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The "8L" that you refer to denotes a 4.88 Limited Slip rear axle ratio. I am unsure what the "C" stands for. A truck that has an axle code of "4L" has a 4.30 rear gear ratio. Additionally, F-450's were initially produced with 4.30 rear axle gears standard and 4.88 gears were part of the High Capacity Trailer Towing Package, which also required a limited slip rear, which that truck has. A 4x4 450 with 4.30 rear gears is rated to pull a 20,500 lbs. 5th wheel/gooseneck trailer. A 4x4 450 with the 4.88 rear is rated to pull a 24,500 lbs. 5th wheel/gooseneck trailer. Yes, the 4.88 rear gears will decrease fuel economy, but you can solve that issue by looking into a Gear Vendors Overdrive unit. Yet another piece of info, any of the 450's that were equipped with the High Capacity Trailer Tow Package actually had de-rated engines (325 HP, 600 LB-FT TQ) versus the standard rating in 4.30 equipped 450's (350 HP, 650 LB-FT TQ). This was done in the interest of maintaining engine life with the engine turning higher RPM's. 4.10 gears have not been offered on the F-450.
It might interest you to know that current F-450 pickups can only be built with the 4.30 gears, BUT, you can now order the High Capacity Trailer Towing Package which increases the trucks towing capacity to 24,500 lbs. and it no longer changes the engine power ratings. This was done because the 4.88 450's were fairly fuel thirsty. I am somewhat disappointed by this because the 6.4 likes to rev and I think the steeper 4.88 gears help the engine hit it's sweet spot faster on heavy loads for better pulling performance.
Hope this helps.
Last edited by ponyexpress94; 08-02-2009 at 12:42 PM.