Gettin' my gears installed today and noticed the size difference in the pinion gear.

Guess which one is the 4.30 and which one is the 3.73.

 

How much for the swap.

 

4.30 left / 3.73 right : lower Ratio = smaller pinion

 

Smaller = more torque

 

Correct! SupeRobertduty! But not what I had expected.

Not sure how smaller = more torque...

 

It's all about the gear ratio...fewer teeth(smaller) on the pinion means it has to turn more times vs. the ring gear, hence a mechanical advantage over the 3.73's. If you compare ring gears, you should notice that the gear thickness of the 4.30's is much bigger..has to make up the difference in pinon diameter.

 

There is no decrease in strength large v/s small pinion, what there is however is a stronger leverage advantage. This may, only in extreme cases, allow the pinion gear to fail. This is not due to smaller diameter but rather the lower leverage ratio.
In the drag raceing world lower gears is a pluss but also a negative. The leverage advantage makes you stronger but it also places more stress on the smaller pinion... Hope that makes sense.

 

The gears are very strong, but designed to pull in one direction only. Sounds like common sense, but many people don't understand that.

Example:
Next time you have a buddy burried to the door handles in mud, pull him with the back of your truck while you're headed forward, not using reverse, with him hooked to the front of your truck while you try to pull him out.

 

On the ring gear side, the 4:30's are weaker than the 3:73's. More teeth means less material for each one.

 

You guys should see the pinion on a set of 2.73s. I was shocked when I pulled it out of the rear end on my Mustang when I did my gear swap.

 

A Toyota 8" 5.71 ratio is the smallest I have seen, And they have pretty short life span.
The smaller the pinion the weaker (in most cases) a 9" or 14 Bolt are the best in this pinion area.
Lower Ratio: Also means more heat

 

That is common missconception, there are exactly the same amount of material in the teeth just not the same amount behind the teath. But this area is solid steel and it isn't what gives anyway..

Think of it like this, you have a ball 3" round with 1" spikes all over it, now take another ball 1" round again with 1" spikes all over it. Now the spikes are still the same size but the ball is smaller. The gears are the exact same size but what they are attached to is smaller in dia.

The pinion gears are exactly the same strength (if heat treated the same tensil strength) but what makes a lower gear pinion fail is the leverage that is added with lower ratio and anytime you add leverage it makes it easier to break whatever you are prying on.

 

[quote=4wheelfurry;6019984]That is common missconception, there are exactly the same amount of material in the teeth just not the same amount behind the teath. But this area is solid steel and it isn't what gives anyway..

That is exactly why there is a limit to the numerically higher ratios for a given ring gear diameter. You simply run out of material for a certain number of teeth.

Think of a ring gear with no teeth. Then machine in 10 teeth at x thickness. If you now machine 20 teeth, they will be less material. The spacing stays the same to mate with the pinion gear. More teeth equals less material per tooth.

 

This is why I'm running 4.10's in my FJ40. The 4.89's couldn't keep the pinion together.
I may swap to 4.56's this summer though.

 

I have 5:38s in my F250. Know I need a doubler on my Transfercase!