Leaky 400 oil pan - The 1947 - Present Chevrolet & GMC Truck Message Board Network

threeonthetree · 04-08-2010, 09:50 PM

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.

James McClure · 04-08-2010, 10:05 PM

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

smashingchuck · 04-09-2010, 12:20 AM

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/

82chevy350 · 04-09-2010, 12:25 AM

i agree i aint ever had a leak with them

westofb · 04-09-2010, 12:50 AM

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).

threeonthetree · 04-09-2010, 07:49 AM

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.

threeonthetree · 04-09-2010, 08:52 AM

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

threeonthetree · 04-09-2010, 06:49 PM

Bump

rfmaster · 04-09-2010, 07:57 PM

Quote:

Originally Posted by threeonthetree

Bump

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

cableguy0 · 04-09-2010, 08:58 PM

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.

rfmaster · 04-11-2010, 01:44 AM

Quote:

Originally Posted by smashingchuck

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/

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

82chevy350 · 04-11-2010, 10:37 AM

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

zac · 04-11-2010, 10:52 AM

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.

CEE1NG_RED · 08-18-2012, 11:15 PM

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).

bowtiemanchevyman · 08-18-2012, 11:32 PM

Quote:

Originally Posted by CEE1NG_RED

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).

no you dont need to touch that.

bowtiemanchevyman · 08-18-2012, 11:41 PM

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.

bilfman · 08-20-2012, 01:48 AM

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.

Posted · 07-31-2014, 10:31 AM

Quote:

Originally Posted by smashingchuck

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/

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??

SCOTI · 07-31-2014, 10:36 AM

Quote:

Originally Posted by Posted

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??

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.

04-08-2010, 09:50 PM	#1
threeonthetree Registered User Join Date: Feb 2009 Location: Wausau, WI Posts: 975	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. __________________ Smoking Tires Since 1992 1969 c10 AKA SIN 1985 SSWB TRAZER (super short wheel base)

04-08-2010, 10:05 PM	#2
James McClure One shot, one kill. Join Date: Dec 2007 Location: Saratoga Springs NY Posts: 859	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 __________________ 1984 K20 350M engine with 465,000 miles. Well, it's finally done!! Almost 2 years of work, but it was really worth the effort. Little stuff left to do is mount winch, wet sand & buff out and build belly pan\running boards. Body work takes lots and LOTS of beer!!!! God, Guts and Guns made America and God, Guts and Guns will preserve it! The worst thing you could do is get into my sights, but that don't matter, you'll never know it, cause you'll never hear the shotJim or Paladin whichever you choose.

04-09-2010, 12:20 AM	#3
smashingchuck It'd be alot cooler if you did Join Date: May 2003 Location: Three Rivers, MI Posts: 2,345	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/ __________________ 78 Build Thread 4Runner Build

04-09-2010, 12:25 AM	#4
82chevy350 Registered User Join Date: Sep 2009 Location: Van Buren, AR Posts: 321	Re: Leaky 400 oil pan i agree i aint ever had a leak with them __________________ Drive It Like Ya Stole It '82 Primer White c10 2wd LWB 350 sbc t350 (Hot Rod) '90 2wd LWB Silverado 350 tbi 700R4 (Daily Driver) '53 m38a1 Willys Jeep (Toy)

04-09-2010, 12:50 AM	#5
westofb I really hate wet sanding! Join Date: Dec 2008 Location: Brookfield, MO Posts: 601	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). __________________ Jeff, 68 C-10 75 C-20, now a C-10! 10 F-150

04-09-2010, 07:49 AM	#6
threeonthetree Registered User Join Date: Feb 2009 Location: Wausau, WI Posts: 975	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. __________________ Smoking Tires Since 1992 1969 c10 AKA SIN 1985 SSWB TRAZER (super short wheel base)

04-09-2010, 08:52 AM	#7
threeonthetree Registered User Join Date: Feb 2009 Location: Wausau, WI Posts: 975	Re: Leaky 400 oil pan so does replacing the rear main require removing the whole crank or just the last main cap? __________________ Smoking Tires Since 1992 1969 c10 AKA SIN 1985 SSWB TRAZER (super short wheel base)

04-09-2010, 06:49 PM	#8
threeonthetree Registered User Join Date: Feb 2009 Location: Wausau, WI Posts: 975	Re: Leaky 400 oil pan Bump __________________ Smoking Tires Since 1992 1969 c10 AKA SIN 1985 SSWB TRAZER (super short wheel base)

04-09-2010, 08:58 PM	#10
cableguy0 Senior Member Join Date: Apr 2000 Location: Delta,Pa Posts: 14,950	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. __________________ Owner of North Point Car Care in Dundalk Md. We specialize in custom exhaust on both modern and classic vehicles. We are a full service auto shop from classics to modern vehicles. Feel free to contact me with questions. I will give a 10% discount to any board member.

04-11-2010, 10:37 AM	#12
82chevy350 Registered User Join Date: Sep 2009 Location: Van Buren, AR Posts: 321	Re: Leaky 400 oil pan i used the high temp orange gasket sealer with it works good no leaks __________________ Drive It Like Ya Stole It '82 Primer White c10 2wd LWB 350 sbc t350 (Hot Rod) '90 2wd LWB Silverado 350 tbi 700R4 (Daily Driver) '53 m38a1 Willys Jeep (Toy)

04-11-2010, 10:52 AM	#13
zac Registered User Join Date: Jul 2008 Location: louisville, ky Posts: 502	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.

08-18-2012, 11:15 PM	#14
CEE1NG_RED Registered User Join Date: Oct 2009 Location: LBC California Posts: 497	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). __________________ - 1967 Chevrolet C/10 SWB fleetside (New Project). - 1969 Chevrolet C/10 SWB fleetside (SOLD) - 2000 Ford Mustang 232 (DD) - 2003 Ford SVT Cobra "Terminator" 281 (Once in a blue moon driver/weekend driver)

08-18-2012, 11:41 PM	#16
bowtiemanchevyman Registered User Join Date: Nov 2011 Location: rock springs wyoming Posts: 182	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.

08-20-2012, 01:48 AM	#17
bilfman Registered User Join Date: Dec 2011 Location: Regina, SK, Canada Posts: 622	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. __________________ 1979 Chevy Dually Crew 4X4 454, D60 Tru-trac, D70 Detroit Locker, 3.73, 4L80E/NP205 1971 GMC 3/4 Ton 4X4



Register or Log In To remove these advertisements.

Register or Log In To remove these advertisements.