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11 inch drums? Or how to attack this 8 3/4?

CaseyCuda

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Well I'm staring at my rear end with a cool question. As you might have seen or noticed my car is a junk yard salvage story and the rear drums are missing all the hard ware inside the drums. I saw on eBay a set of 10 inch drums with all hardware. So I measured mine and the drums on this rear end are 11 inside diameter and skinny compared to the front drums. I'm not a expert here and it's a 1970 barracuda with a 8 3/4 with a 489 case and 3.23 gears open rear end. For a stock 318 car I don't think this rear end is correct. Can I get some help? And advise on the drums?
 

moparleo

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The most critical parts are the backing plates. Do you have them and what do they measure? " Rear drum brakes are not unusual with a four wheel drum car. On a front disc car, the fronts do 80% of the stopping so doesn't require large rear brakes. The best thing to do at this point is round up the parts for a disc brake conversion. You will never regret it. If you have never driven an old car with four wheels drum brakes before, get ready to scare your self. After a few hard stops the brake shoes heat up and your car will go which ever direction it wants to go. And the harder you try to stop, the worse it gets. Oh and forget about stopping after you drive through a large water puddle or in the rain. It will just keep going. Safety is the reason that the whole automotive industry went to disc brakes as standard equipment form late 72 and up.
 

challenger6pak

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No, it is not correct. You can use them (11 inch) if you go with disc in the front and proportion the front to rear braking correctly. Right now your braking will be unbalanced and could cause a spin out in the right situation.
 
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CaseyCuda

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Ok the backing plates measure 12 from rim to rim. I already have front disc brakes off of a 76 volare. I was thinking of going with drums in the rear for cost sake. But right now it's apart as I wait to buy a Detroit locker. How hard would it be to find a disc brake for a 8.75 with 30 spline axels. And anyone got a clue what this rear end came from. I thought it should have been a 741 or 742 not a 489. I know there is mixed feelings about the 489.
 

challenger6pak

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No way to know what the rear came from without measurements. It may be the original rear with larger brakes added. What are your plans with the car? You should be fine with the disc and drums. As Leo pointed out, 80% of the braking will come from the front disc.
 

CaseyCuda

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Thanks Leo and sixpack. My plans are a solid driver with some weekend dragging in the summer. Not looking to make it a daily driver or picture perfect resto. Why I was ok with the drums. Well if these 11 inch drums are salvageable (one needs to be turned) know any good source for the hardware. Or maybe I should go with these 10 inch from eBay. I know disc will be more expensive but if the price gap is small let's see.
 

challenger6pak

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Use the Volare front disc. They are good brakes. You will need an adjustable proportioning valve to dial in the rear 11 inch drums. You will also need a disc brake master cylinder. The brakes will work great with your plans for the car. When you say Locker rear, do you mean a sure grip? A complete locker rear will not work well on the street.
 

CaseyCuda

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Nope I tried to find a sure grip and finally just settled on getting an eaton locker for a 8 3/4. I looked at auburn and I'd rather a locker over a spool.
 

Cazbah362

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Casey = couple of thoughts. 11' brakes are a desirable setup with many parts readily available and within budget at places like Rock-Auto (78 Cordoba is what I am using). Why not use them? A proportioning valve could be purchased from anywhere, sounds like you will need one anyways, there about $115 for a Wilwood at Summit.

As for the rear end parts, I would call or check Dr. Diff website, many of the parts are there too (http://www.doctordiff.com/). Also, he has many of the disc brake setups, lockers etc you have spoken about. He also had rear disc kits if you really want to go that way.

And 742 and 489 are the desirable chunks (carriers) due to the pinion size and setup methods, you will find many more parts out there for the 489, especially gear sets, 742 will come in a close second.

As a driver and not a hanger queen one off numbers matching setup, this would work very nicely and can be sourced on a budget.
 
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CaseyCuda

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Thank you for the info and the site. I will price these and get according. The 11 inc drums were the first direction ANd as you say being a driver I want to have fun but not kill my budget. Thanks again.
 
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