Rear disc on A-body

[sabre67]

Just wanted your opinions if you have did this conversion,on your A body. Good bad or ugly? Just wanted some opinions before deciding to jump in . Thanks guys and gals

 

[jbc426]

Just wanted your opinions if you have did this conversion,on your A body. Good bad or ugly? Just wanted some opinions before deciding to jump in . Thanks guys and gals

11 3/4" Police/Taxi rotors up front with Firm Feel's brake pads. Rears are a Dr Diff Econo kit with a 2006 Mustang Cobra R rear disc and caliper with parking brake. Master cylinder is just under an inch in bore-size. No adjustable proportioning valve, as it doesn't need it. Possibly one of the best, most predictable brake set-ups I've ever driven on a Mopar. It is so good, that I am running the same set-up with a power booster on my E-Body. It doesn't need the power booster though, and makes the brakes a bit touchy.

 

[ScampMike]

4 wheel disk on a 70's A-body? - you betcha!! set up properly, you'll wonder why you waited so long.

 

[halifaxhops]

Got them on my 8 1/4 love them just remember almost every kit you need 15" rims.

 

[roccodart440]

I've done it 2x and used TSM the first time, Wilwood the 2nd time.

I would never run anything but discs on the rear of my car and out of the 2 I used I prefer the Wilwood.

 

[AJ/FormS]

For a streeter, with stock or near stock sized tires, I wouldn't bother.
The rear brakes do so little work, it's almost pathetic.
Go out and do three 30mph to zero stops, and measure the stopping distances.Average them out.
Then clamp the rear brake hose off and repeat. And remeasure. And calculate the percent difference.If the rear locks up, you may have a problem keeping the back in the back.And you already have too much brake in the back. But say that you are curious. Rip the P-valve out of your Combination valve, and bleed the air out.Repeat the 30 to zero test, now with full line pressure to the back. Lemme know what happens.

 

[roccodart440]

Here is why I run rear discs. Because I have only owned 67-69 darts.

So right off the bat you need to swap to the big bolt pattern.

Now you need brakes with the BBP. So at that point if you need new brake why not go with discs?

Better look, better function, simpler, modern, etc, etc

 

[jbc426]

Just wanted your opinions if you have did this conversion,on your A body. Good bad or ugly? Just wanted some opinions before deciding to jump in . Thanks guys and gals

Another nice thing about rear disc's is that unlike a drum style brake that self engergises as a result of the brake shoes getting wedged into the drum on application, the disc brake does not self-energize which helps cut down on unexpected lock-up during a sudden application of the brakes.

There is also a device that acts like a brake line shock absorber that is used on a lot of race cars that flattens/reduces the sudden pressure spike and resultant rear brake lock-up that can occur during sudden braking. It does not reduce the line pressure, but only the sudden spike in pressure experienced during a sudden paniced brake application. It's about $100, is not at all like an adjustable proportioning valve, is very effective and is easy to install.

 

[65 Dartman]

Got them on my 8 1/4 love them just remember almost every kit you need 15" rims.

I have them on an 8.75 that will be going in my Dart wagon. The adapters were from member Dodgedifferent2, calipers and rotors sourced locally and the soft flex line from the hard line to the caliper through Rock Auto (metric to the caliper, SAE to the hard line). The kit takes 94 - 04 standard Mustang calipers and rotors AND 14 inch Magnum 500s fit no problem! Haven't checked regular steel wheels or Rallyes yet.

 

[68coupe]

11 3/4" Police/Taxi rotors up front with Firm Feel's brake pads. Rears are a Dr Diff Econo kit with a 2006 Mustang Cobra R rear disc and caliper with parking brake. Master cylinder is just under an inch in bore-size. No adjustable proportioning valve, as it doesn't need it. Possibly one of the best, most predictable brake set-ups I've ever driven on a Mopar. It is so good, that I am running the same set-up with a power booster on my E-Body. It doesn't need the power booster though, and makes the brakes a bit touchy.

