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Thread: PAIN IN THE REAR... main seal, that is!

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    Member Mark J's Avatar
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    PAIN IN THE REAR... main seal, that is!

    So it's me again - Mark, novice jeep mechanic.
    Jeep is running as you all know. As I drive I've noticed, of course, all the "new" sounds. So far they are manageable.
    Back in 1995, when I parked it for these few years, it leaked. Well now it's REALLY leaking. I've probably "puddled" about 3/4 of a quart, since I started driving it almost daily for short distances about 6 weeks ago or so.
    I'm 87.6% sure it's coming from the main seal. And I know this has been discussed on this forum, but I can't seem to find the answer I want! haha

    First... The oil pan gasket is 40 years old at least so I bought a new one to put in. I think they may alleviate some of the leaks.
    Second... The "S" word: Is there a stop leak that MIGHT slow the flow down a little? Blue Devil?
    Last... If I do want to replace the rear main seal, can it be done by just lowering the crank? I read up a little on this but I don't know if I'm up to the task. I know it's more than lowering the crank though, of course. Rope seal? Rubber?

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    Super Moderator LarrBeard's Avatar
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    All old Jeeps drip, but you are right - three pints definitely qualifies as a leak.

    '"...First... The oil pan gasket is 40 years old at least so I bought a new one to put in." Typically (I won't say never) oil pan gaskets won't leak unless you break the seal by removing the pan. You'll need the gasket if you pull the pan though.

    A word of caution. When you put the pan back on - don't overtighten the bolts. Overtight puts ripples in the gasket flange and then it will really leak. The pan on the '48 had more ripples than the pond on a breezy day and there is a lot of black silicone sealer on the pan and gasket to seal it up. Should the pan ever come off again, I'll probably replace it with one with fewer ripples.

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    Super Moderator bmorgil's Avatar
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    Mark, A quick diagnosis is to see if it drips more when it is running as opposed to when it just sits. The oil of course blows all over as you drive so it can be very dificult to find the leak as you know! When there is oil pressure, the rear main seal is going to leak if it is going to leak. If it is as bad as you indicate (3 pints yikes) I would expect a steady drip at 20 to 30 psi of oil pressure. In neutral have someone hold the rpm up so you can build some pressure and peer underneath. If the main seal is pumping oil it will start to drip at the bell housing to block.

    I think there is a very good chance it is leaking at the rear main. You really cant install the wick seal (rope) without removing the crank, unless you like main seal leaks. To do it right it has to be "packed" into the cap and block then the crank is installed. You can use a new style metal backed seal (be sure you have the right one). You can do this one with the motor in the vehicle. You carefully and with a lot of lube, being careful not to cut the seal, work it around the crank in the block then reinstall the cap. The side packing on the main cap and the interface between the cap and the block are also common leak points. Don't trim the side rubber too far and use black silicone sparingly where the cap and block and side seals all come together. The service manual will help you here on the seal points. And as Larry said do try to use a torque wrench on the oil pan bolts if you can. Over torquing ruins it all. Though you can pound the pan back into shape, it is now weak around the holes and will probably just dent when you try to re-tighten it.

    Keep us posted on your progress Mark. This is a common attempted thing changing the rear main in the vehicle. I have accomplished it on a few different types of motors. The Willys does pose some problems at the main cap. The side seals and pan can be a little challenging on an engine stand. It gets a little more interesting in the vehicle. All the oldies start leaking when there is pressure! They just need a little TLC. No do not put in any "magic poop".
    Last edited by bmorgil; 07-30-2021 at 08:02 AM.

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    Member Mark J's Avatar
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    Thanks all! I have a weekend of work and probably not on the jeep but I'll keep it's flat metal diaper underneath it!
    Here's a shot of the daily puddle (sounds like a tabloid) just for a visual clarification.
    Attached Images Attached Images

  5. #5
    Senior Member 5JeepsAz's Avatar
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    Quote Originally Posted by Mark J View Post
    Here's a shot of the daily puddle
    Now that's a build name if we ever heard one. Youve already got a great title. I vote Retitle the thread immediately anyway!

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    Super Moderator LarrBeard's Avatar
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    In 2019 when we came to Toledo for the Arena Exhibit, the ladies who parked us came around with the disposable aluminum baking pans to protect the arena floor and asked us how many we needed. The question wasn't "Are you going to drip?", it was more like "How much will you drip?"

