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#1035454 - 02/24/16 04:54 PM 9 inch vs. 12 bolt  
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awssum Offline
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gulfport, ms
Been looking at going with a 9 inch versus a 12 bolt I have already. What the pros and cons of both rearends under a 87 MCSS?

#1035456 - 02/24/16 05:01 PM Re: 9 inch vs. 12 bolt [Re: awssum]  
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SSLance Offline
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Rear disc brake setups are cheaper for the 9", also the housings can be found at a much better price than the 12 bolt...but the 9" puts a bit more drag on the drive train than the 12 bolt.

Is your 12 bolt already set up for a G-body? If so I'd run with it if you can.


Lance
1985 Monte Carlo SS Street Car
#1035458 - 02/24/16 06:03 PM Re: 9 inch vs. 12 bolt [Re: awssum]  
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MC96 Offline
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St. Johns MI
What lance said about brake stuff is true for just about every part on a 9" compared to a 12 bolt...

Some guys just want to stay all GM, which is fine until you want to switch gears in an hour instead of a weekend.


86 SS
400SBC, 4l80e, MSD Atomic injection/trans controller, Tilt glass clip, all tubular arms, corvette brakes, 9" rear
In progress
#1035463 - 02/24/16 08:41 PM Re: 9 inch vs. 12 bolt [Re: awssum]  
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TooSlow406 Offline
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durability on a 9" is slightly better than a 12-bolt. but the reason people use those is more for the ease of swapping gears and posi. And now you can find 9" made for our cars all over the place.
GM never made a 12-bolt for a g body. you can, however, make one from a 68-72 coil spring car work. but like mine, its a bit longer than the 7.5"- you'd have to cut it down a little.


1985 Monte 406sbc, RHS ported 220s, Schoenfeld 1 3/4", 3" exhaust, Dynomax Ultra-Flo, Holley ported Strip Dominator, Dual Holley Blues, Holley HP 950, Comp roller 236/245, .570/.574
#1035467 - 02/24/16 08:51 PM Re: 9 inch vs. 12 bolt [Re: awssum]  
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Joe87monteSS Offline
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I got brakes for my 12 bolt for less than 50 bucks. LS1 Camaro rear disks bolt on just fine. I only needed to make a spacer to center the rotor in the abutment bracket.

Wheel offset may be an issue depending on what year 12 bolt you have. I have one from a 69 chevelle.

No need to cut it down. I prefer the wider rear because it'll allow the calipers to clear the frame.

Get the 12 bolt swap control arms from UMI and it'll go right in.


Joey
Engine/head builder/machinist
1987 Monte Carlo SS 383/4 Speed
2004 Silverado
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#1035470 - 02/24/16 09:11 PM Re: 9 inch vs. 12 bolt [Re: awssum]  
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awssum Offline
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gulfport, ms
I have a 72 Chevelle 12 bolt with posi and UMI upper control arms already. But I want to have rear disc brakes and was wondering should I sell my 12 bolt stuff and go Quick Performance 9 inch route.

#1035473 - 02/24/16 10:28 PM Re: 9 inch vs. 12 bolt [Re: awssum]  
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MC96 Offline
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You could do that.

Disc brakes are WAAYYYY less complicated and cheaper than everyone thinks.

Do you have a welder?


86 SS
400SBC, 4l80e, MSD Atomic injection/trans controller, Tilt glass clip, all tubular arms, corvette brakes, 9" rear
In progress
#1035474 - 02/24/16 10:34 PM Re: 9 inch vs. 12 bolt [Re: awssum]  
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ls1_monte Offline
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Seems like people have had issues with the 9" leaking out the axle tubes.


'87 Monte SS With a stock 11,000 mile '98 LS1/T56.

#1035492 - 02/25/16 01:26 AM Re: 9 inch vs. 12 bolt [Re: awssum]  
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SSLance Offline
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I fought that fight for a long time with my 9", but I finally found the right fix.


