10" or 11" brakes?

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halfafish

halfafish

Damn those rabbits, and their holes!
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I'm putting together the 8-3/4 for my 69 Dart. Currently it's a 340/727 car, but I do have a 383/A833 I may go to. I have a complete setup, paid for, of 10" BBP rear drums on hand. I have everything to go 11" drums except the shoes and drums, which are easy enough to find. For fun, maybe even a little spirited street driving and corner carving, is there any huge difference between the two brake sets? Cost isn't really an issue, more of performance wondering if the 10" is enough, or if I should go 11". Front brakes are the 73+ disc BBP upgrades.
 
Since most of the braking is done with the fronts I think it is more a factor of body weight. A body's are relitivly light and 10x 1.75 to 10x2.5 were standard.

Worst thing to happen is to increase the rear braking ability and have the rear lockup and swap ends

Just my opionion
 
Depends on what you do in the front. If you stay with the 10.87” disks in the front then the 10x2.5” drums in the back will be fine. You can run the 11x2.5” drums, but you’d probably need to use 7/8” wheel cylinders to keep the brake bias right. So at that point you’re just adding a bunch of weight for not much improvement in actually stopping.

But, if you use the 11.75” disks up front the 11x2.5” drums out back are a great addition. And if you’re planning any corner carving the larger fronts will help a lot. Some of it of course depends on your tires. I ran 11.75” disks and 11x2.5” drums on my Challenger for the entire time I was driving it, so 70k miles. They worked great. And I ran the same combination on my Duster for awhile too before I went to DoctorDiff’s 13” disk kit. And I ran those with the 11x2.5’s for quite awhile, they worked well.
 
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money is not an option ??? why even bother with rear drums ?? go with a rear disk brake set up !!!
 
11" drums are heavy!!! I think the drums are close to 30 lbs each.That means you have to accelerate that mass to get the car moving. If you did an A-B test, your car would accelerate slower with the 11". Sounds like you are more interested in drag racing anyway with those different tire sizes.
Corner carving to me means more handling with not much braking. Unless you are going downhill or doing multiple maximum stops in a row.
 
KosmicKuda said:
11" drums are heavy!!! I think the drums are close to 30 lbs each.That means you have to accelerate that mass to get the car moving. If you did an A-B test, your car would accelerate slower with the 11". Sounds like you are more interested in drag racing anyway with those different tire sizes.
Corner carving to me means more handling with not much braking. Unless you are going downhill or doing multiple maximum stops in a row.
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It does depend on what drums you use too. A lot of the 11x2.5" drums are finned, which makes them heavier. But it also makes them dissipate heat better, so it's a trade off. There used to be non-finned 11x2.5" drums available but I haven't looked recently. You'd have to be johnny on the spot with a stop watch to notice the difference unless you've got a stock /6. With a half decent 340 or 383 like the OP has you're not going to feel the difference in acceleration on the old butt dyno. My Challenger basically had a stock 318 in it, and even with 3.23's I never had an issue spinning up the 275/40/17's I had on it if I wanted to. I'm not saying adding rotating mass is good, it's not, but 10x2.5" vs 11x2.5" on the brakes isn't adding so much weight that it's immediately noticeable. The braking difference is noticeable though.
 
I took another look at the brakes, the rears are 11x2" not 2.5". The drums must be lighter, they are about the same as the 10" ones I took off.
 
halfafish said:
I took another look at the brakes, the rears are 11x2" not 2.5". The drums must be lighter, they are about the same as the 10" ones I took off.
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The 11x2's were all non-finned iirc, it's the finned 11x2.5" drums that are super heavy. Not as much selection for drums and shoes for the 11x2's but they're out there. If you have all the stuff for 10x2.5" and not for the 11x2's I'd probably just use the 10x2.5's unless you're gonna run 11.75" rotors up front.
 
72bluNblu said:
The 11x2's were all non-finned iirc
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You are correct sir, these are non-finned. The 10" brakes coming off are SBP and only the 1-3/4" wide versions. I do have an entire setup for the 11x2. The drums can be turned and I will get a full rebuild kit for it.

@maddawg57 what year/model van did your 11x2 drums come from? The local parts guys can't order anything if they don't have year, make, and model.
 
halfafish said:
You are correct sir, these are non-finned. The 10" brakes coming off are SBP and only the 1-3/4" wide versions. I do have an entire setup for the 11x2. The drums can be turned and I will get a full rebuild kit for it.

@maddawg57 what year/model van did your 11x2 drums come from? The local parts guys can't order anything if they don't have year, make, and model.
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That I am not sure that part was done when I got the car. Narrowed Moser, rear van drum setup, line loc, dual master cylinder ,and adjustable proportioning valve were already on it . All I did was the front disc swap.
 
@72bluNblu I have all the parts for the 11x2 rear drums. I checked the wheel cylinders that spec for those drums, they are 15/16". Your post above says to run 7/8" cylinders, but that was for the 11x2.5" brakes. I am going to run a prop valve when I plumb everything in. Are these 15/16" cylinders workable, or should I look for the smaller ones?
 
halfafish said:
@72bluNblu I have all the parts for the 11x2 rear drums. I checked the wheel cylinders that spec for those drums, they are 15/16". Your post above says to run 7/8" cylinders, but that was for the 11x2.5" brakes. I am going to run a prop valve when I plumb everything in. Are these 15/16" cylinders workable, or should I look for the smaller ones?
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I think you’ll be ok with the 15/16”. The only times I know of that guys liked the 7/8” better they were running 11x2.5’s with the smaller 10.95” front disks. Going up to 11.75” disks eliminates the need to use the smaller wheel cylinders. I would guess that the smaller 11x2’s are a big enough change not to need them too. But a lot of that will depend on your car, it’s weight balance, tires sizes etc. An adjustable prop valve on the rear line would solve that. Or if it locks the rear up prematurely you could always go to the 7/8” wheel cylinders later.
 
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Many thanks for your insight sir! I will report back when I give this a test run or two.
 
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