Differential

No more than likely it will spit oil out the vent on top of axle. Just pull the fill plug until it quits draining on a level surface and will be filled okay.

I would estimate a used replacement with labor to be around 1200.00. Make sure the gear ratio is the same as the original one.

Hi dick61045. Welcome to the forum. Don't forget, you're going to have to change the gears in the front axle too. I have a much better idea since this isn't a common problem. Look for a diesel shop that specializes in fuel injection systems. We have one in my town that does a modification to the injector pump that increases fuel mileage and boosts horsepower and torque a lot. They are also approved by Chrysler for performing warranty repairs.

You can also install the boxes they call "chips" that modify pump timing and increase power. My friend has two dually diesels with these boxes and either one will just about tear the tires off the wheels.

Caradiodoc

You're going to have to change the gear ratio in the front differential to match the rear one unless you want the front and rear wheels to turn at different speeds in four-wheel-drive. Engine noise will go way up. Luckily your truck has a solid front axle. With independent suspension, or worse yet, Ford's twin I-beam front end, there is no way to eliminate tire wear with any alignment settings. If your lift kit included a dropped pitman arm to keep the same geometry for the steering linkage, handling should remain somewhat normal.

Yup, but you have to do both axles and they need to be set up by a specialist to adjust the proper preload and backlash. I did two axles with the service manuals handy. I don't ever want to do another one.

I'm still confused on what you were told about stress. The stress comes from the rubber control arm bushings being in a permanent twist from the suspension being lowered to raise the truck. The gear ratio has noting to do with that. 4.56s will give you quicker acceleration and usually lower fuel mileage but it won't change anything else. I can see where someone might think there would be less pressure on the universal joints but they can take that. The wear is also a factor of how far the needle bearings roll back and forth in the cups each drive shaft revolution. At the design height the cups are meant to turn back and forth a little so the needle bearings never stay in one spot and create dents in the rolling surfaces. Raising the truck increases the drive shaft angle which does not eliminate that rolling back and forth but it makes them roll further which I suppose could make them wear faster.

I think I'd talk with a few more people before you go to such an extreme measure of changing gear ratio without knowing what they're trying to solve. The impression I get is someone is trying to sell you an unneeded service.

Too much to explain you will have to purchase a manual from your local store, beginning operation and if you have any questions let me know and I will answer them for you

The bearings should be the same. Sounds like the idea is for the faster-turning drive shaft to offset the need for the wheels to turn slower since the outer circumference will be bigger. You may run into an issue with the speedometer. As I recall, the speed sensor is still run by a plastic gear in the tail housing of the transmission. The service manual should have a chart that crosses the tire size and axle ratio to determine the correct number of teeth on that gear. Some car models have a pulse generator, then the tire size and axle ratio have to programmed in with a scanner. Those have a very limited number of choices and if you modify something enough and the needed choice isn't listed, you're out of luck.

In your case, a higher gear ratio and larger tire circumference might offset each other enough that the speedometer will be close. Look for one of those roadside speed indicators to check your speedometer. I've found them to be pretty accurate.

You can go to a larger axle physically but you do have to stay with the gear ratio that matches the front so the two drive shafts turn at the same speed. Look for a small metal tag under one of the differential cover bolts. The gear ratio will be stamped on it.

There is also a consideration with the brake size because that was carefully designed in with the size of the front brakes to create a balanced braking system front-to-rear. Look at the shoe width, lining length, and drum diameter first. If those are different the braking forces will be different. If they're the same you also must consider the diameter of the wheel cylinders. That affects how much force is put on the shoes. If you have rear-wheel anti-lock brakes, that will reduce easy rear-wheel lockup, but still, that is the type of thing insurance investigators and lawyers look for when they're trying to shift some of the blame for the crash from the other guy who ran the red light onto you.