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Originally Posted by Fred SS
Originally Posted by 88ssBrent
It is an option thats out there, umi has a kit for the conversion. The problem for me is every one of them uve ran across has not been cheap.

"1978-1988 GM G-Body 12-Bolt Swap Lower Control Arm and Adjustable Upper Control Arm Kit - UMI Performance Inc." https://www.umiperformance.com/home...rm-and-adjustable-upper-control-arm-kit/


How much wider is an A-Body 12-Bolt over the 7.5 G-body?

Fred

68-72 A-body 12-bolts are ~1.5" per side wider and that might be a no go if you got some coin in your rims already. I tried mocking it up with rear IROC rims and it puts the sidewall bump right at the lip of the fender.

Earlier years are narrower but I can't remember the specifics.

Last edited by stew'86MCSS396; 09/05/21 11:14 PM.

1985 GMC Caballero 4.3L V6 TBI 200C w/ 2.41 peg leg
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. If the 68-72 is 3" wider than the Monte, (from above) then the Monte would be 59.5"

Rear end widths in inches (wheel mount surface to wheel mount surface)

57.75 1962-1967 Chevy II/Nova
58.00 1978-1988 Chevy Malibu, Monte Carlo
59.50 1968-1982 Corvette
60.00 1955-1964 Chevy Car
60.00 1967-1969 Camaro
60.25 1968-1979 Chevy II/Nova
60.50 1984-1995 Corvette
60.50 1964-1967 Chevelle
62.00 1955-1959 Chevy Pickup
62.50 1968-1972 Chevelle
62.50 1970-1981 Camaro/Firebird

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If you throw out the leaf spring 12 bolts from that list if becomes a very short donor list.

As we know one of the G-bodies shortcomings is the narrow rear width which is because of the narrow track width needed to fit into the narrower body widths of the new mid-sized G-body. When they put the blueprints into the reducing copier in 1977 they punched 5% and the A-Body rolling chassis is now a 78 A/G-body, wrap a pretty body around it, race it in NASCAR, you end up with a Monte Carlo SS.

If you want to stay in the area of a zero offset wheel you can't deviate much from 58". So pretty much stuck buying someone's rear end the correct width.

Would also think there is little money to be saved by buying the parts and doing the assemble, just makes it easier to hide the expensive purchases. No matter which route you go it's expensive and more expensive.

Brent, UCA and LCA are now adjustable?
Bob

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Originally Posted by Tunedss86
. If the 68-72 is 3" wider than the Monte, (from above) then the Monte would be 59.5"

Rear end widths in inches (wheel mount surface to wheel mount surface)

57.75 1962-1967 Chevy II/Nova
58.00 1978-1988 Chevy Malibu, Monte Carlo
59.50 1968-1982 Corvette
60.00 1955-1964 Chevy Car
60.00 1967-1969 Camaro
60.25 1968-1979 Chevy II/Nova
60.50 1984-1995 Corvette
60.50 1964-1967 Chevelle
62.00 1955-1959 Chevy Pickup
62.50 1968-1972 Chevelle
62.50 1970-1981 Camaro/Firebird

I like how I'm somewhat being quoted for what is deemed misinformation. I think the last 2 on the list is wrong. With axles for a 68-72 Chevelle 12-bolt being a smidgen over 30"x2=60", the crosspins must be over 2" wide in these rearends. It's all moot if the OP wants to run the same rims he has on the car now but I'll go crawl under the house and take some measurements of the axles I removed and the '70 Chevelle rear I own.

Last edited by stew'86MCSS396; 09/06/21 10:52 AM.

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Everything is still stock except for 2" drop spindles in the front, and Aldan "coilovers" on all four corners. Im still open to all options because I still have lots of homework to do. I don't want to spend $3000+ on a rearend then come up with another chunk of change for all new rear suspension. Only way I would spring for new suspension is if I got a good deal on a rear end and it made sense.

I'm open to all rear ends and have access to a jig with most bushing options available. I have tig, mig, and comfortable shortening an axle. Im also comfortable welding brackets on tubes, but if using a cast center housing it would need the upper control arm points. Also if anyone is curious currie has the factory style lower control arm mounts to buy separate if needed.

The issue with most used rearends is by the time I make them check all the boxes im not far off the price for a new rearend. I want it to fit my wheels ( offset and lug pattern), be able to use my coilovers, a helical style differential, where im at now have a 3.73 gear ratio, and still undecided on brakes so that could factor in new axle flanges. Every used 12 bolt i have found with the upper mounts has not been cheap so far.

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Originally Posted by stew'86MCSS396

I like how I'm somewhat being quoted for what is deemed misinformation. I think the last 2 on the list is wrong. With axles for a 68-72 Chevelle 12-bolt being a smidgen over 30"x2=60", the crosspins must be over 2" wide in these rearends. It's all moot if the OP wants to run the same rims he has on the car now but I'll go crawl under the house and take some measurements of the axles I removed and the '70 Chevelle rear I own.


I wasn't indicating anything was "misinformation". Those numbers are just some I found on the net at some point.

