Author Topic: 12 bolt backing plates  (Read 2574 times)

SS396

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12 bolt backing plates
« on: August 29, 2011, 08:55:01 PM »
Does anybody know who sells  repo backing plates for a 68 12 bolt that is close to original as in appearance and thickness. Even better is it still possible to buy GM ones anywhere? Mine are badly rusted and beyond salvage.

1967RS/SS

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Re: 12 bolt backing plates
« Reply #1 on: August 29, 2011, 11:54:47 PM »
Don't know about the quality of their backing plates, but inline tube sells new ones.  I asked about their rear drum brake kit and the said there stuff is made in the USA.  Maybe an option???
1967 RS/SS L-48
Van Nuys 01C
Joe

mopar346

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Re: 12 bolt backing plates
« Reply #2 on: September 01, 2011, 12:09:57 AM »
I believe 10 bolt stuff swap over, I am not sure if they are identical though.

L78 steve

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Re: 12 bolt backing plates
« Reply #3 on: September 02, 2011, 02:33:38 PM »
10 bolt plates are identical.
69 Z/28 Dover White X33,ZL2,PS,M20,Std.int.04C
67 SS/RS Mt. Green 1W,2LGSR,3SL,4K,5BY,07C
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BlackoutSteve

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Re: 12 bolt backing plates
« Reply #4 on: November 27, 2012, 02:23:33 AM »
Found this on-topic thread in a search.. :)

Also regarding the backing plates..
I aquired a used pair that have splash shields welded to them. I didn't know splash shields were ever added to drum backing plates and thought someone must have once added them. I was also considering removing them until I did a short Google search and found some with..

The afore mention In-Line Tube website has the option of with and without..
http://inlinetube.com/Drum%20Brakes/Drum%20Brakes.htm



Question: Where the shielded plates ever a Camaro option, standard or never available on them? If not, what were these normally fitted to?

Also, looking at the ones that I have that came off a 68 Camaro (no idea if original to the car), were the welds normally that rough? This is mainly why I assumed a back-yard welder had added them.

Restoring my RHD 69 Jane in Melbourne, Australia.
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BlackoutSteve

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Re: 12 bolt backing plates
« Reply #5 on: November 27, 2012, 02:32:09 AM »
Also, there are two different bore sizes for rear wheel cylinders available for rear drums.. 7/8" and 15/16"..

Was only one size available on 1st Gens, or were both sizes used depending on the application?
Thanks
Restoring my RHD 69 Jane in Melbourne, Australia.
http://www.usmuscle.com.au/Forum/showthread.php?t=2840

z28rich

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Re: 12 bolt backing plates
« Reply #6 on: November 27, 2012, 05:12:00 AM »
Found this on-topic thread in a search.. :)

Also regarding the backing plates..
I aquired a used pair that have splash shields welded to them. I didn't know splash shields were ever added to drum backing plates and thought someone must have once added them. I was also considering removing them until I did a short Google search and found some with..

The afore mention In-Line Tube website has the option of with and without..
http://inlinetube.com/Drum%20Brakes/Drum%20Brakes.htm



Question: Where the shielded plates ever a Camaro option, standard or never available on them? If not, what were these normally fitted to?

Also, looking at the ones that I have that came off a 68 Camaro (no idea if original to the car), were the welds normally that rough? This is mainly why I assumed a back-yard welder had added them.




those were added.

69Z28-RS

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Re: 12 bolt backing plates
« Reply #7 on: November 27, 2012, 05:36:59 AM »
One can tell that isn't a factory weld....  looks more like my welding....  LOL....
Gary W / 09C 69Z28-RS, 72 B 720 cowl console rosewood tint
69 Corvette convertible, silver/black 350 hp,
60 Corvette white/red, 72 Corvette coupe, '70 Mach I 
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BlackoutSteve

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Re: 12 bolt backing plates
« Reply #8 on: November 27, 2012, 07:48:31 AM »
Thanks, then I guess I was right to question them..  :P

Any idea what bore size is correct re: the wheel cylinders?
Restoring my RHD 69 Jane in Melbourne, Australia.
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KurtS

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Re: 12 bolt backing plates
« Reply #9 on: November 27, 2012, 07:17:57 PM »
That's a lot of work to find the right arc of metal to weld into place. Lots of factory welds aren't pretty, look at the subframe. :)
Not to say these are original, but I've seen these used somewhere before - maybe on later cars?
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william

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Re: 12 bolt backing plates
« Reply #10 on: November 27, 2012, 11:38:55 PM »
GM serviced 1st gen backing plates well into the '90s but the part numbers changed. They are in group 5.001 if someone has a P & A manual from that period. Maybe had other applications and could still be available.

