main seal - The 1947 - Present Chevrolet & GMC Truck Message Board Network

phlegm · 10-20-2006, 10:58 PM

How bad is a rear main seal to change on a 3 spd 71? what are the steps.

qksilver · 10-20-2006, 11:04 PM

depends on how easy it is to remove the oil pan. It can be sneaked by but I was 20 year younger

phlegm · 10-21-2006, 01:32 AM

Pan has to be pulled too, its leaking, but I have done that before on another truck.

Ole Blue 68 · 10-21-2006, 07:10 PM

I always liked this "how to" because of the diagrams. I don't think it mentions it but the pan does have to come out like you said. Also, it should be a two piece seal.

http://www.autozone.com/servlet/UiBr...3d800514cd.jsp

Green Machine · 10-21-2006, 10:08 PM

Heres my 2 cents for what is is worth. As easy as it is to pull the motors on these trucks, I would just yank the motor, bellhousing and tranny as a unit and get it out where you can work on it. If that rear seal leaking, likly it needs all gaskets replaced, except maybe the head gaskets. The engine may be dirty and the engine bay may need cleaned up anyway. It really does not take that long to yank one out, versus many hours on your back under the truck with no room, with crap and oil dripping all over your face. I've done it both ways and I vote for pulling on these.

phlegm · 10-22-2006, 12:23 AM

I wish I was equipped to pull one, but then if the shop is going to cost me 300 I beet I could get a lift for that much.

Green Machine · 10-22-2006, 02:34 AM

I was wondering if that might be your situation. So far I have not had to buy an engine hoist or stand, nor a car trailer for our projects. I have been able to borrow them. Guess I have friends in high places, or maybe they are just high friends in places ? Anyway, it is surely do-able in the truck, and there is something about having the crank at a certain position that will let the pan clear the counter weights easier when it is removed. Don't remember right now where that is, but hopefully someone else will chime in with that info.

70GMCer · 10-22-2006, 07:13 AM

Here's a little write up I did on dropping the pan and replacing the gasket.

http://67-72chevytrucks.com/vboard/s...91#post1487791

I've replaced the main seal before. No big deal. You will need a torque wrench to tighten the rear cap after putting the seal in. Remember, keep everything as clean as you can. Years ago, when they had the rope type seal, they were a ***** to put in. The newer plastic ones slip in around the crank. I do agree with "Green Machine" though, to pull the engine if it is really dirty.

steve

jamon8 · 10-22-2006, 10:52 AM

replace the oil pump while you are in there

phlegm · 10-23-2006, 11:09 AM

Hey steve,

I see you did this on a big block, will I need to lift the 350 to get the pan cover off too?

thanks, and thanks everyone for the advice.

70GMCer · 10-23-2006, 04:01 PM

I didn't do this on a BBC. It was a 350 I did the change on.....

phlegm · 10-23-2006, 04:11 PM

Sorry, that was the crack talking again.... lol. Great write up. was it absolutely neccesary to lift the block a few inches? also, do you along with the others think I should change the oil pump while I am in there? The engine had rebuild about 30k ago, but I am not sure what they did and did not do.

Werewolf · 10-23-2006, 04:51 PM

Hey! Nice meeting you this weekend, it was fun.

No, I don't think you should have to change the oil pump if the engine was just rebuilt. The pump *should* have been replaced with the rebuild. If you're making good oil pressure, don't worry about it. If you wanted to go to a high volume pump or something like that, having the pan off would be the best possible time. You can also glance at your main caps, maybe get a good torque wrench and make sure they're all torqued to specs still. I see no reason why they should ever move, though.

Whether you have to lift the engine some to drop the pan largely depends on the type of pan you have. I don't *think* you have to worry about it with a stock pan, but I'm honestly not sure, as every time I've had a pan off, the engine was out of the vehicle in question.

