A local Jeep service department quoted me $270 to change the fluid in both of my differentials at the 12,000 mile mark. I stood there staring at the guy with my mouth hanging open. He wanted how much?!? "You've got to be joking." I wondered if the fluid cost $300 a gallon or if draining the differentials was like doing major maintenance. I went online, read about it, and it wasn't that hard. I got the all of the parts to do it for under $50, including tools I would keep forever, and I did it myself in a few hours, and saved myself a bundle. Never again will I think about paying someone to drain differential fluid and replace it. You can do this too. It's a little stinky, but that's the worst of it.

What Are Differentials?

Differentials. When you first look under your front bumper, there sure is a bunch of stuff under there. But, when you know what you are looking at, the Jeep front end is really quite simple. Highlighted above in yellow is the differential - AKA "The Pumpkin" - AKA "the diff". The differential is the blob in the middle of the axle where the drive shaft and the axle connect. Inside that thing are lots of big, heavy-duty gears that make the turning of the driveshaft transmit to the turning of each wheel. There are two differentials, one in the front and one in the back.

Track Bar. You can also see highlighted the track bar, which connects the axle to the frame. There is one in front and another in the back. It keeps the axle from floating left and right so that all four wheels line up with each other. Without it, your left side wheel might stick out and your right side wheel would be too far inside, and your wheels would wander around back and forth.

Drag Link. The drag link is another bar like the track bar that connects the right wheel's ball joint with the steering column. When you turn the steering wheel, the column turns, and it pulls the drag link back and forth, which pulls the ball joint. It has a turnbuckle on it and two bolts that hold it tight so that you can adjust it to make your steering wheel straight when your wheels are pointed straight. The shock absorber looking thing on the drag link is the steering stabilizer. It helps prevent vibrations from all of these connecting rods going down the road hitting bumps.

Steering Tie Rod. This bar goes from the drag link end on one side to the driver's side wheel on the other. It is adjustable, just like the drag link, so that you can set the toe-in when doing a front end alignment. Otherwise, it pulls the driver's side wheel when the passenger wheel turns.

You will need to know what these are when you get under your Jeep's front end to do your differential service, because on a stock Jeep that is not lifted, the track bar gets in the way of you reaching certain bolts unless you put the front end up on a jack stand. The tie rod gets in the way when you are trying to take the cover off and put it back on. If you get confused while trying to do your diffs, and you post a message asking for help, you don't want to have to say "What is that thingy next to that other thingy? It is in my way."

Overview of this Task

Our goal is to get old fluid out of the differential by removing the cover and having the old fluid ooze into our oil pan, clean the cover off, make a new gasket using RTV, stick the cover back on, and then fill up the diff with new fluid. It is that simple.

This is Going to Stink

There is something I should warn you about before you begin this job. Unlike motor oil, coolant, washer fluid, transmission fluid, or brake fluid, the stuff you put in your differentials smells pretty bad. It doesn't smell gross, like rotting garbage. You won't get sick or anything like that. It just has a really powerful odor to it that gets on your hands which soap and water really don't get rid of the first time. Shop towels that have gear lube on them are best thrown out, not washed. And you don't want something soaked with gear lube in your garage, because it will stink up the place. Again, the smell is not nauseating or horrible, but it is quite powerful and stinky. You'll see.

One Diff or Two

I cannot say yet, having done this job three times now, whether I prefer doing one diff per day or pushing through to get both fo them done on the same day. Diff fluid changes are quite a bit of physical labor, and I find it a little exhausting to do both of them on the same day. However, it is very efficient to do, but you end up moving the catch pan back and forth. You will have to decide. I recommend the first time you do this, just do one diff end to end, then do the next one on another day. Then, you can decide if it would be too much work or time to do both.

This write up is for the front differential - on my Jeep that's a Dana 30. The rear is done the same way, except for a few differences. My Dana 35 rear axle has a rubber insert for a fill plug instead of a turning bolt. Also, you really have to jack up both sides of the Jeep to get good access to the rear diff on an unlifted Jeep, because the gas tank is in the way. If you can do one differential, you can do them both.

Tools You Will Need

********************************
***** PICTURE GOES HERE *********
*************************************

3/8" Ratchet Wrench. You will need this to remove the screws that hold the differential covers on.

