12 bolt gasket replacement - The 1947 - Present Chevrolet & GMC Truck Message Board Network

ACES · 02-02-2006, 03:30 PM

I am replacing the gasket on my 12 bolt today. I've never done this before. I did not find any metal shavings inside. I scraped the old gasket off and have put the new Fel Pro gasket and cover one. I have not tightened it. How tight should I turn the bolts?
How much oil should I add?
I got 80W-90 Gear lubricant.
I'm guessing that I put it in through the hole in the top where the hose is.
The hose looks terrible too. I should probably replace it while I'm there.

Any words of advice or warning?

I took a couple of pics of the differential. I'll post them in a little while.

68/72parts · 02-02-2006, 03:43 PM

I would recommend using a good quality silicone RTV instead of the gasket. It will seal better and not leak in the long run if applied properly. As for amount of fluid you pull out the check plug, hopefully you did this already? and fill the diff until fluid just starts to come out of the hole, make sure the truck is reasonably level first. 80-90w will work fine or a good synthetic would be my choice. When you apply the silicone you dont need much just a nice 1/4inch thick bead all the way around. make sure to kleen off the excess before it dries.

ACES · 02-02-2006, 03:56 PM

68/72 parts -I have located the check plug. It has an orange tag on it that says to only put gear oil recommended for limited slip differential in. I'm gonna have to get some different oil. I'll look for some silicone RTV while I'm there.

67ChevyRedneck · 02-02-2006, 04:07 PM

Quote:

Originally Posted by 68/72parts

I would recommend using a good quality silicone RTV instead of the gasket. It will seal better and not leak in the long run if applied properly. As for amount of fluid you pull out the check plug, hopefully you did this already? and fill the diff until fluid just starts to come out of the hole, make sure the truck is reasonably level first. 80-90w will work fine or a good synthetic would be my choice. When you apply the silicone you dont need much just a nice 1/4inch thick bead all the way around. make sure to kleen off the excess before it dries.

I agree, I just did this last weekend. And yes, if you have a limited slip rear, you do need the special "limited slip, or Positraction" rearend gear oil. If I remember right I bought two of the smaller bottles of fluid and it was enough, I think they were 1 quart bottles??? Memory sucks.

68haywagon · 02-02-2006, 04:27 PM

I used a gasket, no leaks at all. I would not use silicone, because when I need to get in there again I don't feel like scraping and peeling silicone. I agree about how much to put in though.

Mike

ACES · 02-02-2006, 04:41 PM

well guys, I'm back from Advance Auto. I've got the Silicone RTV and two bottles of Synthetic gear oil for Limited slip. I think since I've already got the gasket on there, I'm gonna leave it there, but if I have problems I'm gonna take it off and do the Silicone.

ACES · 02-02-2006, 04:41 PM

How tight should the bolts be?

MrC1 · 02-02-2006, 04:42 PM

You can also buy limited slip additive separately, but you shouldn't need it. There are many 80-120 weight oils out there made for limited slip diffs, probably most of what you find on the shelf at a parts store.

Anybody know what hose he's talking about? That scares the heck outta me!

cdowns · 02-02-2006, 04:43 PM

it would be ALOT better if you used asynthetic gearoil such as royal purple or moibil1 they're rated for posi's so you don't need the additive// the biggest cause of leaking after removing and replacing a diff cover is overtightening max of agout 12-15 ft lbs// overtightening causes boltholes in the cover to bulge out causeing leaks

bighead · 02-02-2006, 04:45 PM

Vent hose.

67ChevyRedneck · 02-02-2006, 04:52 PM

Quote:

Originally Posted by bighead

Vent hose.

It runs from the top of the differential over to the driverside frame rail... or so its supposed to....

jimfulco · 02-02-2006, 05:31 PM

I hate silicone. If you want an easily removable gasket, paint both sides with Permatex #3 Aviation Sealer or Permatex Super 300 (in the little white plastic can). It won't leak unless the cover is distorted, and it will come off easily with an easy pry with a screwdriver. Another coat of goo, and it will seal again. Gas and oil won't touch it, but alcohol cleans it up easily.

I glue gaskets to the cover with yellow 3M so they won't come loose, and use the Permatex on the other side so it'll come loose when I want it to.

