hey guys i am going to do the 2008 diesel diff cover swap this week coming up and wanted some opinions and suggestions on the gear oil and type of rtv sealant i should use.

i found that my local store has: (they are the same price for either) i also have a LS.

mobil 1 75w-140 ls gear oil.
royal purple 75w-140 gear oil.

they also have two types of permatex sealant rtv:

Permatex Ultra Black Maximum Oil Resistance RTV Silicone Gasket Maker.
Permatex® Gear Oil RTV Sealant.

i went to permatex website and found that the gear oil rtv sealant is recommended

http://www.permatex.com/products/Aut...tv_sealant.htm


Permatex® Gear Oil RTV Sealant
OEM specified. Specially formulated to withstand the harsh gear oil environment found in differentials and transfer cases. Because gear oil has friction modifiers that break down normal RTV and cause leaking, this specialty silicone has been tested to OEM specifications to ensure complete sealing. As a gasket maker it seeks and seals leak paths that cut gaskets cannot.

lastly when i lay a bead on the new diff cover should i immediately install the cover on the diff and tighten to 24lb or hand tighten the tq it up in 1-2 hrs of setting up then wait 24-48hrs until i fill the diff up with oil?

 

I just ordered my 08 diff cover yesterday - going to pick it up from Ford today!!!

I plan on going with Mobil 1 fluids. I don't think there's much of a gain worth using RP.
I've always used just plain ole Black RTV for diffs. That "specially formulated" stuff sounds kinda cool - but do we need it? I've never had a diff leak after using the regular stuff. (or I've never owned it long enough afterwards to see if it leaked)
As far as "letting it set up", this can be quite a debate. There are a few out there that are very sensitive to this question. I think it's personal preference. I've always applied the RTV, then waited as long as it takes for me to get my tools and all the bolts ready. Not rushing, and not sitting by a clock. Personally, I don't think it's that much of an issue. I may be wrong - but I'm ok with it.
I've NEVER waited 24-48 hours before filling - I've never had the time to do it. Just filled em right up, and don't look back.

 

Spend the extra money and buy the Permatex "Right Stuff" silicone gasket sealant. I used traditional permatex gasket maker first and had some seeping and pulled the cover off again and used the right stuff and sealed it up perfectly. You need a silicone that cures fairly hard which the "Right Stuff" does. I waited about an hour before I added oil. For oil I used Amsoil Severe Gear 75-140 and didn't add any friction modifier.

Either oil you listed is OK IMO. I would add it straight and see if you get any chatter. I have two new bottles of Amsoil Slip-Lock Additive I didn't use.

 

That Gear Oil RTV looks like the ticket. It is a new product. If you can find it, might as well give it a test. If you can't find it, this stuff has always worked fine:
http://www.permatex.com/products/Aut...sket_Maker.htm

 

My truck is also a LS. If I run the Mobil 1, should I also put a bottle of the Ford Additive in? This is where I don't quite understand. Is posi-additive no longer required with these new fluids?

 

In the case of Mobil-1, they sell it with and without the additive. The one with the additive says limited slip right on the bottle. If you use that one, don't add any more. If you happen to get chattering you can add more, but you probably won't.

 

As far as Royal Purple, they make good products, but not worth all the hype.
As for how to set up the RTV, I have heard that you are supposed to apply immediately, and have heard to let it set a while. Both theories are half right. The proper method is to lay the bead and allow it to set up just enough to where it does not stick to your finger, but is still soft and gooey inside. Best way to do this is to dab a small blob on something like a piece of cardboard so that you can feel the RTV without risking damaging the fluid on the cover. Here is how I usually do it.

1. Place a pan under the diff and loosen all the diffy bolts making sure to loosen the top bolt about a quarter of an inch only.
2. Remove all the other bolts, and pop the diff cover from the housing. The top bolt should be retained, so that the cover does not come all the way off which will lead to a huge mess.
3. Remove the top bolt when drained completely, then take off the diff cover.
4. Clean the cover with brake cleaner and scrape the old RTV off.
5. Apply RTV to the pan evenly. Go inside the bolts in a uniform line.
6. Wipe out all excessive oil from the chunk, then use the brake cleaner to remove the rest of the oil completely. Be sure to wipe any excess brake cleaner that may puddle in the chunk out and avoid spraying the cleaner around any seals.
7. Carefully apply the cover, as by this time the RTV is properly set and ready for install.
8. (This is where a lot of people go wrong, by skipping this process), install the bolts, and finger tighten them just to the point to where the heads touch the cover. Then, tighten the bolts down in a cross torque pattern roughly 1/2 turn. Repeat this process until the diff cover is properly seated. Finally, torque the cover to proper specs. When snugging the bolts down as well as torquing them, do the bottom bolt first, then move to the top, then sides, then another bottom bolt, then another top bolt, etc. This will assure that the cover maintains a proper seal at the bottom. This process will take a little longer than just finger tighten then torquing them, but will assure that the cover mates to the diff evenly. If you finger tighten them and then torque them without "walking the cover" there is a chance that the first bolt torqued can squeeze out too much RTV and cause a leak.
Lastly, remove the fill plug and fill with proper oil. I do like to wait an hour or so before filling if at all possible, just to allow any squeezed RTV to set up properly. Reinstall the plug and you are done.

 

Cool. I'll just get the stuff with the additive. What's the capacity of the rear diff anyhow? Think 3 quarts will do it, or 4?

 

It takes about 3.5 qts in the rear. Assuming you have a SRW F250-F350.

 

You'll want to buy 4 quarts of oil because you won't be able to suck all the oil up the pump. I let my empty bottles drain and dumped what drained out into the last bottle. The synthetic gear lubes are slippery so FM amount can vary. You don't want to just dump in FM you don't need. Best bet IMO is to get the oil without FM and add it if you get chatter.

 

There is so much room under a Superduty, I didn't even need a pump or funnel to fill. Just stuck the nozzle of the bottle in the hole and squeezed until the bottle was pushing air. Did that with all four bottles, then drained what was left in 3 bottles into the 4th, and squeezed what I need out of that. Didn't spill a drop.

On edit: I did slip a piece of 3/8" polyflo tube over the nozzle, now that I think about it. But I'm not even sure that was necessary.

 

^^^^ X2. Also, if you do the change on a slight uphill incline it will aid in filling without spilling. Just be sure to use chocks and set the Ebrake.

 

I've done diff work before so I'm not all that concerned with the process - I even have one of those silly hand pumps that screws onto the bottles.

I just wasn't sure about the fluid / friction modifier. I'm going to Wally-World this weekend to see what's on their shelves. If there's nothing WITH FM added, I'll just get the regular (synthetic of course) fluid and add the bottle of Ford FM I have on the shelf. mmmmmm, it's sooo stinky.... hahaa

 

The Amsoil bottles are not typical gear oil bottles they don't have a spout, thats why I mentioned the pump. I have the hand pump Amsoil sells that fits all of their quart, gallon and 2.5 gallon jugs.

This is the friction modifier I have and didn't use, have 2 4oz. bottles of it. I'd say 4oz. would be more than enough to get rid of any chatter you may have. Like I said before I wouldn't use it unless you have to. http://www.amsoil.com/storefront/ada.aspx