I am building a Dakota for drags,and want the lightest, cheapest rear brakes possible. Will the 9 backing plates and drums work on an 8 3/4? FWIW, I am using aftermarket 35 spline axles.

only 9" brakes that work an an 8 3/4 are early A body ones with the 4" bolt pattern, the flange offset is different as well. Which basically means not compatible with your existing axles.

10 drums are the cheapest lightest swap, right now.

cheapen too much and you won't be able to stop.

well, there IS usually a fence down there, or a sand trap, or a river.

Aerospace makes the lightest IIRC, or LAMB.

Your Dakota might have come with finned drums, drums without fins are available in both 10" and 11" and should be lighter.

Way out side the cheap parameter though

Strange "S-Series" rear disc.

I have a set of 11" backing plates, and whatever the 8 1/4 in the Dak came with. What is the lighter setup, the narrow 11" drums or the wide 10"?

rockauto lists weights of the drums.

not sure what a narrow 11" is.

or a wide 10".

applications?

For the 87 M body the 10" is 19lbs, 11": is 23lbs for just the drums.

Guess you can figure which is more all together (hint 11")

Steve - actually the 11" incurs a double penalty. The majority of the drum's mass is at the perimeter, this means the rotational inertia is much higher. So, in addition to the extra weight you have to accelerate and carry unsprung, you also have to accelerate this mass rotationally! That is why a disk brake rotor, even if it weighs about the same, is better for racing. The mass of the rotor is distributed differently and its moment of inertia will be lower (given the same total weight).

Oh I agree a disc setup is "lighter" in use but cheaper? Most disc kits are a lot more than a stock drum setup, especially if you already have it on hand. Just trying to stick to the cheapest parameter.

Example, using Dr Diff's site for reference, 10" drum setup complete is $350, cheapest rear disc kit, for drag race use only no E brake which is important if they do safety inspections for registration like in TX, is $509. No weights listed for either. Cheapest rear disc with e brake is $600.

If I had no brakes to begin with I'd probably go with a disc setup in back myself.

Thanks for the physics lesson. I will know what I have to work with this weekend, and go to the junkyard if needed.