Author Topic: Rear Brake Standard Diameter  (Read 5178 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

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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...
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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
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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
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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.
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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
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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
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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
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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. 

 

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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.. :)
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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
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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
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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
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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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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
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Camarocards

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Re: Rear Brake Standard Diameter
« Reply #15 on: February 11, 2014, 07:40:55 PM »
Well how about that! I thought I was the only one that was missing that section.  ;D

Thanks for the '69 section 5. I'll keep it with my '68 Service Manual and until someone else comes up with section 5 for the '68 version.

Thanks again!
Bob
'68 SS L35 01D

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Re: Rear Brake Standard Diameter
« Reply #16 on: February 11, 2014, 08:00:57 PM »
FWIW, here's the sheet out of the 67 chassis repair manual.  Put it with the 69 spec sheet and maybe they'll have a baby  ;D  The specs for turning front discs is found in Section 5, page 5-29 of the 67 manual.




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Re: Rear Brake Standard Diameter
« Reply #17 on: February 11, 2014, 08:09:38 PM »
Well how about that! I thought I was the only one that was missing that section.  ;D

Thanks for the '69 section 5. I'll keep it with my '68 Service Manual and until someone else comes up with section 5 for the '68 version.

I don't believe the '68 Chassis Service Manual has a section 5 in the specifications section.  My mint '68 Chassis Service Manual (copyright 1967) doesn't have it.  I checked my '69 Chassis Service Manual (copyright 1968) and it does have a section 5.  One thing I noticed is, if you look at Gary's photo of the '69 section 5 page (reply #14), you'll see Section 5 is in parentheses while none of the other sections are!  Why?
???

Paul

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Re: Rear Brake Standard Diameter
« Reply #18 on: February 11, 2014, 08:21:03 PM »
Well how about that! I thought I was the only one that was missing that section.  ;D

Thanks for the '69 section 5. I'll keep it with my '68 Service Manual and until someone else comes up with section 5 for the '68 version.

I don't believe the '68 Chassis Service Manual has a section 5 in the specifications section.  My mint '68 Chassis Service Manual (copyright 1967) doesn't have it.  I checked my '69 Chassis Service Manual (copyright 1968) and it does have a section 5.  One thing I noticed is, if you look at Gary's photo of the '69 section 5 page (reply #14), you'll see Section 5 is in parentheses while none of the other sections are!  Why?
???

Paul,
I ordered my manuals from Helm in 1976 after purchase of my car.  It also is copyrighted 1968. Are you saying that your Section 5 in your spec section is not in parenthesis?  or it is?  :)    Curiousity killed the cat you know..  :)   but if it killed humans, I'd have been dead by age 12.. :)
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Re: Rear Brake Standard Diameter
« Reply #19 on: February 11, 2014, 08:29:33 PM »
Gary, my service manual is the same as yours... (SECTION 5).  I just referenced your photo so other members could see what I was saying.  There must be a reason for the parentheses.

Paul

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Re: Rear Brake Standard Diameter
« Reply #20 on: February 11, 2014, 08:32:56 PM »
OK..   :)    seems you have the same 'curiousity' affliction that I have.. :)
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Re: Rear Brake Standard Diameter
« Reply #21 on: February 11, 2014, 09:19:18 PM »
Yup, it amazing we are both still alive!   ;D

Paul

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Re: Rear Brake Standard Diameter
« Reply #22 on: February 11, 2014, 09:24:29 PM »
Yup, it amazing we are both still alive!   ;D

Paul

I had my first car wreck at age 6..  how old were you?  :)
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Re: Rear Brake Standard Diameter
« Reply #23 on: February 11, 2014, 09:26:14 PM »
Five and a half!   ;)

Paul

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Re: Rear Brake Standard Diameter
« Reply #24 on: February 11, 2014, 10:08:20 PM »
Well, I'm glad you guys survived to share those brake specs!

Well how about that! I thought I was the only one that was missing that section.  ;D

Thanks for the '69 section 5. I'll keep it with my '68 Service Manual and until someone else comes up with section 5 for the '68 version.

Thanks again!

