Just changed the gear oil after the new gear break-in and seem to have a small leak from the top of the cover. When I did the change I took the old one off, cleaned the mating surface, put on Gold high temp gasket maker and reinstalled. I wasn't too sure what the torque value was for the cover bolts so I snugged them up fairly tight. I also waited about two hours in 60 to 70 degree temps before adding the new oil.

Not sure why I have the leak (especially on the top), so here are a few questions -

Should I do the job all over again?
What are the torque values on the cover bolts, maybe I tightened them too much?
Should I have waited 24 hours for the gasket maker to "harden before adding the new oil?"

Thanks

Chris

 

One thing with RTV (silicone, sounds like what you used), wait for 15 minutes or so before installing the cover. Allow the silicone to skin over - the skin is what makes the gasket.

If you didn't use RTV, I would suggest it - get a good high-temp, gasoline-safe (sensor-safe it says sometimes - smells like dirt) RTV from Permatex.

I've done the rear cover on the 8.8" rear in my '96 t-bird twice - the rear cover is a load-bearing member because it's independent rear suspension ... never a leak. However, I DID let it fully cure for 24 hours, so there may be something to that.

But most important, let it "skin" over first.

 

The Sterling 10.5" rear cover bolts should be torqued to 29-39 ft/lbs according to my service CD for 2001. Should be the same for '03

 

The torque is 19-29 Foot lbs for that size fastener.

To leak out the top you must have a significant void OR you are building a LOT of pressure inside the diff.

On the drivers side there is a vent tube going from a fitting on the axle tube to a holder higher on the frame that should have a "U" shaped bend to prevent water form getting in but air to get out. I always put a small motorcycle breather filter on these vents to prevent mud daubers and other crap from getting in. Check the vent tube and make sure it is not bent, missing, plugged, collapsed or pinched.

When I use a paper, cork, or other fiber type gasket I don't get too **** about de-greasing.... BUT if the new gasket is going to be from a tube of RTV (room temperature vulcanizing) goo... then I get super **** on cleaning and de-greasing BOTH the mating surfaces. Carb cleaner, B-12, MEK (dangerous stuff) or any other industrial strength cleaner to get both metal surfaces completely oil free are needed to make sure the permatex, RTV, gasket maker goo sticks.

Always a good Idea to wait at LEAST 80% or more of the time recommended for the product.

The only good news is that it is not critical to do it today and of course it is a tall truck so it is an easy job to do.

Yes you need to find a clean location and a clean pan to catch your EXPENSIVE lube, and do the job again.

I use the Ford tube of goo.

I cut the plastic nozzle to give me about a bead the diameter of a pencil.

I make a round loop of goo around each bolt hole.

I lay a bead from each bolt hole to the next right down the middle of the metal flange.

I lay a bead completely around the out side if the cover, this bead is completely on the flat flange but out side the perimeter of the bolt holes and I start and stop the continuous bead at the top.

Once the cover is all bolted down there is a LOT of squished out goo. But the way I do it most is out side and I feel very little is squished to the inside.

Of course you must tighten each of the bolts a little at a time all the way around and in a cross pattern to equally push the cover against the diff housing.

Once it is snugged up pretty tight than just once around in a criss cross to bring each bolt up to 24Ft LBs (middle of the spec) should be just right.

I do mine about twice a year and it is right at an hour job with all the cleaning and the PITA slow filling job.

 

Twice a year? Why so often? I change mine at 50,000 mile intervals (which is at least twice as often as Ford recommends) unless I've been over the hubs in water.

 

Fred, why the discrepancy on the torque? Service manual says 29-39. Haven't been under my truck to change the rear fluid yet, so I have no idea what size fastener it is...

Good points on degreasing and looping around bolt holes too!

 

Use what the manual calls for, I looked up by bolt size and assumed grade 5 or lighter.

If it calls for 29-39 then I assume they are grade 8 and that is curious but not unheard of.

Mine don't leak at 24-26 and I think when I torque them it "feels" about right for my semi calibrated wrist so I never questioned it.

The question on why twice a year for me.... Once to get the initial crap out because American manufacturing is low tech and I don't want all the ground up crap in my axle bearings.

Later I do it as part of my getting the LS unit back working. And to flush the crap again. I have 4x4 because I use it a lot. Some of my "further back in the sticks" locations cause me to do a fair amount of 2-3 foot deep creek/small river fording.

If you get crap, water, mud, or a ton of dust into the rear end it must be flushed and serviced. (take a look at the vent tube and think if a lot of sand and dust can get inside your rear end) Why Ford or other American manufactures do not put a filter here is very curious to me.

You folks do know that the differential lube is also for the inner and outer axle bearings right?

I have not had to change a set of axle bearings in over twenty years. Almost every truck I have sold or traded still has the Factory bearings in it.

 

Hope you're not talking to me

The Dana 60 in my highboy had at least 350K miles on the original spindles and bearings - goes to show what gear lube will do for wheel bearings ...

 

As usual, thanks for the info! Got the diff. cover installed (again) yesterday using the black RTV goo and will fill with Amsoil 75W 145 tonight. I caked the black RTV on fairly thick so hopefully things will seal up nicely.

Chris

 

Why don't they use rubber or cork gaskets anymore? Seems like it would be a lot easier to use one of those without having to worry about the gooy mess of RTV, waiting 24 hours for the RTV to harden, putting on too much/little.... I usually change out my trani and axle fluids about once a year and sure would like to make it a little easier on myself.

Chris

 

Some, like Mag-Hytec, use an o-ring as a seal. Had my Mag-Hytec on for 6 months, no leaks.

 

Just seems to me that it would be much easier to use an o-ring type gasket instead of worrying about the parts being clean enough, the right amount of RTV, drying time, etc.... I am doing a lot of towing and would like to change out the fluid anually, but do not want to hassle with the mess and the time it takes to do it.

 

So get yourself a Mag-Hytec (or something similar). It seals with an o-ring, has a drain plug, dipstick and a port for a temp sensor. It's well built, functional and looks very cool, IMO.

 

Why not stick a hose in the fill plug and pump it out without removing the cover? If you want to change it as much as every year, the left over oil (if any) wouldn't contaminate the new stuff TOO much, eh?

 

I just pulled the Mag cover off my Dodge (to sell) and it had worked great for a year and a half. Sold the cover within 2 hours of posting it so they are a great investment. Also, I was told and hence always used the gray RTV on OEM covers and it works great. Like I said, just put the stock cover back on with the gray stuff; just run it around the cover/bolt holes, put it on right away, then wait a hour before pouring in the new oil. Never had a leak.