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12 bolt vs. 14 bolt

A

aceroth

1/2 ton status
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I'm currently running a 12-bolt behind a tired 350 but am about to swap a 375hp 383 into it and the 12 bolt is leaking from the left axle. I have shopped around and can get bearings and seals for the 12-bolt done for $550. Question is whether I should drop money into the 12-bolt or get a 14-bolt for $1K ($300 core, $650 bearings/seals) $1,200 if I need to regear. I will wheel the truck some but not hard. I mostly drive like an old lady but still have doubts about putting money into a 12-bolt with the new motor.

I may decide to do the axles/seals myself which would save $300-$400 but not sure that matters much to the question of whether I keep the 12-bolt or go to the 14 since the savings is similar (as long as I can find a 14-bolt with the right gears).
 
If you decide to keep the 12 bolt, you might want to drop some cash on Yukon axle shafts.
Sure, the stock 12b shafts are better than a 10 bolt.
But with age, metal fatigue, wear on the axle due to bearings, wear on the splines.. just replace them.

I swapped a 12 bolt with 3.73's a Powertrax no slip unit, new shafts, bearings and seals into my m1009 to replace the 10 bolt with its 3.08's and gov bomb carrier.

In your case, your motor will be making 215 more horsepower than my 6.2 J code.
Even more reason to beef up.

If I had to do it again, I'd spend the money on a 14 bolt FF.
In fact, I will some day.
 
If I go 14 bolt, it will be a full floater




QUOTE="sweetk30, post: 3922901, member: 18425"]axles and seals = basic easy level stuff .

and what 14 bolt ? semi float or full floater ?[/QUOTE]
 
Its on 33s now. Might go to 35s but no bigger.



QUOTE="SpeedlabDan, post: 3922904, member: 85004"]What size tires?[/QUOTE]
 
If you go full float you will be changing front hubs, rotors etc. as you will be 8 lug. And wheels too. Have you broke axles? Front or rear? If not you may consider a 14 semi with 6 lugs.
 
Yeah, I thought about the wheel thing. I am on steelies now so no bug loss there but loving new hubs and brakes less.
 
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I'm still running my 12bolt with Moser axles and a locker. 35x12.5 and a 383 with 490 lbft. I'm running it till it breaks.
If you were goin over a 35 I'd say go semi float 14 which I may do when the time comes.
14bff are huge and heavy for tires that small if you're gonna wheel it
 
I'd guess most 14 bolt axles bought used in good condition could be slapped in and used without doing more than a fluid change..
It's not that often they "wear out" unless they got run low on gear lube,or have like 200,000+ miles on them..
 
No locker? Just an open diff?

What gears?

I would imagine I would likely keep the 12 bolt. Its really when you get into harder wheeling and especially adding traction aiding diffs to said 12 bolt that they show their weakness. I know alot of folks who have wheeled 12 bolts and 10 bolts for a long time with very little issue.

I used to be a bigger axle all the time guy but it sounds like with your use the 12 bolt will be fine
 
If you feel that upgrades and wheeling are even possibly in your future, don't put any money into the 12 bolt. The 12 bolt isn't a bad axle you just need to understand its limitations and decide if its ok for what you do with your truck. I recently swapped an AAM 10.5 (late model 14B with discs) into a K5. Did seals, brakes and a Detroit locker myself. All in including buying the axle, seals, detroit, calipers, pads and rotors I was at $1000. Its awesome and I will never have to worry about it. Buy once, cry once.
 
That's what I'm kind of thinking. I can get a junkyard 14 bolt for $160. As long as it has the right gears, do bearings and seals myself for $250 and discs for another $300. $700 all in for a way better setup than I have now.



HankScorpio said:
If you feel that upgrades and wheeling are even possibly in your future, don't put any money into the 12 bolt. The 12 bolt isn't a bad axle you just need to understand its limitations and decide if its ok for what you do with your truck. I recently swapped an AAM 10.5 (late model 14B with discs) into a K5. Did seals, brakes and a Detroit locker myself. All in including buying the axle, seals, detroit, calipers, pads and rotors I was at $1000. Its awesome and I will never have to worry about it. Buy once, cry once.
Click to expand...
 
sweetk30 said:
what bearings on a 14ff . ?

almost every one i have ever had apart didnt need bearings unless regear or major damage .

pull them / check them / if good oil them and reinstall them .
Click to expand...

I have opened up 3 in a row that had good bearings that I didn't feel needed replaced.
 
Most 3/4 ton trucks get driven around empty much of the time,so the rear diff doesn't get much load put on it..few owners haul heavy loads constantly too,excepting those hauling or towing campers..
Therefore they don't normally fail or get much excess wear..it takes a lot of high miles to wear one out if it has been kept full of lube and had it changed at regular intervals..
 
Will the tires even touch the ground running 33s with a 14 bolt?


All seriousness with 35s max stick with the 12 bolt if you plan on wheeling. Unless you like you spotter repenting "rear diff, rear diff, rear diff"
 
205/55/16 tires on stock gm 8lug steel rims . your not getting a 2.5ton or up good floor jack under the diff tho . but it clears the floor and rolls .

002-jpg.277533
 
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