Rear Main Seal Replacement - The 1947 - Present Chevrolet & GMC Truck Message Board Network

Transformula · 03-18-2013, 02:00 PM

Here is a little write up on how a rear main seal is replaced on a 1985 C10 with a 350. I'm sure all 2WD v8 chassis are similar from 73-87. You don't even need to raise the engine. A heplful hint: Drain the oil the night before and put the plug back in. The next morning, drain the remaining oil. Now the oil had a chance to drip off the crankshaft, oil pickup, etc. and you don't wind up with it all over you or the ground. I put down a rubber mat for comfort and keeping the floor clean. Then I turn the crankshaft so that the timing mark points to the ground. Remove all the oil pan bolts and pry it free from the block.

Transformula · 03-18-2013, 02:06 PM

After the pan is off, clean up the block of all gasket material. Remove the oil pump and drive rod. I set them in the oil pan for safe and clean keeping. Then remove the main cap. You will have to tap it on the sides to work it loose. Removing the seal from the cap is the easy part. To remove the top half from the block, use a small drift or punch to tap it upward on one side and it will start to come out the other side. Use needle nosed pliers to finish pulling it out. Mine came out pretty easy, once it was tapped free.

Transformula · 03-18-2013, 02:14 PM

After all the seal pieces are out, use some sprat cleaner to clean the cap, block, pan sealing area, etc. Now you can paint the pan if you want to. install the new seal into the cap with the lip toward the front (Oil side of seal.) I use high temp grease to fill the cavity to provide lubrication on start up. The seal I used came with a little "Shoe Horn" that protects the top seal from damage when putting it in. Fill the seal with grease like the lower part and put it against the crank. Rotate it into the seal area using the shoe horn between the block and seal. Put some grease on the crank journal and a little dab of RTV on the part of the cap that goes against the block and a tiny tiny bit on the ends of the seal. Install the cap in place and tighten the bolts to about 65 lb.ft.

Transformula · 03-18-2013, 02:21 PM

After the main cap is on and tightened, now is the time to install the oil pump and drive rod. Replacing the pump is a good idea if you think it needs it. I put the drive rod onto the pump and raise it into place. Turning the rod at the same time until the tang lines up with the distributor. You should not have to force it, it will go right up when aligned. Tighten this bolt down to spec also. Now you can put up the oil pan with a nice fresh gasket. I used the one piece Fel Pro gasket and it works well.
I'm sure I forgot a lot of little details, like thrusting the crank back and forth before tightening the final torque on the main cap, or removing anything else like cooler line brackets, but I just wanted to show how easy this repair really is in one of our trucks. WIth the truck jacked up with the tyres just barely off the ground, It took me about 90 minutes of actual work time, maybe 2 hours of total garage time.
Good luck with your repair!!

**LEEVON** · 03-18-2013, 04:40 PM

Nice write-up! I sometimes have to jack the engine to remove the pan for some reason though.

bilfman · 03-18-2013, 05:29 PM

Thanx for the write up.

INSIDIOUS '86 · 03-18-2013, 06:49 PM

Good job, when you pull the pan it is also a good idea to clean it out.

Your bearing looks pretty decent. Checking the thrust and the front bearing give you a pretty good indication of engine condition
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Transformula · 03-18-2013, 08:40 PM

I would definately agree on cleaning the pan out! I did, just forgot to mention it. Glad to be able to help out here. I know this type of question comes up a lot!

JellyBeanDriver · 03-18-2013, 10:40 PM

You made it look easy! Might have a go at it on the 454 in our 86' C30 ranch truck.
Oil pan looks a bit more difficult to get out.

Transformula · 03-19-2013, 08:27 AM

Quote:

Originally Posted by JellyBeanDriver

You made it look easy! Might have a go at it on the 454 in our 86' C30 ranch truck.
Oil pan looks a bit more difficult to get out.

I tell ya, I had no more than about 2 inches between the front area of the crossmember and the pan. When I slid it out with the crank positioned right, the pan touched NEITHER the crank or the crossmember! I didn't think it would fit out until I tried it. Removing the converter cover and the crank being in the right position are key!

