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Old 08-07-2019, 09:57 AM   #1
KMC3420
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12 bolt rear diff cover

Does anyone know of a good source to find a new 12 bolt rear diff cover, the stamped steel ones in black? Just like the original. I found one on eBay and have purchased it and it now is listed as out of stock. I can only find chrome covers which I donít want. Thanks.
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Old 08-07-2019, 10:09 AM   #2
71meangreenc10
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Re: 12 bolt rear diff cover

I got mine from rockauto. They have some in chrome and black.

Smitty
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Old 08-07-2019, 10:16 AM   #3
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Re: 12 bolt rear diff cover

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Originally Posted by 71meangreenc10 View Post
I got mine from rockauto. They have some in chrome and black.

Smitty
How long ago was that because I currently donít see any listed even on rock auto? I am only seeing the chrome ones.
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Old 08-07-2019, 11:13 AM   #4
1971Stepside
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Re: 12 bolt rear diff cover

I would like to find one of these as well. I purchased one local (used) and when it showed up it had a dent in it.
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Old 08-07-2019, 11:26 AM   #5
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Re: 12 bolt rear diff cover

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Originally Posted by 1971Stepside View Post
I would like to find one of these as well. I purchased one local (used) and when it showed up it had a dent in it.
I purchased this one from eBay: https://www.ebay.com/itm/Chevy-GM-GM...=1000240844025

And it was then out of stock. I contacted them this AM about it and was told it would be shipping from their California warehouse. I will let you know if it shows up and how it looks.

I was needing a plan B.
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Old 08-07-2019, 11:33 AM   #6
1971Stepside
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Re: 12 bolt rear diff cover

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I will let you know if it shows up and how it looks.
Please do. I'm curious if these are as heavy as the originals. The chrome ones leak
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1971 C10 Stepside. LSx 6.0 with BTR Stage IV, Speed Engineering Headers, 4L80e transmission w/3000 Circle-D Stall. 3.73. Posi. Purchased this truck when I was 17. I started the rebuild (or take apart) in 1993. I have drug it around all over the country in pieces. Other toys always push it aside, but one day....one fine day, she will be back on the road.

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Old 08-07-2019, 11:40 AM   #7
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Re: 12 bolt rear diff cover

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Please do. I'm curious if these are as heavy as the originals. The chrome ones leak
Will do, the tracking is showing delivery for Monday so I will for sure keep you updated. I was surprised I couldn't find just a plain black steel one fairly easily. I plan on running a steel core gasket as well. If I can find one for a truck 12 bolt, the below is for a car.

https://www.summitracing.com/parts/fog-1232-3/overview/

EDIT, FOUND THE TRUCK VERSION:
https://www.summitracing.com/parts/l...CABEgKamvD_BwE
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Old 08-07-2019, 12:02 PM   #8
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Re: 12 bolt rear diff cover

Buy a chrome one and scuff it up and paint it black. Then scuff the mounting surface in the same manner. Use sealant and a gasket. I’ve done this on two trucks and no leaks for years now.
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Old 08-07-2019, 12:19 PM   #9
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Re: 12 bolt rear diff cover

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Buy a chrome one and scuff it up and paint it black. Then scuff the mounting surface in the same manner. Use sealant and a gasket. Iíve done this on two trucks and no leaks for years now.
Thanks Leddzepp, I have never had much luck painting over chrome, even when I scuffed it. I plan on blasting the black coating off the new cover I get and putting 3 coats of SPI epoxy primer on it. I bought the LubeLocker Differential Cover Gasket which is aluminum cored, so gonna give that a go without any sealant for now.
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Old 08-07-2019, 12:24 PM   #10
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Re: 12 bolt rear diff cover

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Thanks Leddzepp, I have never had much luck painting over chrome, even when I scuffed it. I plan on blasting the black coating off the new cover I get and putting 3 coats of SPI epoxy primer on it. I bought the LubeLocker Differential Cover Gasket which is aluminum cored, so gonna give that a go without any sealant for now.
That gasket sounds like it will do the trick. Next time I do a differential service Iíll have to try one. I use that type on my valve covers and no leaks there so makes sense to use one on the diff.
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Old 08-07-2019, 12:27 PM   #11
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Re: 12 bolt rear diff cover

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That gasket sounds like it will do the trick. Next time I do a differential service Iíll have to try one. I use that type on my valve covers and no leaks there so makes sense to use one on the diff.
Fingers crossed it works good. Little pricy, but hopefully do it right once, plus it is reusable.
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Old 08-09-2019, 07:10 AM   #12
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Re: 12 bolt rear diff cover

i would like to know your results with that gasket
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Old 08-09-2019, 09:33 AM   #13
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Re: 12 bolt rear diff cover

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i would like to know your results with that gasket
I am a ways off from actually logging any actual miles but I will take some pictures of the gasket once I get it and post here, and when I get it installed on my rearend.
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Old 08-09-2019, 07:39 PM   #14
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Re: 12 bolt rear diff cover

I haven't used a gasket on a diff cover in almost 25 years of servicing old cars and trucks. Never had a leak. Always just used a small bead of black RTV.

