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Load capacity for a GM 14 bolt, semi-floating rear?


 
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JDemaris
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PostPosted: Sun Aug 15, 2010 4:59 am    Post subject: Load capacity for a GM 14 bolt, semi-floating rear? Reply to specific post Reply with quote

I'm trying to find the safe-max load capacity for a GM rear from a 3/4 ton Suburban. Weight load is all I care about, not pulling capacity. Weight load is determined by the axles and wheel bearing, whereas pulling is determined by the size of the ring and pinion.

14 bolt, 9.5" ring gear, semi-floating, 8 lug.

The "max axle specs" posted on many truck door pillars don't do me any good. They take into account the sring package and are not just for the axle itself.

I do know this axle as a max torque allowed at the input (where the driveshaft hooks) of 2,100 foot lbs. The GM 10 bolt axle has a max input of 1500 foot lbs.

I don't care about the torque though, just want to know the weight-carrying capacity that is rated "safe" for constant use.

I've got a diesel 4WD mini-motorhome that weighs 7000 lbs. and at present has two 10 bolt axles under it with 235/75-15" tires. I am supposing the axles are at their max and maybe a little over? Been fine for two years now, but - I'm thinking of sticking in bigger axles with 16" tires. All depends on the gain.

I have a pair of axles I pulled out of an 89 GMC 3/4 ton diesel Suburban. Front is 10 bolt and rear is the 14 bolt I mentioned. As far as the front 10 bolt rear, I'm assuming it has bigger wheel bearings then it would if in a 1/2 ton rig - but I'll have to research it.

If I use this setup, I'm also getting much bigger brakes which will be nice to have.

Back in 1976, Chevroltet and GMC sold factory-authorized K5 Blazers and Jimmys with motorhome bodies installed - and got sued over it - and forced to stop. The reason was - the rigs came with a GVW of 6500 lbs. - and as soon a gear and three adults got in, it was usually over that weight.
These setups were called "Blazer Chalets" or "GMC Casa Grandes." I've got several
On the GM literature for 1976, they show the front 10 bolt axle with a max. load of 3600 lbs. and the rear 12 bolt axle with 4000 lbs. max. The 12 bolt has the same axles and wheel-bearings as the 10 bolt axle, so I assume 10 bolt axles are also rating 4000 lbs. max for weight load?
Axles and weight limits take load and pulling capacity into account. I assume the 12 bolt used in 70s 1/2-tons is rated higher then the 10 bolt because it can pull more, NOT carry more.

I've got to assume the 14 bolt semi-floater is rated up around 5000 lbs. or more, but I've yet to find any specific specs for load capacity.
 
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Allan in NE
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PostPosted: Sun Aug 15, 2010 5:51 am    Post subject: Re: Load capacity for a GM 14 bolt, semi-floating rear? Reply to specific post Reply with quote

Have no idea,

However, can tell ya that I've got a 2 1/2 ton truck that I routinely gross at 20 ton.

Just don't think you're going to have any trouble with the floater in that outfit.

Allan
 
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JK-NY
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PostPosted: Sun Aug 15, 2010 10:09 am    Post subject: Re: Load capacity for a GM 14 bolt, semi-floating rear? Reply to specific post Reply with quote

I cant give youy an actual weight , but I had a 1986 Chevy 4wd hd 3/4 ton (K20 ) with that rear axle (4.10 ratio)and it had a gvwr of 8600#.
 
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JDemaris
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PostPosted: Sun Aug 15, 2010 10:17 am    Post subject: Re: Load capacity for a GM 14 bolt, semi-floating rear? Reply to specific post Reply with quote

I know most all axles will carry much more then the published load-capacity. I assume they won't last as long when overloaded, but I know many work fine.

I'd just like to see the specs.

My GM 10 bolt rear 8.5" has axle bearings that measure: Inside diameter=1.6180"; Outside diameter=2.5778"; Width=1.303"

My GM 14 bolf SF 9.5" rear has axle bearings that measure: Inside diameter=1.7080"; Width=1.320"; Outside diameter=3.0880"

That's a pretty substantial difference. The 10 bolt is rated 4,000 lbs. so it seems the 12 bolt must be 5000-6000 lbs.
 
