explain 14bolt FF & SF and more Q's

[1low4x4]

I have a 14 bolt semi float rear with 4.10s...I don't remember how I identified that, but I did it on this site. The glove box says 4.10s.

I hear tell the FF is better...what is the difference and why didn't they just build the stronger one?

Also, I have a 350, 4L80e, stock tires and at 70 I want to say I'm turning 2200 rpm? Around that, and that's with converter locked up.

If I was to install 3.73s would that drop rpm? Also I've heard it would hurt my towing...and towing from a light or whatever...take off. Low end.

Any input?

 

[theblindchicken]

A 14 bolt sf has a 9.5" ring gear compared to the 14 bolt ff's 10.5" ring gear. The full floating axle design is stronger due to the larger ring gear as well as that the axle shafts don't carry any of the hauling load whereas the axle shafts in a semi-float carry a portion of the load being hauled. Essentially meaning that the only forces acting on the axle shafts are the torque being applied from the differential and the resistance to movement being applied from the wheels.

A major advantage that the full floating axle design (which most 4 wheeler guys love) is that the axle shaft can be easily removed if damaged, since the axle shaft plays no part in holding the wheel to the hub or holding it up at all. The axle tube carries all of this weight.

The rear differential gearing plays a big part in your tow rating. The lower the numerical ratio to one, the harder your engine has to work to tow/haul from a standing start. Even without a load, the lower ratio affects your acceleration quite a bit. On the plus side, the higher gears help your highway fuel economy as well as your top speed. But going too low can have an adverse effect in that it may place your highway rpms outside your engine's preferred powerband and decrease your fuel economy.

The higher the numerical ratio to one, the easier it is for your engine to tow/haul from a standing start. Your acceleration will be much quicker, but your top speed will be lower. At highway speeds, you will be running higher rpms which can lower your fuel economy.

From what I've noticed, most tend to stick around 3.73:1, 4.10/4.11:1, 4.56:1 gearing because it allows them to have easier towing, a decent top speed, and decent acceleration. Your fuel economy really comes into play when you factor in your transmission and your choice of tires.

Hope all that helps.

 

[HotRodPC]

Good explanation there TBC. I'll add, for MOST applications, the 14b SF 9.5 rear axle is plenty strong.

I think your set up is just perfect as is Nick. Having the 4L80-E so you have OD, you are compensating the low 4.10's just fine. The 4L80-E also has a farily tall 1st gear compared to say a 700r4 having a 3.06 ratio first gear, and your 4L80-E has a 2.48 ratio first gear. So the 4.10's do help with the 2.48 first gear ratio in take offs and towing from a dead stop. You might drop 200-300 rpm to go to the 3.73s at 70mph, but then you just might drop out of your power band range where the motor doesn't have the rpms up high enough, then you'll start struggling with constant convreter unlock and lock up, and downshfiting in and out of of OD to 3rd back and forth. All of the going on will certainly put excessive wear on your drivetrain, and more strain on your motor. I think I'd leave well enough along if it were me.