Big Block Rear Main Seal Replacement... is it worth it? - Chevelle Tech
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post #1 of 15 (permalink) Old Jul 6th, 20, 4:42 PM Thread Starter
Bill
 
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Big Block Rear Main Seal Replacement... is it worth it?

I have a 72 Chevelle the previous owner put a 454 from a mid 70s truck in, and it's leaking out of the rear main seal area. Its a built up motor so I'm assuming it has a high volume oil pump and that's whats causing the issue. I've read to do the job you have to disconnect the trans (its a manual), and jack up the motor so its best to just pull the whole thing out. I guess my question here is, is it best just to live with it and keep an eye on your oil level? I have good oil pressure driving around town and the motor is plenty strong. Recently, I drove it Philly to Pittsburgh without issue in the drivetrain. I'd be interested in what you guys think.
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post #2 of 15 (permalink) Old Jul 6th, 20, 8:19 PM
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Re: Big Block Rear Main Seal Replacement... is it worth it?

Bill,

The first thing you should do is go to the parts store and buy a bottle of leak tracing die along with a cheap UV flashlight. Put the die in the oil and run it for another hundred miles. Way too many people have been fooled by oil leaks coming from valve covers, intakes etc and the oil all ends down at the bottom of the engine. The die will enable you to see exactly where it is coming from.

A high volume pump really should not have any effect on the rear main seal leaking. The seal is not under any type of oil pressure. Unless main bearing clearances are so crazy loose that a bunch of oil is getting through the bearing. Even then it really should not be leaking.

I know guys that have done rear main seals with the engine in the car but I don't see how you can do it and get everything cleaned up properly. Even with a lift I dont think I would attempt it. If you do decide its the seal I really think it is worth pulling the engine to do it right.
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post #3 of 15 (permalink) Old Jul 6th, 20, 9:02 PM
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Re: Big Block Rear Main Seal Replacement... is it worth it?

Bill is right as usual. do the dye thing, make sure the oil is not leaking down from the top somewhere. If it turns out to really the seal, pull it and fix it. nothing worse than a nice car leaving oil everywhere. it doesn't have to be that way.
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post #4 of 15 (permalink) Old Jul 6th, 20, 9:14 PM
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Re: Big Block Rear Main Seal Replacement... is it worth it?

Let's take a moment to diagnose the issue.

First pull the transmission dust cover/inspection plate to see if the front of the flywheel is wet with oil. If it is then go to number 2. If it's not wet you could have an oil pan gasket leak. An oil pan gasket leak is a small byte easier to deal with.

Second (this is number 2) get a bottle of "Blue Devil Rear Main Sealer." Ya, I know, but it's worth a try -- I actually do see a lot of positive responses with it. AND it's way easier than replacing the rear main seal, eh?
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post #5 of 15 (permalink) Old Jul 6th, 20, 9:53 PM
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Re: Big Block Rear Main Seal Replacement... is it worth it?

Quote:
Originally Posted by NickeyChevelle View Post
bottle of "Blue Devil Rear Main Sealer."

If it is anything like their cooling system and head gasket sealer the only place it belongs is in the trash can.
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post #6 of 15 (permalink) Old Jul 7th, 20, 7:03 AM
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Re: Big Block Rear Main Seal Replacement... is it worth it?

I have one that's not worth the trouble, so I put a diaper on it.

CLEAN the dust cover, particularly around the drain hole and each side. I use brake parts cleaner. Then get the biggest feminine pad (pad, not tampon) you can find and put it over the hole. Tape it in place with Gorilla duct tape. Swap it out every time you change the oil. No driveway drips!!!

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post #7 of 15 (permalink) Old Jul 7th, 20, 10:22 AM
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Re: Big Block Rear Main Seal Replacement... is it worth it?

Quote:
Originally Posted by BillK View Post
If it is anything like their cooling system and head gasket sealer the only place it belongs is in the trash can.
If it works, and it has for some, it would be a lot better than pulling the engine, tearing the engine down, etc.

I say give it a try, then bitch that it don't work.
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post #8 of 15 (permalink) Old Jul 7th, 20, 10:42 AM
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Re: Big Block Rear Main Seal Replacement... is it worth it?

Quote:
Originally Posted by NickeyChevelle View Post
If it works, and it has for some, it would be a lot better than pulling the engine, tearing the engine down, etc.

I say give it a try, then bitch that it don't work.

The problem is not if it works or not. The head gasket sealer turns to "cement" in the cooling system and then when it starts leaking again you play heck getting it out.



Most seal leak repair chemicals work by swelling up the seal with a solvent of some type. This also softens any other rubber parts in the engine like the valve stem seals, front seal etc. Might work short term but in the end you have to fix it right anyway.
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post #9 of 15 (permalink) Old Jul 7th, 20, 4:06 PM
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Re: Big Block Rear Main Seal Replacement... is it worth it?

like to use degreaser/pressure washer then add your dye or just watch it, would be a relief it it was a valve cover, intake manifold or sender.

How bad is it??? Slight drip here/there wait til winter hits if its really bugging you or oiling your car/exhaust down go to it

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post #10 of 15 (permalink) Old Jul 7th, 20, 5:14 PM
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Re: Big Block Rear Main Seal Replacement... is it worth it?

Quote:
Originally Posted by BillK View Post
The problem is not if it works or not. The head gasket sealer turns to "cement" in the cooling system and then when it starts leaking again you play heck getting it out.



Most seal leak repair chemicals work by swelling up the seal with a solvent of some type. This also softens any other rubber parts in the engine like the valve stem seals, front seal etc. Might work short term but in the end you have to fix it right anyway.
"Head Gasket Sealer" is not being discussed. Please take a moment to view the videos on Youtube that show the success of the product.

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post #11 of 15 (permalink) Old Jul 7th, 20, 7:21 PM
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Re: Big Block Rear Main Seal Replacement... is it worth it?

Here’s a HotRod magazine article, take it for what it’s worth.
https://www.hotrod.com/articles/blue...r-main-sealer/
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post #12 of 15 (permalink) Old Jul 8th, 20, 8:47 AM
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Re: Big Block Rear Main Seal Replacement... is it worth it?

i'm also curious as to just how bad it leaks??when you park does it leave a drop or a puddle the size of a 50 cent piece?
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post #13 of 15 (permalink) Old Jul 8th, 20, 11:35 AM
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Re: Big Block Rear Main Seal Replacement... is it worth it?

Quote:
Originally Posted by SSJohn View Post
Here’s a HotRod magazine article, take it for what it’s worth.
https://www.hotrod.com/articles/blue...r-main-sealer/
Unless I missed it, they never said whether or not it worked. The article is nowhere near complete.

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post #14 of 15 (permalink) Old Jul 8th, 20, 10:43 PM
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Re: Big Block Rear Main Seal Replacement... is it worth it?

>>> Most seal leak repair chemicals work by swelling up the seal with a solvent of some type. This also softens any other rubber parts in the engine like the valve stem seals, front seal etc. >>>Might work short term but in the end you have to fix it right anyway.

What Bill said. Really.

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post #15 of 15 (permalink) Old Jul 10th, 20, 1:00 PM
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Re: Big Block Rear Main Seal Replacement... is it worth it?

I like the Kotex idea
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