I noticed a little seepage yesterday and since I don't know when, if ever, the fluid has been changed, I thought I would jump on this project. I've researched this site and others but wanted to make sure of a few things before I start:

1. Gasket or RTV?
2. What friction additive?
3. What type fluid best for 2001 7.3?
4. Fill plug looks like Allen or Torque wrench to remove? Will 3/8 rachet work?
5. The fill plug is on engine side of diff. - drivers side (if that means anything)?

Any other advice is most welcome.

Thanks, Jed

 

Here's a photo of my diff

 

One of thing, or a warning I should say. I did not have this seepage until I put tires on the truck the other day. The tire place jacked the truck by putting jack on Diff to jack up whole back end. The truck rocked back and forth when they were changing tires. You can see the jack marks on the diff. I cannot prove they caused the leak nor can I now, at this point, prove it not leaking or seeping before the tire change. I am not even sure how a jack could even cause this. Oh well, needed changing anyway.

 

1. RTV - oil resistant

2. Don't use friction additive unless you need it. Most synthetic fluids do not require the additive. I used XL-3 when I changed to Amsoil and had some problems because the LSD turned into a LGD (limited grip differential). I would recommend (this is just my opinion) to change the fluid and then go out for a short drive. If you are getting some skipping/chunking when making a turn, then go back and put a small amount of additive in and try again. Keep doing this until the differential gears interact with each other smoothly.

3. Fluid is thing of personal opinion. I decided to go with Amsoil 75w140 because I like Amsoil products except the engine I use T6.

4. It should be a square 3/8 but may have been replaced by a previous owner if you are not the original.

Advice: Get some brake cleaner and clean the lid very thoroughly. Use some emory cloth to get remaining gasket off the case and the lid. Use a plastic back or two to cover the gears while you are cleaning the gasket material off the case. There will be a small puddle of fluid that will not want to drain in the bottom of the case, get it too! Let the RTV sit for the prescribed time before installing the lid to the case. Use some penetrating fluid on the bolts prior to removal. I like ATF/acetone 50/50 mixture, others like PB Blaster, whatever your flavor is will help.

Check the vent hose to see if it is blocked and supported properly. Replace it if needed, I replaced mine and cleaned the port that it hooked to on the axle.

That stuff smells bad, so use gloves if you can.

 

Thank you.

 

Further to what Sous said (again ) X2 on spare use of the LSD additive.

An upgrade to consider is the aluminum 08 diff cover, pn 8C3Z4033A. You'll need longer bolts, 5/16" x 1-1/4" coarse thread. Nice to have the extra cooling when towing, and the Ford part is much cheaper than the bling aftermarket units.

FTE has some good pic-heavy threads on these subjects, unleash your google fu.

 

X2 on the aluminum rear diff cover - It is a nice piece & well worth the money .

 

those covers can rust through, might be why yours is leaking?

 

Looks like your cover may have a hole in it. The pressure from jacking it up probably did cause it if one of the tabs hit the cover. I also used Amsoil because it dose cool down quicker when towing up grades then your normal oils. Know this by gauges. I used one tube of the modifier. It says you don't need it but most poeple do. Go to a parking lot and drive figure 8's to see how it preforms. That will tell you if you need it.

 

Until I get it drained and changed, I plan to check the current fluid level. If it is low, what type fluid should I top it off with? May not need any, but wanted pick some up in case it was low.

Thanks

 

75w140

 

Synthetic ?

 

Go to a local junk yard and get a aluminum cover along with the bolts. The covers will be all over the place.

 

I will give that a try. Thanks

 

75w140 is synthetic