Last edited by Tunedss86; 09/06/21 04:31 PM.
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No moot points here. I enjoy the conversation about any rearend option as it might help me or help others so any rear end discussion is welcome in this thread.

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Brent, I too enjoy this conversation. I have not decided if I will have my 7.5 upgraded as Gordon (AkronAero) said or go with a Moser 12-bolt. For my needs, street driving only (no autox nor drag strip), an upgraded 7.5 should handle my needs as Gordon said. The S60 and 9" are overkill for me. The Moser 12 Bolt is very tempting for me since it is a bolt in operation, no searching for or adapting emergency brake cables and strong enough to handle a future 383 or LS.

Fred

Last edited by Fred SS; 09/06/21 08:58 PM. Reason: re-word

87 SS, Harwood hood, UMI trailing arms. Hooker 2050 Headers (Jet Hot Coated). Hooker Cat-Back Exhaust, Goodwrench 350, Ported TPI, Trick Flow 56cc alum heads, SLP runners, Comp Cams 260AH-12 cam, Trick Flow roller rockers, TCI 2400 stall converter, Denny's 3.5" Driveshaft, GBodyParts GNX Replica Wheels 18x8 & 18x9. F-Body Serpentine Belt Sys.
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Originally Posted by Tunedss86
Originally Posted by stew'86MCSS396

I like how I'm somewhat being quoted for what is deemed misinformation. I think the last 2 on the list is wrong. With axles for a 68-72 Chevelle 12-bolt being a smidgen over 30"x2=60", the crosspins must be over 2" wide in these rearends. It's all moot if the OP wants to run the same rims he has on the car now but I'll go crawl under the house and take some measurements of the axles I removed and the '70 Chevelle rear I own.


I wasn't indicating anything was "misinformation". Those numbers are just some I found on the net at some point.

It's all G!!! It's funny I used the search terms "12-bolt+rearend+widths," clicked on 3 different hits and got 3 different answers!!! I should have never indicated that last one on the list was wrong either as I don't have one in the stable to measure just that when you order axles for that particular year/make/model, last 2 on the list are all lumped together. Also, found a Chevelle forum thread that aftermarket axles can vary in length from one manufacture to another. I don't have drums on the '68-'72 A-body 12-bolt in the crawl space and it does have Moser axles but I did get 61" axle flange to axle flange.


1985 GMC Caballero 4.3L V6 TBI 200C w/ 2.41 peg leg
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When I did my 9 inch swap it took about a full day. I had an extra hand for part of it. I was able to use existing emergency brake cables. Even used original brake lines. Didnt have to change driveshaft, just install conversion joint. This winter I will make new brake lines when I install sway bar to clear clamps. I went with the Strange housing for the adjustable lower bar and shock mounts. If I could figure out how to uploading pictures I would post.


1987 Monte Carlo SS. 355 SBC, Pro Systems carb. 2004R non lock up 10" PTC converter
UMI front and rear control arms. Strange 9 Inch, 31 Spline Axles, 3.89 TruTrac.
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Originally Posted by Wilson
When I did my 9 inch swap it took about a full day. I had an extra hand for part of it. I was able to use existing emergency brake cables. Even used original brake lines. Didnt have to change driveshaft, just install conversion joint. This winter I will make new brake lines when I install sway bar to clear clamps. I went with the Strange housing for the adjustable lower bar and shock mounts. If I could figure out how to uploading pictures I would post.


Ross, I would be more than glad to upload pictures to this thread with credit to the owner if anyone would like. My email address is in my profile, just send my way and I will post.

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Here is a bracket kit that curries has for the the g body when wanting to use a 12 bolt.

"CE-7012GP - GM G-Body Suspension Bracket Set - (12 Bolt Housings) - Currie Enterprises" https://www.currieenterprises.com/CE-7012GP

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Did you decide what setup you are going with.


1987 Monte Carlo SS. 355 SBC, Pro Systems carb. 2004R non lock up 10" PTC converter
UMI front and rear control arms. Strange 9 Inch, 31 Spline Axles, 3.89 TruTrac.
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Unfortunately not yet, it shouldn't be this hard but it seems there is a lot more to weed thru than I had planned.

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Brent, I have been having an email exchange with Moser concerning their 12-Bolt. I thought I would pass along what I have learned. Apparently, their 12-Bolt comes with the brake lines only if the drum brake option is selected. If the disk brake upgrade is selected, the customer has to source the brake lines. But they do supply the flex hose from the calipers. Either option comes with the parking brake cables installed. They also said that they can weld-on the tabs, if asked, that supports the hard line to flex hose fitting. Also their 12-bolt does not come with the bump stop support brackets installed. They do not supply that. Look like most aftermarket rear ends do not have that bracket. I figured I could attach a bump stop to the underside of the frame at the axle centerline. I need the bump stops because my 3.5 inch driveshaft has been making contact with the stiffener that is attached to the underside of the body, under the rear seat.