X2, thanks guys!
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Re: Rear Brake Standard Diameter
« Reply #25 on: February 11, 2014, 11:08:00 PM »
Five and a half!   ;)

Paul

Mine was in an old brown '50 Ford tudor (my dad's hunting/fishing car) that was parked against a shed over his boat..  I was just TOO curious not to push that little round chrome button while 'pretending' to drive it.. and I got more than I bargained for, both when the car jumped forward against one of the supports for the shed, and a second time when dad got home....   :(
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68Zproject

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Re: Rear Brake Standard Diameter
« Reply #26 on: February 11, 2014, 11:11:33 PM »
I have a chassis service manual (68) and it has section 5 (brakes).
68Z28

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Re: Rear Brake Standard Diameter
« Reply #27 on: February 11, 2014, 11:13:41 PM »
I have a chassis service manual (68) and it has section 5 (brakes).

Is your service manual dated?

Paul

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Re: Rear Brake Standard Diameter
« Reply #28 on: February 11, 2014, 11:24:26 PM »
I have a chassis service manual (68) and it has section 5 (brakes).
...a section 5 under Specifications?
Please post it....
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Steve68

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Re: Rear Brake Standard Diameter
« Reply #29 on: February 11, 2014, 11:58:33 PM »
No section 5 spec page in service manual specification section. Page 5-21 contains the information you're looking for.......0.060 is max.
« Last Edit: February 12, 2014, 12:42:44 AM by Steve68 »

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Re: Rear Brake Standard Diameter
« Reply #30 on: February 12, 2014, 03:59:42 AM »
Section 5 in the Specifications at the back had (or would have had) some additional data, including torques and nominal dimensions of the brake drums and shoes...  It seems the '68 SM had a glitch (either in the initial release or ??)..
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Re: Rear Brake Standard Diameter
« Reply #31 on: February 12, 2014, 06:03:15 PM »
Section 5 in the Specifications at the back had (or would have had) some additional data, including torques and nominal dimensions of the brake drums and shoes...  It seems the '68 SM had a glitch (either in the initial release or ??)..

Gary, it would be good to have the charts that are in the 67 and 69 for quick reference, especially the torque chart.  I compared page 5-21 that Steve mentions in the 68 SM, and it is virtually the same as 5-22 in the 67 SM.

Think maybe the same guy that decided we didn't need options listed on the cowl tag in 68 was in charge of the SM?  ??? ;D ???
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Re: Rear Brake Standard Diameter
« Reply #32 on: February 12, 2014, 06:11:26 PM »
Section 5 in the Specifications at the back had (or would have had) some additional data, including torques and nominal dimensions of the brake drums and shoes...  It seems the '68 SM had a glitch (either in the initial release or ??)..

Gary, it would be good to have the charts that are in the 67 and 69 for quick reference, especially the torque chart.  I compared page 5-21 that Steve mentions in the 68 SM, and it is virtually the same as 5-22 in the 67 SM.

Think maybe the same guy that decided we didn't need options listed on the cowl tag in 68 was in charge of the SM?  ??? ;D ???

I've already returned my manuals to their 'basement' storage spot.. :) , but I recall that the 'brake drum' information in the main Section 5 was the same information in the '67 and '69 manuals.   In the Specifications (at the back of the SM), the '67 manual contained separate charts for 'Torque Settings' and 'Brakes', but the '69 manual combined this information into a single chart (which I scanned and posted on an earlier post).   A quick review of those two charts did not indicate any differences in the information, just that the two charts were combined into ONE for the '69 manual.   I think from this you'd be safe to rely on information from either the '67 or '69 SMs to obtain data for your '68.   If you really want the two charts from the '67 manual page, let me know and I will retrieve that manual page and scan/post it.. :)
Going back thru the messages I see that Pete had already posted the two charts from the '67 manual, so you have access to the Specs section for Brakes from both the '67 and '69 manuals.   I'm suspecting that the '68 manuals that some of you have simply had an error for that page to be missing in the specs section (but it should contain the same information as either of the other manuals, unless the '68 was unique and different, which i don't think would be true).

