I want to change my differential's oil, and the transfer case oil, on my 1990 XLT. It is a 5.8, auto trans. It has the manual transfer case with floor shifter. Please don't ask me what kind it is! Anyway, I know the front diff has a plug, so that one is easy. Dumb question #1: does the rear diff have a plug? I would just go look, but it is raining a lot and will be raining all weekend. There is a tropical depression moving into Central Florida right now. I just want to know what I'm up against, as far as these changes. If the rear doesn't have a plug, and from what I remember about Fords, it has no removable cover, I think you have to remove the pumpkin. How easy is this? Last, I want to change the transfer case oil. Is this one easy or hard? I've done it on a 4X4 Ramcharger and it was pretty easy. I'm not expecting anyone to give me step by step directions here, I'm getting a repair manual so I will know the correct weights and capacities. Just wondering if there will be any surprises, and anything funny that I should look out for. Thanks!

 

JB, the Ford 8.8 rear has a fill plug facing forward, the rear cover plate gets pulled to drain it. You were probably thinking of the old Ford 9" rear, that has the removeable carrier and closed back end. The Borg-Warner transfer case has both fill and drain plugs, at least the electric shift model does. Would think the manual shift would too. For the rear, you need to know whether you have LS or not to know if the friction modifier needs to be added, but you probably have that figured out.
Its a pain working outside, sometimes, okay, lots of times!

 

Actually no, I don't know anything about the friction modifier, or what kind of rear diff I have. What is that?

 

Take a look at the door sticker for axle code. If it has an H in it, like H9, then it is a Limited Slip 3.55 ratio. A non-LS 3.55 would be axle code 19 instead. If the door sticker is unreadable, try a tag on the diff cover bolts. A 3L55 is LS, a 355 is not.
The LS diff needs xx ounces of the proper friction modifier added to the axle oil. This is for the LS clutch plates that are between the side gears, they transmit some torque to a non-spinning wheel if the other one is spinning, like one wheel on a slippery surface. It is simply a friction connection between axle shafts, and that friction can be overcome so you can turn a corner without scrubbing rubber off the tires. If/when the clutches wear out, it just becomes like a regular open type diff. For long LS life, it is important not to have the clutches slipping a lot, like putting a different diameter tire on one rear wheel. Don't use the regular size spare in the rear if you have aftermarket big diameter tires. Your book info should specify how much friction modifier, and what type for LS.

 

I have an H9, so that must be a limited slip. I have 31's on it now, if I got a flat and put the stock spare on it for a short time, would it mess things up? A 31 is really not that much taller than a stock tire

 

PS - Is there such a thing as a limited slip differential on the front? In other words, do I need to think about the friction modifier for the front as well? Thanks for all your help.

 

No LS on the front diff, so no modifier needed there.
No problem, JB!

 

 

I am going to be driving the Bronco to Colorado next week and I have a lot to do before I go. I do want to change the oils before I go, though. I got an estimate from the local Ford dealer to change the two diff's and the transfer case for $90 plus fluids. I found out that there is no drain plug on the front diff, I thought there was but that was the fill plug. You need a pump to get the oil out. So considering that I would have to buy a pump, do you think $90 is reasonable? At least they would use all of the proper Ford factory oils.

 

Our local Ford dealer beats Jifty L, etc in standard fluid changes incl the diff and case..also beats em on coolant change incl a full flush. Another Ford dealer just gobs in da money and charges outrageous prices.
If you're in the 60k mile or 12 k mile range ask for the total maint package cost for those years..it is actually cheaper than ala carte at the better priced dealer here ($202 for compl tranny fluid change incl torgue converter and new plugs, air filter, diff, and xfer case, hub, wheel bearings, splines, etc.

 

So would you say $90 plus fluids is in line with the reasonable dealer, or the other one?

 

sure...90 is about right. for your own info, call jify lube and ask them for a price too.
just checked both dealers
simple oil.filter change..low dealer is 19.95 but has a coupon for 14.95 through OCT ...high dealer is 24.95
both of course use MC parts/fluids only.