**70STOVEBOLT** · 02-02-2006, 07:27 PM

Also, two of the bolts require a thread sealant, as they go all the way through the housing and are below the lube level. I forget which two they are, but if you don't put thread sealant on them, you will get a leak there.

ACES · 02-03-2006, 10:04 AM

Does anyone know which two bolts require thread sealant?

cdowns · 02-03-2006, 10:07 AM

i always put sealant on all bolts in the rear cover

67ChevyRedneck · 02-03-2006, 10:31 AM

Quote:

Originally Posted by 70STOVEBOLT

Also, two of the bolts require a thread sealant, as they go all the way through the housing and are below the lube level. I forget which two they are, but if you don't put thread sealant on them, you will get a leak there.

Crap, y'all tell me this now?

02-02-2006, 03:30 PM	#1
ACES Life is a gamble Join Date: Oct 2003 Location: Lee's Summit, MO Posts: 796	12 bolt gasket replacement I am replacing the gasket on my 12 bolt today. I've never done this before. I did not find any metal shavings inside. I scraped the old gasket off and have put the new Fel Pro gasket and cover one. I have not tightened it. How tight should I turn the bolts? How much oil should I add? I got 80W-90 Gear lubricant. I'm guessing that I put it in through the hole in the top where the hose is. The hose looks terrible too. I should probably replace it while I'm there. Any words of advice or warning? I took a couple of pics of the differential. I'll post them in a little while. __________________ 1970 Orange CST C-10 w/350, posi, Longbed The torpid artist seeks inspiration at any cost, by virtue or by vice, by friend or by fiend, by prayer or by wine. -- Ralph Waldo Emerson

02-02-2006, 03:43 PM	#2
68/72parts Registered User Join Date: Jan 2006 Location: Chilliwack B.C Posts: 59	Re: 12 bolt gasket replacement I would recommend using a good quality silicone RTV instead of the gasket. It will seal better and not leak in the long run if applied properly. As for amount of fluid you pull out the check plug, hopefully you did this already? and fill the diff until fluid just starts to come out of the hole, make sure the truck is reasonably level first. 80-90w will work fine or a good synthetic would be my choice. When you apply the silicone you dont need much just a nice 1/4inch thick bead all the way around. make sure to kleen off the excess before it dries.

02-02-2006, 04:27 PM	#5
68haywagon I'm watching you! Join Date: Feb 2005 Location: Levittown, PA Posts: 1,822	Re: 12 bolt gasket replacement I used a gasket, no leaks at all. I would not use silicone, because when I need to get in there again I don't feel like scraping and peeling silicone. I agree about how much to put in though. Mike __________________ 2012 Chevrolet Silverado 1500 Z71 4WD 1993 Chevrolet C-1500 W/T - Blue - 4.3L V-6, 4 speed auto - Dad's (RIP) 1992 Chevrolet S10 - LS swap project 1968 Chevrolet C-10 longbed fleetside - sold

02-02-2006, 04:41 PM	#6
ACES Life is a gamble Join Date: Oct 2003 Location: Lee's Summit, MO Posts: 796	Re: 12 bolt gasket replacement well guys, I'm back from Advance Auto. I've got the Silicone RTV and two bottles of Synthetic gear oil for Limited slip. I think since I've already got the gasket on there, I'm gonna leave it there, but if I have problems I'm gonna take it off and do the Silicone. __________________ 1970 Orange CST C-10 w/350, posi, Longbed The torpid artist seeks inspiration at any cost, by virtue or by vice, by friend or by fiend, by prayer or by wine. -- Ralph Waldo Emerson

02-02-2006, 04:41 PM	#7
ACES Life is a gamble Join Date: Oct 2003 Location: Lee's Summit, MO Posts: 796	Re: 12 bolt gasket replacement How tight should the bolts be? __________________ 1970 Orange CST C-10 w/350, posi, Longbed The torpid artist seeks inspiration at any cost, by virtue or by vice, by friend or by fiend, by prayer or by wine. -- Ralph Waldo Emerson

