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Old 10-10-2008, 11:47 PM   #12
stillsmokin
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Join Date: Sep 2008
Location: The Midwest
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Re: 7200# rear axle (HO72) extreme application

Quote:
Originally Posted by pumpkin View Post
From what I've been able to find out, the difference between the ho 52 and ho72 is that the ho72 has an adjustable deflection bushing directly opposite the pinion gear, so the ring gear cannot deflect away. I would say the ho52 is comparable to a 14 bolt, and the ho 72 is just a bit better. I've been colecting these rear ends for a while now, and have picked them up from 3/4 ton to 3 ton trucks. I do believe, like all things that are built too good, they just stopped making them because they were way stronger than needed. I don't know how they would hold up in major extreme use, but I would use one over a 14 bolt or dana 70. I am not familiar with a dana 80.
According to the 68 chevrolet overhual manual the difference between the 7200# and 5200# axles is the brake size. The manual also implies these are not actually "eaton" units rather, scaled down single speed eaton designs that GM produced. The "eaton brand" designation is used at 18,000 pounds and heavier in the manual. The "HO72, HO52" is not a GM axle designation by the way, apparently somebody invented this over time, and they are NOT 12.5" either, that would be the 11,000# unit. The 5200/7200# axle are 10.125" ring gear. I believe the load bolt design is simply a later design revision. These load bolt third members have additional oiling passages for the revised tapered roller pinion bearing vs. the ball roller/no load bolt/no oil passage earlier version. GM quit producing them due to "high production" costs but it is becoming apparent now the quality of materials used was definately top notch, so the costs were well worth it. Yet the offroad magazines have yet to even list it as a high strength axle, it's amazing these people still get a paycheck.

I just heard in a conversation how a ford puller down the road ran a 14 bolt for a few months last year because he kept breaking axle shafts in a dana 60. Then, he found more power and twisted off the pinion in the 14 bolt, He then went with a 5200/7200# axle and he is now twisting the driveshafts off at the middle of the stubshaft, they wanted advice.
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86 Chevy K30 Crew Cab, USAF(retired), TH400/NP205, 28K miles
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92 Dodge, Cummins, SLED PULLER, 5'' hood exit, NV4500UHD, dual disk clutch, Borg Warner S400 charger, GM 7200#/14B hybrid rear

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69 GMC k2500, 427, 4 speed, Rockwell 221, 7200# rear, detroit, disk brake front, 5.13's
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