So your rear main seal is leaking *despite* the fact that the engine was just rebuilt? Can you bring it back to the builder and point it out? I should have asked you how bad it was leaking, because it's hard to get a 2 piece to not leak even a little bit.

phlegm · 10-23-2006, 05:00 PM

Enjoyed meeting you too Wolf,

I would like to take it back but it was a PO that did / had the work done. Plus since I dont think it was driven a lot in the last few years he had it 30k could easily have been 10 yrs ago.

I am thinking of tackling this myself with it still in the truck.... but just thinking at this point. There is a guy in the church that I go to that can bail me out if I need it.

70GMCer · 10-23-2006, 07:04 PM

You will have to lift the engine up to get the pan off. If not, the front of the pan will hit the 1st main cap. I wouldn't change the oil pump if you had good pressure.

matthufham · 10-23-2006, 07:41 PM

i had a leaky oil pan gasket for the longest time and i had replaced it a good 4 times. you need to lift the engine up about 3-5 inches if you want to replace the oil pan or gasket. it was easy with my engine lift. take carb off, put on lift plate where carb was, take off fan shroud and lift. the rear main requires the same procedure plus replacing the rear main seal.

xfsketch · 07-02-2007, 09:52 PM

I am doing my rear main seal right now 72 chevy 350 and I had to un bolt the motor mounts and jack my motor up about 2" to clear the hump on the oil pan. I just slid it on its side and it came right out. i jacked the motor up with a bottle jack and piece of 2x4. I placed the jack under the pulleys/harmonic balancer because I already had the pan off. It would be wise to lift your engine put wood blocks between the motor and mounts then let the jack down and remove the oil pan. I always do things the hard way lol!

10-20-2006, 10:58 PM	#1
phlegm Still Green but learning Join Date: Nov 2004 Location: Central NC Posts: 1,895	main seal How bad is a rear main seal to change on a 3 spd 71? what are the steps. __________________ -- Cory 71 Cheyenne 10 - SWB, 350, "3 on the tree" AC cab 07 Suburban LTZ 4x4 2010 Acura TL 98 Mastercraft "FrankenStar" 225 27253 UPS/USPS IIOY....nope never was

10-20-2006, 11:04 PM	#2
qksilver Senior Member Join Date: Dec 2004 Location: Southern Pines NC Posts: 3,853	Re: main seal depends on how easy it is to remove the oil pan. It can be sneaked by but I was 20 year younger

10-21-2006, 01:32 AM	#3
phlegm Still Green but learning Join Date: Nov 2004 Location: Central NC Posts: 1,895	Re: main seal Pan has to be pulled too, its leaking, but I have done that before on another truck. __________________ -- Cory 71 Cheyenne 10 - SWB, 350, "3 on the tree" AC cab 07 Suburban LTZ 4x4 2010 Acura TL 98 Mastercraft "FrankenStar" 225 27253 UPS/USPS IIOY....nope never was

10-21-2006, 07:10 PM	#4
Ole Blue 68 Registered User Join Date: Aug 2005 Location: Philly Posts: 1,140	Re: main seal I always liked this "how to" because of the diagrams. I don't think it mentions it but the pan does have to come out like you said. Also, it should be a two piece seal. http://www.autozone.com/servlet/UiBr...3d800514cd.jsp

10-21-2006, 10:08 PM	#5
Green Machine Senior Member Join Date: Jul 2004 Location: Estherville, Iowa Posts: 3,371	Re: main seal Heres my 2 cents for what is is worth. As easy as it is to pull the motors on these trucks, I would just yank the motor, bellhousing and tranny as a unit and get it out where you can work on it. If that rear seal leaking, likly it needs all gaskets replaced, except maybe the head gaskets. The engine may be dirty and the engine bay may need cleaned up anyway. It really does not take that long to yank one out, versus many hours on your back under the truck with no room, with crap and oil dripping all over your face. I've done it both ways and I vote for pulling on these. __________________ 1968 C10 307 3spd Long Fleet ------ http://67-72chevytrucks.com/vboard/s...d.php?t=201103 1970 C10 305 Super T10 Long Fleet --- http://67-72chevytrucks.com/vboard/s...d.php?t=202285 1971 C20 383 TH350 Dana Posi ----- http://67-72chevytrucks.com/vboard/s...d.php?t=206894 2001 GMC Sierra 1500 C3 6.0 Last edited by Green Machine; 10-21-2006 at 10:12 PM.

