Something like that might work, however at this point, I'm more concerned with what I can afford that will work. I can't do anything like the viper calipers because I don't have the money for the rims to fit over them, nor will I at any point in the near future - money is already allocated to an A833OD swap and front suspension overhaul before anything else.

I'm not swapping out rear ends anytime soon, since I want to keep my 2.93 7 1/4 because I'm probably going to be highway commuting for a while. Unless, of course, I absolutely have to because I can't find rear discs to fit that particular axle. I'd much rather have discs in back than drums (which is what started this whole thread), so I may just do a bunch of junkyard crawling and measuring once it's not hailing/snowing/raining.

I'm thinking the easiest way to go at this point will be if I can find rotors that will fit the SBP rears, figure out calipers and mounting styles (fabricated if I have to) I can just snag a Scarebird disc conversion up front rather than having to find 73+ conversion parts for the front.
I wonder if that conversion kit could be adapted to work both front and rear?
Something else to think about.

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<i>D'Artagnan</i>
<img src="http://img.photobucket.com/albums/v432/stephaniexchaos/dart/th_IMG_0326_zpsumhhfxi0.jpg">

What a interesting thread! I have to say that power brakes are a must, don't do the manual brake thing, especially not with discs. Drum brakes are "self-energizing", discs are not. The rotation of the wheel will tend to expand a drum brake shoe, not so with a disc brakes.

Although it is true that rear drum brakes are just fine for normal service I for one don't enjoy working on drum brakes. Give me disc brakes any time! I was stunned to pay MORE for the rear drum brake parts than I did for rebuilt front disc calipers and pads for my D150--crazy but true. I suppose there is no cost benefit for tossing functional rear drums for discs, but then is there anything about automobiles that makes sense money-wise? I dohave to say that two things are worth fixing/improving in any rig, brakes and steering (in that order). I like to have both, but if given a choice I would really like to stop! A project like this could run into $$ pretty fast I think...

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Slanted D150

Power is absolutely NOT necessary. I used a 75 Dart manual master cylinder for my car (4 wheel disc) and it is just fine. Pedal effort is only slightly more than power brakes....feel is way better.

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Yeah....Im the one who destroyed this rare, vintage automobile.....

My D150 had manual disc brakes when I grabbed it off the farm--they DID work. I put power brakes in it regardless--I found the braking to be greatly improved over manual footmashing. Too each his own...Stopping is the desired endpoint, how you manage that is up to the owner.

I have found that when people want disc brakes (converting from drum brakes) that what they really want is "stronger" braking action. I can recall at least 8 Mustang projects I worked on where the owner wanted disc brakes--we suggested trying power brakes first, 6 of those people stuck with the power drums. Note: I am NOT advocating drum brakes however, all things being equal discs win on a bunch of levels--if you want to spend the money.

Power brakes showed up for a reason, boosted hydraulic systems are a pleasure to drive (if they are tuned nd designed right), getting a strong right leg from mashing a pedal isn't my idea of fun. In any case, you are right in that you don't NEED power to operate disc brakes--I am simply pointing out that disc's lack the self energizing nature of drums and therefore the pedal force required might surprise the driver the first few times. I still vote for power brakes...

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Slanted D150

I agree, the feel in a car manual disk brakes are much better than a truck where power assist might be better (bigger heavier vehicle), I have used manual disks in the heavier late dusters and they have better controllability in foot pressure than power discs (which have a tendency to lock up the wheels a bit sooner...) I have stopped my hpak duster from 120 mph many times and manual works great and stops very well compared to drums... also if you use a power booster in an A-body you will limit yourself on manifold selection if upgrading past the supersix in some instances...

But as always to each person they can make their own choice...

-D.Idiot

I suspect the best thing you do if you want rear disks is look for the Grand Cherokee setup and bolt them on. Should work for either the 7.25 or an 8.25 (if I read correctly), and if you are patient you should be able to get them for a reasonable price. I think there is a couple of sets at Pull & Save right now, but I'm not sure if the rear end is the 8.25 or Dana 30 (or if it makes a difference).

Since you don't seem to be in a hurry, I would suggest you keep your eyes open and look for an 8.25". They are getting harder to find, but they are not impossible and if you have time on your side it would be easier. It always seems like the most money is spent when you've broken what you have and need a new one to get it on the road. If you aren't stuck, just keep your eyes open and your ear to the ground.

