Remember that the original drum brakes were designed to stop much smaller tires. Even the larger 11x3" brakes were originally designed to stop bias ply's that were fairly narrow (although on a heavier car). Now, the BBP 10x2.5" rear drums were deemed acceptable on RWD production cars up until '89, but again, that's for OE width tires with relatively hard compound tires. Even based on the ability to "skid" the tires the rear drums become less effective if you're going to wider tires with softer performance compounds. All of that additional grip makes it harder to lock the wheels, and transmits more heat to the brakes. And of course just being able to skid the tires is a poor measurement of braking ability. A rapid brake application can cause a skid- the short, sharp, impulse makes it easier to skid the tire than a slower one, even when the same brake force is reached and surpassed (back to static vs dynamic coefficients, a short impulse overrides and puts you in static mode) So, just because you can stab the brakes and lock them up doesn't necessarily mean that you can exert the same amount of braking force when everything is still rolling (although that's a theoretical discussion, the real life window for that would be small).
The biggest advantage to the disks isn't braking force anyway, the larger drums can provide enough braking force under ideal conditions. The biggest problem with drums is keeping them adjusted properly so you actually have ideal conditions. Self-adjusters don't always do that, look at how they work. For example, if you back out of a driveway and always turn the same direction, you'll find that the wheel on the outside of that turn will lock up first somewhat frequently. Happened to me more than once, for a long time I always parked and backed out of my driveway to go one direction (work). And when I backed out of my spot at work, you guessed it, same direction. Those were the most frequent times I backed the car. That's when the drums adjust, so every now and then the outside tire, which is turning more, gets that extra click on the adjuster while the inside one doesn't. So, on more than one occasion I found myself locking up my right rear tire during panic stops. Sure, it wasn't ALWAYS like that, it would even out pretty quickly with the adjusters, but it only takes one panic stop gone wrong to make for a bad day. Disks are much more consistent from that standpoint.
And of course there are other factors. Heat buildup for the drums, although in normal driving conditions that's not usually a problem. Wet weather conditions, which may not be an issue for most driver's of classics since they're fair weather only drivers, but for daily use that wet weather braking is important. And another overlooked area so far, pad compound. That will be especially true for 11x3's like the OP has, because they're not widely available. Pick a rear caliper that is commonly used for performance cars and you'll have access to every pad compound under the sun. Stick with drums and you usually have two choices, organic or semi-metallic. That's the nice thing about Dr. Diff's kits using Mustang Cobra calipers, you can get anything you want for pad compound and that can significantly improve braking force, modulation, heat, etc. There's a lot to pad selection on anything other than a driver.
I don't know what calipers the MasterPower kit uses, I would look into that for pad availability. Same for the Wilwoods. Sure, you can order them easily, but the local parts store usually won't carry them.
So really it comes down to application, as always.
I welcome any opinions/ ideas. I will also do a poll and see how the votes go.Thanx..
