My 03 f-150 jerks when you let off the brake in 4lo is this normal? I've had the truck for 4 months and never used 4wd

 

It will do all sorts of weird things in 4low.

Pop, clunk and jerk. As long as it works, don't worry about it.

 

well it does all of those things haha

 

You do realize 4lo changes the complete gear ratio right? Now I'm not gonna do the exact math. But let's say you have 3.55 gears stock, 4lo is going to change your gearing to say 4.10's. Not exact math but that why it jerks. I've got 4.10's, mine launches for lack of a better word when I let off the brake in 4lo. Like Tackle said, it'll do all sorts if weird things. The clunck is the transfer case locking the front and rear together.

 

Its normal. 4l changes the gearing it the tcase from 1:1 to 2.64:1

 

Hmm mine doesn't do that - switching it into gear is slightly noticeable, but it's smooth and does not pop, clunk, jerk afterwards or during operation.

Are you sure that's normal?

 

Yeap.
3.55*2.64*(torque converter 1.9)= 17.8:1

 

You forgot the 2.84 first gear if you have a 4r70w.

He said it jerks when he let's off the brake. Depending on the terrian the truck will lerch forward do to the gearing. Op are you steping on the gas too?

 

All gearing in 4 lo would be multiplied by that.

 

Try it with a spooled front and locked rear ha ha