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Guide to Transmission and Axle Service
By Jim Smart/
Printable version
Degree of DifficultyModerate
Estimated Time180 minutes
180 minutes
Though Often Overlooked, These Two Elements are as Important as Changing the Oil

There has long been intense focus on frequent engine oil changes every 3,000-5,000 miles. In truth, oil change intervals can be as short as 3,000 miles or as long 15,000 miles on some new cars. With the high-performance reserves of Mobil 1™ synthetic motor oil, you can have the confidence to go the full mileage or time frame recommended by the vehicle manufacturer*.
Changing Transmission Fluid
With all this attention being paid to engine oil and filter changes, what about the rest of your vehicle’s driveline — the transmission and axle? How many of us never give transmission and axle service any thought? Regardless of what manufacturers say about “life of the unit” lubrication (no fluid changes), clean lubrication beats the socks off dirty lube any day. Clean fluid provides a clean oil wedge between moving parts. It also keeps dirt and debris on the move and away from those moving parts. Clean fluid is also kinder to seals.
Transmission and axle fluid changes should happen at the same time — every 30,000 miles — including the filter. And while your vehicle is in the air, it’s a good time to inspect everything underneath, like the Universal joints, driveshaft, suspension bushings, ball joints, shocks, struts, fuel and brake system hoses. Anything suspect should be replaced.
Drive Axle
Drive axles do a tremendous amount of grunt work and it shows in the condition of gear lube when it’s time for a change. Because gear loads and pressures are high in differentials, they tend to run hot — around 300 Fahrenheit — especially if you’re climbing a hill with a heavy load at highway speeds. This is why drive axles should be serviced every 30,000 miles. And when you service, follow the manufacturer’s specifications with the correct viscosity. If you have a locking differential, don’t forget to go with a friction modifier for smooth and consistent clutch engagement. While you have the differential cover off, check all seals and axle bearings. If your vehicle has over 100,000 miles and has never had axle bearings and seals replaced, do it now.
Transmission Service
Whether you’re working with an automatic or manual transmission, service should be performed every 30,000 miles. Though manual transmissions used to take heavy weight gear lube, today’s newer manuals with tighter tolerances take automatic transmission fluid for easier shifts and cooler operation. Again, check with your manufacturer to see what type of lubricant is recommended.
Whenever you perform automatic transmission service, remember both fluid and filter should be changed. Follow the manufacturer’s recommendations on fluid type and capacity. If you’re wondering where the dipstick is on some applications, it has been phased out and replaced with a service port via the pan or case. This approach to fluid fill prevents overfilling and fluid foaming. Some automatic transmission filters use an o-ring between filter and case, so make sure the old o-ring has been removed.
Before you begin tackling any DIY maintenance or repair job, however, your primary concern should be safety. Following a few safe work practices and investing in protective equipment – like gloves and proper eye protection – should help reduce your chance of injury.
Here are some more suggestions that you may find useful:
*We recommend you follow the oil and filter change frequencies shown in your owner's manual. Generally, this means changing your oil every six months when using Mobil Super™, Mobil Super™ High Mileage and Mobil Super™ Synthetic motor oils, and every year when using Mobil 1 or Mobil 1™ Extended Performance synthetic oils.
Most drive axle assemblies today have a removable pan, which makes service a breeze. Be prepared for installation with a fresh gasket and sealant. If you have an older removable carrier type drive axle found in Fords and some GM vehicles, removal is more involved. You can remove the differential or knock one of the bottom studs in (with a lock nut attached) and allow it to drain. Lube can also be siphoned out.
Preparing to Drain the Fluid from a Drive Axle Assembly
Because axle lube has a strange way of finding even the tiniest leak path, surfaces must be clean and free of scoring. Ideally, you will have a composition silicone and steel gasket if available. Otherwise, go with the best gasket material available.
Clean the Surface Before Applying Axle Lube
Axle service is the time to check for leaks and correct them. This 8.8 integral carrier drive axle has a leaking pinion seal, which must be replaced. You can’t just change a pinion seal because the ring and pinion have to be set up all over again. When the drive flange or yoke is removed, preload changes and must be set again.
Carrier Drive Axle with a Leaking Pinion Seal
When you are performing drive axle service, this is the time to replace axle bearings and seals. Some axle bearings are pressed on, which calls for a hydraulic press.
Replace Axle Bearings and Seals
For seal installation to be leak free, a very thin film of sealant is applied to the perimeter to fill in any irregularities.
Apply a Thin Film of Sealant to the Perimeter
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