How to Replace the Rear Main Seal on Vehicles

One of the hardest seals to replace in an engine is the rear main crankshaft seal. While the seal itself takes less than a half hour to replace by a qualified technician, getting to it is the hard part. Replacing the seal in a Vehicles can be a difficult endeavor, but with patience, some heavy lifting, a little know-how and the right parts, it can be done by anyone with mechanical aptitude and the will to accomplish the task.

Under The Hood:

• How to Replace the Rear Main Seal on a Lincoln Town Car
• How to Replace the Rear Main Seal on a Jeep Grand Cherokee
• How to Replace the Rear Main Seal on a Chevrolet Small Block

 How to Replace the Rear Main Seal on a Lincoln Town Car

Set the parking brake on the Town Car, and place the wheel chocks at both front and back of the driver’s-side rear tire.

Put your safety glasses on, and jack up the front of the Town Car far enough to allow you to place jack stands under the front frame on both sides. Repeat this in the rear of the vehicle so that the entire car is off the ground and resting securely on jack stands, one at each corner of the frame. Make sure the vehicle is sitting high enough that you can pull the transmission out from underneath it if necessary.

Slide under and unbolt the drive shaft, using your socket set. Once you have both ends unbolted, move the drive shaft out of the way.

Slide the jack in, and raise it up so that it is resting a few inches below the transmission pan. Set the two-by-four on the jack head, and raise the jack up until the board contacts the transmission. Disconnect the transmission cooler lines and wiring harness. Wrap a rag around the transmission cooler lines until you remount them, which will prevent dirt from getting inside the lines.

Remove the bolts holding the transmission bell housing to the back of the engine, saving the top bolts for last. You will need the socket extension to reach those bolts.

Unbolt the transmission mount and remove it.

Use the jack to lower the transmission. You will need your helper for this. Get on opposite sides and coax the transmission away from the engine and downward until it clears the chassis. Once the transmission has cleared enough of the undercarriage, remove the shift linkage as well.

Carefully remove the rear main seal from the back of the engine, using the seal puller. Use extreme care so you do not nick the end of the crankshaft; if you do, the engine will leak oil as soon as you start it up again.

Hold the new rear main seal up to where it mounts. Rest a large socket over the new rear main seal. Carefully tap the socket with the rubber mallet until it seats into the engine.

Reinstall the transmission, transmission mount and drive shaft. Reconnect the transmission cooler lines, wiring harness and shift linkage.

Start the engine and let it run for 15 seconds, then shut it off. Check the oil level and add accordingly.

Start the engine again and let it run for a few minutes. Shut it back off, and climb underneath and inspect for leaks. Peer through the inspection cover on the bottom of the transmission bell housing to see the rear main.

Carefully use the jack to lower the Town Car off the jack stands and back onto the ground. Run the engine for 15 minutes; while it is running, put your foot on the brake and shift the transmission through all the gears and back to "Park." Shut the engine off, recheck the oil and transmission fluid levels, and recheck for leaks.

 How to Replace the Rear Main Seal on a Jeep Grand Cherokee

Put on your safety glasses, jack the front of the vehicle up and rest the frame on the jack stands. You may have to use a large socket wrench and some major elbow grease to loosen some of the bolts during the job, so it is important that the vehicle is securely resting on heavy-duty jack stands.

Place the drain pan under the engine drain plug. Use the socket wrench to remove the drain plug. Once the oil has drained, move the drain pan away.

Unbolt and remove the oil pan by moving it toward the rear of the vehicle. You made need to coax the oil pan loose by carefully prying it away in several places if the Cherokee has a lot of miles. Be extremely careful when prying so that you do not damage the sealing surfaces. If the oil pan will not clear the suspension upon removal, you may need to unbolt the sway bar and let it hang to provide you with additional clearance.

Unbolt and remove the rear bearing cap. This may require some extra force. If so, use a breaker bar to get the stubborn bolts loose.