13mm Socket. This is the size socket that fits the screws on the differential cover

Torque Wrench. You need a short handled torque wrench to do this job well. A long handle torque wrench doesn't fit well into this tight place. The torque for the plug is 25 ft-lbs, and the diff cover bolts are torqued to 30 ft-lbs, so it doesn't have to be a powerful torque wrench.

Paper Towels. Bring a whole roll of them outside. Your wife will thank you for not coming inside repeatedly to get more while you are all stinky with gear lube on your hands.

Oil Catch Pan. The same catch pan you use for oil changes is useful here.

Gasket Remover or Putty Knife. Either one will do to scrape the old RTV from the differential cover and housing.

Newspaper or an old refridgerator box. You will need the Sunday edition, and only the sections that are newspaper paper - don't use the slick pages from ads - they don't absorb anything. You will need a lot of this, because changing fluid in diffs is a little bit violent and fluid tends to get everywhere.

Lots of guys swear by old cardboard boxes, like the size of a refridgerator box. They just slide them under the jeep and it soaks up anything you lose. When done, just put it up and use it again and again.

A Rubber Mallet. A BFH or a rubber mallet will work. I prefer a rubber mallet before I surrender to the BFH and risk denting something or bending it. But diff covers are pretty sturdy.

Gear Lube. I prefer to use Mobil 1 75W-90 in my differentials. I have been using it for 40,000 miles, and it is working out just fine so far. The FSM asks you to use 80w-90 lube in your differentials. Close enough. If you are pulling a trailer regularly, the FSM recommends 75w-140 gear lube. Whatever you do, get a gear lube that is for limited slip differentials. That way you won't have to put any additives in it. If it says "great for limited slip differentials", then it is good enough. You can get this at Autozone. You'll need three bottles to pull this off.

A Cheap Hand Pump. While picking up lube, I also grabbed a cheap hand pump. This is the best way to put new fluid into your diffs. You stick the pump into the bottle of lube, and then you suck up the fluid. Then you can stick it into the diff's fill hole and squirt in the fluid.

Non-Toxic Brake Cleaner. Get an aerosol can of brake cleaner while you are at Autozone picking up your gear lube. You will need this to clean out the differential once you open it up.

Floor Jack and Jackstands. If your Jeep has a 3" lift on it, you won't need to jack up your baby to get at the differentials. If you have a stock suspension, then the trackbar will be in the way, and I put the front right frame rail up a few inches on a jack stand until the track bar is out of my way. I prefer 6 ton or heavier duty jack stands because of the wider base (by a factor of 4) over the 3 ton stands.

Bolt Size & Torque Specifications

Bolt	Size	Torque
Differential Cover Bolts	13mm	30 ft-lb
D30 Axle Drain Plug	3/8" Ratchet Wrench Size	20 ft-lb

Step by Step Guide

Take a deep breath. It will be the last clean air you breath for a while. LOL!

1. Block every wheel front and back with chocks, bricks, or wheel stops except the driver's side front wheel.

2. Set the parking brake in the Jeep to ENABLE by pulling up good and hard. This is no time to worry about engaging it too tightly. We want to not have the Jeep roll off of the stand and crush us.

3. Place your automatic transmission in PARK.

4. Place the floor jack underneath the right front lower control arm mount on the frame rail, and lift up the Jeep corner a few inches until the track bar is no longer in front of the differential.

5. Place a jackstand under the frame rail, and then lower the Jeep onto it using safe jack/jackstand practices. Try again if the jackstand is not solidly in contact with the ground. After I do this, I give the Jeep a bump with my hip to see if it will fall off of there. Call me paranoid, but my grandfather's leg was crushed under a car that fell on him back in the 1960's, and he limped for the next 40 years of his life.

6. Spread out a good layer of newspaper far and wide under your Jeep. Remember the Golden Rule of Fluids - they go where the newspaper is not - no matter how far away that is. Place the oil pan on top of the newspaper underneath the differential.

Now your Jeep is ready for work!

7. As with any job, first loosen the fill plug in the differential cover using a 3/8" ratchet wrench end. That's right, the raw socket mount goes right into the Dana 30 differential cover fill plug. The biggest mistake people make when doing fluid changes besides not using enough newspaper is getting all of the fluid out only to find they can't put any new fluid in because the fill plug or cap is stuck. There's nothing quite a silly as having your Jeep being disabled because you didn't check to see if you would be able to put in new fluid before you took the old stuff out. Avoid a tow truck and check the fill plug first.

