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28 vs 30 spline 10 bolt front

michael0584

michael0584

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What is the strength difference between the 10 bolt 28 and 30 spline axles. I just picked up a cheap complete 30 spline 10 bolt front axle. I will be running a 12 bolt in the rear with a mini spool. I would like to run some kind of a lunchbox locker in the front. I am running 33s right now but may move up to 35s, but probably never bigger than that. Will the 10 bolt hold up to 35s and a locker?
 
I'm no expert in axle strength, but from what I've seen with the rears, the splines aren't the weak spot, so I would suspect the fronts to be the same way. Doesn't matter, except in regards to replacement parts. Or at least such a miniscule difference in the grand scheme of the axles that it's not worth worrying about.
 
Many guys that race cars with 8.5 10bolts in the rear upgrade from 28 to 30 spline setups. The amount of splines makes it stronger but this also requires a larger hole in the case which makes it abit weaker in that area. I think its a toss up. I ran 38x16's on my 10 bolt with a lock-rite, it survived but the ball joints went out. I would not recommend anything larger than 35's without stronger axles, joints, etc, also depends on amount of power from the motor.
 
What I understood about the difference in the 28 spline vs 30 spline was that the 28 spline neck done right before the splines, which is the weak spot where they always break and the 30 splines don't neck down. But i think the outer shafts are still 28 splines. Just didn't know how much stronger all this made them.
 
I have never heard anything about the neckdown, but they do usually break right at the splines. You will probably break outers and ujoints long before the inners or carrier.
 
Run the 28 spline if your on stock axleshafts , run the 30 spline stuff if your on aftermarket axleshafts .

My reasoning to 28 spline on factory stuff is that there are many, many more years of solid axle truck to choose from in junkyards and ebay when getting replacements and spares . 30 spline solid axle were only around a few years in factory Blazers/Subs .
 
If the hole in the case is larger, then the axleshaft diameter is larger. Overall diameter of the shaft isn't influenced by spline count UNLESS the axleshaft diameter in the spline area was changed.
 
The major diameter of the shaft (the biggest part, at the splines) is shown by the equation D = (number of splines + 1) / diametrical pitch.

Basically everything (most Dana and GM axles) except coarse spline shafts (like the FF 14 bolt) use a 24 diametrical pitch. So:

(28 + 1) / 24 = 1.208"
(30 + 1) / 24 = 1.29"


Since the torsional strength of a shaft is based on the moment of intertia you can represent the difference in torsional strength as:

(1.29^4)/(1.208^4) = 1.300

The 30 spline shaft should be approximately 30% harder to break than its 28 spline counterpart. That's only assuming that the axle shafts have a similar profile, if the 30 spline shaft necks down a lot it won't be as strong. AFAIK 28 and 30 spline shafts are pretty similar in profile so its probably safe to say that 30 spline shafts are at least 25% stronger than 28 spline 10 bolt shafts.

I have heard that GM used the same carrier for both 28 and 30 spline axles and simply bored out the journal bearings to fit the larger shaft. Apparently this can cause some carrier failure issues, particularly with lunchbox style lockers.
 
Thanks, I guess i will run the 30 spline, If I ever break a shaft then its time to go 1 tons. I will leave it open for now maybe I can find a good used detroit or something better than a lunchbox to put in since they would be common from the 10 bolt rears of 88-98 trucks.
 
I cant do the math but I can say from experience. 30 spline axles 10B fronts are quite a bit stronger than 27 spline. Problem is the rest of the running gear.:D U joints, carrier, spider gears,
I am locked front and rear with 30 spline 10 Bs. I an usually careful and drive like I run 10 bolts. The only problem I have had is U joints. But that is fairly common with any axle that is run hard.
 
Yea I plan on putting in new spicer ujoints, I hear they are stronger than the stuff you get at most parts stores.
 
Spicers are good. So are NEAPCO Brute force U joints. I have had good luck with them. I get them from Carquest
 
The 30-spline shafts on front 10-bolts neck down to the same diameter as the neck-down on the 28-spline shafts, so there really isn't any strength increase. The u-joints and the stubs are exactly the same also and in my experience you have just as good as a chance to break a u-joint or stub versus an inner axle.

The only reason they offered 30-spline in the front is because they switched to 30-spline in the rear and by making the front the same they only had to make one set of carriers. The rear axles did get a decent axle shaft strength increase because the shafts do not neck-down.......but not the front.

As being the proud owner of a K5 with a 30-spline front 10-bolt for years I will definitely agree that finding replacement shafts is a big PITA. The only replacements I ever found were people selling OEM stuff used. I could never find any place selling new OEM stuff or aftermarket replacements, and I looked a lot!
 
Sounds like you didn't look hard enough. Superior makes both stock replacement and chromo shafts for 10b 30 spline front axles. Several others make chromos as well (Alloy USA and Yukon come to mind).
 
I think I will run the 28s till I break them since I have a spare set of 28s. Then If break them I will go to 30s.
 
MaxPF said:
Sounds like you didn't look hard enough. Superior makes both stock replacement and chromo shafts for 10b 30 spline front axles. Several others make chromos as well (Alloy USA and Yukon come to mind).
Click to expand...

Should of clarified......this was back in the late 90's, early 2k, don't even think any of those companies were around. It wasn't even common knowledge at that time a front 30-spline 10-bolt existed, even Stephen at ORD didn't believe me until I sent pictures.

I did order front shafts a few times but always received D44 shafts, which are not the same.
 
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