What MC did you go with? Is it a disc/drum or disc/disc? If a disk/drum, did you remove the residual valve? Thanks

 

[jbc426]

What MC did you go with? Is it a disc/drum or disc/disc? If a disk/drum, did you remove the residual valve? Thanks

I got the master cylinder from Dr Diff. It's the <1" bore cast iron version that works for 4 drums or 4 discs. No residual pressure valves were in it.

 

[69wacuda]

I am just about to install my rear disc setup and i wanted to get a confirmation of use of the Prop valves. Do i use one or not? I purchased an adjustable one with the turn knob, as well as, purchasing the red and blue residual "in-line" valves. Do I need to use anything at all?

 

[AJ/FormS]

I have no experience doing this, but;
Considering that the rear brake pressure is strangled by the proportioning valve in an attempt to protect the driver from spinning out; for a streeter, I have, IMO,better things to spend my money on.
There is no reason to condemn this endeavor, but just remember to test,test,test. If the rear locks up first,they say the rear will come around and put you into a spin. I was very careful and somewhat conservative in setting up my rear brakes, and so far, the rear has always stayed in the rear.

 

[72Dart6pack]

My rear disk set up. All new hardward from Dr Diff.

 

[72bluNblu]

For a streeter, with stock or near stock sized tires, I wouldn't bother.
The rear brakes do so little work, it's almost pathetic.
Go out and do three 30mph to zero stops, and measure the stopping distances.Average them out.
Then clamp the rear brake hose off and repeat. And remeasure. And calculate the percent difference.If the rear locks up, you may have a problem keeping the back in the back.And you already have too much brake in the back. But say that you are curious. Rip the P-valve out of your Combination valve, and bleed the air out.Repeat the 30 to zero test, now with full line pressure to the back. Lemme know what happens.

I have no experience doing this, but;
Considering that the rear brake pressure is strangled by the proportioning valve in an attempt to protect the driver from spinning out; for a streeter, I have, IMO,better things to spend my money on.
There is no reason to condemn this endeavor, but just remember to test,test,test. If the rear locks up first,they say the rear will come around and put you into a spin. I was very careful and somewhat conservative in setting up my rear brakes, and so far, the rear has always stayed in the rear.

Mopar muscle did a rear disk conversion on a '73 Dart Sport and checked the stopping distances between the rear drums and rear disks. The result was that from 60 mph factory disks up front and factory drums in the back the car took 133 feet, 6 inches to stop. After the rear disk conversion, the stoping distance improved to 122 feet 4 inches. That's 11 feet. Maybe it doesn't sound like a lot, but that's almost a car length. 11 feet makes a near miss no big deal, and a solid hit a near miss. The rear disks absolutely make a difference. The online article is kind of a tease, the final stopping distance is in the tags under the pictures for the article, it's on the second to last picture. The hardcopy article is easier to follow, but that's the way it goes.

Rear Disc Brakes - All Bound Up - Mopar Muscle Magazine

Pedal feel changes as well, you can get more precision and feel out of the rear disks because they aren't a self energizing system. Better feel means less lock ups, and that means better braking and stopping distances. That's real world.

I am just about to install my rear disc setup and i wanted to get a confirmation of use of the Prop valves. Do i use one or not? I purchased an adjustable one with the turn knob, as well as, purchasing the red and blue residual "in-line" valves. Do I need to use anything at all?

Yes, you want a proportioning valve. Front to rear brake bias depends on a whole lot of things, weight balance, tire size, rotor and pad size, pad compound, etc. You want to be able to adjust the front to rear bias, especially if you've done through the trouble of upgrading to disks all around. Without a prop valve, you'd apply the same pressure front and rear on a car that probably does between 70-80% of the braking in the front and only 20-30% in the rear.

You shouldn't need either of the residual valves for a 4 wheel disk system. One is for running drums with a disk prop valve, the other is lighter and is generally used on disk systems where the m/c is mounted low (like under the pedal) to keep fluid from backing up into the m/c.