BlackoutSteve

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Re: 12 bolt backing plates
« Reply #11 on: November 28, 2012, 06:33:13 AM »
That's a lot of work to find the right arc of metal to weld into place. Lots of factory welds aren't pretty, look at the subframe. :)
Not to say these are original, but I've seen these used somewhere before - maybe on later cars?

My thought exactly Kurt.. Appearance of the subframe welds and the effort to cut out the shape of the shield.. Hmmm..
Thanks William. I didn't see any numbers stamped on them and after stripping the paint, they appeared to have been sand blasted at one point.
Restoring my RHD 69 Jane in Melbourne, Australia.
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69Z28-RS

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Re: 12 bolt backing plates
« Reply #12 on: November 29, 2012, 02:14:15 AM »
a factory frame weld may have welding flash, etc, but they generally aren't ground off as in the photos of that backing plate.  I suspect some one took those plates off another backing plate, and welding them to their factory backing plates, then ground off their 'welding ugly'..  :)
Gary W / 09C 69Z28-RS, 72 B 720 cowl console rosewood tint
69 Corvette convertible, silver/black 350 hp,
60 Corvette white/red, 72 Corvette coupe, '70 Mach I 
90 ZR1 red/red #246, 90 ZR1 white/gray #2466
72 El Camino, '55-'56-'57 Nomads, '55-'57 B/A Sedan

hotrod68

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Re: 12 bolt backing plates
« Reply #13 on: November 29, 2012, 03:50:12 AM »
   10-bolt plates will work, but you may have to grind the center axle bearing holes oversize a tad. I have a new Moser 12-bolt under my car and I used the backing plates from an old 10-bolt. I don't know of the Moser axle bearings are bigger than standard GM or not because I used C-clip eliminators. But the holes only need to be enlarged slightly. I used a carbide bit in a grinder and it's a snap. Hope this helps.

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68camaroz28

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Re: 12 bolt backing plates
« Reply #14 on: November 29, 2012, 05:04:02 AM »
Will look for a better pic but here is one of our 68's rear backing plates and other than a normal clean & prepare for paint (no grinding) its untouched.
Chick
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MyRed67

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Re: 12 bolt backing plates
« Reply #15 on: November 29, 2012, 06:55:40 AM »
 I have a '69 12 Bolt Posi under my car, (I changed the Perches to Mono)and it has the shields.  They were spot welded on from the factory.  Looks exactly like Chicks pic. above.
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BlackoutSteve

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Re: 12 bolt backing plates
« Reply #16 on: November 29, 2012, 09:02:55 AM »
   10-bolt plates will work, but you may have to grind the center axle bearing holes oversize a tad. I have a new Moser 12-bolt under my car and I used the backing plates from an old 10-bolt. I don't know of the Moser axle bearings are bigger than standard GM or not because I used C-clip eliminators. But the holes only need to be enlarged slightly. I used a carbide bit in a grinder and it's a snap. Hope this helps.



Thanks guys..
Pretty sure 10 and 12 bolt axles use the same wheel bearings and backing plates, but Moser are making 12 bolts and strongly suggesting they supply them using big Ford Torino press-on bearings and retainer plates.. Thay are a far better and safer way of retaining the axles as opposed to C-Clips, and C-Clip eliminators are still a no-no for the street. http://www.moserengineering.com/moser/faq/
Anyway, the Torino bearings are 3.150" OD as opposed to tiny 12 Bolt 2.255" OD so the backing plates need to be opened up to ~3.200" so the bearing will pass through when installing. Much easier and neater done on a lathe if you have access to one, which is what I had done.
Restoring my RHD 69 Jane in Melbourne, Australia.
http://www.usmuscle.com.au/Forum/showthread.php?t=2840

BlackoutSteve

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Re: 12 bolt backing plates
« Reply #17 on: November 29, 2012, 09:03:48 AM »
PS. I found out that Camaro rear drum wheel cylinders have a 7/8" bore.
Restoring my RHD 69 Jane in Melbourne, Australia.
http://www.usmuscle.com.au/Forum/showthread.php?t=2840