10-22-2006, 12:23 AM	#6
phlegm Still Green but learning Join Date: Nov 2004 Location: Central NC Posts: 1,895	Re: main seal I wish I was equipped to pull one, but then if the shop is going to cost me 300 I beet I could get a lift for that much. __________________ -- Cory 71 Cheyenne 10 - SWB, 350, "3 on the tree" AC cab 07 Suburban LTZ 4x4 2010 Acura TL 98 Mastercraft "FrankenStar" 225 27253 UPS/USPS IIOY....nope never was

10-22-2006, 02:34 AM	#7
Green Machine Senior Member Join Date: Jul 2004 Location: Estherville, Iowa Posts: 3,371	Re: main seal I was wondering if that might be your situation. So far I have not had to buy an engine hoist or stand, nor a car trailer for our projects. I have been able to borrow them. Guess I have friends in high places, or maybe they are just high friends in places ? Anyway, it is surely do-able in the truck, and there is something about having the crank at a certain position that will let the pan clear the counter weights easier when it is removed. Don't remember right now where that is, but hopefully someone else will chime in with that info. __________________ 1968 C10 307 3spd Long Fleet ------ http://67-72chevytrucks.com/vboard/s...d.php?t=201103 1970 C10 305 Super T10 Long Fleet --- http://67-72chevytrucks.com/vboard/s...d.php?t=202285 1971 C20 383 TH350 Dana Posi ----- http://67-72chevytrucks.com/vboard/s...d.php?t=206894 2001 GMC Sierra 1500 C3 6.0

10-22-2006, 07:13 AM	#8
70GMCer Senior Member Join Date: Apr 2005 Location: Joppa, Maryland Posts: 4,408	Re: main seal Here's a little write up I did on dropping the pan and replacing the gasket. http://67-72chevytrucks.com/vboard/s...91#post1487791 I've replaced the main seal before. No big deal. You will need a torque wrench to tighten the rear cap after putting the seal in. Remember, keep everything as clean as you can. Years ago, when they had the rope type seal, they were a ***** to put in. The newer plastic ones slip in around the crank. I do agree with "Green Machine" though, to pull the engine if it is really dirty. steve __________________ 1997 GMC Sierra Ext 1965 Mustang Last edited by 70GMCer; 10-22-2006 at 07:14 AM.

10-22-2006, 10:52 AM	#9
jamon8 Registered User Join Date: Apr 2006 Location: southern Il Posts: 335	Re: main seal replace the oil pump while you are in there

10-23-2006, 11:09 AM	#10
phlegm Still Green but learning Join Date: Nov 2004 Location: Central NC Posts: 1,895	Re: main seal Hey steve, I see you did this on a big block, will I need to lift the 350 to get the pan cover off too? thanks, and thanks everyone for the advice. __________________ -- Cory 71 Cheyenne 10 - SWB, 350, "3 on the tree" AC cab 07 Suburban LTZ 4x4 2010 Acura TL 98 Mastercraft "FrankenStar" 225 27253 UPS/USPS IIOY....nope never was

10-23-2006, 04:01 PM	#11
70GMCer Senior Member Join Date: Apr 2005 Location: Joppa, Maryland Posts: 4,408	Re: main seal I didn't do this on a BBC. It was a 350 I did the change on..... __________________ 1997 GMC Sierra Ext 1965 Mustang