8. Begin removing the bolts that hold on the differential cover. Start with the bottom most bolt, and work your way left and right and gradually up to the top bolt. When you get to the top bolt, just loosen it, don't remove it. Hey, put those bolts somewhere safe where your kids or pets won't eat them or kick them into the yard. You will need every last one of them to get a good seal when you put the cover back on.

Sometimes bolts don't want to come off very easily, and you can't budge them. In that case, break out the Mac Daddy Breaker Bar (1/2 ratchet wrench that doesn't ratchet) and put on a converter and give yourself some excellent leverage. The bolts will come off quite easily if you get a longer handle to use.

The first time I did this, I really beat up my hands. Mechanics gloves help to prevent the cuts you might get from pushing really hard to undo those bolts and having them suddenly release, sending your hand flying up into sharp objects above the differential. As you acquire skill, this stops happening, because you begin to get a feel for a bolt releasing and build up reflexes to stop your hand before you injure yourself.

9. Pick up the mallet and start pounding first one side and then the other of your differential cover. Notice that without the bolts in, only a little fluid might leak out. That's because the last guy put RTV gasket maker on the cover when he put it back on. RTV dries to a rubber like material that works like a gasket. It prevents leaks. This will not be as easy as you might assume. I usually spend a while whacking at these things before they finally start to come loose. Keep hitting it, left a couple of times, right a couple of times, and it will start to loosen. When it gives, fluid comes out, and might go everywhere. You did put down newspaper, right?

When you get the cover good and loose, the fluid will start leaking out of the diff. When it finally swings free, the fluid will pour out. The main mess comes from the fact that the diff starts leaking while you are pounding on the cover with the hammer. That makes it squirt everywhere. I hope you aren't wearing your Sunday best while doing this.

10. When the cover comes free, finish removing the top bolt, and set the cover to the side. Exposed before you are the gears that your Jeep uses for power.

Look at all the pretty gears. When I first opened mine, I enjoyed spending a moment looking at it trying to figure out how all of that worked. Back to work!

11. Clean the differential cover. Use a putty knife or a gasket remover. Scrape all of the rubbery goo from the cover without putting any serious scratches or gouges in the cover. Just get all of the old RTV off of the cover. Be thorough and patient. This is the longest part of the job. When you are done, spray brake cleaner on the cover, and wipe it down good with a paper towel. You don't want any little bits of RTV going back into your gears, so be extra thorough.

Here's my diff cover getting a good polishing!

12. Cover the gears with paper towels to protect them, and then scrape the RTV off of the differential housing. What a pain! It's like cleaning up after you paint windows or something. Get all of the rubbery stuff that could interfere with the new seal you are going to make. Don't get any in your gears!

You can see how I stuffed paper towels into the housing around the gears to protect them from any crud I scraped off of the housing from getting in them.

13. Remove the paper towels when the housing is clean and spray the gears down with brake cleaner. I shoot lots of this into the housing. It breaks down all of the filth in there and washes it down to the bottom of the housing. The differential housing has a dip in in on the bottom where brake cleaner can puddle. Wipe inside the housing as good as you can and wipe off the gears. You wil not be able to thoroughly clean everything in there, but do what you can. Make sure you use paper towels to soak up every drop of it from in there so that the housing can dry out. You don't want an industrial grade solvent chewing up your gear lube after you do all of this work!

14. Get out the RTV and your clean diff cover, and put down a good, thick bead of RTV around the edges of the cover. Don't fill up the bolt holes with it, but do go around both sides of every bolt hole. I prefer to use a blue RTV from autozone that is tacky instantly and doesn't have a wait time before I can put the cover back on.

Here's a picture of the bead I made with the RTV.

Some RTV requires you to wait before you apply the cover. Some says apply immediately. Follow the instructions on your tube of RTV gasket maker.

15. Carefully bolt the cover back on. Lift it up to the differential housing being extremely careful not to let any RTV touch the gears. Be careful also to put the cover on right side up (the fill hole goes on the right). And hold it in place carefully, lining up the bolt holes. Don't let it slip around, and use a couple of bolts to get it to stay lined up and in place as quick as you can.