JellyBeanDriver · 03-20-2013, 12:12 AM

Quote:

Originally Posted by Transformula

I tell ya, I had no more than about 2 inches between the front area of the crossmember and the pan. When I slid it out with the crank positioned right, the pan touched NEITHER the crank or the crossmember! I didn't think it would fit out until I tried it. Removing the converter cover and the crank being in the right position are key!

Good to know. I almost considered doing it a few weeks ago when I had the trans out to replace the freeze plugs on the back of the block. Thought I'd have to drop the crank though for the half in the block. Didn't think it would 'roll' out.

LostMy65 · 10-18-2015, 07:57 PM

Thanks for this write up.

enaberif · 10-18-2015, 08:03 PM

This write up has flaws and I hope people don't follow it directly.

You never want to put rtv on the seal AT ALL. And there is also a difference as some blocks are 1 piece and others are 2 piece.

On the 2 piece block you should also stagger the joints slightly so they aren't together.

03-18-2013, 02:00 PM	#1
Transformula Registered User Join Date: Nov 2010 Location: Las Vegas, Nevada Posts: 160	Rear Main Seal Replacement Here is a little write up on how a rear main seal is replaced on a 1985 C10 with a 350. I'm sure all 2WD v8 chassis are similar from 73-87. You don't even need to raise the engine. A heplful hint: Drain the oil the night before and put the plug back in. The next morning, drain the remaining oil. Now the oil had a chance to drip off the crankshaft, oil pickup, etc. and you don't wind up with it all over you or the ground. I put down a rubber mat for comfort and keeping the floor clean. Then I turn the crankshaft so that the timing mark points to the ground. Remove all the oil pan bolts and pry it free from the block. Attached Images __________________ T.Y.N Custom Works..... Because "Stock" Sucks! 1971 K 10 GMC Long Bed 1977 Formula T/A Frame off Resto-Mod 1995 FXDL Harley Low Rider 1985 C10 ShortWide 91 Burb front.

03-18-2013, 02:06 PM	#2
Transformula Registered User Join Date: Nov 2010 Location: Las Vegas, Nevada Posts: 160	Re: Rear Main Seal Replacement After the pan is off, clean up the block of all gasket material. Remove the oil pump and drive rod. I set them in the oil pan for safe and clean keeping. Then remove the main cap. You will have to tap it on the sides to work it loose. Removing the seal from the cap is the easy part. To remove the top half from the block, use a small drift or punch to tap it upward on one side and it will start to come out the other side. Use needle nosed pliers to finish pulling it out. Mine came out pretty easy, once it was tapped free. Attached Images __________________ T.Y.N Custom Works..... Because "Stock" Sucks! 1971 K 10 GMC Long Bed 1977 Formula T/A Frame off Resto-Mod 1995 FXDL Harley Low Rider 1985 C10 ShortWide 91 Burb front.

03-18-2013, 02:14 PM	#3
Transformula Registered User Join Date: Nov 2010 Location: Las Vegas, Nevada Posts: 160	Re: Rear Main Seal Replacement After all the seal pieces are out, use some sprat cleaner to clean the cap, block, pan sealing area, etc. Now you can paint the pan if you want to. install the new seal into the cap with the lip toward the front (Oil side of seal.) I use high temp grease to fill the cavity to provide lubrication on start up. The seal I used came with a little "Shoe Horn" that protects the top seal from damage when putting it in. Fill the seal with grease like the lower part and put it against the crank. Rotate it into the seal area using the shoe horn between the block and seal. Put some grease on the crank journal and a little dab of RTV on the part of the cap that goes against the block and a tiny tiny bit on the ends of the seal. Install the cap in place and tighten the bolts to about 65 lb.ft. Attached Images __________________ T.Y.N Custom Works..... Because "Stock" Sucks! 1971 K 10 GMC Long Bed 1977 Formula T/A Frame off Resto-Mod 1995 FXDL Harley Low Rider 1985 C10 ShortWide 91 Burb front.

