ~$1000 for the rebuild, gain 1 mpg, it will take you 50k-100k miles to recover the cost of the rebuild if gas stays at $3/gallon. Because the engine has to work harder to accelerate from a stop, it's conceivable to actually lose gas mileage in city driving with a higher gear ratio.

    But the answer to your question is, yes, you can regear the differential.
  3. finalday7

    finalday7 Epic Member 5+ Years ROTM Winner 1000 Posts

    Yeah you can just like Mrshorty said but I don't think thats it's worth it. You could spend 50 bucks on a K&N Filter and 300 on a programmer and yield much better results.
  4. phoebeisis

    phoebeisis Epic Member 5+ Years 1000 Posts

    Thanks for the info.Probably right that it won't work from a $$ point of view.It would take 100,000 miles if I just got 1 mpg-and I agree 1 mpg would be the best I could hope for,and more like .5 mpg might be realistic.
    I'm planning to slowly replace wear items-motor-trans-shocks-diff- as the $$ become available since I like this truck,and I sure as heck don't have $35000 to buy a new one.
  5. Wayne S

    Wayne S New Member

    If wanting to drop the RPM on the highway, the better/easier thing to do is when it comes time to replace tires, just get a taller tire.

    I agree with the other mods though. A good air intake, exhaust, and programmer can probably get you 2-3 mpg on the highway.
  6. Cableguy

    Cableguy Epic Member 5+ Years ROTM Winner 1000 Posts

    If I remember rightly 3.42 is the cut off point. 3.73's are on a different size carrier. So the answer is yes that ring gear should bolt back in there no problem.
  7. phoebeisis

    phoebeisis Epic Member 5+ Years 1000 Posts

    Thanks.Part of my reason for considering the taller gearing is that when I change out the motor, if I have the extra $$,I might go to a GM OEM 383E stroker motor.It is a straight drop in with some sort of factory warranty.GM rates it at 340 HP-430 LB-FT vs 250hp for the stock 5.7.I can buy the 383E for $4400 delivered-the stock 5.7 Goodwrench is about $2500 delivered.No other manufacturer offers NEW-NEW NOT REBUILT- motors,especially a new preformance motor for that little money.
    Of course the taller gearing would negate any acceleration gain from the 383E,but a lot of performance stuff doesn't make sense from a $ and cents point of view, but I just like it.
    WayneS thanks.Good idea, but I wonder if the taller profile will hurt mpg.I kinda like the low stepin-even though the tiny 235/75 15 wheels look wimpy!

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