Gary
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Old 08-09-2019, 10:09 PM   #15
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Re: 12 bolt rear diff cover

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I haven't used a gasket on a diff cover in almost 25 years of servicing old cars and trucks. Never had a leak. Always just used a small bead of black RTV.

Gary
Iím only 32 so I know you have forgotten more than I have learned at this point in my life, so if that works for you I wouldnít change a thing. I have scraped RTV off of many heads though that had small oil leaks over the course of time. I will give this gasket a go for now, but good to know I can revert back to RTV if needed. I will have a good flat cover to use hopefully soon.
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Old 08-09-2019, 11:58 PM   #16
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Re: 12 bolt rear diff cover

When I replaced my differential oil, first checked that the filler bolt would come off without a problem. I knew I didn't want to mess with it if I was going to have to fight with a rusty old filler bolt and wanted to be able to drive the truck to my expert mechanic who bails me out of bad situations. When I didn't have trouble with the filler bolt, I figured the rest would be good.

I drained the oil.

I cleaned the differential housing and cover surfaces, and cleaned up and painted the outside of the cover with some POR-15. That thing is never going to rust again.


I installed the gasket that was offered to me across the counter at O'Reilly Auto Parts, which happened to be a $6 Fel-Pro gasket. I used a thin spread of plain gasket sealant RTV and bolted the cover on and let it sit for 24 hours before filling. I was careful to not over tighten the bolts, and used a dab of blue gel loctite on the bolt threads.
It doesn't leak and I don't have any left over parts, so I guess I'm good to go.

I'll have to guard my good straight un-dented cover, since apparently they aren't just readily available. But if I do find myself needing one, the first people I will ask are you folks here on the forum, with a want-to-buy ad the premium membership allows me.
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Old 08-10-2019, 05:01 AM   #17
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Re: 12 bolt rear diff cover

I was looking for an original for some time, when a very kind member here not only gave me one, but sandblasted it for me as well. POR 15 was my choice for finishing it. This forum is full of great people!
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Old 08-10-2019, 07:12 AM   #18
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Re: 12 bolt rear diff cover

I haven’t received my cover yet so my next go to will be a WTB add if it is required. I know there are plenty of great members on here who would help us out.
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Old 08-12-2019, 11:02 PM   #19
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Re: 12 bolt rear diff cover

I received my diff cover today. It is a heavy gauge piece with no flex to it. The holes match my gasket exactly. The only difference I see is my new cover doesnít have the ridges around the bolt holes that a stock cover does. I think it will work very well with my new gasket seal. It has the ridges on both sides.
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Old 08-13-2019, 09:28 AM   #20
1971Stepside
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Re: 12 bolt rear diff cover

Thanks for the update. How does the thickness compare to the stock one?

Looks like I will have to get one of these ordered.
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1971 C10 Stepside. LSx 6.0 with BTR Stage IV, Speed Engineering Headers, 4L80e transmission w/3000 Circle-D Stall. 3.73. Posi. Purchased this truck when I was 17. I started the rebuild (or take apart) in 1993. I have drug it around all over the country in pieces. Other toys always push it aside, but one day....one fine day, she will be back on the road.

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"I can't complain, but sometimes I still do. Life's been good to me so far."
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Old 08-13-2019, 10:15 AM   #21
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Re: 12 bolt rear diff cover

Both are measuring 1/16Ē.
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Old 08-13-2019, 10:21 AM   #22
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Re: 12 bolt rear diff cover

Thanks for the detailed pictures.. !
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Old 08-13-2019, 10:25 AM   #23
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Re: 12 bolt rear diff cover

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Thanks for the detailed pictures.. !
You bet! Even though sideways! Posting from my phone does that
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Old 08-13-2019, 05:32 PM   #24
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Re: 12 bolt rear diff cover

Can anyone offer an explanation why the diff cover on my 71 GMC has so much surface rust on it ? Itís the original cover I believe, funny thing is the truck has lived its entire life in Eastern Oregon where we have little rust issues. The rest of the vehicle has almost no rust except underneath the battery tray, pretty typical...any ideas ?...
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Old 08-13-2019, 07:58 PM   #25
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Re: 12 bolt rear diff cover

The explanation I offer is the paint on that item was thin, but sufficient to last the full 10 year expected lifespan of the truck. On the bright side, if that's the most serious rust problem you have, it will easy to get one of those POR-15 starter kits for about $22 and take care of it once and for all the next time you change the differential oil.
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