Rear Differential Maintenance

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image of rear differential cover
Rear Differential Cover

Rear differential maintenance and changing the fluid is not required as much these days as with many other maintenance services on modern vehicles. But completely ignoring the differential is not recommended in case problems should develop.

A regular maintenance routine includes inspecting the gear lubricant level and condition. You can check your owner’s manual for recommended intervals and your auto repair manuals for specifications as well as the types of fluids to be used.

In the case of rear wheel drive vehicles different types of gear oil are used in different makes and models. Since there is no filter inside fluid can become contaminated with metal flakes and moisture.

Most rear differentials will have magnets either mounted inside or as part of the drain plug to help remove metal particles from the circulating lubricant. In some limited slip rear differentials special lubricants that contain a friction modifier are required. Failure to use this special recommended fluid can cause drivability problems, increased wear and annoying noises.

Recommended inspection points

image of axle seals and bearings
Axle Seals and Bearings

As with many parts on the car rubber seals are susceptible to wear and leakage. The rear differential contains a few of these lip type seals. One area to check is where the drive shaft attaches to the pinion yoke known as the pinion seal. Any fluid leak from this area should be repaired before lack of lubrication damages internal components.

Rear axle seals are also made out of rubber. A leaking rear axle seal can cause the same type of problems with lack of lubrication. But more importantly a rear axle seal leak can dump fluid onto your rear brake pads or shoes.

image of differential cover gasket
Differential Cover Gasket

This type of problem can increase stopping distances and cause other problems. On many rear differentials the cover that fits on the back is another point of a possible leak to develop. This is also a cover that may need to be removed for regular maintenance.

Most differential covers use a gasket. Sometimes auto mechanics will take a shortcut and replace that factory gasket with silicone. This is not a recommended procedure and can wind up causing a leak down the road.

Rear differential maintenance is important because the entire assembly does not carry more than a few quarts of lubricant. Even a small leak that goes unnoticed can cause the fluid level to be low enough to starve axle bearings and cause other problems. An occasional visual inspection of the parts mentioned above can provide an early warning and save you from expensive repair costs.

The drive train subject is not covered on the internet as much as other auto repair information subjects. I decided to put together a section dedicated to these systems on my you fix cars website. You can see this area located in the left hand navigation under manual drive trains.

Can't fix your car problem on your own? Ask a live mechanic!

14 Replies to “Rear Differential Maintenance”

  1. Gary Schwartz

    We had a rain storm the other night and I end up going through large amount of water. In fact, my car was half way floating and on the ground. I did get it out within five minutes on dry pavement again. With this happening, can water get into the differential or is it a seal unit? I am going to have both the transmission and differential changed. What is your recommendation on that?

    Thanks for all of your help.

    Gary Schwartz

  2. Mark

    Gary: Both the transmission and differential are sealed units but both have vent lines to let pressure out. These vent lines usually have check valves on them to let pressure out and stop water from coming in. But I have seen the vent check valves get stuck. I do recommend the fluid changes you have planned. I would also notify the mechanic of what happened so he can inspect for water intrusion.

  3. Gary Schwartz

    Mark: I’m sorry to bother you again. The other day we had heavy rains here. On the way home from work, I was caught in a stream of water which left my car partially floating for about 5 minutes. I was able to get on dry pavemant after that, but the car quite lousy. I lived about 2 block from ther and was able to get the car home. I checked the oil and found that there was water in the engine due to the milky color of the oil. I know that the water went throughthe air intake. Called a towed truck and had them tow it to a Ford dealer were they look at it. I did explain to them what happened. They told me that they started the engine up(which I thought was a stupid idea knowing that they had water in the enginel). What is your suggestion? Should they replace the engine, or take off the heads and see what type of damage there may be, or change the oil a few time and go from there. Do you also think I should have the car junked? It is in show room condition and has 75000 on it. I just needed a second opinion in what I should do. Thanks, Gary.

  4. Mark

    Gary: I do believe that a second opinion may be needed in your situation but by someone who could actually see the car I think would be best. In most cases I do recommend paying some diagnosis for disassemble to see what is wrong inside. When water enters the intake while the motor is running it usually causes heavy damage. This is called hydrostatic lock. The pistons can not compress the large amount of water and will often crack pistons and break connecting rods. You may consider contacting your car insurance company to see if this type of damage is covered under your full coverage policy.

  5. MAC

    Hi Mark, I own a 2003 Subaru Baja. Is it true that the rear differential should be change at lease every 20,000 miles?

  6. Mark

    Mac: In the end I would have to recommend following the maintenance guidelines in the owners manual. But I think the frequency of fluid changes also relates to how you use your Subaru Baja. If you Baja often and submerge the axles in mud and water then more frequent differential fluid changes are recommended. If you see milky fluid on servicing then the axle and pinion seals should be inspected.

  7. Michelly

    Hi. I had my 04 Tahoe in this morning after several weeks of strange noises (whining/grinding/friction, clicking/clunking) all of which seem to occur randomly. The diagnosis was rear differential needs replaced at $2200 (assuming they can scavenge some used parts). With 160k on the vehicle, is it worth replacing or should we get rid of the car?

  8. Mark

    Michelly: “With 160k on the vehicle is it worth replacing or should we get rid of it” This is a tough call that I can’t make. I do recommend getting a second estimate ( the first estimate seems high unless there is case or carrier damage. Also an overall evaluation on the TRUE condition of the truck should be performed to see what will be needed in the near future before you shell out 2,200 bucks.

  9. Michelly

    Thanks, Mark! Actually, the power steering/brake pump went out this morning so that’s another $350! We’re thinking this may be the end.

  10. Tammy

    We own a 2003 Dodge Ram 2 wheel drive, how often does the rear differential fluid need to be changed and what would be the normal cost of all that?
    Tks Tammy

  11. Mark

    Tammy: Generally speaking a light duty pick-up truck would have a service recommendation of about every 30k miles. But to be sure please check the owners manual. If you have lost the one for your 2003 Dodge Ram 2 wheel drive they can often be found for free online. Costs of the service differs with the hourly labor charges. In my town this service goes for about 185 bucks at the dealership.

  12. Linda


    I just had my clutch replaced and a wheel bearing on my 2003 Subaru Forester and the differential seal blew right after. They repaired that without a charge….said they must have nicked it during clutch repair. My question is, has there been damage done that will cause serious problems down the road. I had to drive it for 5 days before I got it back to the dealer.

    • Mark Gittelman

      John: I recommend picking up your parts and fluid at the Dodge dealer. On the ST model it might have a locking differential that uses different lubricant. The dealer parts department can run the VIN and see what type of rear end the truck has.

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