Author Topic: Rear drum size with big block ? Difinitive answer?  (Read 351 times)

Offline Matt1968

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Rear drum size with big block ? Difinitive answer?
« on: March 06, 2017, 08:06:14 PM »
I have searched and it only has lead to confusion.  68 390 GT,  I know the drum diameter is 10",  but I read where people have insisted that the (pad) width is 1 3/4",  then some are saying 2"  and some are saying 2.5"

Anyone?

Offline ruppstang

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Re: Rear drum size with big block ? Difinitive answer?
« Reply #1 on: March 06, 2017, 08:24:13 PM »
If it has discs up front it should have 1 3/4 pads on the back. If drums all around them 2 inch on the back.

Offline Andrew@MagMustangs

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Re: Rear drum size with big block ? Difinitive answer?
« Reply #2 on: March 06, 2017, 08:52:59 PM »
The brakes are defined by their 'Shoe Width' and the brake drum should have some extra width on the shoe surface to allow spacing on both sides of the shoe. ie; if your drum has a 2" full width on the brake surface then it wouldn't fit 2" width shoes, it would fit the 1.75" width shoes.
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Offline Matt1968

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Re: Rear drum size with big block ? Difinitive answer?
« Reply #3 on: March 07, 2017, 01:41:14 PM »
If it has discs up front it should have 1 3/4 pads on the back. If drums all around them 2 inch on the back.

A big block car has the small pads?  Had no idea

Offline sportyworty

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Re: Rear drum size with big block ? Difinitive answer?
« Reply #4 on: March 08, 2017, 12:22:13 AM »
All 68 V8 Mustang/Cougar cars used the dual groove 2.00" drum that utilized the 1.75" shoes. In 1969 they went to the 2.25" drum and 2.00" shoe.

Offline preaction

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Re: Rear drum size with big block ? Difinitive answer?
« Reply #5 on: March 09, 2017, 09:51:26 PM »
Service manual calls for 1 3/4'' for replacements, always a quick and easy way to look.
8R02S125064- January 6 1968  SJ   7F93S591808 - April 28 1967  Dearborn   7F91S544039 - December 17 1966 Dearborn

Offline ruppstang

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Re: Rear drum size with big block ? Difinitive answer?
« Reply #6 on: March 11, 2017, 10:06:27 AM »
All 68 V8 Mustang/Cougar cars used the dual groove 2.00" drum that utilized the 1.75" shoes. In 1969 they went to the 2.25" drum and 2.00" shoe.

Kerry where did you find this information, service manual?
I found mine in a Bendix parts service book. I must have read it incorrectly or it was incorrect.

Offline sportyworty

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Re: Rear drum size with big block ? Difinitive answer?
« Reply #7 on: March 12, 2017, 12:20:22 PM »
My information is from studying original cars. I provide complete rear assemblies for 68-70 428 CJ and B2 cars. You will find that the 428 Reg and SAAC have discussed the 1968 Brakes several times over the years in the archives. Someone may have posted some literature as some point. We are all in agreement that big suspension cars received the same size brakes as the small suspension cars. I source most of the drums and backing plates from the more common small block cars. The dated coded dual groove 2.00 wide drum is what was used until the up size in 1969 production too the 2.25 Drum.

Just a note that the 1968 MPC (very rare) is the manual to have for correct 1968 line parts. The later manuals are full of replacement and service parts used after production. I have a set of 74-75 MPC and have found them to be of little value.

Offline ruppstang

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Re: Rear drum size with big block ? Difinitive answer?
« Reply #8 on: March 12, 2017, 12:41:07 PM »
Thanks for the explanation.

Offline sportyworty

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Re: Rear drum size with big block ? Difinitive answer?
« Reply #9 on: March 12, 2017, 04:49:23 PM »
You are very welcome sir

Offline preaction

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Re: Rear drum size with big block ? Difinitive answer?
« Reply #10 on: March 12, 2017, 07:22:35 PM »
Kerry, can you comment on how helpful a August of 69 MPC would be ?
8R02S125064- January 6 1968  SJ   7F93S591808 - April 28 1967  Dearborn   7F91S544039 - December 17 1966 Dearborn

Offline sportyworty

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Re: Rear drum size with big block ? Difinitive answer?
« Reply #11 on: March 12, 2017, 09:36:31 PM »
Paul I would consider the Fall 69 MPC to be a good source for 68 and of course excellent for 69. These loose leaf binder pages were updated almost monthly. The problem can be the fact that most counter people inserted the updates and tossed the original. If a part is superceded often times considered better or a supplier change it may not be the part installed on the line or be referenced. For some reason the 67 and earlier MPC are easier to find. The 68-70 are really tough to find.

Offline J_Speegle

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Re: Rear drum size with big block ? Difinitive answer?
« Reply #12 on: March 13, 2017, 07:18:30 PM »
Paul I would consider the Fall 69 MPC to be a good source for 68 and of course excellent for 69. These loose leaf binder pages were updated almost monthly. The problem can be the fact that most counter people inserted the updates and tossed the original.....

+1 My 67 version has a spattering of spring 68 pages intermixed with the earlier pages. Pretty typical as you offered
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