98 Expedition Rear Axle - Fluid and Modifyer

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Going to tackle the rear axle seal project on my 98 Expedition. Dealer said he has 4 oz bottles of friction modifier. I asked how many bottles I need for this axle, he said 1, but "some use 2 to play it safe" 1) How much friction modifier do I need in this axle? 2) What oil do I use? 3) What sealant for the differential cover 4) What sealant for the vent screw
 
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An extra bottle won't hurt, but you could try one and see if it chatters. If it does add another bottle. I would use 75w140 synthetic Use ultra black for cover RTV
 
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You can tell if its limited slip by lifting one wheel off the ground, brake off, and transmission in neutral. A regular non limited slip you can turn the wheel and the driveshaft by hand. A limited slip the wheels lock together, so you can't turn one wheel with the other one on the ground.
 

OVERKILL

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You probably have the 9.75" rear axle, as that's what I had in my 2002 and my parents have in their 2000 since I assume you have the tow package. It calls for 75w-140 and a bottle of the fluid which you noted if it has limited slip. If you only put in one bottle, you may find it binds and chatters around corners, which my 2002 did. I just left it, as I found the rear worked better in snow with less slip. You can always add the second bottle later if needed. Some fluids come with the additive already in them. I used the Ford grey gasket sealer on the diff cover, that stuff is incredible. I also used the Motorcraft diff fluid.
 
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A few thoughts: 1. Here is a link to your owner's manual if you do not have one - http://www.fordservicecontent.com/Ford_Content/catalog/owner_guides/98exdog1e.pdf 2. According to the OM, you need to add one 4 oz. bottle of FM to the oil. 3. You will receive many opinions on which oil to use. I use Amsoil in all of my axles, but you can pick up any 75W-140 synthetic axle oil at a local store. Mobil1, Castrol, Valvoline, SuperTech, any of these will be fine in your axle. 4. You will need 3 quarts (5.5-5.8 pints) of it. 5. I always used a new gasket and silicone to seal my axle cover after draining and cleaning the interior (there is bound to be quite a bit of metal "goo" inside). 6. I use a bit of teflon tape on the fill plug when re-installing it. 7. Make sure that you can unscrew the fill plug before removing the cover (just to be sure that it is not "frozen"); a 3/8" extension and ratchet should suffice. Hope this helps!
 

Astro14

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So, still trying to fix this thing, instead of consolidating? I really encourage you to read what I posted in response to your earlier question: https://www.bobistheoilguy.com/foru...tive-to-unaffordable-new-suv#Post5365194 DIY will help save you some money...but I would consolidate and drive only what you need, not what you want, or what you like... Back to this thread. Does this have a LSD? If so, you need the Friction Modifier, and one bottle is fine. Many oils already have it, so the answer to your questions... 1) It depends 2) any 75W140 (or whatever your OM recommends, my old expedition took 75W140). Mobil 1 Synthetic is inexpensive and available in 74W140 with the FM. 3) Any oil resistant RTV. Permatex makes a good use. Use a fresh tube. You don't want leaks. 4) Why would you need to re-seal the vent? I would leave that alone. If there's oil around it, that's because it was, well, venting...so, clean it up and leave it alone. While you're doing this work, I would check your parking brake operation. My 2000 Expedition (5.4L, tow package, 3.73 rear end, LSD) had that parking brake seize up every winter. Disassemble, clean it, hit it with zinc primer, grease the appropriate points and hope to get another year out of it. Price of living in the salt belt with it.
 

Astro14

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Originally Posted by 2015_PSD
A few thoughts: 1. Here is a link to your owner's manual if you do not have one - http://www.fordservicecontent.com/Ford_Content/catalog/owner_guides/98exdog1e.pdf 2. According to the OM, you need to add one 4 oz. bottle of FM to the oil. 3. You will receive many opinions on which oil to use. I use Amsoil in all of my axles, but you can pick up any 75W-140 synthetic axle oil at a local store. Mobil1, Castrol, Valvoline, SuperTech, any of these will be fine in your axle. 4. You will need 3 quarts (5.5-5.8 pints) of it. 5. I always used a new gasket and silicone to seal my axle cover after draining and cleaning the interior (there is bound to be quite a bit of metal "goo" inside). 6. I use a bit of teflon tape on the fill plug when re-installing it. 7. Make sure that you can unscrew the fill plug before removing the cover (just to be sure that it is not "frozen"); a 3/8" extension and ratchet should suffice. Hope this helps!
That's GOLD right there...A suggestion that I was given dozens of years ago - you want to discover that you're unable to refill while there is still fluid in there. You've still got options. If you can't get the fill plug loose, and then you drain the oil, you're in deep yogurt...
 
