Rear Diff Fluid

[Justin Grant]

I have a '98 Explorer Sport going on 200K. The manual states that the differential fluid is good for the life of the vehicle. Does anybody know how true this is to the vehicle? Or if I should just go ahead and replace it?

 

[Mbrooks420]

Replace it. It’s cheap insurance. I’m sure it is FOUL by now.

 

[drdoom]

Drain and put some fresh in there Justin.

 

[koda2000]

If your truck's rear diff is limited slip, don't forget to add Ford limited slip friction modifier to the 75W140 full synthetic gear oil.

 

[swshawaii]

+4. At 200k, once you break the seal and see what's in there, you'll be glad you're replacing it.

Old gear lube looks and smells really nasty, just have lot's of cleaning materials handy.

 

[CDW6212R]

Oh yes, the nastiest fluid you'll smell by far. When you get the wheels off, gently lift each axle by hand, and see how much play there is. Look for and wetness around the bottom part of the brakes assembly, the inner part where the parking brakes are. What you're looking for is evidence of an axle seal leaking at all, or worse, a worn axle, which would let the axle move up and down a more than normal(maybe 1/8"). I did all of that on my 98 two years ago when I bought it. New axles bearings, seals, axle grease, parking brakes and hardware, brake pads, gear oil modifier, all for maybe $100.

 

[bobflood]

When Ford says "life of the vehicle" what they really mean is "until the warranty runs out!" There is no such thing as lifetime fluid.

 

[swshawaii]

^ Agree. From the company that recommends the first fluid change at 150k for 5R55 series transmissions.

 

[Mbrooks420]

They were banking on most 5Rs to fail by then

 

[96eb96]

^ Agree. From the company that recommends the first fluid change at 150k for 5R55 series transmissions.

Will never reach that mileage on stock fluid, so you never have to worry about the service! You just dispose of it and it is maintenance free/lubed for life!

 

[koda2000]

Will never reach that mileage on stock fluid, so you never have to worry about the service! You just dispose of it and it is maintenance free/lubed for life!

Not true. My '01 Sport Trac had 184k on it when I bought it 2.5 years ago. The trans fluid was the dirtiest I've even seen (absolutely black, as was the engine oil). The trans had obviously never been serviced. I removed the pan and added a drain plug. Trans pan findings weren't too bad. I put in 4-5 qts of fresh Mercon V and a new Wix filter. Started it up and the fluid is still black (hence the need for the drain plug). If the truck lives until spring I'll drain the pan again and put in another 4-5 qts of fresh fluid. I hope to at least see a hint of pink afterwards. I'm afraid to do a full flush. Forward gears work perfectly, but something makes a weird noise if you put reverse under a heavy load.

 

[CDW6212R]

Not true. My '01 Sport Trac had 184k on it when I bought it 2.5 years ago. The trans fluid was the dirtiest I've even seen (absolutely black, as was the engine oil). The trans had obviously never been serviced. I removed the pan and added a drain plug. Trans pan findings weren't too bad. I put in 4-5 qts of fresh Mercon V and a new Wix filter. Started it up and the fluid is still black (hence the need for the drain plug). If the truck lives until spring I'll drain the pan again and put in another 4-5 qts of fresh fluid. I hope to at least see a hint of pink afterwards. I'm afraid to do a full flush. Forward gears work perfectly, but something makes a weird noise if you put reverse under a heavy load.

That sounds like my AWD TC fluid, it was full black when I changed it the first time. Now on the 3rd change it was dark but almost transparent.

If you are careful and brief, you can pump a lot out by removing just the ATF cooler hose. Shut it off once it starts to spit, that won't hurt the pump etc. Others tell of letting it run to get most ATF out, I think being happy to get a few quarts out quickly in a short time is plenty for freshening the fluid. I'm glad the 4R's still have a drain plug in the torque converters.

 

[96eb96]

Not true. My '01 Sport Trac had 184k on it when I bought it 2.5 years ago. The trans fluid was the dirtiest I've even seen (absolutely black, as was the engine oil). The trans had obviously never been serviced. I removed the pan and added a drain plug. Trans pan findings weren't too bad. I put in 4-5 qts of fresh Mercon V and a new Wix filter. Started it up and the fluid is still black (hence the need for the drain plug). If the truck lives until spring I'll drain the pan again and put in another 4-5 qts of fresh fluid. I hope to at least see a hint of pink afterwards. I'm afraid to do a full flush. Forward gears work perfectly, but something makes a weird noise if you put reverse under a heavy load.

On an original trans? That is quite rare. Maybe it was replaced @ 75K? Black could be clutch material.

 

[koda2000]

That sounds like my AWD TC fluid, it was full black when I changed it the first time. Now on the 3rd change it was dark but almost transparent.

If you are careful and brief, you can pump a lot out by removing just the ATF cooler hose. Shut it off once it starts to spit, that won't hurt the pump etc. Others tell of letting it run to get most ATF out, I think being happy to get a few quarts out quickly in a short time is plenty for freshening the fluid. I'm glad the 4R's still have a drain plug in the torque converters.

I once saw (on Hot Rod TV, or whatever it's called these days) where they drilled a hole in the TC to drain it and the plugged the hole wit a pop rivet. With my luck it would leak like crazy. I have a transfer pump, I wonder if I could suck out any of the fluid from the TC using the trans cooler line?

 

[Mbrooks420]

The 4r70w doesn’t have a torque converter drain plug?

 

[koda2000]

The 4r70w doesn’t have a torque converter drain plug?

Yes the 4r70w TC has a drain plug, but the 5r55's TC didn't.

 

[Mbrooks420]

Ahhh, I forgot you had a SOHC as well.

 

[96eb96]

I once saw (on Hot Rod TV, or whatever it's called these days) where they drilled a hole in the TC to drain it and the plugged the hole wit a pop rivet. With my luck it would leak like crazy. I have a transfer pump, I wonder if I could suck out any of the fluid from the TC using the trans cooler line?

The XX55Es have a thermostatic valve, I think the TC keeps its fluid until it gets hot.

 

[koda2000]

Ahhh, I forgot you had a SOHC as well.

Yup, two V8's and one stinking SOHC left at this point.

 

[CDW6212R]

The 4r70w doesn’t have a torque converter drain plug?

...
I'm glad the 4R's still have a drain plug in the torque converters.

I got the full 12+ quarts out of my 98 transmission last year. The TC had a gallon in it, and I had the VB out for an hour or so. It took over 14 quarts to fill it back up, since I changed to a deep pan.
On these super cold mornings, I wish I had a thermostatic switch to keep the ATF from looping through the coolers. I'm going to put one together when I get the time, it's taking over five minutes to get some heat in the trans first thing.