16. Finger tighten all bolts you can to hold the cover on the differential.

17. Torque the bolts down. Start with the bottom bolt, then do the top bolt. Work your way clockwise around the differential, torquing each bolt to 30 ft-lbs, one at a time, always doing the one on the opposite side immediately after each one you do.

18. Wait one hour for the RTV to dry before putting in lube.

19. Get out the gear lube, stick the pump in it, stick it in, pull up a load of lube, and then stick it into the fill hole. Push the handle and pump in the lube. The front differential on a Dana 30 like mine needs 1.2 liters or 2.5 pints of fluid in it. The Dana 35, which I have in the rear, takes 1.66 liters or 3.5 pints. Usually the bottles of gear lube have little measuring marks on the side and a little translucent slit through which you can see how much fluid is in the bottle and how much is left. And usually those measurements are in ounces, not pints or liters.

2.5 pints = 40 oz. 3.5 pints = 56 oz. These are US measurements, so if you are reading this in another country, I can't help you with the metric system or differences between UK and US volume measurements. In the UK, these measurements do not work. Usually the bottles come in 1 quart sizes, and that's 32 oz for those of you who hate math.

Use the right kind. If you do some serious towing, use 75w-140.

20. Replace the fill plug and torque it down to 25 ft/lbs.

21. Take the fluid that fell into the pan to your local Autozone and recycle it to preserve Mother Nature for the rest of us. Remember: TREAD LIGHTLY!

Finally, that stinky job is all done! And you saved some serious money, acquired a few more useful tools, and can now do the other differential with greater confidence.

Ruh-Roh!

This is the part of the write-up where I consider some possible mistakes you could make to help you diagnose problems you have after you are done.

Gear Lube Keeps Squirting Back Out. When you are trying to pump gear lube into the housing, sometimes you point the hose right at the gears, and the lube just comes right back out. Try moving it around to point at empty space inside the differential.

It's leaking. You have only one option. Yes, you know the answer. You have to do it all over again. There is no way to patch it so that it will stop leaking. But be sure you have a leak first. Sometimes it just looks wet on bottom because you spilled some lube. Wipe off the differential really good to remove any traces of a leak, and let it sit overnight and see if it is really leaking. If it is, you will have to do everything over again. Check your diffs regularly by peeking at them to see if they are leaking. To check fluid levels, remove the fill plug, stick in your finger, and see if you find lube up to the edge of the hole. If so, it's fine.

I can't remove a bolt. Get out the 1/2" Mac Daddy Breaker Bar, put a converter on it to make it fit your 13mm socket, and then rip that bolt off of there.

There's a thingy in the way and I can't reach the top bolts on the front diff. Read the directions. I said jack it up, and learn the names of the parts in your suspension up front and stop calling stuff a "thingy."

Horrible grinding noise. You did something terribly wrong. Stop driving vehicle immediately and have it towed to a mechanic to open up the diff and pull your ratchet wrench out of the housing - or whatever it is you got into your gears.

Gear lube under the tub. If you look under your Jeep's body in front of the rear differential, and you see spatter that looks like it radiates outward from the place where the driveshaft goes into the differential, then your pinion seal is bad. Put in a new seal, or pay someone to do it.

Feedback

Just wanted to say thanks again! I just changed (15 minutes ago) the fluids in my diffs according to your instructions! I check out this site often and want to thank you for putting up such a great site! I hope there will be more tips and tutorials in the future.

~tyrus smalley

Hey there,

Just wanted to say thanks for this website. I bought a 2006 Wrangler X w/manual transmission two years ago. About all I could do on my own is change my own oil and rotate the tires. Now, next week, I'll be attempting to change the differential fluid and to lube the front end for the first time on my own (heading to AutoZone this afternoon to pick up everything I need!).

I'd like to upgrade the stock tires too eventually, so looking forward to that and changing out the speedometer gear (again, thanks for making it easy), along with the other maintenance items you have up. Looking forward to you finishing filling out the DIY service checklist; I have no idea even where to start for the brake service.

Once again, great site. I have it at the top of my Jeep bookmarks. Have a good one!

Best,
Eric Harkness
Tucson, AZ

Help with Axle Service Online

Stu's Write Up is on his index page. Just do a find on changing diff fluid. and you'll see it. He has designed the site to force everyone through the front door, so I can't link right to the article for you. But it is there, and it is excellent.

4x4xplor.com has a great write up on differential service.