Leaky 400 oil pan
 

My dad owns a 75 gmc 3/4 with a 400 sbc and turbo 350. It leaks a lot he says. He has replaced oils pan gasket and tranny gasket and filter. Someone is telling him that there is a gaket on top of crank.. I don't think that. Where could it be leaking.

Re: Leaky 400 oil pan
 

First one must determine which oil is leaking, eng or trans, then the where comes into play. With the eng, lets start at the top. Valve covers (make sure the oil returns at either end of the cyl heads are open) next, intake manifold end seals, next, cam end cap (unlikely unless you did a cam) next, rear main seal. If you aren't mechanicly inclined have someone do that for you. Trans, front pump seal (converter) front pump "O" ring & gasket, filler tube seal, detent cable seal, speedo adapter seals, shift modulator seal, servo cover seal, drive shaft seal, and lastly, shift shaft seal. That about covers it. Now get it clean under there and find the exact area where the leak shows up. Pull the converter cover before cleanup. Hope this helps. Jim

Re: Leaky 400 oil pan
 

I would highly recommend a 1 piece oil pan gasket if he not already running one. Fel-Pro makes them. Well worth the few extra $$$.

http://www.summitracing.com/parts/FEL-OS34510T/

http://static.summitracing.com/globa...os34510t_w.jpg

Re: Leaky 400 oil pan
 

i agree i aint ever had a leak with them

Re: Leaky 400 oil pan
 

the gasket over the crank would be known as the rear main seal...as they get some age on them, they harden and are prone to leaking. Really bad ones can leak a large amount in a very short time! Oh yeah, changing this gasket (actually a seal) in the truck is not for the faint of heart, can be done, just not very easily, takes a few specialized tools (you have to remove the oil pan, then the oil pump, then the rear main cap to gain access to it, need to re torque bolts specs).

Re: Leaky 400 oil pan
 

Already have replaced pan gasket with one pictured above.
So I'm looking at a rear main? Lots of work to change that. But I could do it.

Re: Leaky 400 oil pan
 

so does replacing the rear main require removing the whole crank or just the last main cap?

Re: Leaky 400 oil pan
 

Bump

Re: Leaky 400 oil pan
 

Before replacing anything try to figure the source of the leak!. Get engine de-greaser and see where it is coming from. Rear China wall leaks can be mistaken for rear main seal since it is tough to see back there. Use a small mirror to see if it solid or not.

//RF

Re: Leaky 400 oil pan
 

Once the pan is off and out of the way. The rear main only requires removal of the last main cap. The rear of the intake will leak and look the same as a rear main. Valve covers also will drip oil in that area. Its likely that the rear main is leaking if this is an older built engine. The intake gaskets also are likely leaking especially if someone used the rubber seals instead of rtv on the end caps.

Re: Leaky 400 oil pan
 

Do not mean to hijack this thread, but do you use black RTV with that one piece FEL-PRO gasket?? Or install it dry???

Re: Leaky 400 oil pan
 

i used the high temp orange gasket sealer with it works good no leaks

Re: Leaky 400 oil pan
 

Replacing the rear main seal is doable. I did it last fall on my '79 K20. It comes with a small plastic "tool" of sorts that helps you slide the upper seal in place. You basically just push it into place. It is apparently very important to get the gasket sealer in exactly the right spot. I would recommend looking at any shop manual on how to replace the rear seal on an sbc. That's what I did. Mine was probably easier than most since I did it with the trans removed.

I would also agree that your dad should replace his intake gasket and probably rocker cover gaskets. Oil seems to come from everywhere on these engines. Good luck.

Re: Leaky 400 oil pan
 

When replacing the oil pan, do you also need to remove the timing cover since the are almost touching each other (well, in my '78 350 Chevy motor).

Re: Leaky 400 oil pan
 

no you dont need to touch that.

Re: Leaky 400 oil pan
 

When you change a rear main it is so easy. A way to make it easy is to loosen all the main caps a little so the crank will lower down a little. That will make it so easy to put the seal in. and a torque wrench is really cheap. Sears has them for $80, and one way to make it less messy is to let it set over night with the pan off and let it drip on a piece of cardboard.

Re: Leaky 400 oil pan
 

If you have oil on your clutch or torque converter then probably the rear main seal. Most oil leaks on a sbc come from the rear of the valve covers or the rear of the intake.

So if you dont have a ton of oil under your bellhousing area then it is most probably valve covers or the rear of the intake.
As valve covers get old they warp from the tightening process and generally lose seal. New covers, pounding the old ones straight and using 'wings' to increase the pressure put on a greater area of the gasket really helps. I like to silicone the gaskets to the valve cover and leave the head side bare. Makes it easy to remove and reuse.

Re: Leaky 400 oil pan
 

This what I am using, and I am leaking at the front engine on the round part around the crank. I have a chrome pan. Should I take it off and sand chrome and reseal with permatex and put back in place. Was wondering if the cork gaskets are better??

Re: Leaky 400 oil pan
 

Chrome pans usually = "Made In China" part.
Use an OE pan. Beyond that, I would do the dab of silicone @ the corners of the timing cover & rear main seal for insurance.