Lance
1985 Monte Carlo SS Street Car
#1035504 - 02/25/16 03:18 AM Re: 9 inch vs. 12 bolt [Re: awssum]  
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upflying Offline
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Don't forget to consider an 8.5" 10 bolt.


86 MCSS Notchback coupe, LS3, 4L65E, QP 9", Eaton Truetrac, 4 wheel disc, column shift, Dakota Digital, silver with maroon bench interior

#1035509 - 02/25/16 03:57 AM Re: 9 inch vs. 12 bolt [Re: awssum]  
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TooSlow406 Offline
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same dimensions as the 7.5, but a lot better ring and pinion. still better off going with a 9", or atleast a 12-bolt.


1985 Monte 406sbc, RHS ported 220s, Schoenfeld 1 3/4", 3" exhaust, Dynomax Ultra-Flo, Holley ported Strip Dominator, Dual Holley Blues, Holley HP 950, Comp roller 236/245, .570/.574
#1035541 - 02/25/16 07:39 PM Re: 9 inch vs. 12 bolt [Re: awssum]  
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Joe87monteSS Offline
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Since you already have the 12 bolt, I would use it.

The rear disk brakes came from a 2000 Camaro/Firebird.


Joey
Engine/head builder/machinist
1987 Monte Carlo SS 383/4 Speed
2004 Silverado
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#1035544 - 02/25/16 08:41 PM Re: 9 inch vs. 12 bolt [Re: awssum]  
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awssum Offline
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gulfport, ms
If I put the 12 bolt in do it need to be cut down to put stock wheels on. If so would I need new axles or reuse old axle for stock 10 bolt length?

#1035550 - 02/25/16 10:53 PM Re: 9 inch vs. 12 bolt [Re: awssum]  
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id almost garrantee you will have to cut the tubes, if you want the wheels to stay inside the well. i think mine measures like 84" in length, while my 7.5 is like 64", something like that.

I'm only using it because i already have it, with 4.56s and posi. its a BOP rear, so it came factory with bolt-in axles.

You would have to buy new axles, if you cut the rear, yes. But you'd want new ones anyway so they dont break. and you can get good ones with stock splines, if you dont want to change the posi


1985 Monte 406sbc, RHS ported 220s, Schoenfeld 1 3/4", 3" exhaust, Dynomax Ultra-Flo, Holley ported Strip Dominator, Dual Holley Blues, Holley HP 950, Comp roller 236/245, .570/.574
#1035552 - 02/25/16 11:23 PM Re: 9 inch vs. 12 bolt [Re: awssum]  
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The PC Surgeon Offline
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Salisbury Mills, NY
I toss a small bead of permatex black silicone whenever I seat my 35 spline axles in place, never leaks.

#1035577 - 02/26/16 04:37 PM Re: 9 inch vs. 12 bolt [Re: awssum]  
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SSLance Offline
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Which bearings do you run on it, I can't remember?


Lance
1985 Monte Carlo SS Street Car
#1035582 - 02/26/16 06:14 PM Re: 9 inch vs. 12 bolt [Re: SSLance]  
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I would get the 12 bolt with a nodular housing. Use 1/4 wall axle tubes and run 3" ford bearing ends with C clip eliminators.


Enjoy life, family first!
#1035594 - 02/27/16 02:08 AM Re: 9 inch vs. 12 bolt [Re: awssum]  
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Then you have the option of putting big bearing ford housing ends on... anything.



Oh SNAP! I'm a Vet! Stuff for Sale
#1035610 - 02/27/16 10:48 PM Re: 9 inch vs. 12 bolt [Re: awssum]  
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Hey-O Offline
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St. Charles Mo
Nothing is cheap. When you decided to do this, you had to know it's thousands just to get into the game. I went 12 bolt Currie, no regrets here..... Refer back to the first two sentences, they got me.


... " HEY - O " ... LET THE HORSES RUN

#1035817 - 03/03/16 04:43 PM Re: 9 inch vs. 12 bolt [Re: awssum]  
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awssum Offline
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gulfport, ms
If I cut the 12 bolt down to the stock 7.5 length what length would the new axles need to be? Thinking about ordering axles from Moser though.

