Need advice on changing diff fluids

[mikepier]

My 99 XLT now has 91,000 miles. Since I bought it new, I had not changed out the front and rear diff fluids. So yesterday I attempted to try and pump out the rear diff fluid. I realize because the fluid was so thick and because it was cold outside, it was kind of hard to use my hand siphon pump and get the fluid to flow through a small tube. The Auto Parts store had like a handpump for $13 ( looked kind of like a greasegun) to suck the fluid out, but I was wondering has anyone used something else to get the fluid out with success, also am I better off doing this in the summertime when its warm?

 

[KPSquared]

Don't know about the front in your '99, but for the rear, just pull the cover, drain it out, buy some RTV sealant and throw the cover back on. You'll never get all the fluid out with a pump. Even with the cover off, make sure you tilt the axle back and forth to get fluid out of the axle tubes. Way easier than pumping oil. With gear oil, it's always better to work with it in a heated shop or in the summer. If you run your rig for 20 miles or so, it'll be a lot thinner cause of the heat from running the gears.

 

[gmanpaint]

The best way to remove the fluid is to remove the cover and let drain. Then clean it out with rags, and run a magnet around inside to remove any metal flakes.

To pump out the fluid you need a pretty good pump. Gear oil is thick. To thin it out, just drive it for a bit,(to heat it up) then hurry up and start the pumping. I have done this with the front diff on occasion when I didn't feel like dropping the entire diff.

 

[mikepier]

Don't know about the front in your '99, but for the rear, just pull the cover, drain it out, buy some RTV sealant and throw the cover back on. You'll never get all the fluid out with a pump. Even with the cover off, make sure you tilt the axle back and forth to get fluid out of the axle tubes. Way easier than pumping oil. With gear oil, it's always better to work with it in a heated shop or in the summer. If you run your rig for 20 miles or so, it'll be a lot thinner cause of the heat from running the gears.

So your saying I don't need a diff gasket? Is that what the RTV stuff is for?

 

[96eb96]

So your saying I don't need a diff gasket? Is that what the RTV stuff is for?

Do not use a gasket, use RTV and follow the instructions. This is what Ford suggests. Make sure the mating surfaces are clean. It came from the factory that way.

 

[SmoothJimmy]

RTV Red is your choice. ALSO, note that from the factory the fronts are filled with Dino 75W90. If your gonna go synth, make sure all that Dino is out.

 

[mikepier]

RTV Red is your choice. ALSO, note that from the factory the fronts are filled with Dino 75W90. If your gonna go synth, make sure all that Dino is out.

When you say red, you mean the hi-temp stuff?
On Permatex website they have a hi-temp red, and also one specifically for diffs, but I assumed if I used the all-purpose blue it would be fine too.

http://www.permatex.com/products/Automotive/automotive_gasketing/gasket_makers.htm

 

[budwich]

DON'T TAKE YOUR COVER OFF UNTIL YOUR GET YOUR FILL PLUG OFF... otherwise you will have "fun" getting fluid back in... not impossible as there are lots of posts from people wondering what to do.

 

[SmoothJimmy]

the RTV red more for the 'heavy duty' applicability more so than the temp. The blue could work too, I suppose, but I used the red for this job.

 

[96eb96]

Black is ok too . It says maximum oil resistance! I was told to use that by Ford. They are all fine.

 

[mikepier]

RTV Red is your choice. ALSO, note that from the factory the fronts are filled with Dino 75W90. If your gonna go synth, make sure all that Dino is out.

You sure about that? My manual says the front is just 80w90.

 

[mikepier]

DON'T TAKE YOUR COVER OFF UNTIL YOUR GET YOUR FILL PLUG OFF... otherwise you will have "fun" getting fluid back in... not impossible as there are lots of posts from people wondering what to do.

The plug comes out fine, I'm more concerned removing the cover bolts after 11 years. They look pretty rusty.

 

[rileyrs]

hit them with some pb blaster the day before you pull the cover, then they'll come off alot easier.

 

[mikepier]

Well, I got to see if the bolts come loose, so I tested one today, and it came loose with no problem, so I'm going to try and tackle it tomorrow.
I did not get the RTV yet, but once you apply it on the cover, how long should you wait before putting it back on the axle? Should you put the cover back on right away or does it need to cure a little first?

 

[gmanpaint]

Install the cover right after you finished your RTV bead. Go around the bolt holes as well with it. I lay a nice constant bead all the way around the diff itself, going around the bolt holes as I go. Tighten the bolts kinda random so it will apply even pressure to the cover as the gap closes.

Some people do both the cover and diff, it just depends on the person. I think a bead on the diff is plenty, as long as you get a good bead on it.

 

[mikepier]

Well I tackled the job today and it went pretty smooth. The old oil looked find of foamy on the gears. Kind of what I expect after 11 years. I spray painted the cover black, and it took approx 3 quarts of fluid, no leaks.
Now for the front, that is a different story altogether. Looks like I'll be buying a suction gun at the auto parts store. It looks like you have to drop the whole axle just to get to the cover. If you are going to go through that trouble, you might as well wait until the whole front axle/diff needs replacing. So I think just a simple suck and fill will do for now.

 

[gmanpaint]

3 qts is 1/2 qt too much. in the rear. Your manual says how much fluids everything needs.

The front diff does indeed need to be dropped to remove the cover. This is the best and most thorough way to change the fluids and clean out any junk. It's a job, thats for sure.

I have a high viscosity pump that attaches to a drill. One tube goes in the diff (bend and shove towards the bottom) and the other into a drain pan. You might want to measure how much you removed just to see if you indeed get most of it out. The front only takes aprox 1.5 qts.

 

[mikepier]

3 qts is 1/2 qt too much. in the rear. Your manual says how much fluids everything needs.

From memory, I think my owners manual says 5.8 pints for the rear, which is almost 3 quarts. I remember I had a little leftover in the last bottle, plus some spillage here and there, so I think I got the right amount in.
Meanwhile my Chiltons manual says 5.5 pints ( 2 1/2 quarts). Why the difference, I don't know.

 

[mikepier]

Did the front today with a suction pump from AutoZone for $11.99. Managed to get out a little more than 1 1/2 quarts ( manual says it holds 1.8 quarts). Pumped back the new stuff, and all is well. Like the rear, the fluid looked black and thin. But again this is 11 year old axle fluid.