Carefully push the top seal out with a wooden dowel or other non-metallic, long, thin object. If you shove a screwdriver or another metal object in there, you may score the crankshaft or sealing surface.

Slide in the new top piece of the seal after putting a pea-sized dab of RTV sealant on the end tabs.

Install the bottom piece of the seal in the bearing cap and reinstall after lubing the lip of the seal with a finger tip of fresh oil. Torque the bolts on the bearing cap to the amount specified in the Haynes Repair Manual.

Clean the sealing surfaces of the oil pan and install the new oil pan gasket.

Reinstall the oil pan. If you removed the sway bar mounts during the oil pan removal, replace them now.

Replace the oil filter and fill the engine with new oil.

Carefully put the Jeep back on the ground and start the engine. Inspect the underside to ensure no leaks are evident.

 How to Replace the Rear Main Seal on a Chevrolet Small Block

Jack up the vehicle, using the floor jack. Support the vehicle with jack stands. Slide the drain pan under the oil pan drain bolt. Remove the drain bolt and allow the oil to drain. Dispose of the oil in an appropriate manner. Reinstall the oil drain bolt, so you don't lose it.

Place the block of wood on the floor jack. Jack it up enough to support the engine. Remove the engine mount through bolts, using the appropriate sockets. Remove the oil pan bolts, using the appropriate socket. Jack the engine up high enough so that you can lower the oil pan enough to remove the oil pump.

Remove the two bolts holding the oil pump onto the block. Put the oil pump in the pan. Remove the pan. You may have to jack up the engine a bit higher to fit the oil pan out between the frame and transmission.

Remove the rear main bearing cap, using the appropriate socket. Pry the oil seal from the bearing cap, taking care not to scratch the cap. Drive the top half of the seal from the rear main bearing, using the brass pin punch and small hammer. Once it is out far enough, grab the end of it with the pliers and pull it the rest of the way out. Make sure you have at least an inch to grab onto, else the ends of the seal will just fray, and you won't be able to pull it out. The seal fits tightly in the bearing, so you will need to use some muscle to pull it out.

Clean the rear main bearing cap and crankshaft with a non-abrasive cleaner and shop rags.

Make an oil seal installation tool from the 0.004-inch shim stock by shaping the end to ½-inch long by 1/64-inch wide. Coat the new seal with engine oil, but do not coat the ends of the seal.

Position the installation tool between the crankshaft and the seal seat in the cylinder case. Position the new seal between the crankshaft and the top of the tool, ensuring that the seal bead contacts the tip of the tool. Ensure that the seal's lip is toward the front of the engine.

Work the seal into the bearing, using the installation tool as a shoe horn to protect the seal's bead from the sharp edge of the seal seat surface in the cylinder case. Roll the seal around the crankshaft. Once the ends of the seal are flush with the engine block, remove the installation tool.

Install the lower half of the seal into the lower half of the rear main bearing cap, using the same procedure and installation tool as the previous step. Apply RTV silicone to the cap-to-case mating surfaces. Install the rear main bearing cap, keeping the sealant off the seal's mating line.

Install the rear main bearing cap bolts. Tap the crankshaft with the lead hammer forward, then rearward, to line up the thrust surfaces. Tighten the bearing bolts to the proper specification for your year small block.

Slide the oil pan into place, then reinstall the oil pump. It is recommended that you replace the oil pan gasket, especially if it is a cork gasket. Lift the pan up and install the oil pan bolts. Tighten the bolts firmly. Lower the engine back onto the mounts and reinstall the mount through bolts and tighten them firmly.

Lower the vehicle off the jack stands, using the floor jack. Fill then engine with the appropriate amount of oil for your year vehicle. If you cannot find the appropriate amount, put four and one-half quarts in, start the engine and allow it to run for two minutes. Shut the engine off. Check the oil and top off the oil as needed. Start the vehicle and check for oil leaks at the rear main seal and oil pan mating surface.