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Old 11-25-2012, 10:37 AM
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Pinion seal leak for the third time

Ok, here's the next issue to take care of: Pinion seal was leaking and spraying frame and exhaust when I went to look at the Jeep to buy. PO said seal had just been fixed. I told him to get it redone as mechanic should warranty the work. So he took it back in and it appeared fixed when I bought it. It is now leaking again less than 500 miles later; this time running out the bottom and dripping off the transfer case. Called mechanic and he said bring it back again this week, maybe a bad bearing is causing it to fail. This will be the third installation/repair. Hard to tell if yoke has any movement as it would be difficult to detect micromovement/vibration manually.
Couple questions:
1. If it is being properly installed, what could be causing the repeat failures? 2. If it is a bearing (or something else), what cost am I looking at?

I watched a couple good youtube videos on changing the pinion seal and both narrators were emphatic that you had to mark the driveshaft and yoke position as well as the degree of tightening the nut.
1. If that wasn't done properly the first time would the jeep still drive fine but cause the seal to fail or would you see some other problem if things had not been lined up properly?
2. If that is what happened, how would a small town mechanic find out how to line everything up again correctly and tighten the nut to the correct torque without a jeep manual?
3. If the only place to find it is in the manual, can someone give me the specifications to give this mechanic?
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Old 11-25-2012, 10:55 AM   #2
Knows a couple things...

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Getting a pinion seal to properly seat (and seal) in the pinion shaft opening isn't always real easy to do. The issue is it's hard to get the seal 'started' in the opening since it is fairly rigid and it keeps wanting to cock at an angle. If the installer tries to pound it in with it cocked even slightly, the seal can be damaged.

Or the seal seating surface in the axle housing itself might have been gouged during the removal process.

What usually gets it sealed properly is to apply some good RTV to the outside edge of the seal like what the local Chrysler dealer sells which is less affected by the presence of gear lube like Permatex RTV is. RTV is like silicone for your bathtub & comes in a tube. I'd pick up a tube at your local Jeep dealer's parts department and hand it to the next seal installer to apply around the edge of the new seal. And if you don't have a Jeep or Chrysler dealership close by, get some Permatex Gear Oil RTV Sealant which is specially/better formulated to withstand the gear lube that is inside our axles. About half of my local auto parts stores carry it, maybe more by now since it has only been out for a year or two by now. That particular stuff works better for this application than all the other RTVs do with the exception of the Mopar RTV I mentioned.

To me, the the key to getting a problem seal to seal is the use of RTV around its perimeter. And if the seating surface in the pinion shaft axle was gouged/scratched, the RTV (which stands for Room Temperature Vulcanization) should be enough to seal it.

They also need to apply a little bearing grease (not RTV) around the inside seal opening where it seats against the pinion shaft.

After the seal is installed, I have always had 100% good luck just tightening the pinion nut to 170-180 ft-lbs. as I was advised to do by Tom Wood probably 15 years ago. There is a long procedure in the factory manual for setting the pinion nut's tightness but for just replacing the pinion seal, I would just have him tighten it as I described. The mechanic should apply some blue locktite to the pinion nut so it won't come loose.

I'm certainly no expert auto mechanic but I've replaced a 6-8 pinion seals over the past 15 years & don't think any of the ever leaked afterward when I replace them like this.

When you have a choice, buy American.
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Old 11-25-2012, 12:35 PM   #3
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Did both front and rear pinion seals last year and haven't had problems with either. Pulled out old ones ( takes some elbow grease and cursing but it will come out.) took some emery cloth and clean the inside of the diff where the outer edge contacts it. Put some RTV on the new seal. Now take your time to make sure the seal is square to the opening, get it started then take a socket and tap it in. Don't go crazy cause you can damage it then your back where you started. Put the nut back on with blue lock tight and torque to spec. 20,000 kms and not leave for me yet. And I wheel it quite often.
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Old 11-25-2012, 02:18 PM   #4
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It's possible the seal surface on the yoke has rusted/corroded/pitted as well. This will wear out a new seal in short order. It can be completely replaced or repaired with a speedy sleeve.
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Old 11-25-2012, 04:47 PM   #5
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Also ensure the diff vent tube is not plugged. If it is, it could cause the diff to pressurize which would push the oil out of the weakest seal.
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Old 11-25-2012, 08:57 PM   #6
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I would like to add that if there is some other issue with the driveline it could lead to the wearing of the seal. Make sure the trans mount is solid, make sure the yolk is not scored, and make sure the seal is installed using the above recommendations. The vent is also a good suggestion. I had fluid coming out of the output seal on my K1500 but my first thought, that it was a simple output seal, was incorrect; turns out the input seal was shot--allowing trans fluid through to the TC. The increased pressure (vent was plugged) pushed fluid out the back.

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