I have a 1998 2WD XLT with 4.6L Auto and 3.55LS rear-end. I have about 73K on the odo. Towing is limited to a PWC trailer under 2K. Most miles are driven unloaded. I do not submerge the rear-end when launching the PWC. I doubt that any water has ever gotten in the diff.
Ford Owner's Manual says no fluid change will ever be necessary unless the rear-end is submerged.
Local dealers say to change between 60K and 100K. They claim the manual is wrong.
The cost for this service at Ford dealers is $120 to $165. A local repair shop quoted $120. Jiffy Lube quoted $32.99. Yes, I know the JL price is impossible. The synthetic gear oil costs $18.75 per quart at dealer. I believe it takes about 4 quarts.
I will probably go with my selling dealer for $120 (coupon special). They claim they also do a full inspect for this price.
How often do most of you believe this should be done?
Do you believe the $120 is a fair price?
Do you recommend the Motorcraft 75W140 Synthetic fluid?
Thank you for your replies.

 

personally save yourself some money take a hour or two on a weekend and change it yourself...basic tools can get the job done....120$...ill have to get a quote from my work..but gosh, does sound a wee bit expensive...

 

You need 3 quarts of the 75-140 lube. About U$9 a bottle at Walmart. One tube of Limited Slip additive (U$10 at Ford or U$6 at autostore).
A 3/8 ratched with 4 in extension for the filler plug and metric socket for cover bolts. One tube of gasket sealant for the cover.
Takes about 30 minutes to do. The gear lube bottle fits perfectly up by the filler plug so you don't need a pump.

Fritz

 

Answer: If you use AMSOIL Gear Oil NEVER,

 

RedFord150-
Yes, you should change it and it's time now. Towing and/or submersion increases urgency. Any lube that meets the specs is fine. Dealer or local shop is a call best made by recommendation, but I wouldn't recommend GooberLube. I prefer to do my own and Fritz did a nice job covering that method.

 

Thank you Max and Fritz,
I assume there is a recommended torque setting and torque pattern when re-installing the differential cover. Do you know what it might be?
Should I be inspecting the gears or bearings for 'scoring' or some other unusual wear or play?
My local Wal-Mart and Auto parts store both have a 'semi-synthetic' 75W140. The manual calls for a full synthetic. I assume this means I am stuck with dealer parts dept. I feel more comfortable using the OEM fluids. Oh well, it is worth a few $ to do it right.
I have never done this before and am usually intimidated by drive train work. My worst fear is popping the cover and having some tiny part go flying. Once I find it, than I have to figure out where it goes. I guess it is time to buy a book..
Once I get this done, how often should I do it in the future?
Thanks again for all of your help.

 

Walmart has the SuperTech 75-140 all synthetic.
Filler plug torque = 15-30 ft/lbs
Cover bolts = 28-38 ft/lbs
No sequence given. I start them all and then tighten.
According to Ford, if you use the synth 75-130, it is lubricated for life. Unless submerged or overheated then it must be changed. I change mine every 30,000m just for fun and to inspect the gears and LS clutches.
There are no small parts inside the differential. If a spring pops out it will most likely take your head off and you won't have to worry about putting it back in.

Fritz

 

Local dealership stated it is a lifetime lubricant and never needs servicing unless submerged or leaking. You all have me concerned that it needs changing. I have 110,000 miles on the engine with no service to the rear diff.

 

RedFord150- You're Welcome ! It's really simple. The Ford lube works perfectly if you prefer it. You don't really need a book for this procedure. Do a search and read a few threads here and you'll find plenty of information and tips.

OE812- All lubes include ingredients that degenerate and get dirty.

30K-60K would be a substantial lube life depending on type. At that mileage it's generally nasty as hell.

 

For torque sequence I'd recommend doing it just like a wheel. Start with every other bolt and just snug them up. Then go around again (every other bolt until you hit them all) taking them to about 2/3 - 3/4 of the final torque. Then a final time taking them to the full torque.

This might be overkill but it's a good routine for me. If I always do it this way then I never worry about missing one or having one come loose. I'm also a perfectionist so I like cleaning and lubing the bolt threads in order to get a more accurate torque.

 

Which economy-based diff fluid could I use to meet the Ford Spec?

 

As Fritz stated, the SuperTech 75W140 synthetic at Wally World is readily available, economical, and will cut shipping costs. Mobil1 makes a lube in this weight that may be available in your area. They have a find-by-zip code service on their website. Richmond, Amsoil, and Redline all make lubes in this weight for a comparable price, but you generally have to factor in a shipping/handling type fee at Summit or Jegs.

 

I changed mine at 82k miles with RedLine 85W140 and just recently,105k miles,with Amsoil Series 2000 75W140 @ $9.20 a quart. Just find a local Amsoil dealer and they will hook you up!
BTW,I use a gasket when I put my cover back on.Any parts store that sells FelPro gaskets will have it;
FelPro part # RDS-55431 = 8.8 differential
FelPro part # RDS-55394 =9.75 differential

Also,if you have a LS differential you will need 4oz. of friction modifier.After adding the fluid and modifier find an open parking lot and do at least 8-10 figure 8s to distribute the oil and modifier evenly within the differential and axle.

 

My advice is that if the limited slip is working okay, ie. not grabbing in the corners, leave it alone. I changed mine when the clutches were grabbing in the corners. Then I found out it takes two bottles of the friction modifier to keep the clutches from grabbing in the corners. If it ain't broke, don't fix it.

 

I have the conventional diff with 3.30 rear gear ratio....