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VA
A good portion of the 97-03 Expeditions had open rear diffs...even if they were 4WD. Look on your door sticker for axle ID, there is also a metal tag on one of the rear diff cover bolts.
 
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If you have limited slip, use 2 bottles of FM and 75w140 lube. Warning: That Ford friction modifier is one nasty smelling concoction. Use it in a well ventilated area and make sure you don't wear anything you care about. Because if you get any on your clothes you might as well throw them out.
 
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Use 1 bottle of the modifier. The 2nd bottle is for soaking new clutches before installation. Sometimes you need the second bottle if after the change you get chattering when doing the figure 8s.
 
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Wisconsin
You can always use a gear oil that is rated for limited slip diffs like valvoline synpower and then just add one bottle of friction modifer like I do. For the sealant I just use permatex ultrablack. Never used a gasket and they don't use a gasket from the factory. Just intially tighten the cover bolts till the silicone gets squeezed out a little then let it sit for several hours to dry then tighten them up i believe they are torqued to 30 or 35 ft lbs But yes indeed remove the fill plug first If its seized heating it a little with a small propane or mapp torch usually helps to get it free. Are you doing the axleshaft seals?
 

Fitz98

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643
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Florida
Picked up parts from dealer. Regarding friction modifier, counter person said it doesn't hurt to add the 2nd bottle initially. I am just trying to figure if I was to need the 2nd bottle after the fill, I would need a way to extract 4 oz from the fill hole. Any reason NOT to add the 2nd bottle? Or better to use 1 bottle with this Valvoline Valvoline Gear Oil Or 1 bottle with this Mobil LS Mobile 1 LS Gear Oil
 

OVERKILL

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Originally Posted by PowerSurge
Adding the second bottle of friction modifier won't hurt a thing.
This. All it will do is allow the clutches to slip a bit more.
 

Fitz98

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Originally Posted by PowerSurge
Warning: That Ford friction modifier is one nasty smelling concoction. Use it in a well ventilated area and make sure you don't wear anything you care about. Because if you get any on your clothes you might as well throw them out.
Funny how you said this. I bought 2 bottles at dealership and stopped by mechanic on the way home to have AC checked in Suburban. When I got home, the truck smelled horrible. I thought it was just from mechanic's clothes while sitting in my truck, but was getting worse. Turns out one bottle had a very slight leak from a cracked seal. A few drops of that was contaminating the whole interior. Fortunately, the leak went onto a rag I had in my truck under the bag that had the leaking bottle.
 

Fitz98

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Originally Posted by mk378
You can tell if its limited slip by lifting one wheel off the ground, brake off, and transmission in neutral. A regular non limited slip you can turn the wheel and the driveshaft by hand. A limited slip the wheels lock together, so you can't turn one wheel with the other one on the ground.
I performed this test. My axle code says I have 3.73 Limited Slip differential, but when I lifted 1 rear wheel off ground and transmission in neutral, I could spin the wheel (with some slight effort).
 
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Either it's not LSD (due to swapping of parts by a previous owner), or the clutch is completely shot. Either way you don't need any stinking friction modifier.
 
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Nowthen, MN
Originally Posted by Fitz98
Picked up parts from dealer. Regarding friction modifier, counter person said it doesn't hurt to add the 2nd bottle initially. I am just trying to figure if I was to need the 2nd bottle after the fill, I would need a way to extract 4 oz from the fill hole. Any reason NOT to add the 2nd bottle? Or better to use 1 bottle with this Valvoline Valvoline Gear Oil Or 1 bottle with this Mobil LS Mobile 1 LS Gear Oil
You shouldn't need to add any friction modifier with the Valvoline or M1 gear oils, they already have it.
 
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