I have a 99 F150 4.6 with a 8.8 /3.55 L/S rear. The small bolt that holds the pinion shalf in the diff broke and the shaft itself broke. When I removed the cover, ifound the broken pieces, the spider gears, and the broken spring cage from the spiders......what do I do now?
Besides replacing parts

 

Might be better ( possibly cheaper) to get a whole rear end from a salvage yard, AND do a whole rear end swap.

If you do pull a trailer, trail hard or haul regularly...maybe up grade to a heavier 9 3/4 rear end, with better ratio gear set 4:10 or 4:56

 

I would highly recommend replacing your 8.8 rear axle with a 9.75. You have already broken an 8.8 so it will break again.

 

This is the second rear that has broken in the last two years, the last one broke the ring gear. I did a direct replacement with another 8.8; so I might have to take your advice and upgrade. I already bought the parts to repair the rear, I am not sure what order they go back in.

 

I broke 3 8.8 diffs in tghis truck and 2 on my 97. When the 8.8 broke for the 3rd time I swapped in a 9.75. I had to shorten the driveshaft because there was never a 9.75 configured with a 5 speed and transfercase. So I could not order one. Sell your parts and swap.