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GM 12-Bolt to 14BFF Swap (1st Gen) Questions...

Discussion in '1969-1972 K5 Blazer | Truck | Suburban' started by Greg72, Aug 17, 2001.

  1. Greg72

    Greg72 "Might As Well..." Staff Member Super Moderator

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    OK Folks I need to do a sanity check here. I have an opportunity to make an even trade of my GM 12-Bolt for a 14B Full-Floater.

    Sounds good right....? [​IMG]

    Except that the more I look into this conversion, there seem to be a LOT of hidden expenses:

    1. My Alcoa 6-Lug Wheels won't fit anymore. Buy two new 8-Lug Wheels, and carry two spares. (One 6 Lug, One 8)
    2. Spring Perches are different. Find a local shop to cut and move spring perches to fit (narrower?) 1st Gen layout.
    3. Shock Mounts are also different. Again get a local shop to weld on new mounts
    4. Rear Driveshaft won't work anymore....different U-Joint, and pinion length is different than a 12-Bolt.
    5. Open Diff - Just like what I have now, but it just seems WRONG to own a 14-Bolt and not stuff it with a Detroit!!! [​IMG]

    Have I missed anything? I want to get excited about my "free" 14-Bolt axle......but this list of items certainly adds plenty of cost to the deal. The R&P is the same as my current axle, so at least there won't be a gear change too!!!

    I am looking for a little of the old "Been There, Done That" advice here.......Thanks for the help folks!

    -Greg72
     
  2. Burt4x4

    Burt4x4 3/4 ton status

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    This is how I see it.
    14boltFF is not rare so there are many opertunitys to aquire one. Is your 12bolt going out on you?
    You said you would have to trade your 12bolt for the 14....I wouldn't. Only cuz If I was swaping axels I would want to take my time build the axel the way I wanted it the first time, then get all the parts and research done and in one weekend do the swap. This way your rig is not down and you will be able to make all of thoes extream wheelin trips you have been dyin to go on!! Hey you can't be a rookie wheelier your whole life!!
    I also know you should beable to find a 14FF and not have to move the spring perchs.
    I have no experiance with a 14bolt....
    just my .02c

    72K5[​IMG]Led Zeppelin[​IMG]Rock ON![​IMG]
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  3. Greg72

    Greg72 "Might As Well..." Staff Member Super Moderator

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    I know.....I know!!!!

    "take your time and think it through" is always good advice.....so why do I always get SO excited about chances to mess around with something on my K5? [​IMG]

    I found another post that said that if you find a 1-Ton Truck from (73 - ?) it will already have the spring perches in the right place....for some reason the 3/4 Ton stuff was in a different position. But then 4-Wheel &amp; Offroad says look for a '73 - '83 Suburban or Pickup for the simplest swap (I think they mean for the 2nd Gen Boys though...!)

    This 14-Bolt thing could really mushroom out of control.....why just slap a 3.73 rear in, why not put some 4.10's or 4.56's while I'm at it? And hey since I have to deal with buying new wheels, why not just buy a complete SET of 8-Bolt wheels with some 37 inchers, and a Dana60 with matching gearsetup front too?...... YIKES!!!! [​IMG]


    FOCUS...FOCUS....FOCUS....Only one obsessive project at a time!
    -Greg72
     
  4. EricM

    EricM Registered Member

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    I did a 14bolt swap on my 72 jimmy and didn't have to move the spring perches. It depends what truck the rear came from. If it is from a 1 ton the perches will line up if it is from a 3/4 ton they will need to be moved. As far as shock mounts I fabbed my own similar to the mounts on UAV so I could run the 9012's. There is a conversion u-joint that can be used to mate the 1/2 ton d-shaft to the rear end.
    However I would convert the front to 8 lug at the same time carrying two spares would be a waste off space.
     
  5. bitchin4x4

    bitchin4x4 1/2 ton status

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    ha ha! ;-)

    I did the conversion on my 72 Jimmy to a 14 bolt ff. I used my other 3/4 ton truck axles and swapped out. I had to change the shockmounts, spring perches, and driveshaft. Don't recall what it costed and I am thinking I don't want to know! ;-)

    But.. at that time I did everything pretty much that you said on the posting I am replying too. New wheels, lift, everything.

    If it ain't broke, break it!
     
  6. JBOY

    JBOY Registered Member

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    choices, choices, they can drive you nuts, huh? esp where to spend your cash on your blazer!
    i was in the same boat and talked myself into probably the most expensive route, a custom made dynatrac dana 60 with the original 6-lug configuration. ordered it with 4:10's and then had the front geared to match. it's great but pricey ~2500ish. it has 1/2" lugs so i upgraded the front to match that also (avoiding 2 sets of wheel lugs &amp; locks, similar to the 2 spares). you can order with disc brakes if you really want to spend more$$$$$$

    the cheapest is prob finding a '73 &amp; up being parted and taking the dana 44 from the front, they seem to pop up alot. you can also steal a sway bar off one and add it to yours. i haven't done that yet, but helped do one on a friend's K20. he ended up buying a beat up, motorless, trannyless '75 K20 just to steal the axles, then gave the remains to a salvage guy. that way he got all the drive train he needed to complete the swap, drive shafts, u-bolts, etc. (u-bolts, another hidden cost, esp with your lift).

    Greg, what have you been up to anyway? i've enjoyed my "summer off" (layed off).
    later!