#1035819 - 03/03/16 06:28 PM Re: 9 inch vs. 12 bolt [Re: awssum]  
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MC96 Offline
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St. Johns MI
Call Shane at Moser, he's a savant.
If you are ordering custom axles they can make the brake offset any number you want, so you do have somewhat of a range that you could narrow the rear within
(Brake offset is the distance from the HOUSING flange to the AXLE or WHEEL flange, so the end of the tube to where the wheel sets against)
Usually brake offset is 2.38 (maybe 2-3/8ths?) or 2.5. 2.5 is more common for aftermarket bolt on brake kits.

You can make the rear whatever length you want but the LCA mount sets pretty far out on our cars. Having bolt in ford 9 style ends, you end up with the ends pretty close to the LCA mount. So you MAY have to go with the 2-3/8(?)s to get the housing end away from the LCA mount

SO if you want a rear that puts the wheel flanges at the same location as the stock rear, you need to subtract 5 inches (2x your brake offset) to get your housing flange to housing flange width, also make sure to see if there is still room to put the LCA on the tube.

So what Shane would need to know if you cut it down yourself is what brake offset you want, what you cut out of each tube, what hosuing ends you are going with, and if you still have them what length the axles are now. To know what you cut out make sure you measure before and after at the flange, from where it presses into the center is a good spot.

You really should have the correct fixture to make sure you weld the ends on to the tube at a perfect 90 degrees but it isnt 100% necessary. Just use a housing end like the new allstar ones. They have a step that goes in the ID of a 3in tube and helps both center and true it to the bore.

If I were doing it I would
Buy a cheap bolt on brake kit
Weld (tack) the LCA mounts on
Cut the rear to length
Bolt the brake kit to the housing end and tack the housing end to the tube, with the caliper and everything on it.
Bolt it in the car

This way you can test fit and "clock" if necessary the housing end so that the caliper doesnt hit the frame or the LCA.
The Housing end doesnt care which way it is clocked just make sure your caliper has its bleeder up.

You can do this and save a lot of money. Just think it through, tack before you finish weld anything.

Last edited by MC96; 03/03/16 06:30 PM.

86 SS
400SBC, 4l80e, MSD Atomic injection/trans controller, Tilt glass clip, all tubular arms, corvette brakes, 9" rear
In progress
#1035821 - 03/03/16 06:39 PM Re: 9 inch vs. 12 bolt [Re: awssum]  
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MC96 Offline
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http://dcaracefab.com/
or
getdiscbrakes.com

Cheap and easy ford 9 disc kits, they use the same caliper as the front of our cars as well


86 SS
400SBC, 4l80e, MSD Atomic injection/trans controller, Tilt glass clip, all tubular arms, corvette brakes, 9" rear
In progress
#1036498 - 03/19/16 01:29 AM Re: 9 inch vs. 12 bolt [Re: awssum]  
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awssum Offline
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gulfport, ms
So once I have rearend cut down to stock 7.5 length and get axles is it best to get disc brakes from LS1 car in junkyard or order from part store?

#1037795 - 04/15/16 08:31 PM Re: 9 inch vs. 12 bolt [Re: awssum]  
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awssum Offline
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Can anyone answer my questions on the brakes from a LS1 to 12 bolt?

#1037798 - 04/15/16 09:21 PM Re: 9 inch vs. 12 bolt [Re: awssum]  
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Joe87monteSS Offline
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I wouldn't cut it down at all. If i'm not mistaken, your factory wheels will still fit unless your car is lowered.

If you use the stock 12 bolt, with the stock housing ends, you can bolt on a rear disc brake set up from a 1998-2002 Camaro. They are extremely easy to find, and literally bolt right on. You will only need to make a spacer that will center the rotor in the abutment bracket, and fab up a way to mount the e brake cables.

If you have the rear cut down, you will need to determine what housing ends they will use, and figure out what brakes to use on those housing ends.


Joey
Engine/head builder/machinist
1987 Monte Carlo SS 383/4 Speed
2004 Silverado
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