So to my surprise, our old differentials don’t have covers to facilitate inspection and oil changes!! I have to pull the center section to change the oil.
In order to do that I have to pull the rear axles. I’m worried I’ll open up a can of worms and have to chase down expensive other repairs, all just to change the diff oil (seals, etc.).
Any experience/wisdom? Thanks!
Depending on how long it’s been since seals have been changed, I would at least remove and replace axles seals, while axles are out, check bearings for noise and smoothness because this is a good time to replace them. you will also need a carrier gasket and copper washers for the studs.
One option is to put the rear up on jack stands. Disconnect the driveshaft and remove the fill plug.
Spin a wheel / axle to turn the gears. This will force a good amount of gear lube out of the fill plug.
Keep turning until you aren’t getting much more out.
Refill it with fresh gear lube, close the fill plug and turn the wheel / axle some more to mix the fresh lube in there.
Repeat the process to do a flush on the system, if you have a mind to.
Yeah, it’s messy, so have a big ol’ catch pan underneath, and have paper towels standing by.
Wear rubber gloves so your hands don’t smell too much like axle grease for the next week or so.
Or you could take it to a quickie lube place, where they’ll use a suction hose to draw out the old lube and then refill with fresh.
…I guess if you had a suction hose of some sort you could just do it that way yourself, and make less of a mess. But where’s the fun in that?
Catlover - yep… that’s the can of worms I don’t want to get into at the moment. As of now, things are “not broken” so I’d rather not get into all that until time and money permit a rear end rebuild.
Mike - that does sound fun and messy 
The quick lube may be my best option just for the oil change.
Additional question… is it possible to crack the center section a hair without pulling axles? Just enough for the oil to leak out over days.
If that is even possible with the axles still in, would that ruin the gasket on the center section and I’ll never get a good seal again?
Thanks
Don’t do it. Go with what Mike said.
Using a tube and pump to get the old gear oil out is by far the best method if you just want to change it. You can get everything you need at Wal-Mart. The pump itself and all the tube you need will set you back less than $10, and even if it’s ruined by the gear oil and falls apart afterwards, you won’t feel too cheated.
Don’t crack the seal on your diff unless you intend to change parts out. Mike and Catlover are right. If there’s a problem with your diff, you will almost always hear it long before it fails (unless you try putting slicks on a car with an 8" diff and a hopped up motor. grin)
Thanks all!
I cant recall if the 8 or 9" have a particular bolt that is dedicated to a “drain”. Typically its one of the bolts towards the bottom of the center section, You remove just the one bolt and it will drain the diff and you fill via the fill plug.
If you have not been into your diff in a while or ever its a good idea to pull it apart to put eyes on everything. One fault to only sucking out the fluid is you can not visually inspect all the parts or see how much(if any) material is laying at the bottom. You worry about opening a can of worms but its possible to find a future can of worms in there that can be prevented by inspection. Pulling the axles is easy and seals are cheap and easy to replace so I would say pull it apart, clean and inspect very well, reseal and reinstall.
Don’t forget the friction modifier if you have a limited slip
As I remember a Ford 9 Inch diff has all studs on the housing. It must be a Ford 8 or 8.8 that has a bolt drain.
Another choice would be a turkey baster with a piece of tygon tubing on the end. You can suck up the gear oil then use the baster to suck up new oil and inject it into the gear case.
You can also use the same pump used for pumping the fluid in via the fill plug. You’ll just need to pick up rubber tube to put into the housing. Most carriers have a fill plug on left side of the yoke. They can be very difficult to break loose if it’s been some time. Holding the pump and pumping is tiring.
P.S. If you have a track lok and are using the separate fluid don’t get it on you. You’ll stink for a week.
-Keith