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12Bolt is it really that bad of an axle??....more

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by Impex, Mar 29, 2000.

  1. Impex

    Impex 1/2 ton status

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    Like when would i want to up grade to the 14? with like 35s or are 35s pretty good with the 12 or would i be better off with 33s with the 12? see what i mean...
    is it alot stronger then the 10

    Thanks
     
  2. Depdog

    Depdog 1/2 ton status Author

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    The 12 bolt is deff. stronger than the 10, its as strong as a Ford 9" just uses c-clips to retain the axles. I have 35x12.5x15's on mine and I wheel it pretty damn hard. Never broken a stock shaft yet. Going to upgrade to either Moser Shafts or to the Warn Full Floater kit. Not sure whick yet. Leaning towards the Moser, because of the cheaper price and if (GOD forbid) I should destroy a rear axle, I can still get parts just about anywhere for it.

    Depdog

    <font color=blue>"Lead, Follow, or BECOME the Trail"</font color=blue>
     
  3. '73 K5

    '73 K5 1/2 ton status

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    The 12 bolt is definitely better than the 10 bolt but not tons different. I wouldn't go more than 33's with a 10 bolt and maybe 36's with a stock 12, but it depends more on the way you drive instead of what size tires.
    I don't think the 12 bolt is as strong as the Ford 9 inch. Unfortunately the Ford unit offers a slightly bigger ring gear, but the big advantage in strength is the fact that you can put some fatty 35 spline axles in a 9. I've even seen some trucks with 40 spline axles in a 9 inch.
    Just do what I did instead of messing with a heavy 14 bolt that robs you of some ground clearance. For my 12 bolt, I bought Moser shafts, limited slip diff, U.S. Gear ring and pinions, new seals and bearings and a TA Performance diff cover.
    The parts are in my garage and not on the truck yet. I'm only going to run 33 inch tires, but I want to be able to thrash my Blazer and have the rear axle hold together.

    '73 K5
    Chevy good...Ford bad
     
  4. BurbinOR

    BurbinOR 3/4 ton status

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    Much like the WRONGLY [​IMG] maligned NP203, the 12 bolt can be made better. Buy the new Four Wheeler, has a bolt-in full floater kit. Look, I know the 14 bolt is stronger, and I keep hearing that the NP205 is stronger, but to be honest, I have had 203's in all 4 of my 5 K-5's, and NEVER had a problem. This is with up to 38" tires, ultra high gears (3.08 with 35's - ugggh), and a 454 with a LUMPY cam and enough torque to almost break your neck. And that same 454 with the 3.08 gears and 35 inchers was putting the power through, you guessed it, a 12 bolt. Maybe I have just been lucky, but they can't be that bad. Maybe the extremists among this group have broken them, and they should get 14 bolts for reliability. Enough of my soapbox, thanks for listening.

    '79 - 406 w/IROC TPI - K5#5 - a <font color=orange>sickness[​IMG] <font color=blue>you never get enough of!! [​IMG]
     
  5. 89Jimmy

    89Jimmy 1/2 ton status

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    My 12 bolt has stood up well with moser axle bearings and oem quality guts in 3.73,(should have gone 4.11 but didn't want to spring for a new carrier for the dana 44 up front.) I'm not saying it can't be be broken. We probably all know folks that can break an anvil with a rubber mallet. It has held up fine for me and if I trash an axle, I'll go with moser replacements and then watch the mud fly!
    John
     
  6. Donovan

    Donovan 1/2 ton status

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    I had a 12 bolt in my blazer but I just ripped all of the teeth of the ring gear. Oh well. I have a caddy 500 in it and 31 inch tires. The big thing with 12 bolts and Dana axles is the caps on the diff. They will flex under load. I know that Mark Williams make new caps for Dana 60 and car 12 bolts don't know if they are the same as truck caps. What happens is that the cap flexs and you lose the backlash in the gear. Enough times of this flex you break the ring gear or break the cap. Fix that problem and you have a pretty good axle. Oh and get rid of the C-clips but even those are not that bad.

    Donovan
     
  7. jarheadk5

    jarheadk5 1/2 ton status

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    Someone said it earlier, but...
    You can get diff covers from Summit, Jeg's, etc. that have bearing cap preload hardware. The bolts get torqued to a certain value, and they press on the bearing caps to help prevent that gear-killing flex. They are sturdy-looking enough to probably prevent some housing flex, too. Not sure about long-term use, but tech reps wherever you buy one from could probably answer that for you.

    [​IMG] Semper Maintenance!
    [​IMG] So many ideas, so little money...
     
  8. mudfanatic

    mudfanatic 1/2 ton status

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    I run 33's and I have seen people run 35's with 12 bolts with no problems, However I have seen 2 rigs with 38's break 12 bolt axles. I would think that a stock 12 bolt axle would hold up to 35's until you can afford the moser upgrade
    '77 K5

    <font color=red>mudfanatic</font color=red>[​IMG]
     
  9. AZK5

    AZK5 1/2 ton status

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    Who sells Moser axles? Does any one know a price for a couple of 12 bolt Moser axles?
    CB
     
  10. dremu

    dremu Officious Thread Derailer Premium Member

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    Uhh, Frank:

    "I have had 203's in all 4 of my 5 K-5's, and NEVER had a problem."

