Author Topic: Rear Brake Standard Diameter  (Read 5179 times)

Camarocards

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Rear Brake Standard Diameter
« on: February 11, 2014, 02:23:05 AM »
Does anyone know what the standard (inside) diameter of a '68 rear brake drum is? The Service manual states that it can be rebored 0.020" over the standard bore but I could not find what dimension the standard bore is.

Thanks,

Bob
Bob
'68 SS L35 01D

69Z28-RS

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Re: Rear Brake Standard Diameter
« Reply #1 on: February 11, 2014, 05:15:19 AM »
I suspect you are referring to the wheel cylinder, rather than the drum?
per this link, the rear drum brake wheel cylinder diameter is stated to be 7/8"  (0.0875 ")..
http://www.partsgeek.com/catalog/1968/chevrolet/camaro/brake/drum_brake_wheel_cylinder_repair_kit.html
I don't have my service manual handy, so this was the best I could do. 

PS.   The drum itself will have a specification stamped into it; how much it can be turned down is generally stamped into the back edge of the drum.   
There is also a angle cut on the back inner edge of the brake surface, which can be used as a quick indication of how much it could be turned down...
Gary W / 09C 69Z28-RS, 72 B 720 cowl console rosewood tint
69 Corvette convertible, silver/black 350 hp,
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Camarocards

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Re: Rear Brake Standard Diameter
« Reply #2 on: February 11, 2014, 11:56:36 AM »
Thanks Gary. I am indeed referring to the drum not the wheel cylinder. I too, thought that the maximum rebore diameter would also be on the drum but unless I'm totally missing it, it's not on the drum. The only thing I've found is a part number and a (casting date?) code. See pics below.

Thanks,

Bob
Bob
'68 SS L35 01D

Camarocards

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Re: Rear Brake Standard Diameter
« Reply #3 on: February 11, 2014, 12:23:56 PM »
For what it's worth, I found the article below which states that the maximum allowable inner diameter of the drum was not cast into the drum until 1971. Don't know whether or not this is true.

Bob
Bob
'68 SS L35 01D

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Re: Rear Brake Standard Diameter
« Reply #4 on: February 11, 2014, 02:46:35 PM »
The Service Manual should have the correct information if you can't find it anywhere else.  I may have a '67 Service Manual; I'll check later today if no one else responds who has it more 'handy'..   Basically you want to know the maximum diameter to which the rear drum can be turned down.
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

Camarocards

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Re: Rear Brake Standard Diameter
« Reply #5 on: February 11, 2014, 03:22:25 PM »
Gary, yes, that is exactly want I'm after. Couldn't find it in the '68 Service manual but maybe it's listed in another manual??

Thanks!
Bob
'68 SS L35 01D

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Re: Rear Brake Standard Diameter
« Reply #6 on: February 11, 2014, 04:21:30 PM »
The last time I carried a brake drum to have it turned, the shop had a data base which told them a maximum for turning it, based on the year/type of car (but O'Reilly's data differed slightly from the information printed on my drum).  I have no idea if all '67/68/69 rear drums are the same size or not...  Does it matter if it's a 10 bolt or 12 bolt rear?   Does it matter if your front brakes are drums or disks?  I don't know the answer to those questions without research.   Have you checked the CRG data base to see if that is covered??
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

Camarocards

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Re: Rear Brake Standard Diameter
« Reply #7 on: February 11, 2014, 04:33:07 PM »
Yep. That was one of the first places I looked but came up empty handed there as well. Perhaps I'll give my local Midas shop a call to see if their DB goes back that far.
Bob
'68 SS L35 01D

Petes L48

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Re: Rear Brake Standard Diameter
« Reply #8 on: February 11, 2014, 04:58:58 PM »
The 67 service manual also says your can rebore to .060 over, if you use .030 oversized shoes.  According to the Specifications Section 5 of the manual, the drums are 9 1/2 inch diameter. 

 

69Z28-RS

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Re: Rear Brake Standard Diameter
« Reply #9 on: February 11, 2014, 06:03:33 PM »
The 67 service manual also says your can rebore to .060 over, if you use .030 oversized shoes.  According to the Specifications Section 5 of the manual, the drums are 9 1/2 inch diameter.  The standard brake drum diameter for camaro models (9.5") is found in the service manual in the rear specification section 5, and is the same for Chevelle, Nova, and Camaro models.

Pete beat me to it, and what he says is correct.   You can turn the brake drums a maximum of 0.020 inches over the 9.5" std diameter and still use 'standard brake shoes.  If your drums need turning to more than 9.520, then you should turn it to 0.060" over *(ie.  9.560") and use shoes which are 0.030 'oversize' in order to maintain proper braking.   I'd suggest you make sure the 030 oversize shoes are available before following this path... :)

PS.  I have both '67 and '69 Chevy Service Manuals, they both read exactly the same, so I'm certain the '68 is identical.. :)
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

Camarocards

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Re: Rear Brake Standard Diameter
« Reply #10 on: February 11, 2014, 06:11:41 PM »
Thanks. I did notice that manual states that it could be bored 0.060" over (attached picture) but no reference to what the standard dimension is.

What I have now just discovered is that there is no section 5 in the Specifications section of the '68 Service manual. If goes from Section 4 (Rear Axle) to Section 6 (Engine)! Maybe that's why I couldn't find the standard dimension!   ;D
Bob
'68 SS L35 01D

Camarocards

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Re: Rear Brake Standard Diameter
« Reply #11 on: February 11, 2014, 06:21:18 PM »
Many thanks Pete and Gary. Mystery solved!

For what it's worth, attached are 3 consecutive pages of the '68 manual which shows the omission of section 5.
Bob
'68 SS L35 01D

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Re: Rear Brake Standard Diameter
« Reply #12 on: February 11, 2014, 06:36:52 PM »
Someone wanted that page more than the manual wanted to keep it?  :)   Those pages are easily torn out and lost.
Maybe someone who has the '68 manual can scan that page and provide it to you?
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

lakeholme

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Re: Rear Brake Standard Diameter
« Reply #13 on: February 11, 2014, 07:10:32 PM »
Someone wanted that page more than the manual wanted to keep it?  :)   Those pages are easily torn out and lost.
Maybe someone who has the '68 manual can scan that page and provide it to you?


Well, I've got good news and bad news!  The good news is:
My 68 manual does not have a section 5 either....
And the bad news is:
My 68 manual does not have a section 5 either....
Apparently the 68 reprints are all missing a section 5.
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69Z28-RS

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Re: Rear Brake Standard Diameter
« Reply #14 on: February 11, 2014, 07:20:54 PM »
The best I can do is provide you the Brake Specs from the '69 Service Manual:  (attached)..
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