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Two Piece Rear Main Seal Replacement

Discussion in 'The Garage' started by jrsheets, Jul 1, 2004.

  1. jrsheets

    jrsheets Registered Member

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    Ok, so i figure that my 85 with 305, 700r4 has the two piece main seal. I need to replace it. I haven't done this work before. Do i need to LIFT the engine?!!? A well experienced mechanic here at my dealership said so. He said it was to get the oil pan out. I don't remember there being anything obstructive in the way. So i call BS on that. Im concentrating on the lower seal, but i giess i should replace them both while im there?

    I pretty much have the procedure down after i get the oil pan off. Is there anything else i need to be aware of?

    Im just going buy a HUGE plastic tarp and bucket!!!

    /forums/images/graemlins/dunno.gif
     
  2. XHitman396

    XHitman396 1/2 ton status

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    dont you have to pull the crank to get to the upper seal? i just watched a buddy rebuild his motor, and i thought that the only way to put the main on was to have the crank gone... maybe not...
     
  3. diesel4me

    diesel4me 1 ton status Premium Member

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    If you have too you can loosen the main bearing caps and let the crank hang down a little,I have done several without doing that,but its a bitch-- /forums/images/graemlins/ignore.gifthey make special tool to help,like the "chineese fingers"thing,but most of the time they dont help much--most of mine went in with my "american"fingers.If you do have to loosen the main caps,be very certain none of the bearing shells move out of position before you tourque them to the proper specs.You dont have to loosen them much,if at all. /forums/images/graemlins/crazy.gif
     
  4. JSH

    JSH Registered Member

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    It's been a while since I did mine but it seems like I was able to get the pan off without lifting or disassembling anything. I believe I took off the access cover for the SM465 too. Then if was just a tedious job of feeding the upper seal around in its race, I think I made a kind of a hook out of some soft wire to pull it around. Messy job with oil dripping off the crank into your face constantly, it helps if you pull the pan and give it a long time to drip before you start-oil in your eyes hurts! Take the time to replace your pan gasket at the same time-I'm sure you were probably planning on that anyway-it's not worth trying to reuse them.
     
  5. bryguy00b

    bryguy00b 3/4 ton status

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    yea not only oil dripping in your face but in my case..dried up mud to! i was puttin a new pan on my truck last night..man after that i was coverd in mud/oil...not a very "fun" job..but the rear main dunno ive never done one, cept for in school on a learning engine..
     
  6. jrsheets

    jrsheets Registered Member

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    well, thanks guys, i plan on letting the engine drain for atleast a couple of days prior to starting the job. I will buy both seals, if I have to muchtrouble getting the top to go, i may just skip it and see what happens. Not what i really want to do, but i don't want to screw anything else up in the process either. Replacing oil ain't to bad, but replacing a messed up engine is serious. I'll take no risks on this one.
     
  7. backcountry

    backcountry 1/2 ton status

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    As long as you can remove your oil pan without difficulty the job is very easy.

    It is a good idea to let it sit for a few days before you begin. Otherwise oil will drip on you the whole time.

    When you purchase a new seal, make sure you use the silicon seal. It holds up better. I think the part number is 2900.

    Once you remove the pan, remove your oil pump then the rear main cap.

    Remove the main cap seal and clean the cap with brake cleaner or something. You can then set the seal in place. When you do this however, do not use any sealant and be sure to that one side of the seal is slightly higher than the flat edge of the main cap. This will promote a better seal.

    Now, Use a soft small rod such as aluminum to push the upper seal out. You will need to bend it as you go to contour the crank journal. As long as someone before you did not use silicon on the seal during instalation it should be easy to remove. (For this reason, you do not use sealant) Now, use the spray tube on your can of brake cleaner and clean the area where your upper seal goes. Let it dry for a few min.

    Now, be very careful when installing upper seal. The back side can be damaged very easy. The ring that the seal sets on is very sharp. If you cut the back of the seal during instalation, you may have a leak.

    Ok, grab the seal and make absolutly sure that you face the lip of the seal towards the front of your truck. Do the same with the main cap. Now, place a small amount of grease on the lip of the seal and a slight amount on the crank main journal. Set the seal onto the rear main journal; press the seal into the crank so the lip of the seal sinks into the crank. Rotate the seal into place slowly. Do not force it. Keep constant pressure with the seal into the crank. It should rotate into position without difficulty. Make sure to consider the offset to compensate for the main cap seal. Now apply a small amount of silicon to the end of the half seal that is in the block. Carefully replace the main bearing cap and torque it and oil pump to spec.

    One of the biggest mistakes I see people do is: they cant wait to see if it works, so the get in their vehicle and fire it up and take it for a drive. BIG mistake!

    The silicon is not dry yet and the oil pressure is going to be high because the vehicle is cold. This could certainly cause it to instantly leak. Let it sit overnight as per the drying time instructions on your silicon product.


    Have fun be and be patient! /forums/images/graemlins/peace.gif
     
  8. backcountry

    backcountry 1/2 ton status

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    Joey,

    Are you absolutly sure your rear main is out? /forums/images/graemlins/thinking.gif Alot of motor leaks mask themselves as rear main seal leaks so be sure to check everything. /forums/images/graemlins/eek.gif

    I spray my engine and trans with Simple Green and let it sit for a while. I then steam clean them. Then take it for a drive and check; oil pressure sending unit, distrubutor base, valve covers and rear of intake manifold. All those place when leaking end up in the rear main area on the bell housing. /forums/images/graemlins/peace.gif
     

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