12 Bolt Housing

steve69
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12 Bolt Housing

Postby steve69 » Fri Nov 21, 2014 6:13 pm

Hi
I just bought a 1969 12 bolt housing only - with bearing caps and bolts. 3959038 NF - K 13 8 - KF 1123 B. This codes out to 1969 3.55 posi (large ring gear). The K 13 8 looks like 1968, but the housing in 1969 ( late). The whole unit has light rust, but no pitting, all the edges and casting no's. are sharp, not worn down. It was sitting inside for years. I wondered why it would have been stripped down and left unused, then I found the problem. Three of the 12 cover bolt holes were stripped, drilled and tapped poorly/incorrectly. It has a good code, an L34/L35 rear, I think it is well worth repairing, I'm assuming you probably ran into this before. What's the best way to repair these threaded holes? Why do they list this as large ring gear, aren't all 12 bolt ring gears the the same size? Please correct me if my info is wrong. Thanks

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monzaz
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Re: 12 Bolt Housing

Postby monzaz » Tue Nov 25, 2014 1:45 pm

Ok lets tackle the easy stuff first.
GM labeled the 10 bolt as SMALL RING GEAR and 12 bolts as LARGE ring gear. That is it.

NOW the holes. Humm. Well we would need to evaluate how bad the drill and tap is. IF very bad you can helicoil the hole to a larger size then helicoil to smaller 5/16 original. Welding up the hole is not really an option as it is cast and will be hell to redrill.
That is about all you can do. BUT if this is done correctly it will look good and work good too.

Are the bolt holes of the rear cover on the bottom or the top of the casting or scattered around?

WE would definitely fix that rear. :)

Jim
J D Race

steve69
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Re: 12 Bolt Housing

Postby steve69 » Tue Nov 25, 2014 4:29 pm

Thanks.

If counted clockwise from the top right bolt being #1, the bad ones are #6, #8, #11. Can I send a pic?
I have a couple more rears.
Next, I went looking for internals for this rear. I found one advertised only as a 12 bolt. I went to look at it. Series 3 posi, spacer w/ Zoom 4.56 gears. Original axles, no backing plates or drums. I asked what happened to the original gears. He had them in the Zoom box, original 3.31 gears. The housing was correctly modified for a G body, except for the width. They had it in a 79 Malibu. It was dirty and sitting ouside, but it turned, both axles same direction. I bought it, and cleaned it up to find the codes. This one is CCF 1106 K with the E below, K169 3969278, which codes out to a 70 Chevelle 3.31 posi. So now I have the 3 series carrier and axles for my KF, I can strip it and sell the housing to a G body owner, or do I restore the original perches and shock mounts and have a 70 Chevelle CCF 3.31, or sell the housing to a 70 Chevelle owner who needs the codes?? I guess it comes down to how rare that housing is. Also, there is a square box with a line through it cast above the 3969278. I have seen an X, but not this. Could it be a N in a box? Again, please correct any wrong info.

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monzaz
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Re: 12 Bolt Housing

Postby monzaz » Tue Nov 25, 2014 11:41 pm

Easier to fix the cover holes BUT I also have not seem the damage.... Still way easier to fix than all those perches and stuff someone welded on the chevelle housing for the G-body fit. Jim
J D Race

steve69
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Re: 12 Bolt Housing

Postby steve69 » Mon Dec 08, 2014 8:53 pm

Hey Jim,
Is the CCF 3.31 hard to find and worth restoring to it's proper condition? Also, I'd like to know how rare the KF 3.55 is. I'm keeping it, and putting in my 69, but I'd still like to know if it's scarce and what it's worth, if you wouldn't mind sharing that info. I've got some 10 bolt BOP questions I'll post in that section. Thanks

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monzaz
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Re: 12 Bolt Housing

Postby monzaz » Tue Dec 09, 2014 8:13 am

Usually the steeper the ratio on the tube will always be more rare. AS far as worth doing...??? That is always a question of how bad people want the ratio.

3.31 is the original SS car ratio. ANY original POSI 12 bolt rear housing in a clean condition will be worth good money these days.

3.55 would be a bit more rare. 3.73 even more rare. BUT back in the day KK code was pretty popular ratio and we have run across many of this ratio code.

As stated before knowing or guessing what these rears would be worth will all depend on the cleanliness of the housing condition of the internal parts and how original the rear is.

500.00 -3500.00 can be the prices of 12 bolt rears. EVERYTHING is only worth what someone will pay for it. :)

Not exactly what you wanted but we NEVER have a set price for 12 bolt original rears. TOO many factors in the builds. we get from 1250- 2000 for most.

Jim Mitschke
J D Race
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steve69
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Re: 12 Bolt Housing

Postby steve69 » Wed Dec 17, 2014 11:46 am

Jim,
That was a great answer, a lot of good info. Thanks.


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