03-18-2013, 02:21 PM	#4
Transformula Registered User Join Date: Nov 2010 Location: Las Vegas, Nevada Posts: 160	Re: Rear Main Seal Replacement After the main cap is on and tightened, now is the time to install the oil pump and drive rod. Replacing the pump is a good idea if you think it needs it. I put the drive rod onto the pump and raise it into place. Turning the rod at the same time until the tang lines up with the distributor. You should not have to force it, it will go right up when aligned. Tighten this bolt down to spec also. Now you can put up the oil pan with a nice fresh gasket. I used the one piece Fel Pro gasket and it works well. I'm sure I forgot a lot of little details, like thrusting the crank back and forth before tightening the final torque on the main cap, or removing anything else like cooler line brackets, but I just wanted to show how easy this repair really is in one of our trucks. WIth the truck jacked up with the tyres just barely off the ground, It took me about 90 minutes of actual work time, maybe 2 hours of total garage time. Good luck with your repair!! __________________ T.Y.N Custom Works..... Because "Stock" Sucks! 1971 K 10 GMC Long Bed 1977 Formula T/A Frame off Resto-Mod 1995 FXDL Harley Low Rider 1985 C10 ShortWide 91 Burb front.

03-18-2013, 04:40 PM	#5
LEEVON Registered User Join Date: Jul 2006 Location: Ozark, MO Posts: 4,887	Re: Rear Main Seal Replacement Nice write-up! I sometimes have to jack the engine to remove the pan for some reason though. __________________ '20 Silverado Trail Boss ~ '17 Tahoe ~ '79 K15 Sierra Grande ~ '76 Blazer 2wd ~ '71 Cheyenne swb ~ '55 Pontiac Safari ~'50 3100 bagged ~ '80 Wife ~ Late model kids

03-18-2013, 05:29 PM	#6
bilfman Registered User Join Date: Dec 2011 Location: Regina, SK, Canada Posts: 622	Re: Rear Main Seal Replacement Thanx for the write up. __________________ 1979 Chevy Dually Crew 4X4 454, D60 Tru-trac, D70 Detroit Locker, 3.73, 4L80E/NP205 1971 GMC 3/4 Ton 4X4

03-18-2013, 06:49 PM	#7
INSIDIOUS '86 Registered User Join Date: Jul 2009 Location: washington Posts: 4,178	Re: Rear Main Seal Replacement Good job, when you pull the pan it is also a good idea to clean it out. Your bearing looks pretty decent. Checking the thrust and the front bearing give you a pretty good indication of engine condition Posted via Mobile Device __________________ 377 sbc thumpr cam autogear m23 muncie 3:73 Detroit trutrac 3''spintech prostreet mufflers xpipe 1 3/4 headers build thread !http://67-72chevytrucks.com/vboard/s...d.php?t=577217 Iroc gauge threadhttp://67-72chevytrucks.com/vboard/s...d.php?t=554511

03-18-2013, 08:40 PM	#8
Transformula Registered User Join Date: Nov 2010 Location: Las Vegas, Nevada Posts: 160	Re: Rear Main Seal Replacement I would definately agree on cleaning the pan out! I did, just forgot to mention it. Glad to be able to help out here. I know this type of question comes up a lot! __________________ T.Y.N Custom Works..... Because "Stock" Sucks! 1971 K 10 GMC Long Bed 1977 Formula T/A Frame off Resto-Mod 1995 FXDL Harley Low Rider 1985 C10 ShortWide 91 Burb front.

03-18-2013, 10:40 PM	#9
JellyBeanDriver Registered User Join Date: Jul 2012 Location: United States Posts: 268	Re: Rear Main Seal Replacement You made it look easy! Might have a go at it on the 454 in our 86' C30 ranch truck. Oil pan looks a bit more difficult to get out.

10-18-2015, 07:57 PM	#12
LostMy65 But Found Her 25yrs Later! Join Date: Oct 2010 Location: Oregon City, Oregon Posts: 10,525	Re: Rear Main Seal Replacement Thanks for this write up. __________________ I lost my 65 - Found it 25 years later: http://67-72chevytrucks.com/vboard/s...d.php?t=426650 66 C20 Service Truck: http://67-72chevytrucks.com/vboard/s...d.php?t=428035

10-18-2015, 08:03 PM	#13
enaberif Registered User Join Date: Jan 2009 Location: Calgary, AB Posts: 1,181	Re: Rear Main Seal Replacement This write up has flaws and I hope people don't follow it directly. You never want to put rtv on the seal AT ALL. And there is also a difference as some blocks are 1 piece and others are 2 piece. On the 2 piece block you should also stagger the joints slightly so they aren't together.



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