10-23-2006, 04:11 PM	#12
phlegm Still Green but learning Join Date: Nov 2004 Location: Central NC Posts: 1,895	Re: main seal Sorry, that was the crack talking again.... lol. Great write up. was it absolutely neccesary to lift the block a few inches? also, do you along with the others think I should change the oil pump while I am in there? The engine had rebuild about 30k ago, but I am not sure what they did and did not do. __________________ -- Cory 71 Cheyenne 10 - SWB, 350, "3 on the tree" AC cab 07 Suburban LTZ 4x4 2010 Acura TL 98 Mastercraft "FrankenStar" 225 27253 UPS/USPS IIOY....nope never was

10-23-2006, 04:51 PM	#13
Werewolf Woof? Join Date: Jun 2005 Location: Raleigh, NC Posts: 276	Re: main seal Hey! Nice meeting you this weekend, it was fun. No, I don't think you should have to change the oil pump if the engine was just rebuilt. The pump should have been replaced with the rebuild. If you're making good oil pressure, don't worry about it. If you wanted to go to a high volume pump or something like that, having the pan off would be the best possible time. You can also glance at your main caps, maybe get a good torque wrench and make sure they're all torqued to specs still. I see no reason why they should ever move, though. Whether you have to lift the engine some to drop the pan largely depends on the type of pan you have. I don't think you have to worry about it with a stock pan, but I'm honestly not sure, as every time I've had a pan off, the engine was out of the vehicle in question. So your rear main seal is leaking despite the fact that the engine was just rebuilt? Can you bring it back to the builder and point it out? I should have asked you how bad it was leaking, because it's hard to get a 2 piece to not leak even a little bit. __________________ 1968 LWB CST BB 2004 Avalanche Z71 LT3. 2003 S-10 ZR2 (hers). 1997 Astro 1992 Caprice wagon, 500k stock miles. Nursing wounds after a bad wreck. 1997 Saturn - need gas mileage from something!

10-23-2006, 05:00 PM	#14
phlegm Still Green but learning Join Date: Nov 2004 Location: Central NC Posts: 1,895	Re: main seal Enjoyed meeting you too Wolf, I would like to take it back but it was a PO that did / had the work done. Plus since I dont think it was driven a lot in the last few years he had it 30k could easily have been 10 yrs ago. I am thinking of tackling this myself with it still in the truck.... but just thinking at this point. There is a guy in the church that I go to that can bail me out if I need it. __________________ -- Cory 71 Cheyenne 10 - SWB, 350, "3 on the tree" AC cab 07 Suburban LTZ 4x4 2010 Acura TL 98 Mastercraft "FrankenStar" 225 27253 UPS/USPS IIOY....nope never was Last edited by phlegm; 10-23-2006 at 05:01 PM.

10-23-2006, 07:04 PM	#15
70GMCer Senior Member Join Date: Apr 2005 Location: Joppa, Maryland Posts: 4,408	Re: main seal You will have to lift the engine up to get the pan off. If not, the front of the pan will hit the 1st main cap. I wouldn't change the oil pump if you had good pressure. __________________ 1997 GMC Sierra Ext 1965 Mustang



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10-23-2006, 07:41 PM	#16
matthufham Registered User Join Date: Feb 2005 Location: Carl Junction, Missouri Posts: 2,061	Re: main seal i had a leaky oil pan gasket for the longest time and i had replaced it a good 4 times. you need to lift the engine up about 3-5 inches if you want to replace the oil pan or gasket. it was easy with my engine lift. take carb off, put on lift plate where carb was, take off fan shroud and lift. the rear main requires the same procedure plus replacing the rear main seal.

07-02-2007, 09:52 PM	#17
xfsketch 72 fleetside longbed 350 Join Date: Feb 2006 Location: Ohio Posts: 169	Re: main seal I am doing my rear main seal right now 72 chevy 350 and I had to un bolt the motor mounts and jack my motor up about 2" to clear the hump on the oil pan. I just slid it on its side and it came right out. i jacked the motor up with a bottle jack and piece of 2x4. I placed the jack under the pulleys/harmonic balancer because I already had the pan off. It would be wise to lift your engine put wood blocks between the motor and mounts then let the jack down and remove the oil pan. I always do things the hard way lol!

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