 

[AJ/FormS]

I get that, but it's a lot easier and cheaper to tweak the rear line pressure and wheel-cylinder size.
The factory engineered system was for a completely different parameter than what most of us are doing.
With 295s,and 10x2s, and the rest of my combo,I have a lot of rear brake bias and the rear actually does a lot of the work.So much so, that I regularly replace the rear shoes more often than the front pads. But, I'm only running 235/60s up front.
Anybody with non-factory tires , and who is still running the factory biasing, is missing out. And even more so if running big and littles.
And that link never explored this.

 

[72bluNblu]

I get that, but it's a lot easier and cheaper to tweak the rear line pressure and wheel-cylinder size.
The factory engineered system was for a completely different parameter than what most of us are doing.
With 295s,and 10x2s, and the rest of my combo,I have a lot of rear brake bias and the rear actually does a lot of the work.So much so, that I regularly replace the rear shoes more often than the front pads. But, I'm only running 235/60s up front.
Anybody with non-factory tires , and who is still running the factory biasing, is missing out. And even more so if running big and littles.
And that link never explored this.

Well to be fair, the car in the article definitely has different size tires. The article isn't great for details, the only real thing it has going for it is that they actually measured the stopping distance. But, they made no mention of an adjustable proportioning valve being installed or tuned, either before or after the rear disk install. They did mention that the stock combination valve has an internal metering valve that needs to be disabled, but they didn't actually say if they used a stock combo valve with the metering defeated and an adjustable prop valve or not. So you can't really assume the car was properly balanced before, or after, the install of the rear disks. Since they bothered to test before the rear disk brake install I'm willing to give them some benefit of the doubt and assume that the car was probably tuned to a similar level before and after. Not necessarily tuned to max performance in either case, but probably in the same ballpark for tuning.

I tend to agree that the rear drums should be able to provide more than enough stopping power to balance the car. But, that assumes they're adjusted properly, not wet, and not overheated. And because of the way the self-adjusters work you can't always assume they're properly adjusted. Those of us that drive in the rain can't always assume they're dry, and if you're doing any kind of driving with frequent repeated moderate to hard braking scenario's you might not be able to assume they're not overheated. Plus, just the pedal feel and extra sensitivity you get with the disks is enough to have the car stop more consistently, because you get much better threshold feel without the self energizing brakes. I think the biggest advantage gained going to rear disks isn't the braking force, but the added consistency you get from the disks.

The car from the article. Definitely not stock, front and rear sway bars, larger tires, and subframe connectors (in other pictures in the article).

 

[DGrace]

Here is why I run rear discs. Because I have only owned 67-69 darts.

So right off the bat you need to swap to the big bolt pattern.

Now you need brakes with the BBP. So at that point if you need new brake why not go with discs?

Better look, better function, simpler, modern, etc, etc

View attachment 1714945746

Are those Weld S71's - 15"? Also, are they a low pad and what Wilwood kit clears them? Looks great and thank you!

 

[roccodart440]

I am just about to install my rear disc setup and i wanted to get a confirmation of use of the Prop valves. Do i use one or not? I purchased an adjustable one with the turn knob, as well as, purchasing the red and blue residual "in-line" valves. Do I need to use anything at all?

I used nothing. All factory, just swapped to 4 wheels discs. Car originally had 4 wheel drums. I did swap to a 7/8 master though for pedal feel.

 

[roccodart440]

Are those Weld S71's - 15"? Also, are they a low pad and what Wilwood kit clears them? Looks great and thank you!

They are. I'm not sure what pad height they are. I don't remember. They have low, med and high.

I can tell you that the rears are 15" wheels, 11.25 wide and 3.5" backspace.

look that size up on summit and you may find not all 3 pad heights were available for that wheel.

 

[ir3333]

Nah...listen to A.J. The rear only supplies bout 25% of the braking.For a street car spend your
money on something else unless you want the "bling".

