Whether the front diff is spinning or not, it's under no load compared to the rear. It's the pressure between the loaded gear teeth that breaks down the oil and gets metal floating around. I say just do the rears, if you're in 2WD 95% of the time. Maybe do the front every other or every third rear change.

 

awesome guys. Thanks

 

I have a question on this too. I brought my truck into the stealership the other day for its 25,000km service. They wanted $350 to change my fluid, stating that it was so pricey because the "rear is synthetic". Well, I went to my auto parts store, snagged the fluid for 30 bucks (synthetic and all). My question is, is it really that hard to change the fluid in our trucks? My Ford was basically: unplug, drain, plug, fill.

 

the back is really easy. The fronts can be a real pain the butt. A few threads on here discuss that. I have never done it. If you have a Mr. Lube, get an oil change done, and the will usually knock a few bucks on the diff change. I think they charge $89.99, but had them offer me 79.99 each.

 

You just pop the covers off, drain and then back on, and fill from the fill plug. The rear is cake, the front is only difficult because the space provided to do so.

 

$350 to change the rear is an insult.

I just changed my rear diff fluid. It requires 2.13 litres of oil, so you have to buy a third bottle. I went with Valvoline conventional, 80W 140, which is heavier than reccomended. The 75W 140 was available only in synthetic.

They're just gears. Hypoid gears have been around for 100 years, and the 9.25 axle is old as the hills. No need for expensive product. I can't speak for limited slip axles.

My Valvoline was branded as for heavy-duty use, including trucks and SUV's. That's all I need to hear. The higher viscosity just means it's a little thicker when cold. Big deal. Total cost was about $30, including a tube of red RTV.

Steps:

1) Remove the diff cover bolts.

2) Pull the filler plug to let air in as the oil drains.

3) Position your oil pan under the diff.

4) Use a screwdriver, strong knife, etc to pry the housing loose. Go slowly, and start at the bottom, and you will be able to control the oil draining.

5) Remove the cover, oil continues to drain.

6) Wipe the magnet embedded in the bottom of the housing if you want. I gave it a few wipes to get the bulk of the dirt and metal off. Mine just looked like black paste.

7) Use a razor blade and Scotchbrite abrasive pad to remove *ALL* the RTV from both surfaces. Bits of RTV will end up on or near the ring gear, so make sure it's all clean before you put it back together. It takes a little elbow grease, but I got both surfaces shiny before I reassembled.

8) Wipe out the last of the oil that won't drain. Wipe the inside of the cover clean. Double check your mating surfaces.

9) Apply a thick bead of red RTV around the cover. I made a 1/2" zig zag pattern. Double back and draw a circle around each bolt hole. You don't want to have to take it apart again for a leak.

10) Line up the cover as best you can, and start a couple bolts. Once the first two go in, the rest are aligned perfectly. Make sure you have the cover oriented correctly.

11) Torque the bolts down. I went by feel, nice and snug using a 12" ratchet.

12) Fill the diff through the filler hole. 2.13 L for the 9.25" axle. Each bottle is just short of a liter, so I used about 2 1/3 bottles.

13) Don't forget to pop the filler plug back in

14) Let the RTV set up for an hour, and take her for a spin. Full "hardness" in 24 hours.

Total time, 45 minutes tops. Cost $30. No leaks, works great. As easy as an engine oil change.

 

I would have gone with synthetic cramerica.

it's what the diffs are filled with from the factory.

plus the synthetic gives you less friction, which, in turn, nets you better mpgs.

I did both my diffs at the college in the parking lot, and replaced with AMSOil

 

as for reassembly you're method is partially correct.

you apply the rtv sealant to the diff, just as you stated.

but where the difference comes in at, is you put the cover on, hand tighten the bolts, let the sit for half hour to an hour to slightly set up, then you torque to specific tolerance, then you fill it up.

the setting for half hour is stated on the rtv sealant tube.

and it's the way I was told how to do it from a bunch of people and teachers at the auto lab at the college.

 

its easy ive done my front and rear

 

I wouldn't go as far as saying it's EASY.

the rear, yes.

the front is tricky. getting the cover lined up took me about 20 minutes of fanaggling with it before I got it lined up.

if you don't have patience, have someone do the front for you.