# Rear Main Seal Replacement - Need recommendations



## Roqetman (Aug 31, 2015)

Hello GTO fans. I have my ‘65 in the shop to have the engine mounts and real main seal replaced. Engine mounts no big deal. Rear main seal.. is a big deal and expensive since the engine will have to pulled out of the car. This engine was rebuilt in 2004 and has low miles. My question is this, is the Viton seal the way to go? I see where Ames and Butler have these in one piece and two piece. With the one piece, the crank has to be out and one cut made on the seal to install it. I’ve read on this forum where the new seals still leak and/or it’s hit or miss whether it leaks for not. Is it worth the extra cost of crank removal to install the one piece? Or… are the 2 piece seals just as good? I would think the Viton seal would be, should be much better than the rope seal. And if it’s likely to leak anyway… I’ll just not replace it and spend the money on motor oil. Any recommendations are greatly appreciated. Thanks, Roqetman.


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## Lemans guy (Oct 14, 2014)

I put a one piece rear min seal in on a new rebuilt and it still leaked and yes it was put in properly and very carefully. The only thing that stopped the leak was the ME Wagner dual flow PCV valve. Many discussions on it on the forum.

before I spent all that money or effort or both I would get the Wagner valve for $130 and install it yourself, very easy and very tunable to your car. And see if that relieves the leak. If it does you saved much time and effort and if it does not you have not lost either as the Wagner valve is a great addition to save your engine from all those corrosive vapors and the accompanying crankcase pressure that causes those seals to leak.

GO to ME Wagner’s website and read up on it. Watch their video read their data. Not related to them in any just know that it works very well. But it will not fix every seal, some are just bad leaky seals.


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## Roqetman (Aug 31, 2015)

I’ve read about the Wagnor PCV and that would be great if it deduced the leak. Mine is bleeding oil pretty bad even though it was rebuilt in 2004 and has low miles on it. Does the PCV have to be adjusted/tuned? If so, does it come with good instructions? Thanks for the input!


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## Roqetman (Aug 31, 2015)

With regard to the rear main seal, the latest edition of Hemming Muscle Machines has an article where they’re building an Olds 455 and used a Ford neoprene seal, part #BS40032 for better oil retention as compared to the rope seal. Is neoprene better that Viton? And I have no idea how to cross reference a Ford seal to a Pontiac seal. I understand the 389 has a 3” crank whereas the 421-455 have 3.25” crank. Has anyone had any experience finding a neoprene seal for a Pontiac?


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## Lemans guy (Oct 14, 2014)

The Wagner valve is easy to adjust, you do it with a vacuums gauge, it has complete instructions and there is a video on ME Wagner’s website…..I’d your low mileage engine has a lot of crankcase pressure a new seal of whatever rubber could leak as well.


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## Roqetman (Aug 31, 2015)

Yeah, that’s a great idea to try first rather than the expense of pulling the engine to put in a new seal. I went to there website and I’m going to try it! Thanks for the advice!


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## Lemans guy (Oct 14, 2014)

It is very tunable. It will tell you to start with 1 1/2 turns out on the idle circuit to start. But don’t get discouraged if you still have a leak. As you can turn the idle circuit out more and correspondingly adjust the cruise circuit with your handheld vacumn gauge.

My idle circuit had to be 2 1/2 turns out before the main seal quit leaking. You can go to three and after that even to a fixed orifice mode. So give it a good chance to see if you can get rid of the leaks.

Also buy the “Pontiac Adapter” from Wagner so it can be easy to go in and be accessible to tune.


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## Roqetman (Aug 31, 2015)

Thanks for the input! I contacted Wagner about the adapter and they recommended I measure the PCV grommet to get the proper diameter Adapter. My pcv is behind the 4bbl intake in the valley pan.


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