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'15 Chrysler 200S V6
'74 Duster 360, factory 4 speed car

I was going to start a new thread with this question, but it does pertain so I will just put it here. I know it doesn't fit the budget of the originator of the thread, but it does fit where the discussion has gone, and maybe it will be useful info.

Andy, what kind of a ratio do you suggest? I took a brake torque formula and worked up some numbers to compare the ratio's between the front and rears of a couple of higher end cars, and they seem like they are all over the place. These numbers do not take into account flex in the calipers, front to rear proportioning, or different pad friction co-efficients.

C5 Corvette - 1.75:1 (front/rear)
Mustang Cobra - 2.25:1
Gen I or II Viper - 2.22:1
Gen I or II Viper with 40mm rear caliper mod - 2.00:1
Gen III Viper - 1.11:1

The C5 Z06 used the same calipers the standard car and better pads. The Cobra is the standard PBR pad guided calipers on the '98 or so cars, not the Cobra R Brembo setup.

Maybe friction co-efficient plays a huge part, but right now it seems like you can't go wrong with any caliper you put on the car. I even found one Vette where the guy ran C5 PBR (2) piston calipers front and back, on a road course. The article said they were shocked that it would work, but in the end said it worked pretty well (don't know about proportioning, though).

One thing that did cross my mind is the fact that both the Vette and Viper run much larger rear tires than front tires, and the Cobra runs the same size all around. Maybe the larger tires allows you to use more rear brake, and thus the Viper and Vette can get away with a lower front/rear ratio.

So Andy, what kind of ratio?

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'15 Chrysler 200S V6
'74 Duster 360, factory 4 speed car

I'm not sure how you're calculating those ratios, for instance the Gen III Viper doesn't look correct. Typically the rear calipers have both smaller pistons and they use a smaller rotor. So the combination of those two factors really drops the rear brake torque when compared to the front.

As for what the correct value is that really depends on the front to rear weight distribution and the height of the center of gravity since both of those factors determine how much weight gets shifted to the front during maximum braking effort.

A typical street car would be set up with 60 to 75% of the brake torque up front but that can vary. A 911 Porsche is going to be quite a bit different than a pickup truck. A typical muscle car with a big block engine is quite front heavy so I'd probably go with at least a 70/30 split for brake torque.

I just used the numbers from above and check a Motor Trend for rotor size. Front pistons are 40/44, rear are 38/42 and rotors are 14" all around.

I used the formula:

Tb = (Ph x Ap x u x 2) x Er

Tb = Torque (brake)
Ph = Hydraulic system pressure
Ap = Area of piston(s) (one side of the caliper on fixed calipers)
u = co-efficient of friction of the brake pad
Er = Effective radius of the rotor

I used 1000 psi for all cases, and .375 for a co-efficient of friction. For the effective radius, I subtracted 1" from the overall radius of the rotor.

I wasn't trying to calculate actual brake torque numbers, I was only trying to look at the relationship between the front and rear numbers on a couple of cars with good brakes. I figured if I used the same numbers for all the cars and front and back, it would show me some kind of relationship.

Interestingly enough, if I use .5 for the front and .25 for the rear friction co-efficients on the Gen III Viper, I get a ratio of 2.20:1. Sounds like you can tune the front to rear bias with the pad compound as well.

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'15 Chrysler 200S V6
'74 Duster 360, factory 4 speed car

Sounds correct but that is an odd result so I guess I'll just say I'm not sure what the Viper engineers had in mind. They did have a problem with the brake balance on the earlier Vipers so maybe they changed their model. It would seem that the car would be tail happy with that much rear bias but I've never driven one so I couldn't say.

There used to be an excellent book on brake design that was written by Puhn, not sure if it is still available or not. He went into the proper way to calculate brake balance starting with weight distribution, center of gravity, etc. Then you do the calcuation that you did and then add in the master cylinder split and the coef of friction of the pads and you're there.

I don't think tire size really matters as long as the tire is capable of holding up the load at each corner. There might be a little difference due to tire size but really a wider tire doesn't have any more grip than a narrower tire. The contact patch is shaped differently but that is about it. I'm not sure it even enters into the discussion much except for fine tuning.

You also need to take tire radius into consideration if different size tires are used F/R........... Larger diameter tire reduces effectiveness of brakes.

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Ed
64 Valiant 225 / 904 / 42:1 manual steering / 9" drum brakes