I have a 97 4x4 F-150 with a limited slip differential. I just noticed today that I had a small oil spot, about the size of a silver dollar, under the rear of my truck. I looked under the truck and the oil was coming from the breather hose that extends up to the frame. It is leaking from the top of the hose and it isn't cracked. I checked the breather hose to make sure it wasn't partially plugged and causing the differential to build pressure but it was clear. I don't think the diff is getting hot but it might be. I don't notice any unusual noises. The diff oil is not overfull. Is it possible for old fluid to make the rear end run hotter than normal? The truck has 110,000 miles on it and I don't know if the gear oil was ever changed. Should I change the gear oil and add new oil and Fords additive and see if it continues?What else could cause this to happen?

Thanks
John

 

Sounds like the ring & pinion are starting to melt down. I would pull the cover and examine the ring & pinion closely. Oil purging from the breather hose is a sign the diff. may have been low on lube at some point in time. Surface hardening of the ring & pinion has gone away due to the low lube occurance and now the gears are "soft". Soft gears don't last long. Good luck, gearman

 

I decided to pull the cover and check it out. Everything looked fine inside. No wear on the bearings or ring and pinion. The gear oil was a little foamy though. I put new gear oil and additive in it and drove it all weekend with no oil coming from the breather now. I guess the old oil must have had a little moisture in it. The guy I bought it from has a bass boat so I guess backing down in the water all of the time must have allowed a little moisture seepage somewhere. Thanks for the suggestions.

John

 

Dont worry about it. My truck did it to once. I noticed, and noted it, but it never happened again. I dont know why or what caused it, but that was 70 K ago so I dont care. Good luck

 

Ford specifies that you have to change the diff oil if the diff is submerged.

 

I am having the same problem, will change the fluid and replace rear seal obviously.

Anything else I should do or check while I am in there?

Do you think that the Motorcraft Friction Modifier will cause any problems with other brands of fluid?

What is the recommended off brand?

Any ideas where to get them, none of my local stores carry the 90w-140..

Can you belive 20.-- a quart from Ford? WOW

 

I would use OEM Ford or Dana part# 43161. Dana friction modifier can be obtained thru you local truck parts distributor (Dana warehouse distributor). See yellow pages.

I have had bad results from generic friction modifier purchased at local auto parts outlets.

 

Thanks...

Is the Dana the same supplier for OEM??

What fluid brand do you recommend?

What do you think of Redline and of like Valvoline or Mobile or the others?

Thanks a bundle,

Dave

 

I cannot confirm that the Dana friction modifier is the same as OEM; however, it looks and smells the same. Dana modifier comes in a 4 oz. bottle. OEM comes in about 8 oz. bottles.

I added (2) bottles of Dana modifier to 8.8" in my Ranger, which I installed a Eaton-Posi in last year. Eaton-Posi and Auburn both use 80W90.

When our 99 F-150 gets its first diff. fluid change, I will delete the synthetic and good with good old 80W90 and (2) bottles of Dana friction modifier. When the trac-loc in the 99 gives me problems--I will install an Eaton-Posi or Auburn Pro series L/S carrier.

I have rebuilt about two thousand differentials in my career and synthetic fluid only prolongs the lube change interval for differentials.

As for Redline oil, I have never used it. I have used LE in a dirt modified race car with 9" Ford diff.--excellent results!

 

Thought I would add to this post. Just bought a (new to me) '02 KR Screw 4x4, with 23K miles on the clock.

Today, I installed a Mag-Hytec cover. Istructions called for five quarts of gear oil. As I have the LS, I also needed eight ounces of friction modifier. I picked up some Royal Purple 75W140 and two bottles of Kendall LS addotive.

The OEM cover came off with out much fuss. About two quarts of slimmy goop came out. Scooped out the remainder. I spayed the gears an interior with WD-40 and dried everything off. The new cover when on straight away. Pured in the friction modifier and added 4.5 quarts of RP to put the level directly in between the low and high indicator lines.

At the low mileage on the truck, some might think I did not need to change the fluid. But I NEEDED the cover. Ok, I wanted the cover. On the new trucks I have had, I liked to change all of the fluids at 500 miles. As the the gears get to know each other, there is some wear. Becuse this is a used truck, I like knowing that all of the fluids are topped off and clean.

Hope this was not too off topic

 

I also installed a Mag-Hytec cover just recently. I also have the LS but did not add friction modifier as I used Amsoil 75w140. I had fluid coming out of the breather tube after a 150 mile trip so I drained a quart of fluid out. (I just let it run out of the axle's fill plug). I drove 300 miles yesterday and I think I still had some fluid coming out of the breather tube. I plan on draining the fluid to see how much is left in the differential now.

I would be interested to know if you also have fluid coming out of the breather tube on a long trip. I drove for long periods at a speed of 70mph or greater when passing.

 

Jerry from Mag-Hytec called me and said that he had some reports of foaming issues with Amsoil and fluid coming out of the breather tubes. He said 5 quarts is the correct level for their F150-9.75 cover and that the extra amount puts some fluid into the axle tubes. He suggested that fluid coming out the breather would not harm anything. Mag-Hytec sells some gear oil from Lubrication engineers and the fellow said he has not had any foaming issues with their gear-oil.

 

I just sent Jerry at Mag-Hytec this email to see what he might say...


Hi Jerry,

I do not know if the Amsoil fluid is foaming because only those of us using
Amsoil are reporting the breather tube vent fluid but...

I have been thinking about it and I have a theory to propose.

My breather tube is about 12 inches from the tire on the drivers side. Lets
say I am driving down the road and the road tilts to the left enough and the
extra differential fluid fills up the left side of the axle.
Now the breather hole on the axle would be closed off with fluid instead of
air. I increase my speed enough to cause more foaming and heat that causes
the air in the differential to expand. This pressure then causes the fluid
to expand up the breather tube.

I noticed that there was a plug in the top of the Mag-Hytec differential
cover. I have been thinking of makeing another breather using this plug.
This would allow expanding air to go out the top of the differential cover
thus relieving pressure going down the axle tubes.

Creating a breather tube on the diff cover might at least prove my theory
correct.

Larry Griffiths

 

Hello,

What is so special about the Mag Hitech Covers?

What is a good price range?

Thanks,

Dave

 

Check out this web site:

http://www.off-road.com/dunes/produc...hytec/feb2001/

It also has a link to www.mag-hytec.com