Rear differential on f150 is leaking,how do i reseal it?(1984 f150 4x4)

remove the rear cover all the bolts except the top 1 just loosen that 1. Put a bucket under the rear diff and open the diff cover and drain out the fluid. clean and reseal the diff. remove the plug on the front of the diff and fill with the correct diff fluid until it is filled up to the hole and replace the plug, clean up and check for leaks. No leake = job is complete.

This is different. In a perfect world, you would run the truck on a dynamometer, get it up to 55 MPH and look under the truck. The fluid is going somewhere.
There is a vent tube on most axles. Follow the tube to find its' end and see if the fluid is traveling away from where you had expected a leak. Check your axle shafts under the rear rotors to see if the Emergency brake drum is oil coated.
Another way to think about this is the original failure. The pinion seal. The seal contacts the rotating flange. If you have a wobble in the driveshaft, (balance issues, U-joints) then the rotating flange can wobble. If you have a bad pinion bearing or carrier bearing, it can work to make the spline gear wobble.
So I am suggesting that the leaking Pinion seal was caused by something and the seal was a casualty of an undetermined cause.
You should be able to add an Ultra-violet dye to the axle fluid to find your leak. Even if it is running from the same place, the current leak will be showing the UV dye.
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I assume you are talking about the rear differential. There is not a drain plug. Two ways you can change fluid - 1) Remove differential cover, let fluid drain, reseal with rtv, and tighten down. To refill there is a plug that you need to remove, fill until fluid comes out the hole. 2) Use a device to **** fluid from fill hole, then refill.

This is caused by a leaking rear axle seal you will need to pull the left rear axle out and change the seal and check for a worn axle bearing, this requires the removal of the differential cover, pin and center block or posi spring and clutch pack (if so equipped) and spider gears and then the "C" clip that retains the axle into the gear carrier, u will need a tube of silicone to reseal the cover and a axle seal installer tool and about 2 hours of your time

First thing is to make sure you chock the front tires so the truck will not roll. Raise the rear end and set it on jack stands. Put the transmission in Neutral and make sure the parking brake is off. Remove the rear tires and disassemble the brakes on the side with the leaking seal. Place a drain pan under the rear differential and remove the cover. Remove the differential shaft lock bolt. You will need to turn the drive shaft by hand to access the bolt. It will be on the right side off the spider gear housing. Only use a 5/16 or 8mm 6 point box end wrench to remove the bolt. After you remove the bolt reach on the top of the spider gear housing and push the differential lock shaft down to remove it. Make sure the spider gears do not rotate after you remove the shaft. If they do you will need to realign everything to reinstall the lock shaft. Push the axle shaft in enough to remove the "C" clip from the tip of it. The axle will now slide out of the rear end. You can use the tip of the axle shaft to remove the axle seal. If you're changing the bearing as well you will need a slide hammer with axle bearing adapters to remove it. You can use a socket and hammer to install the new bearing and seal. Be careful not to damage the bearing and seal. I recommend packing grease in the back side of the seal. This helps prevent the spring on the seal lip from coming off. Assembly is the reverse. Clean off all the gear oil from the differential cover and the axle. You can use RTV as a gasket if the OEM gasket is damaged. Fill the rear end with new gear oil of the proper type. Refer to your owner's manual.

Could be low on differential fluid, leaking from the wheel seal. The Differential gears could also be worn from low on fluid or ears was not lined up and have worn it self out.

Service the rear end, inspect the fluid's condition and measure the any play in the gears in the rear end replace is worn out.

You may buy some time by running 50% to 100% Lucas oil treatment in your rear differential. Good luck and hope your differential is not to badly worn.

Is the front pinion seal leaking any oil? if so replace seal. If not drain oil out of differential and reseal and add oil back.

Should be same, just don't forget differential bolt and pin removal first to allow you to push axle in to remove "C" clip.

Block the front tires. Break the rear lugs loose. Jack up the rear of the truck at the center if possible. remove the wheels & brake drums. Remove the brake shoes,return springs & all the other hardware. Remove the differential cover & drain oil. If you have a posi the next step sucks. You need to remove the threaded pin from the housing & remove the axle retaining clips. All the while,being carefull of the spring in the posi unit. If no posi,then same procedure,minus the "pucker factor". After the axle is out,take a large flat blade screw driver or pry bar & pop the seal out. Keep in mind the axle bearing is probably gone too , so that's another procedure. Keep it apart,you'll be glad you did.

Drain axel of Fluid, Roemve Diff Cover (Push IN on Axel to reseal at Wheel side) Remove KEEPERS From Insied END of axel then Pull OUT on WHEEL END of Axel. use Proper Seal removal tool to remove seal. Also Use PROPER Install tool for SEAL INSTALL Reverse Procedure to Install. In hopes this helps you Out.
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