02-02-2006, 03:56 PM	#3
ACES Life is a gamble Join Date: Oct 2003 Location: Lee's Summit, MO Posts: 796	Re: 12 bolt gasket replacement 68/72 parts -I have located the check plug. It has an orange tag on it that says to only put gear oil recommended for limited slip differential in. I'm gonna have to get some different oil. I'll look for some silicone RTV while I'm there. __________________ 1970 Orange CST C-10 w/350, posi, Longbed The torpid artist seeks inspiration at any cost, by virtue or by vice, by friend or by fiend, by prayer or by wine. -- Ralph Waldo Emerson

02-02-2006, 04:42 PM	#8
MrC1 Dork For Days Join Date: Aug 2005 Location: Dallas Posts: 407	Re: 12 bolt gasket replacement You can also buy limited slip additive separately, but you shouldn't need it. There are many 80-120 weight oils out there made for limited slip diffs, probably most of what you find on the shelf at a parts store. Anybody know what hose he's talking about? That scares the heck outta me! __________________ 1972 C20, 402/700R4 - My first classic truck, bought in September 2005. 85% transformed from "Farm" to "Cool" status! 1970 Dodge Challenger 440, 4sp (my other toy) 12.67 @ 117 MPH, with a pathetic 2.022 60' 2007 Dodge Charger SRT-8 2008 Cadillac CTS All-American garage, baby! Last edited by MrC1; 02-02-2006 at 04:42 PM.

02-02-2006, 04:43 PM	#9
cdowns Senior Member Join Date: Jan 2003 Location: daytonabeach Posts: 22,956	Re: 12 bolt gasket replacement it would be ALOT better if you used asynthetic gearoil such as royal purple or moibil1 they're rated for posi's so you don't need the additive// the biggest cause of leaking after removing and replacing a diff cover is overtightening max of agout 12-15 ft lbs// overtightening causes boltholes in the cover to bulge out causeing leaks __________________ 71c-10 350/2004r/4:11 lowered3/4 longbed/dead by hurricane MEANING OF DEATH::::: SOMEBODY ELSE GETS YOUR STUFF DONT BELIEVE EVERYTHING YOU THINK TAKE MY ADVISE;I DON'T USE IT ANYWAY

02-02-2006, 04:45 PM	#10
bighead Registered User Join Date: Nov 2005 Location: McKinney, Texas Posts: 465	Re: 12 bolt gasket replacement Vent hose.

02-02-2006, 05:31 PM	#12
jimfulco Registered User Join Date: May 2003 Location: Shreveport LA Posts: 3,170	Re: 12 bolt gasket replacement I hate silicone. If you want an easily removable gasket, paint both sides with Permatex #3 Aviation Sealer or Permatex Super 300 (in the little white plastic can). It won't leak unless the cover is distorted, and it will come off easily with an easy pry with a screwdriver. Another coat of goo, and it will seal again. Gas and oil won't touch it, but alcohol cleans it up easily. I glue gaskets to the cover with yellow 3M so they won't come loose, and use the Permatex on the other side so it'll come loose when I want it to. Last edited by jimfulco; 02-02-2006 at 05:33 PM.

02-02-2006, 07:27 PM	#13
70STOVEBOLT Senior Member Join Date: Jun 2005 Location: Winona Lake, IN Posts: 6,538	Re: 12 bolt gasket replacement Also, two of the bolts require a thread sealant, as they go all the way through the housing and are below the lube level. I forget which two they are, but if you don't put thread sealant on them, you will get a leak there.

02-03-2006, 10:04 AM	#14
ACES Life is a gamble Join Date: Oct 2003 Location: Lee's Summit, MO Posts: 796	Re: 12 bolt gasket replacement Does anyone know which two bolts require thread sealant? __________________ 1970 Orange CST C-10 w/350, posi, Longbed The torpid artist seeks inspiration at any cost, by virtue or by vice, by friend or by fiend, by prayer or by wine. -- Ralph Waldo Emerson

02-03-2006, 10:07 AM	#15
cdowns Senior Member Join Date: Jan 2003 Location: daytonabeach Posts: 22,956	Re: 12 bolt gasket replacement i always put sealant on all bolts in the rear cover __________________ 71c-10 350/2004r/4:11 lowered3/4 longbed/dead by hurricane MEANING OF DEATH::::: SOMEBODY ELSE GETS YOUR STUFF DONT BELIEVE EVERYTHING YOU THINK TAKE MY ADVISE;I DON'T USE IT ANYWAY

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