87 SS, Harwood hood, UMI trailing arms. Hooker 2050 Headers (Jet Hot Coated). Hooker Cat-Back Exhaust, Goodwrench 350, Ported TPI, Trick Flow 56cc alum heads, SLP runners, Comp Cams 260AH-12 cam, Trick Flow roller rockers, TCI 2400 stall converter, Denny's 3.5" Driveshaft, GBodyParts GNX Replica Wheels 18x8 & 18x9. F-Body Serpentine Belt Sys.
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Drove my car last weekend to a show. 60 plus miles round trip. No whining of the gearset, kinda shocked since this was my first time doing a set of gears. Love the Trutrac and 11 drums stop as they should. Just ordered a HR sway bar yesterday. Really nice knowing that it is finally bullet proof back there.


1987 Monte Carlo SS. 355 SBC, Pro Systems carb. 2004R non lock up 10" PTC converter
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Currie sells a bracket kit for the 12 bolt that can be welded on. Contact them, maybe they will sell just the ones you need. (I think the ones with the rectangular hole is the bump stop brackets?)

https://www.currieenterprises.com/CE-7012GP

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Originally Posted by Tunedss86
Currie sells a bracket kit for the 12 bolt that can be welded on. Contact them, maybe they will sell just the ones you need. (I think the ones with the rectangular hole is the bump stop


Same kit I posted above, when I called they said they would not seperate.

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Originally Posted by 88ssBrent
Originally Posted by Tunedss86
Currie sells a bracket kit for the 12 bolt that can be welded on. Contact them, maybe they will sell just the ones you need. (I think the ones with the rectangular hole is the bump stop


Same kit I posted above, when I called they said they would not seperate.


Ah sorry, I must have missed that post (or have slept since I read it, LOL)

Check the ebay listing then (Its not mine), $50 for the brackets & bump stops.


Last edited by Tunedss86; 09/17/21 12:50 PM.
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So, I may regret not getting the rearend first but I changed course on my plans for the moment. Im still going to keep an eye out for certain rearends and see if I can come up with something. Im going to build a 396 sbc engine, should be interesting.

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Brent - actually, the longer you delay the more information and intel we collect from you.....
What your personal spin on the 396??? Just that it gives you more stuff to tweak (and learn about)?
Keep us posted...
Gordon


1987 Aerocoupe. Frame-off, notched/mini-tub, 383 with AFRs @ 535HP/487TQ, March Serpentine, 304 SS headers (Jet-Hot) & 304 3" dual exhaust w/ Borlas, Janis 200-4R, TrueTrac w/ girdle and Moser 28, Hydroboost, computer delete, lowered, every part replaced or messed with (several times).
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Brent, by waiting you might luck out and find a decent rear end somewhere. A few years ago, I missed out on an 8.5 Gran National rear that was built up for about $1500. I'm still leaning towards the Moser 12-Bolt. Good luck with your 396 small block. Please keep us posted.


87 SS, Harwood hood, UMI trailing arms. Hooker 2050 Headers (Jet Hot Coated). Hooker Cat-Back Exhaust, Goodwrench 350, Ported TPI, Trick Flow 56cc alum heads, SLP runners, Comp Cams 260AH-12 cam, Trick Flow roller rockers, TCI 2400 stall converter, Denny's 3.5" Driveshaft, GBodyParts GNX Replica Wheels 18x8 & 18x9. F-Body Serpentine Belt Sys.
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Now that my 305 is running to its potential I know for sure I dont have to worry about hooking on launch and the one wheel peel just isnt cool
so I figured i would update this thread, I acquired a fox body 8.8 from a guy I work with pretty cheap. The longer it has set in my garage and the more math I have done It just doesn't seem the route I want to go so i will probably sale it soon.

Recently I ran across another friend of a friend who had taken his rearend out of a 2000 camaro at low mileage years ago and set it in the corner. Only thing left was axles, housing and carrier, gear and pinion had even been robbed. I was hoping the rear ls1 brakes were still there but they were not. I purchased just the carrier for $75 and it looks to be in great shape. It's a torsen zexel 7.625 28 spline 3 series carrier, they are a worm gear style carrier. Plan to just use my GM 3.73 gear and pinion, put in new bearings, shims, and check the backlash. Of course I'll have to pay the $200 for some 28 spline moser axles, might even weld the axle tubes and throw a cover on it, total cost would be around $550-$600. I had almost talked myself into a lock right but they are around $500 and I felt this would be a better option. I'll continue this thread when I get too this project.

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As with most things these days cost has went up on items since I originally priced it out. As said above I checked out the powertrax no-slip for the 7.625 and it's no longer available, the powertrax lock right is available but seems a lot of people don't like the lock up on it and the noise it's $488.35. For the torsen here is an estimate to do the swap and have a posi.

$75 for the carrier (pictured)
$50 timken set 69 carrier bearings and races
$295 moser a102810 28 spline axles
$30 Yukon yspcc-009 c-clips
$25 Yukon sk ss10 super shim pack
$25 timken 5707 wheel bearing and 86605 seal
Weld axle tubes to carrier
Use my existing gm 3.73 ring and pinion

Optional pieces
$200 moser 7105 cover or $215 lpw 301-7.5g cover
$50 moser 7115 main cap stud kit

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