    My answer was "Three please."

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    Super Moderator gmwillys's Avatar
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    The dreaded Willys drip is a common problem. My 2A was doing well until I serviced the transmission/transfer case. After adding the prescribed amount of oil, the darned input shaft steadily leaves a puddle after being driven. If I had to wager, I believe that the scavenger helix is installed backwards on the input shaft. This would push oil out the seal, instead of pulling oil from the seal back to the case. This will be a winter project for another time.

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    Super Moderator bmorgil's Avatar
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    I think you have the classic drip at the input shaft gm. If the helix was backward it would pump out. That design never worked well. They weeped oil under a lot of conditions. The "retro" seal and input retainer can help but only if the surface on the input drive gear is prepared. It was not designed for a seal. Often persons put in the new retro seal design and it still drips because of this.

    I think it will drip on you till it gets a few thimblefuls low on lube., then it might start to slow down. You can certainly say it is a common occurrence no matter what you do. If you have one that doesn't drip, you are a lucky human!

    Mark, keep us informed on the Daily Drip, looking froward to your adventure.

  9. #9
    Senior Member TJones's Avatar
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    Quote Originally Posted by bmorgil View Post
    I think you have the classic drip at the input shaft gm. If the helix was backward it would pump out. That design never worked well. They weeped oil under a lot of conditions. The "retro" seal and input retainer can help but only if the surface on the input drive gear is prepared. It was not designed for a seal. Often persons put in the new retro seal design and it still drips because of this.

    I think it will drip on you till it gets a few thimblefuls low on lube., then it might start to slow down. You can certainly say it is a common occurrence no matter what you do. If you have one that doesn't drip, you are a lucky human!

    Mark, keep us informed on the Daily Drip, looking froward to your adventure.
    Bob when I rebuilt mine the video I watched on YouTube from Rick Stiver on the T90 Rebuild, he suggested putting in the "Retro Seal" and he also suggested putting a speedysleeve on the input shaft where it rides and then putting silicon sealer over the oil return hole on the front of the tranny and it worked pretty well on keeping oil out of the bell housing on mine.

  10. #10
    Super Moderator bmorgil's Avatar
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    That is a perfect solution TJ. The wear sleeve is a carefully prepared seal surface.

    The Rick Stiver video/write up is an excellent source. There is one major mistake that has not been corrected. When removing the reverse idler shaft in a T90 it is driven INTO THE CASE. I think Rick is adamant about using something to reach in and drive it out of the case. This is incorrect. It can cause a few problems as it was designed to be driven into the case. It is easy to do when you drive it into the case as intended. It can be removed the other way but it is not correct, difficult to do and can lead to damage. ON THE T84 the shaft is driven out of the case, DO NOT DRIVE THE IDLER SHAFT OUT OF THE CASE ON THE T90.

    I did write to the CJ forum about the error, but I don't think it was ever corrected. If you refer to the Borg Warner or Jeep service manuals they have the correct procedure. Here is what is written incorrectly on the Rick Stiver instructions. It is important to note this is an incorrect process. The shaft is easily driven INTO the case on a T90.

    This procedure and information is incorrect on a T90: From: http://www.cj3apage.com/index/Tech_T...%20Rebuild.htm

    D-25. Using tool E drive the reverse idler gear shaft out the back of the case. T_90_Rebuild/ReverseIdlerShaftRemovalT.jpg (9627 bytes) (This must be done from inside the case. Caution: do not attempt to drive the shaft into the case from the rear as this can damage the shaft and the case. Remove the reverse idler gear from the case. Some people have found it necessary to use a bent piece of rebar to drive the reverse idler gear out of the case. Use as little force as you can to prevent damage. Whatever you do, don't drive the shaft into the case.)

    (Here is a helpful tip. When driving out the reverse idler shaft, stand the case on its tail end. To do this, place a 3/4" deep-well socket over the end of the shaft, and place 3 more deep-well sockets around the bottom to provide good balance. Have a second person hold the case in place and drive out the shaft. This was much easier than trying to hold the case in place laying flat.)
    Last edited by bmorgil; 08-01-2021 at 11:58 AM.

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