98 5.0 Explorer AWD – very hot front differential

[gksnoop05]

How warm/hot should the front differential be after an hour drive at 60-70mph on a relatively flat, dry highway with no stops. When I touched the front differential case after my last ride it was very, very hot to the touch and I experienced a binding/grinding when slowing down and turning.

 

[Turdle]

I would think anything under 200 degrees ( very hot to touch) is normal. Over 160 degrees will scald your skin. For this reason the touch test does not work.

You can get a handheld infrared temp gauge for relatively little money. They are very handy to have around for lots of things.

http://www.homedepot.com/p/Ryobi-4-to-600-Degree-Non-Contact-Infrared-Thermometer-IR001/100674438

I'm not suggesting you don't have a problem in the differential, usually the AWD noises can be blamed on the front drive shaft, however there could be something else going on.

 

[gksnoop05]

Thanks for the reply. I'm still trying to diagnose the cause of the binding after driving an hour or so and was leaning towards the front diff based on my research of other posts and limited knowledge on AWD. (I'm learning very quickly thanks to the forum though!!)

I still need to check fluids in the front and rear differentials and also the transfer case. I will also look at the drive shaft while I'm down there.

If the front differential did get too hot due to an underlying issue(s), lack of fluid, bad bearings, etc, could that lead to the type of binding I'm experiencing?

To help complete the picture, I have recently replaced the following:
- Front and rear rotors, caliper brackets, brake pads
- Drivers side hub assembly and cv axle (I had a broken dust seal and thought the hub could be the issue)

 

[1996BLKBauer]

I don't know if this helps you, but after driving fro 2 hours around 70mph, I pulled off for some food, I noticed it was difficult to turn the vehicle, and also noticed skipping, it was actually very worrying, I looked for leaks, check the power steering all was good, I let it cool down and it was fine, got back from my trip, changed out all the fluids in the drive line, and it has yet to happen again. I have a feeling that possibly the front diff was low on fluid, or possibly the fluid was bad, it came out black, but didn't smell bad, and it didn't have metal particles in it, but I thought it took a lot more then what came out. I had no leaks either, but I did notice I had RTV on the cover, so somebody was in there at some point, maybe they didn't fill it enough.

 

[gksnoop05]

That makes me feel a little better. I changed out the transfer case fluid last night; very bad smelling, black milk-like consistency.

For the front differential I tried using the transfer pump method, but I'm not sure I was able to remove much of the old fluid. I am going to have to use the method of removing the bottom 3 or 4 screws and prying it open to drain the fluid.

 

[SoNic67]

That makes me feel a little better. I changed out the transfer case fluid last night; very bad smelling, black milk-like consistency.

Milky means water in diff. Maybe was driven in deep water or flooded.
Water is not good for gears.

 

[Turdle]

Was the fluid black with the consistency (thickness) of milk, or was it swiss miss hot chocolate color?

That makes me feel a little better. I changed out the transfer case fluid last night; very bad smelling, black milk-like consistency.

For the front differential I tried using the transfer pump method, but I'm not sure I was able to remove much of the old fluid. I am going to have to use the method of removing the bottom 3 or 4 screws and prying it open to drain the fluid.

I would not pry on the cover. You'll end up with a leak for sure.

 

[SoNic67]

The cover for front diff does not have a solid gasket. "Prying" the cover will break the formed-in-place gasket and it will leak.
I used the "Ultra Black" Permatex gasket-maker (Maximum Oil Resistance RTV Silicone Gasket Maker) for both my front diff in Explorer and for Hyundai transmission cover.
They have other models (Gear Oil RTV Gasket Maker and Automatic Transmission RTV Gasket Maker) but I wanted the best.

 

[gksnoop05]

I knew I should have taken pictures! I think I was recovering from the smell.

Anyway, I would best describe the fluid for the transfer case being opaque, black in color and milk-like consistency.

From the fluid I was able to pull from the front diff, it was slightly more transparent and hot-chocolate in color. However, I want to try and make sure the front diff is completely drained which I will try this weekend and I will take pictures if anyone is interested.

Thanks again for your help and interest. I'm sure everyone realizes the immense help this forum provides!

 

[rb142]

It sounds like there was water in the front diff fluid (probably got in through the vent line), and it may have been low as well. If you take the cover off, you can check the teeth for signs of overheating. Otherwise get it filled up with fresh fluid and see how it runs. It would be a good idea to get all of that old fluid out. You can siphon it out, but you have to use a small tube (like 1/4") and fight a bit to work it down around the gears into the bottom. It takes a long time and a lot of work to pump it out through that little line. (A vacuum siphon gun is useful for this.)