I should have put some jokers in my post. I think it was my last post before bed last night and my mind might have been slightly clouded.
I put a Eaton two speed under drive rear end in my old Class A motorhome, 1.5 ton I.H. chassis years ago, it really helped it a bunch 6.30 or so in under drive and 4.57 in direct, it had a 4.89 ratio in the stock rear end originally. I would leave it in under drive in town and shift it manually out on the road with a electric switch. It worked great for hills and backing the boat trailer into the water slowly Boy, some of the stuff we hot rodder do to get better performance from our vechiles Now back to are original discussion on them no good Ford rear ends of all sizes
Mr.Cab Racing and winning with Mopars since 1964. (Old F--t, Huh)
6.30 or so in under drive and 4.57 in direct, it had a 4.89 ratio in the stock rear end originally. I would leave it in under drive in town and shift it manually out on the road with a electric switch. It worked great for hills and backing the boat trailer into the water slowly 
Boy, some of the stuff we hot rodder do to get better performance from our vechiles
Now back to are original discussion on them no good Ford rear ends of all sizes 
