2000 K3500 7.4L Leaking Rear Main

[Tom P]

Recently purchased the truck knowing there was work to be done. Starts and runs every time but its got a few of those common issues. One of which is a leaking rear main. Curious as to who has done what and how it worked out. A guy at the local lube shop pointed out some snake oil to me called Blue Devil. The guy swears by it. Uses it in a lot of cars that come through his shop and claims it works (60% of the time it works every time ). Its only going to get worse as time goes on. Truck has good oil pressure (typically between 30-50psi). Its not a daily driver so I can afford to have it down, but I know the local chevy dealer wants around 1500 to replace a rear main.

I'd love to fix it properly because I really don't want oil spots in the garage or driveway and it is a significant leak. However I'm assuming that this late model is a one piece rear main and would require me to drop the trans and transfer case to get at it. Has anyone accomplished this? Write up?

 

[df2x4]

How big is a "significant" leak?

My V6 truck would drip a little oil from the rear main seal once in a while, so I got it replaced at a dealer, like a dummy. Pretty sure that cost me over $1k in labor.

My Suburban is now doing the same thing, but it's only a couple drops a day. I just live with it. It never reads low on the dipstick.

If I were you, I'd probably just live with it and check the levels regularly. However if you really want to get the rear main seal replaced, don't go to a GM dealer. Find a reputable independent shop, you'll get it done for half the price.

EDIT - Also, STAY AWAY from the fix-in-a-can stuff.

 

[C30454]

Yes, it is a one piece rear main seal requiring trans removal.

But check FIRST make sure your PCV system is operating properly. Meaning it has the correct GM valve in it, the valve is not plugged or dirty, and there is unrestricted vacuum to it. Also make sure there isn't excessive blowby past the rings. Too much crankcase pressure from either excessive blowby or a reduced or non-functioning PCV system can cause an otherwise good rear main seal to leak, including the new one that you go to much trouble or expense to replace. There is a seal installer tool J-38841 that installs the seal without damage that might save you from doing it twice.

For testing:
You could pull the dipstick, put a vacuum gauge on the tube, and block off the fresh air intake tube that comes from the right side valve cover up to your air intake duct. You should be able to build vacuum on the gauge.

Next, remove the PCV valve from the valve cover and the fresh air tube from the air intake. Start the engine and observe how much if any blowby is escaping from the valve cover(s) OR block of both valve covers, remove the oil fill cap, and observe how much is coming out of there.

It's hard to quantify how much you should or shouldn't see, it's just something you know after repairing cars and trucks for 35 years. But an engine with good rings will see little or nothing at all coming out at idle.

And I would recommend cleaning an OE valve before installing an aftermarket valve of unknown flow and spring rates.





Tom