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Duramax First Generation: 2001-2004 (LB7) Discuss the first generation (2001-2004 LB7) of the 6.6L Duramax diesel engine & associated components. Engine related discussion ONLY.

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Old 09-05-2008, 01:42 PM   #1 (permalink)
kjlindgr
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Rear main seal issue

Hey all!

I seem to have developed a leak in my rear main seal. I never had this issue before and then just last week went on a 500-600 mile trip with the truck. When I got back home, I noticed a good sploch of oil under the truck. I cleaned things up underneath and put some UV dye in the oil. Sure enough, the first drips were coming out of the weep hole in the bottom of the trans bellhousing.

I checked the oil level and it was still at the full mark which had me a bit confused based on the oil that had been dripping out. Thinking it might be injectors "making" oil, I had them checked at the local stealer****. The injectors turned out to be spot on. That's good news anyway.

My main question is how does a rear main seal that hasn't been leaking for 80K miles all of a sudden start pissing this much oil out in a 500-600 mile trip? I would certainly think it would be an incremental leak and not just an all or nothing sort of deal. Anyone?

Another thought I had was that it could be a PCV issue causing abnormal crank case pressure to push oil past the seal. Is this a feasible cause? How do you check the PCV system? Just blow some air through the hoses to make sure they aren't clogged?

If I have to pull the trans and buy the specialty tools to replace the rear main seal, I won't be a happy camper.

Thanks everyone!

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Last edited by kjlindgr; 09-05-2008 at 01:46 PM.
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Old 09-05-2008, 08:59 PM   #2 (permalink)
GET_IT_RAG
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sorry about your trouble. If its been leaking as much as it has, I would think maybe theres a blocked line possibly? And its leaking only when under pressure? I don't know what else it could be maybe something for the turbo?

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Old 09-05-2008, 09:13 PM   #3 (permalink)
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Look in the valley of the engine for dampness,if something is leaking from high, it will leak down the back of the engine, there is a small drain hole in the back of the valley that will allow whatever is collecting in it to leak down the back of the block.
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Old 09-06-2008, 11:38 AM   #4 (permalink)
kjlindgr
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Thanks for the advice guys. When I looked up at the trans, the bellhousing was wet from top to bottom. I was thinking it might be a kinked oil return line or something else like that. This is what prompted me to do the dye test...so I could see where it was coming from since everything was oily.

I wiped everything down real well so that any "fresh" oil was off of it. I would then start the truck and let it idle for 30 seconds or so, shut it off, and hop down to take a peak. Sure enough, there was a little dribble coming out of hole at the bottom of the trans bellhousing.

Just for ****s and grins, is the turbo drain line easy to get at for me to check? I'm thinking the answer to that is going to be a negative since I can't even physically see it with the cluster of stuff going on in the back of the motor.

I'll check the valley today but last time I was up there looking for issues, I didn't notice any wetness on the block up there. I'll check again though.

Keep the ideas flowin!

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2001 Silverado 2500HD extended cab LT
Merchant Auto TC pump plate with new housing
5" straight pipe'd stainless exhaust
China special intake
Cognito tubular upper control arms
Bilstein 5100's all the way around
EFI Live small upgraded tune
33/12.5x20" MT ATZ's on Jesse James I-Beams
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Old 09-11-2008, 10:03 AM   #5 (permalink)
Coghlin
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In '03 model year about february '04 they added a second crank case vent to block. THey said some of the trucks would get the one vent iced up in the winter and blow the seal.

Maybe your crank case vent is plugged with dirt or something causing some back pressure.
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Old 09-11-2008, 10:29 AM   #6 (permalink)
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It takes very little time with a blocked or plugged PCV system to blow that seal right out. It just doesn't tolerate crankcase pressure at all.

Or it could have got one little nick or tear in it from a piece of crap in the oil, metal shaving, etc., or just died of old age.

My gut tells me you'll be diving in to it. It's not a technically hard job....pull trans, pull flywheel, use special tool to remove seal, pop seal in with special tool, reassemble. The actual seal replacement is a 5-minute job, tops. Gettting to it, now that's the PITA.
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Old 09-11-2008, 04:16 PM   #7 (permalink)
kjlindgr
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Quote:
Originally Posted by nwpadmax View Post
My gut tells me you'll be diving in to it. It's not a technically hard job....pull trans, pull flywheel, use special tool to remove seal, pop seal in with special tool, reassemble. The actual seal replacement is a 5-minute job, tops. Gettting to it, now that's the PITA.
That's kinda the part I'm dreading. It also sucks that you need $300 in specialty tools to replace a $30 seal but I guess that's the way things go with vehicles.
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2001 Silverado 2500HD extended cab LT
Merchant Auto TC pump plate with new housing
5" straight pipe'd stainless exhaust
China special intake
Cognito tubular upper control arms
Bilstein 5100's all the way around
EFI Live small upgraded tune
33/12.5x20" MT ATZ's on Jesse James I-Beams
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Old 09-11-2008, 09:39 PM   #8 (permalink)
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If you are good buddies with any GM techs or have a good relationship with a dealer, these are an "essential tool" and they'll have them in the shop, and some will let you borrow them.

Offer to put the tool on your credit card and then credit you when you bring it back.
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Old 08-25-2009, 02:08 PM   #9 (permalink)
Joey-D
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I have a leak also from my the weep hole where the belhousing meets but when I pull the inspection cover its clean as a whistle in there. If I had a bad rear main, the torque converter would be covered in oil right? What really throws me off is it reads I have plenty of oil on the dipstick but I leak what looks to be a quart at a time when I shut her down. I'll take pictures.
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Old 08-25-2009, 02:28 PM   #10 (permalink)
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Here are some pictures. The first is the driveway after I drove it last. It leaked that much. The bell housing then inside the inspection cover and then from the engine compartment looking down. I'm going to try tightening the oil pan buts but this looks to be too serious of a leak to be that. And further, the bottom of the truck isn't covered, it only seem to leak after I drive it and park it.














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