DIY Diagnose and Repair Rear Differential Leak On Your Car or Truck.
If you notice oil spots under the rear of your car or truck or dirt and a greasy film is collecting on the undercarriage, you may have a rear differential leak. This blog covers a simple process for diagnosing the rear differential for a differential leak, pinion seal leak, or axle seal leak, and how to fix it if the rear is leaking.
*Mechanics Tip: Placing items in the order you take them off makes putting them back together a lot easier.*
How to Diagnose and Stop a Rear Differential Leak
1. The Rear Pinion Seal Needs to be Checked for Leaks
Starting at the center of the rear differential or the pumpkin. (The large rounded part of the differential is also known as the pumpkin.) At the front of the pumpkin, located where it connects to the driveshaft is the pinion seal. If the pinion seal is leaking, it will drip on the differential and the differential will be covered in a greasy residue and dirt.
How to fix the Rear Pinion Seal
To fix the pinion seal first remove the driveshaft.
Loosen and remove all bolts from the driveshaft.
You may need to tap the driveshaft with a rubber mallet to loosen it if it’s stuck.
Separate the driveshaft from the differential. There is a chance the exhaust will be in the way. In this case, the exhaust pipe needs to be removed, as well.
Once the driveshaft is removed, remove the pinion nuts from the yoke.
To access the pinion seal you may need to tap the yoke with a rubber mallet to loosen it.
Remove the yoke to access the pinion seal.
Remove the pinion seal and clean the area thoroughly. This is important because if the area isn’t clean, the next seal may fail. *Reverse These Same Steps to Reinstall*
Install a new pinion seal and connect the yoke and tighten it. Connect the driveshaft back to the yoke and torque the bolts to the manufacturer’s specifications. You may need to contact your dealer for this information if you can’t find it online.
Check the differential and transmission fluid levels.
Refill the differential fluid level and the transmission fluid level if any fluid leaked out during the repair.
2. Check the Differential Cover for Leaks
The differential cover is located on the rear of the differential. In some cases, the differential cover is separate from the differential. If the differential cover is a separate part from the, there will be a seal or a gasket. If that seal is leaking, the differential fluid will be coming from the sides of the cover and pooling at the bottom. The differential cover could have dark, greasy, debris-covered areas as well.
Steps for Fixing a Leaking Differential Cove
Get a drain pan or something safe to drain the differential fluid into.
Loosen the bolts on the differential cover.
Pry the differential cover off with a flathead screwdriver or small pry bar.
Let the differential fluid drain into the drain pan.
Clean the differential pan and the differential thoroughly. Failure to clean it well may cause the new gasket to fail.
Place a new gasket on the cover in the same position as the old one.
Place the differential cover back on the differential.
Torque the differential pan bolts to the manufacturer’s specifications. Make sure to get the specs from a trustworthy place.
Fill the differential with new differential fluid.
Take the vehicle for a test drive to make sure it’s functioning as it should.
3. Check the Bottom of the Rear Differential Tube for Leaks
If you see a greasy residue and debris at the bottom of the differential tube, it means the differential tube is leaking. Moisture can be the problem. It can accumulate at the bottom of the differential tube and cause it to rot the tube and leak. Some vehicles will have stickers on the bottom of the differential tube that can hold in moisture and cause the tube to rot. Rot can collect under the sticker and if the sticker is removed, you will see moisture and fluid leaking from the differential tube.
Rotting on the Differential Tube -A rotting differential tube is indicative of a bigger problem and means the differential will likely need to be replaced or overhauled. This type of differential service is usually best left with the professionals. Contact your mechanic and have them give it a look.
4. Check the Differential Vent Tube for Obstructions
On the top of the differential, either located on the differential tube or the pumpkin, there is a vent tube. This vents the air inside the differential. Just make sure that the vent tube is there and not clogged.
5. Check the Axle Seals for Leaks
A Differential can also leak at the axle seals. The axle seals are located at the end of the differential tube. If you find moisture collecting at the seal, that usually means the axle seal is leaking. If the axle seal isn’t leaking the axle tube will be dry at the seal.
How to Fix an Axle Seal Leak
Use a floor jack and jack stands to raise and secure the vehicle, safely.
Remove the wheel and brakes to get a clear view of the axle. Remember to loosen your wheel lugs before the vehicle is completely off the ground.
Take off the differential cover.
Remove the bolt holding the axle in.
Remove the axle.
Clean the area well. You don’t want to get dirt and debris into where the new seal is going.
Remove the axle seal from the axle.
Clean the surfaces where the seal makes contact thoroughly.
Place the axle seal.
Reinstall the axle in the reverse order in which you removed it.
Place and tighten the axle bolt.
Reinstall the differential cover, brakes, and wheel.
Fill the differential fluid
Take the vehicle for a drive to make sure it’s working as it should.