Differentail oil/fluid change

[ptf18]

Fellows Plan on changing the differential fluid in the wife's S/T. Its never been changed. 230k on the meter.

I have no idea what rear end is in it as the code on the driver door tag has long ago disappeared. There's a metal tag on the differential cover bolt but the numbers and letters on the tag do not match anything I find on the internet to inform me what they mean.

You all have given me some tips on attempting to ID the rear end but to no avail.

Anyways... I have changed fluid/oil in differentials before but would like to know of any "tips" you may offer in changing the fluid/oil in this S/T rear end. Quantity? Weight... I think its 75w140? Friction modifier? What does the cover use for a gasket? I assume some type of "liquid" rubber and not a paper gasket. I have have poor luck with that "liquid" rubber gasket stuff. If that is what is used any tips on how to use it properly?

than ks,
ptf18

 

[Mbrooks420]

For the gasket I’d use Ultra Black RTV. They do make rubber and paper gaskets. If I used one of these (unlikely) I’d still RTV it. Follow the directions on thickness and setup time, and apply it to a clean surface and it should do well.

I believe all 8.8s can use the 75/140. If you jack up both wheels and spin one and they both turn in the same direction you have a limited slip and need a bottle of friction modifier (if it’s not included in the gear oil. Some synthetics include it). If they spin opposite directions you have an open diff, and do not need the modifier.

Volume should be right around 3 quarts.

 

[koda2000]

My first tip is, before you remove the diff cover see if the fill plug will come out. I recently had one that won't come out no matter what I tried (heat, breaker bar, pipe, impact wrench) and the plug began to strip out. I ended up removing the ABS sensor and refilling the diff with 3 qts of gear oil that way using a transfer pump.

As far as sealing the cover, I also use Ultra Black RTV. No gasket required, just follow the directions on the tube. I'll never bother with a diff cover gasket again.

Have you tried calling/visiting your Ford dealer to have them look up your vehicles specifics? They should be able to look up your vehicle and tell you what rear diff ratio you have (not that that matters for a fluid change) and whether it's LSD (whic does matter). You used to be able to do this yourself using Ford's ETIS site, but I think they've changed it. If it's LSD you need to add Ford's friction modifier to the gear oil (75W140 full synthetic is what's recommended).

My guess would be you have a 4:10 LSD rear diff if you have 16" wheels. Maybe a 3:73.

 

[oklagp1200r]

Koda2000 is right always and I mean always make sure the fill plug can be removed on anything FIRST!!!!!
I like the ultra red but just make sure once the cover is reinstalled I like to let it setup for about a hour or so before adding the grease BUT that's just me!
Make sure that you wipe out all the grease in that recessed/well area at the bottom of that housing too.
I use to be one of these people that never change the rearend grease on anything unless water intrusion or rebuild even when I turned wrenches for a living BUT now I think differently! Anything now with fluid or in this case grease gets changed very soon after breakin. My ST rearend was rebuilt last year and 1000 miles later I changed the grease to remove contaniments from breakin then will be charged in 50,000 miles again.

 

[swshawaii]

Correct per a TSB all 8.8 rear axles use 75W-140 gear oil. If your VIN sticker is missing, check if the tire sticker is still on the B pillar. Info below does not tell you whether it's an open or limited slip differential, but you can determine rear axle ratio.

Stock Tire Size/ Rear Axle Ratio
235/70-16 = 3:73
255/70-16 = 4:10

 

[koda2000]

Another few tips - While the diff cover is off is the time to check your axle seals (ditto the axle bearings) especially if you have high miles, say over 200k and have never replaced them. And while the axles are out might be a good time to replace your LSD clutches if your LSD is no longer functioning as an LSD. The clutches on our '00 Mountaineer are worn out, but at 245k+ the rear functioning as an open dif is good enough.

 

[koda2000]

Correct per a TSB all 8.8 rear axles use 75W-140 gear oil. If your VIN sticker is missing, check if the tire sticker is still on the B pillar. Info below does not tell you whether it's an open or limited slip differential, but you can determine rear axle ratio.

Stock Tire Size/ Rear Axle Ratio
235/70-16 = 3:73
255/70-16 = 4:10

IIRC, (if your LSD rear dif clutches still work) if you get both rear wheels off the ground, put the trans in neutral and spin one rear tire by hand the other wheel should turn in the same direction. If the other wheel turns in the opposite direction your have an open dif.

 

[ptf18]

Fellows. Thank you all. I did what MBrooks posted. Jacked upped the rear and spun the wheels. The tires turn OPPOSITE of each other. I assume I have a NON- Limited Slip differential. I ordered 6 qts of MotorCraft 75W140 (I'm going to change out the oil/fluid in my Edge later, appears to be the same axle as the tires turn OPPOSITE of each other) and a tube of

Permatex 81182 Gear Oil RTV Gasket Maker

thru Amazon. The shipping was free so all and all it was cheaper than the Ford dealer. I checked some You Tube vid's about using this "new-flangled" gasket/sealer stuff. Some recommend not fully torquing the cover bolts until the stuff has "dried" (next day/24 hrs). It make sense to me as I have lots of time to get this project done. Thoughts?

I'll double check the removal of the fill plug 1st. I have had the one on my Edge out so I know it will come out for me.

Seems like a pretty straight forward project. Hope the weather stays nice.

The tires are the 235/70's. I "assume" the rear end is a 3:73. I have another question about changing the input seal on the differential on my Edge but I'll post that under the Ranger forum.

Thanks Fellows.

 

[koda2000]

If you read the back of the Ultra Black RTV tube (as I suggested earlier) it says to put the goop on the surface and only tighten the bolts by hand, then wait about an hour and then torque the bolts the rest of the way. It also says to wait some number of hours before adding the oil. That's how I do it and it has created a perfect seal every time.

I see I repeated what MBrooks420 said about checking for LSD. I didn't read his post.

 

[Mbrooks420]

If you read the back of the Ultra Black RTV tube (as I suggested earlier) it says to put the goop on the surface and only tighten the bolts by hand, then wait about an hour and then torque the bolts the rest of the way. It also says to wait some number of hours before adding the oil. That's how I do it and it has created a perfect seal every time.

I see I repeated what MBrooks420 said about checking for LSD. I didn't read his post.

Hey, at least we agree on it

If you follow the directions the Ultra Black will almost surely work for you.

 

[oklagp1200r]

Yes double check the fill plug just because it's been out before never ASSUME!!!!