    JBOY
     
  7. Greg72

    Greg72 "Might As Well..." Staff Member Super Moderator

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    JBOY,

    I'm still "off".....since May 1st. Unfortunately, the Bay Area mortgage payment is still due on the first of every month!!!! [​IMG]

    Lots of time to lurk on these boards and contemplate upgrades to the K5. I really gotta get a job soon though.....I am starting to go nuts without one.

    Let's get together for lunch or a BBQ sometime. The pool is 86 degrees these days [​IMG]

    -Greg72
     
  8. JBOY

    JBOY Registered Member

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    sounds like a good plan. did you meet Ryan B at the blazerfest? we traded a few emails and he mentioned meeting with our 3 blazers at 4wheelparts in santa clara some lunch time. i have a fishing trip mon, golf thurs, class wed....geeez, how did i even have time to work? :)

    JBOY
     
  9. tlarsw

    tlarsw 1/2 ton status

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    Do the 14FF swap! Only way to go if you're going to get serious about offroading! Indestructable.

    I did the 14FF swap and had to move the spring perches out.

    I bought a $20 Cheapo grinder from Harbor Freight tools. It took some grinding around the base of the spring perches and beating with a BFH to get them the rest of the way off, but it was easy. Center up the rear axle and weld them back on. I also took this opportunity to turn up the pinion and get a 1350 CV driveshaft. Boy does it run smoother down the road now.

    1986 K10 TPI350/NV4500/Gen2 Doubler/D60(ARB)/14FF(Detroit)/4.56 gears
     
  10. Greg72

    Greg72 "Might As Well..." Staff Member Super Moderator

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    Thanks for the encouragement. I really like Burt4x4's advice too about not getting rid of my 12-Bolt at the same time. It would be nice to get everything ready on the 14-Bolt and THEN swap it in....getting rid of the 12-Bolt and then trying to make the 14BFF work would add a lot of pressure, and probably "down time" to the project.

    We'll see how the funds look....lots of extra little costs (even for this "free" swap) and that kind of takes the momentum out of this project.

    -Greg72
     
  11. 72Blazerod

    72Blazerod 1/2 ton status

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    Would the year of the 3/4 ton axle make a difference as to the location of the spring perches? For example would you still have to move them if you got your axle from a 1972 3/4?

    Thanks,

    Rod

    In Canada we use K5s instead of dog sleds now!
     
  12. californiak5

    californiak5 1/2 ton status

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    They weren’t making the 14BFF in 72 to my recollect. I believe if you were to get a rear axle out of one of those trucks it would end up being a D60 or D70 (I think). And no, the spring perches on those years would not have to be moved.

    See Ya,
    Keith

    [​IMG] <font color=green>Born to Drive My K5</font color=green> [​IMG]

    <a target="_blank" href=http://coloradok5.com/gallery/californiak5>CaliforniaK5's Pictures</a>
     
  13. JBOY

    JBOY Registered Member

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    if i remember correctly, i think the 8-lug 3/4 ton axles that came in '69-72 4x4's would mount in the same place, but the rear-ends were made by Eaton. at least the ones i've seen were that.

    JBOY
     
  14. Burt4x4

    Burt4x4 3/4 ton status

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    That is correct, My faterinlaw has two 3/4 ton 72s and they both have that Eaton rearend. The problem is finding parts for them! New parts are thin from what he has told me....

    72K5[​IMG]Led Zeppelin[​IMG]Rock ON![​IMG]
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  15. POFF

    POFF 1/2 ton status

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    I think I have seen a couple of '72s with 14 bolts. If you find one (a conversion or stock) it should fit fine. Yes a 1 ton axle will bolt up. I put a 3/4 ton axle in my '70 K-20 and I think it cost me about $180 to have the shock mounts and spring pads moved. The best advantage is a Locker is only $350. You can bolt 3/4 ton, 8 lug, front brakes and hubs to your 1/2 ton axle. You can use the same axle shafts. All the front conversion parts are also available from Spicer. If anyone's interested I have a short article I wrote on 8 lug &amp; 14 bolt conversion for 3/4 and 1/2 tons.

    '70 K-20 San Diego, CA
     
  16. 72Blazerod

    72Blazerod 1/2 ton status

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  17. POFF

    POFF 1/2 ton status

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    I'm having problems with my home internet connection, once I get it fixed I'll post it.

    '70 K-20 San Diego, CA
     
  18. POFF

    POFF 1/2 ton status

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  19. 1HIHUM

    1HIHUM 1/2 ton status

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    Hey Greg, what's goin' on? Yeah the 1 ton will bolt right in. Some ( I don't which years) will even have the correct shock mounts. I got mine from my brothers 72 when he parted it. If you decide to take the slower route and build one, I highly reccomend you give Bill a call at Santa Clara truck wreckers( 408-727-2244) He can do all the work, and probably supply the right axle as well. He's good, and priced well. He has done all of my axle and drive shaft work. He also takes trade ins on some parts, so you may even get some money for your 12 bolt when you don't need it anymore. Good luck!

    [image]http://albums.photopoint.com/j/View?u=1328774&a=9975627&p=33244094[/image]
     
  20. Greg72

    Greg72 "Might As Well..." Staff Member Super Moderator

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    1HIHUM,

    Thanks for the info....it will help to have a good lead in the San Jose area when the time comes for the swap. I like using 4WPW for some stuff (parts mostly) but I'm not sure I'd trust them actually working on my truck.....nothing to base that on, just a feeling.

    Somehow, bringing my rig to more of a 'private' shop usually feels more comfortable, and it's always better to get a referral from someone who's already used them and had a good experience.

    Thanks again,

    -Greg72
     

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