I have a 70 challenger that has manual brakes w/front disk. I am in the process of installing a 66 b-body rear and thinking about what brakes to run. I am going to run a 15 inch wheel so i think I would be limited to a 12 inch rotor with disks.My question is other than ease of brake service what would be the advantages (if any) of going to disk rather than 11 inch drums?(I am planning to keep it manual either way).

I've got Dr. Diff's Mustang Cobra-based kit on the back of my Charger which has 15s. I like the extra safety margin and decreased chance of smashing a very hard to replace front clip. I've got F-body front disks with a manual master cylinder. I love the setup, using a '73 Charger distribution/proportioning/block/valve/whatever it's called.

The advantage to rear disc is not nearly as great as just adding front disc. Most of the braking effort is done in the front. For this reason I won't spend a large sum of money to add rear disc to any of my cars. I might consider making my own setup at some point in time, but not very soon.

IMO, it comes down to cost and use. If it's just driven on the street, it's not worth it to me to go to disc rears. If you're racing it, especially road racing, the discs would be a good idea. If price doesn't matter, then go with the discs.

The only reason other than perhaps maintenance/parts availability is for looks. If you want to impress that 17 year old boy down the street wit the 5.0 Mustang you'll need rear discs.

It's a fallacy that discs on the rear offer better braking. First, we all know the rear of the car doesn't do much braking anyway. Second, a drum brake has no trouble locking the rear wheels if called upon to do so, so what is a disc going to add?

Where discs excel is in REPEATED hard stops - not the first hard stop. For a track car that means something but on a street car? Do you almost slam into a Dually, then re-accelerate and try it again right away? Nope.

In fact, most people who look down on drum brakes have never driven a car with properly set up drum on all 4 corners. Drum actually have a much nicer pedal feel than discs.

My brother put rear discs on his car and it doesn't stop any better at the end of the track than it did with the drums. Looks cooler, but it was a waste of money. Also the kit he bought has no provision for a parking brake. The car is an automatic so it's not a big deal. If it were a stick car then having no parking brake is a bad idea.

Does his car have to pass state inspection where he lives? Here in TX you must have a working e-brake.

Inspection or not I need an e brake because the cars going to be a 4 speed. Mostly going to be street driven. If it is raced it will be in a strait line. If it matters the car is 100% steel with a full interior and an aluminum headed big block.(just thought knowing about the weight might help)

Yup, I agree good for looks and impressing (some) people.
Otherwise, save your money......unless you do a lot of road racing

Discs aren't going to be thet much of an improvement.

Don't need em , but they look COOL !

Rear braking is much more limited by tire adhesion than it is anything else. Rear discs look cool but for me, the money is better spent elsewhere.

Sheldon

just put some 11 inch drums on it and drive it

In case you haven't noticed, the quality of drum parts (hardware)has really gone down the tubes in the past 10 years.

Go buy a hardware kit and you'll get crap made in China that in no way equal what was shipped on your car. I've seen lots of self adjusters (star wheels) where the teeth were so poorly formed they won't function.

Rear disc brakes have a few advantages and a few disadvantages. Tough call to make for a street car. The more serious the car the more the balance tips in favor of rear disc brakes.

There are only a few good options for rear disc brakes on a Mopar. A lot of the kits that are available are poorly designed. Some require ball bearings rather than tapered roller bearings and some of the kits don't fit at all. The DoctorDiff kit is the best one I've seen but there are probably a couple of other kits that are also fairly decent.

I had mopar 11.75" disc up front and 11.5" crown victoria front rotors on the rear. I did the front disc first, and the rear disc made a big improvement over the 10" drums that were in there before. But this is on a close to 4,000 lb charger with wide rear tires, so they may not work as well on a smaller car. I've read that rear disc are good for a 20-30 ft stopping distance reduction from 60 mph which is at least a car's length. To get the most of rear discs you need an appropriate booster/master cylinder. I went with a hydroboost because I couldn't find a disc/disc vacuum booster for a mopar.