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1979 K10 axle ratios

Discussion in 'Chevy Trucks' started by ronnunan, Jan 7, 2007.

  1. ronnunan

    ronnunan Junior Member
    Messages: 6

    I have a 79 K10 that I need to regear the axles. It is a frame off resto that I will probably use for mostly highway and cruising. I have a locking rear diff with 3.73 ratios...stock...I also have the doug nash part time conversion on a np203. When driving at highway speeds my trucks rpsare too high. What would you guys suggest for a better highway speed ratio on the axles...I am running with 31 inch tires. Any input would be appreciated.
     
  2. B&B

    B&B PlowSite Fanatic
    Messages: 12,777

    Since it sound's like this is just a pleasure truck and you not going to use it for any hauling or towing and it's mostly highway driving you could gear it pretty high, even with the 31's. You could go with 3.42's but their's not a huge difference between 3.42's and 3.73's so I think you'd be happier going down to 3.08. Now if this truck was going to be used at all for any kind of work I'd never gear it that high but in your case the 3.08's would be good. Also,your truck will have a 12 bolt rear if it's stock.If your going any higher than 3.73 (which it sound's like you are) you going to have to also change the carrier as their's a "case break" between 3.73 and numerically higher gear's and 3.42 and down. In other word's a 3.08 or a 3.42 gear set won't fit your stock carrier. You'll need a carrier out of a truck that came with 3.08's or 3.42's.
     
  3. Detroitdan

    Detroitdan PlowSite.com Addict
    Messages: 1,937

    Depends on what you want to do with it. I wouldn't give up the 3:73s unless I was going to 4:10s. Most of those 1/2 tons came with 3:08s, which would make it more bearable on the highway, but not much low end power. I've had two of those trucks, one with a th350 and 3:73s on 35s, miserable on the highway, next was a th400 with 4:10s on 35s, went great on the highway even with less motor. If I were to build one of those trucks again I would use a 700r4 for the overdrive and lower first gear, and use a 4:10 gear. Another option is to go up to a 33 inch tire, drops your useable gear a bit but also more rolling resistance which saps power.
     
  4. Detroitdan

    Detroitdan PlowSite.com Addict
    Messages: 1,937

    yeah, what he said. I forgot about the carrier sizes, I don't think you can put a 3:08 in there. That 3:73 with a locker may actually be valuable. May want to look around for a parts truck, you can probably find one from the early 80s with 3:08 axles, maybe even a 4 speed auto and 208 case. Then you can just unbolt the springs and swap the whole thing. Faster than changing a gearset I think.
     
  5. ronnunan

    ronnunan Junior Member
    Messages: 6

    clucking noise

    Thanks for the input. Like I said I have the 3.73 and dont want to swap cases to go lower than 3.43...and how much better will it be with the 3.43....
    What got me thinking about all this was I have a clunking noise when turning right or left from a stop....not at higher speeds. Went to an axle place that told me that I didn't have the additive in there...which I didn't. Put the additive in and the noise was reduced but still there 0ccationally. I need to take it in and get it checked out but its another 50 bucks just to look. Any ideas???
     
  6. Detroitdan

    Detroitdan PlowSite.com Addict
    Messages: 1,937

    I think they're supposed to make a little noise aren't they? I wouldn't worry about it. My old 14 bolt Detroit Locker made plenty of noise when you slowed and turned, never had a problem in 175000 miles. I don't think you would even feel the difference going down to a 3:42. Not worthwhile in my opinion.
     
  7. B&B

    B&B PlowSite Fanatic
    Messages: 12,777

    Since your saying that the truck has the factory "locking" diff (aka. Gov-loc) in it then that's what is making your clunking noise. Not an uncommon thing for them to do that when they get old. Also, their's no point in only dropping down to a 3.42 as you'll still have to change the carrier regardless. The case break is 3.73 and up and 3.42 and down so no matter what you go with your gonna have to change the carrier,which by the way isn't a bad idea anyway as the Gov-loc's have a nasty habit of exploding when you least expect it.Around here we call them "Gov- bomb's" just for that reason.
     
  8. ronnunan

    ronnunan Junior Member
    Messages: 6

    heres a pic...

    almost done.

    79 chevy.jpg
     
  9. yzf1000_rider

    yzf1000_rider Senior Member
    Messages: 147