Originally Posted by JimAllen

You could start looking for a six lug 9.75 deal and they are a bolt-in swap. (9.75 inch ring gear (duh) but 34 spline axles. Well up to 35s. Actually an 8.8 is up to 35s too but the OE carriers are a weakness... one which you have cured now. The 31 spline shafts in the 8.8 are actually very strong. Ford specs a SAE1050 carbon steel in their shafts, which is considerably stronger than the SAE1025 or 1040 steel in most other axle shafts. Still, you have an 8.8 in a relatively heavy truck and, combined withteh 35s, that cuts into the strength considerably.

You might be interested in the factory output torque ratings for recent Ford axles (rating for the complete assembly):

8.8 28 spline- 4,600 lbs-ft (short duration), 1,250 lbs-ft (continuous)
8.8 31 spline- 5,100 lbs-ft (short duration), 1,360 lbs-ft (continuous)
9.75- 34-spline- 6,100 lbs-ft (short duration), 1,600 lbs-ft (continuous)
10.25 SF- 35 spline- 8,300 lbs-ft (short duration, 2,000 lbs-ft (continuous)
10.50 FF- 35 spline- 10,660 lbs-ft (short duration), 2,900 lbs-ft (continuous)

Some year back, I was involved in some destructive testing of axles and front axle u-joints. We broke some of the popular types. 30 spline Dana and GMs snapped at under 5,000 lbs-ft. A 31 spline Ford maxed out the test fixture. It couldn't be broken by the machine's maximum output, which was a shade over 6K lbs-ft.

Originally Posted by tbear853

The symptoms offroadn'98 talked about leading up to it, the jumping or jerking .... I think it was something I've talked about before, something I went through back in the '70s with my Swinger 340.

I think he's been spinmning rear wheels and with added stress imposed upon the spider gears by 4.88s multiplying torque on one side and those big tires on the other ...
... lots of pressure there, it likely wouldn't take a long burnout ...
... I think the cross shaft seized to a spider gear and twisted and sheared the retainer bolt and then after it cooled off that now unrestrained cross shaft was being slung out the case part way and hitting the pinion gear as it came over the top and the jumping he felt was that cross shaft hitting the pinion gear and getting knocked violently back into the case ..... and that the implosion was the result of "the straw breaking the camel's back".

The jerk where it was sticking out at low speed stopping the truck, backing up and then hitting it hard ...
... parts busted.

Originally Posted by Patman03SprCrw

you have quite a bit of bearing wear too, get water in the diff by chance?

Originally Posted by offroadn'98

Good info thanks
Is a 10.25 a direct bolt in swap?

Originally Posted by offroadn'98

I think you nailed it. I do admit that i lose traction quite abit. It doesn't hook up good when you nail it off the line even with those tires. Like i said i admit i have been rough on it. I think this comes down to uneducation on my part as to what the limitations of my truck are. Just big tires, big gears and using them to there full potential is what killed it. Just a bad learning experience. Pretty good figureing all that out.

Originally Posted by JimAllen

Yeah, but it has a 7-lug bolt pattern on the wheels (few choices of wheels) and because it's a c-clip unit all the 10.25 full-float lockers don't fit and you have literally only a couple of choices. It came on the 8200 GVW trucks only, of which an average of only about 4 percent of the annual F150 production consisted. For the '08 and up 8200 trucks, they went to the 9.75 with (I think) beefed up axle tubed for the increased GAW. The 10.25 is not a great choice.

Originally Posted by tbear853

I learned it by doing long 2nd gear burnouts with an open diff in my 69 Dart Swinger 340 4spd / 3.91 gears in about 1972-3.

I experienced what you felt ... starting after a particularly long one headed out from New London there on Rt 460 one Sunday. I babied it for a couple days but it got worse and by Tuesday after school, I jacked it up, pulled the axles, dropped the hogshead and saw what was happening BEFORE it self destructed. I could see very plainly the cross shaft was loose, the bolt retaining it sheared, and the end of it beaten and the ends of the teeth on the pinion were chewed up.

Trip to Va Auto Parts out on Wright Shop Road and $25 got me a complete hogshead with the right yoke and 3.23 gears and a new gasket set and I was back in business with better gas mileage to boot. I changed speedo drive gears and since most of our running was from a roll, didn't hurt too bad.

I learned, it just cost me less. I was lucky.

Originally Posted by Klitch

drop the 8.8 all together, the 9.75 will be much better off behind the bigger motor. Also, if you know of anyone still making the 8.8 full float kit let me know, I'd like one on my budget wheeler.

the pinion sheared teeth on a NA 4.6, the carrier split with the L motor.

Originally Posted by Klitch

drop the 8.8 all together, the 9.75 will be much better off behind the bigger motor. Also, if you know of anyone still making the 8.8 full float kit let me know, I'd like one on my budget wheeler.

the pinion sheared teeth on a NA 4.6, the carrier split with the L motor.