    How many Blazer IS that? ;-)

    -- A

    '74 K5 Blazer "Tank Grrl"
    '77 Chalet sans Blazer
    and more to come...
     
  11. 6.2Blazer

    6.2Blazer 1/2 ton status

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    Here's my view on some of these questions.....
    10 vs. 12 bolt - 12's have the advantage in the ring gear and carrier size (8.5" vs. 8.87"), but not by a whole lot. 12 bolt axles shafts are 30 spline, 1.31" dia...older 10-bolts had 28 spline, 1.28" dia shaft, but newer (around '88 and up) 10 bolts use the same size axle shafts as the 12's so it's basically a tie for the shafts.
    A 10-bolt with a full case aftermarket diff (like a Detroit Locker) and 30 spline shafts should be pretty much just as strong, if not stronger than a stock 12, add aftermarket axles (like Moser) and the 10-bolt will be stronger.
    I currently run a 10-bolt with a Detroit, aftermarket gears and axles, and have had no problems. The truck has mainly seen fairly serious trail work (at least once per month) for the last year with 35" tires for the last couple of months and 33's before that. Granted, I don't run a lot of horsepower and I don't abuse it, but it does get run hard. I know it's not bulletproof (I carry a spare axle) but I really like the lighter weight and higher ground clearance (as compared to a 14-bolt). Now if I were to start from scratch (or if I ever break the 10 bolt gears or carrier) I would use a 12 bolt, if I start breaking a lot of axles I'll get the Warn full floating conversion.
    I have also noticed that alot of "big name" people are starting to see the advantages of the 10 or 12 bolts for trail use. There's articles and write-up for the following:
    Jim Allen - Fourwheeler Magazines's Project Blazer - 10 bolt w/ Warn FF, Detroit, 4.10's with 35's and a Banks turbo'ed diesel
    Steve Watson - Off Road Design - switched from a 14 bolt FF to a 12 bolt w/ Warn FF with 35's and a built 383 SBC.
    Tony Salvennini (sp??) - ww.4x4review.com - 10 bolt w/ Detroit, chromoly axles, 35's

    I would consider all of the above at least fairly serious fourwheelers with lots of experience.
     
  12. Mudzer

    Mudzer 1/2 ton status Author

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    If you have the factory Eaton GOV-Lock, I would probably opt for a better dif. I recently exploded one doing some hard wheeling. The transfer case slipped out of 4wd and put all the load on the rear tires while I was climbing a rock ledge. I broke the spider gears in the Eaton. I have since replaced it with a Lock-rite and am very happy. My offroad performance is much better. I like the superior axles tha 4WPW sells. they are stronger than stock and only $100 each. Not bad. My 12 bolt also has a TSM disk brake kit and other mods. I run 35" tires. Keep on rockin with those 12 bolts!

    <font color=red>Mudzer</font color=red>
    1978/91 K5 Blazer
     
  13. 89Jimmy

    89Jimmy 1/2 ton status

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    Several years ago I replaced an axle in a 10 bolt rear with a factory unit. I think I paid about $110 for that at a local GMC dealer. I don't think moser or other aftermarket axles are much more than that.
    John
     
  14. BlueKnight

    BlueKnight 1/2 ton status

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    Well I have a 12bolt in mine running 38" TSL's and 4.56 gears. Power plant sooon to be is a 600hp 396 big block. I have about 400hp 350 in it right now and havent had any trouble with it. I was debating on going to a 14 just for strength but I would have to change my bolt pattern back to a 6 lug (adapters) because I have some custom rims designed for it. That is just a pain. So if this breaks while playing I will then look at beefing it up.
     
  15. '73 K5

    '73 K5 1/2 ton status

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    You can buy the Moser axles I got for my 12 bolt from West Coast Diffs. I think I payed about $220 for both of them

    '73 K5
    Chevy good...Ford bad
     
  16. Depdog

    Depdog 1/2 ton status Author

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    Well, not to be an ass, but Moser sells Moser axles. They have a web site www.moserengineering.com Last time I priced a set, they were around $320 bucks with their new bearings and shipping.

    Depdog

    <font color=blue>"Lead, Follow, or BECOME the Trail"</font color=blue>
     
  17. BurbinOR

    BurbinOR 3/4 ton status

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    OK, you got me...........so in my excitement it should have read "I have had 203's in 4 of my 5 K5's had 203" or something like that........thanks for the grammar catch. Too much time on this site making me goofy........

    '79 - 406 w/IROC TPI - K5#5 - a <font color=orange>sickness[​IMG] <font color=blue>you never get enough of!! [​IMG]
     

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