PS.  In an earlier reply in this thread, I posted these comments:
"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..."
On further reflection this might be incorrect:  I was citing data from my front disk rotor, which was the item I most recently had turned.   It's been so long since I turned a rear drum, that I have to renege on that comment above, as I have no idea if diameter/spec data were ever stamped into drums.  Maybe someone else can clarify that issue?
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60 Corvette white/red, 72 Corvette coupe, '70 Mach I 
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72 El Camino, '55-'56-'57 Nomads, '55-'57 B/A Sedan

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Re: Rear Brake Standard Diameter
« Reply #33 on: February 12, 2014, 07:38:22 PM »
Quote
I'm suspecting that the '68 manuals that some of you have simply had an error for that page to be missing in the specs section (but it should contain the same information as either of the other manuals, unless the '68 was unique and different, which i don't think would be true).

I ordered my service and overhaul manuals using the form in the back of the warranty book right after I brought my car home from the dealer.  June build so I would have thought if there was a missing section that Helm would have known by then and fixed it.

Steve

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Re: Rear Brake Standard Diameter
« Reply #34 on: February 12, 2014, 07:53:53 PM »
Steve,

Have you found that same information (from the Torque/Brake) section of the Specifications at the rear, to be located elsewhere within the '68 manual?   If not, then what other conclusion could you draw other than:
1) all you fellas with '68 manuals "lost" that page somehow?
or 2) Chevy/Helm accidentally left it out?

It doesn't do one much good to know he can 'cut' a drum by either 0.020" or 0.060" from std, IF he can't verify what the Std size was...?
Gary W / 09C 69Z28-RS, 72 B 720 cowl console rosewood tint
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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

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Re: Rear Brake Standard Diameter
« Reply #35 on: February 12, 2014, 08:03:36 PM »
I have a chassis service manual (68) and it has section 5 (brakes).
...a section 5 under Specifications?
Please post it....

Not under specifications.  Just under the sections.  Paul, mine is dated 67.
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Re: Rear Brake Standard Diameter
« Reply #36 on: February 12, 2014, 08:30:24 PM »
Quote
It doesn't do one much good to know he can 'cut' a drum by either 0.020" or 0.060" from std, IF he can't verify what the Std size was...?

9 1/2 inches

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Re: Rear Brake Standard Diameter
« Reply #37 on: February 12, 2014, 09:53:52 PM »
Quote
It doesn't do one much good to know he can 'cut' a drum by either 0.020" or 0.060" from std, IF he can't verify what the Std size was...?

9 1/2 inches

The only location I found that dimension was in the specification section (5) which was missing in the '68 SM..
Gary W / 09C 69Z28-RS, 72 B 720 cowl console rosewood tint
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60 Corvette white/red, 72 Corvette coupe, '70 Mach I 
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Re: Rear Brake Standard Diameter
« Reply #38 on: February 12, 2014, 10:48:47 PM »
Quote
It doesn't do one much good to know he can 'cut' a drum by either 0.020" or 0.060" from std, IF he can't verify what the Std size was...?

9 1/2 inches

The only location I found that dimension was in the specification section (5) which was missing in the '68 SM..

It's called extrapolating.  Let's see, the '67 service manual says 9.5" and the '69 service manual says 9.5", I'll bet the '68s are 9.5" too!   ;)

Paul

Steve68

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Re: Rear Brake Standard Diameter
« Reply #39 on: February 12, 2014, 10:55:28 PM »
Quote
It doesn't do one much good to know he can 'cut' a drum by either 0.020" or 0.060" from std, IF he can't verify what the Std size was...?

9 1/2 inches

The only location I found that dimension was in the specification section (5) which was missing in the '68 SM..

The 1968 "AMA specifications-Passenger Car" provides the information.  See page 19, drum, diameter, front, standard 9.5 and disk 11.0, rear 9.5.

Steve
« Last Edit: February 12, 2014, 11:35:21 PM by Steve68 »

Camarocards

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Re: Rear Brake Standard Diameter
« Reply #40 on: February 13, 2014, 01:19:04 AM »
Many thanks to all who have contributed to this thread. I never thought it would have turned out the way it did. I was just looking for an answer that I thought would be easy to provide................if you have a manual that lists it!,  ;D ;D ;D

Thanks again!

Bob
Bob
'68 SS L35 01D