rear end differential

Someone told me there is fluid within there that you are suppose to change? How often should you change that out?

Every 60,000miles would be best.

Suck it out with a pump and refill with 80w90 or synthetic 75w90.

The amount to fill should be in your owner's manual.

That's good advice - If the axle has been properly service at least once before. Many Saginaw (corporate) axles come assembled with a gasket which covers the oil return holes from the ends of the axle tubes. This is more common on the 8½" axles, but is worth checking on ant of them.

http://72.19.213.157/files/DiffGasket.jpg

Notice that the replacement gasket has slots to uncover the return holes, whereas the OEM gasket does not. Oddly, they USED TO have these holes. Once the correct gasket is installed, subsequent axle oil changes can be accomplished with the suction gun/refill method, so long as you're certain the suction gun is removing all the old oil.

I thought our axles were sealed.

I was taught to loosen the bolts on the cover and allow the fluid to drain out. Then tighten the bolts back up and fill.

In most cases you can't do it that way seeing there is a gasket you have to replace.

We never replaced the gasket. No problem with leaks - at least as long as you weren't careless and tore it.

I thought our axles were sealed.

AFAIK, they are still sealed on the outer ends, like they always were. However, they are not sealed at the inboard ends of the axle tubes, which allows lubricant to eventually work its way to the outboard bearings by a little splash and a little G-force. The notch is just another means for oil reaching the outboard ends to drain back to the main gearcase area/reservoir.

http://72.19.213.157/files/Saginaw10.jpg

silicone has worked for me.

True, but what I meant is that you have to redo the seal when you ever pop it open.