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Thread: Rear Main Seal Replacement on a 98' 4.0 TJ Motor

  1. #1
    Join Date
    Jan 2009

    Rear Main Seal Replacement on a 98' 4.0 TJ Motor

    Rear Main Seal Replacement on a 98' 4.0 TJ Motor

    I finally decided to to fix my rear main oil seal leak, I was tired of leaving a trail of oil everywhere I went. When I started digging into the engine I found that it was time to replace the timing chain as well. With over 140,000 miles on the engine you can say it was time. I will try to explain tear-down as best as possible and any problems that I came across during tear-down. This repair can be done in about 4-5 hours and the cost for all gaskets, oil and filter was only $100.


    *Disconnect Battery* (1)
    First chock the wheels and apply the e-brake for safety since you will be under the jeep and then disconnect the battery.

    *Oil Pan Removal* (2)
    Drain the oil and remove all of the oil pan bolts. When reinstalling oil pan bolts torque to: 10mm bolts to 84 in-lbs & 13mm bolts to 132 in-lbs. You may also need to remove the stater for clearance, I did. When reinstalling the starter torque bolts to 45 ft-lbs.

    I found that the oil pan would not drop free and clear due to the exhaust was in the way.

    I disconnected the two header bolts and still the exhaust would not drop far enough to clear the oil pan. I found that the exhaust is mounted to the transmission mount. To access the transmission mount/exhaust hanger bolts you have to remove the skid plate.

    *Skid Plate Removal* (5)
    The skid plate removal was pretty simple, there is only ten bolts to remove the skid plate but it will take two people to remove.

    Remove the four transmission mount bolts, they are the four small bolts that are in the middle of the skid plate. Then place a floor jack at the rear output shaft yoke, you will only need to lift it about one inch. When reinstalling torque to 40 ft-lbs.

    Remove the six skid plate bolts, there are three bolts per side. This is where two people will be needed to remove the bolts evenly, then you can safely lower the skid plate. When reinstalling torque to 100 ft-lbs.

    Once the skid plate is removed you can safely place a jack stand under the transfer case.

    Now you can loosen or remove the four transmission/exhaust mount bolts to lower the exhaust enough to clear and remove the oil pan. You may also need to remove the starter for clearance, I did. When reinstalling the transmission/exhaust mount bolts torque to 65 ft-lbs, starter bolts to 30 ft-lbs.

    *Rear Main Bearing Cap Removal* (10)
    To access the rear main bearing cap you will need to remove the fourteen bearing cap girdle bolts. Remove and set it aside. When reinstalling torque to 40 ft-lbs.

    Remove the two bolts holding rear main bearing cap and carefully remove the bearing cap. When reinstalling torque to 80 ft-lbs.

    Carefully push out the upper half of the seal from the block. This may take some time but just have patience and take your time.

    When installing the new seals, the lower bearing cap seal is indexed but the top is not, it is very important that the top seal is oriented in the same direction as the lower seal. The V-notch should face the front of the motor. You can use soapy water to aid in installing the upper seal.

    While the oil pan is off you can inspect and clean the oil pump pick-up screen. There was small plastic shavings in my oil pump pick-up, later I found that the timing chain damper (small plastic peace that is in the timing cover) was scraped away due to a worn/stretched timing chain.

    (15) (16)
    The timing chain can be inspected while the oil pan is off. Simply use a screwdriver or a long extension and push on the chain, if there is 3/8" or more slack in the chain it is time to replace the chain. As you can see I had 3/4", which means bad ignition timing and poor gas mileage.

    Now the Jeep is drip free, now my wife can stop saying The Jeep is like the BP oil spill leaving oil everywhere.

  2. #2
    Join Date
    Jan 2006

    Re: Rear Main Seal Replacement on a 98' 4.0 TJ Motor

    Nice write up. My '98 is due as well just got to find the time.

  3. #3
    Join Date
    Jul 2006
    Far East Mesa

    Re: Rear Main Seal Replacement on a 98' 4.0 TJ Motor

    Nice write up Thanks for taking the time

  4. #4
    Join Date
    Dec 2003
    North Phoenix

    Re: Rear Main Seal Replacement on a 98' 4.0 TJ Motor

    Very nice write up.... two things I would add

    good seal kits come with a "shoe horn" (piece of thin plastic cut to fit back side of seal journal, to protect backside from sharp edge of engine block when installing seal). If your seal kit did not come with one, cut one out of thin plastic... makes installation incredibly easy, much less prone to leak later

    while you have the skid pan off, remove front driveshaft, if has a zerk (is a flush zerk) grease centering pin/ball. If (as most late model factory ones do not) disassemble CV and grease the needle bearings (inside ball)... failure to do so will (not can, WILL) lead to very expensive damage to driveshaft, which eventually will fail, swing around and take out your transmission and transfercase.
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  5. #5
    Join Date
    Jan 2009

    Re: Rear Main Seal Replacement on a 98' 4.0 TJ Motor

    I agree with you on both your comments (OlenyJeeps). I used FelPro gaskets and it did come with the little plastic shoe horn your were talking about. I highly recommend using it because the block edge is a machined surface, which is very sharp and a new seal is going to fit tighter then the old one. So if the seal has trouble going in it will twice as hard to pull it out. The front drive shaft part I already encountered that problem, if you look closer at the pictures you will see fresh paint on the drive shaft. For months I was hearing a squeaking sound at low speeds. I thought it was my brakes, was the CV-joint you were taking about, I found out if it is squeaking its time for new a CV-joint and U-joints. You are also correct on the skid plate, it dose have to come off to remove the front drive shaft. As you were saying now is the time to grease it up. Thanks for your comments!

  6. #6
    Join Date
    Apr 2009
    Mesa, Arizona

    Re: Rear Main Seal Replacement on a 98' 4.0 TJ Motor

    Thanks for the write up sent some rep.

    Impossible is a word only to be found in the dictionary of fools

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