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Rick Kr
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PostPosted: Sun Aug 15, 2010 11:13 am    Post subject: Re: Load capacity for a GM 14 bolt, semi-floating rear? Reply to specific post Reply with quote

JD,

Copied this from Four Wheelers website.

However, most people are not aware of the less common six-lug, semi-floating version of the 14-bolt axle. GM called it the "9.5" 14-bolt (after its ring-gear diameter) and offered it exclusively in light-duty 3/4-ton pickups built between 1986 and "93. While not as strong as its eight-lug cousin, the semi-floating 14-bolt rearend does sport some noteworthy attributes. For instance, the all-important width measurement from wheel mounting surface to wheel mounting surface is 67 inches-perfect for most 1/2-ton pickups. Generally, you wouldn"t even need to change mounting brackets to bolt this housing right into the rear of a 1/2-ton GM pickup because the leaf spring architecture is identical. We like the fact that the ring gear measures out at a healthy 9 1/2-inch diameter, and the 33-spline axleshafts have a 1.370-inch diameter-a sure improvement in strength over the typical 1/2-ton shafts. This less grown-up version of the 14-bolt may not have the extra pinion support bearing of its eight-lug cousin, but it"s rated to handle 5,000 lb-ft of torque, so it"s no lightweight either. Moreover, aftermarket suppliers such as Randy"s Ring and Pinion offer all the upgrade goodies you need to make this rear end survive with up to 37-inch-tall rubber. As a result, owners of virtually any GM 1/2-ton pickup offered with six-lug wheels can benefit greatly from a semi-float 14-bolt axle upgrade.

Here is the kicker: Thanks to the semi-floating design, a factory-style wheel will bolt right up. This means you do not have to spend your hard-earned cash on eight-lug wheels to get vast improvements in overall axle strength. We think these axles are the cat"s meow for trucks equipped from the factory with 10- or 12-bolt rear axles.

JD IIRC
9.5" were 6 lug semi floaters GVW 7700lb, GAWR RR around 5000 or 5200 lbs.
10.5" were 8 bolt full floaters. I think those were commonly at 8600GVW and 6000lb GAWR RR.

Then Dana 60/70 were in the 3500 series. These had 6000lb GWARR. 8600 GVW

Later I think the 3500 went to a 9200GVW still with a 6000 axle rating. I use to have all this info, but pitched it about 10 years ago, thinking I would never look at it.

Not sure my numbers are correct, maybe someone else can verify them.
 
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JDemaris
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PostPosted: Mon Aug 16, 2010 4:02 am    Post subject: Re: Load capacity for a GM 14 bolt, semi-floating rear? Reply to specific post Reply with quote

Thanks. That's more info that I've found anywhere else in one place. It still doesn't mention actual weight load capacity, but I guess I can infer. I knew that some of the 14 SF versions were made for 6-lug wheels to go into 1/2 ton trucks. Mine are 8 lug, which is fine with me. I wanted to upgrade from the exisiting 235/75-15" tires anyway since HD tires in that size are scarce. Going to the 8 lug 16" wheels will allow me to use 235/85-16" tires with a much heavier load-range.

I compared the 14 bolt axle assembly to the exisiting 10 bolt. It's a bolt-in swap. Only change I have to make is the pinion flange. 3/4 ton pinion flange is made for a bigger universal joint, so I have to buy - either a conversion flange, or a conversion universal joint. NAPA sells a joint that is 1/2 ton on one end, and 3/4 ton on the other which is probably the easiest way to get my driveshaft hooked up. But, if I use the conversion flange instead, I'll have the heavier 3/4 joint. Since this area is a weak-point anyway, I might go for the conversion flange.
 
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Rick Kr
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PostPosted: Mon Aug 16, 2010 7:26 am    Post subject: Re: Load capacity for a GM 14 bolt, semi-floating rear? Reply to specific post Reply with quote

JD,

I think a lot of the axle ratings at the time were limited by the load capacity of the tires themselves.

Not saying you should go overload those axles, but I would think that corporate 14 bolt should be plenty under a 7000lb motorhome.

Rick
 
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