 

[roccodart440]

Nah...listen to A.J. The rear only supplies bout 25% of the braking.For a street car spend your
money on something else unless you want the "bling".

New cars come with rear discs for a reason and it isn't bling.

Now spending the extra on cross drilled and slotted rotors..yeah, perhaps bling!

 

[hemi71x]

[FOR SALE] - REBUILT Factory "REAR" Disc Brakes From A 1975 Chrysler Imperial 9 1/4" Inch Axle

I've got this for your consideration.
We can talk price, if interested.
Jim V.

 

[ir3333]

new cars com with rear discs for a reason all right....they are throw away items,wear fast and are great money makers like ball bearings instead of tapered rollers.
But build your car the way way you like it...it's all good!

 

[AJ/FormS]

New cars have rear wheel disc,mostly on the upscale models.
And the rotors and calipers are teensey compared to the fronts.
And then they often still have a drum parking brake.Or a complicated, prone to failure,mechanical application of the piston.
It is all too easy to overbrake the rear with 4 same-size tires, and then you invariably get a spin. So they give you all manner of electronic controls for ABS and anti-skid.
Whereas if they had just stayed with the drum brake, it would have greatly simplified the system.
IMO, upscale cars have rear disc brakes, for one of three reasons ;
1) to satisfy sales. People just think rear disc brakes are better.
2) perhaps to satisfy some assembly-line speed
3) perhaps to satisfy a lawsuit when their 160mph car crashes on a 65mph roadway. For some reason, brakes don't work when the car is; sliding sideways, spinning, flying, or otherwise not moving in a semi-straight line with the tires connected to the road.Most of us know that after the car reaches a certain angle of 4-wheel sliding, there is no recovery unless by supernatural intervention and after 50/60 mph, the window of opportunity is very small, and no amount of rear brake in the world is gonna save it.When the rear lets go you are usually done for. I usually just steer opposite and lock 'em all up, then hope I don't hit anything. Of course I never have, cuz I pick my spots carefully,lol.
It is also my opinion that just because something can be done, does not mean that it should be done. And rear disc brakes on a street car is to me, a prime example.
10x 2s can easily be set up to overbrake the rear of a 3400 pound plus streetcar with 4 same size tires on it.
Now with really big sticky meats back there, well that's another story. But not many are running those on the street, mostly cuz it costs a lotta money to get them in there, and then more money when they wear out;like once every summer.
But if you do put big sticky meats back there, be sure to upgrade the rear brake system too, cuz you can get out of amazingly tuff spots if the rear is braking really hard. But really, it's the 400hp plus engine that makes all the trouble, and if a stock upscale model, it's the 130mph engine in the 30/40mph chassis, that is the biggest offender.And if a CUV, or an SUV, well; drive them at your own risk
The following is not a reflection of what I believe, but only provided for your amusement.
With the conspiracy theory that says world governments are out to get us, it seems reasonable to think that with nearly every person in North America owning multiple cars, that those vehicles need to be designed to kill as many of us as they can, while looking as if the car is not to blame. Hence all the electronic controls and airbags and dependence on hundred year old gas burners. Look, if sea-plankton can be found on the space station, 250 miles straight up,and only over the ocean part-time,lol; why are we worrying about pollution controls? Why not just let it all float away,lol. Then we could have 102 pump gas again and run 11 plus compression engines,with out all the failure prone, expensive when they need repair,control systems.
I cringe every time I am forced to buy one of these modern,controlled to the nth degree, vehicles. I'll take a vintage carbed car any day over the modern do-dadded up money pit on the market today. Just gimme a new-metal, 77 Aspen Wagon, with a small V8 automatic, with disc/drums thank you very much. I'll put some nice shocks on it,and some decent tires, and call her done. Ok well small V8 is somewhat misleading. I thing a 380 should do it. 380hp that is,lol. And a 6 speed auto. And if I flip it on it's roof I'll know exactly who to blame. Not the tires, not the suspension,not the high CG, and most especially not the undersized rear drum brakes,lol.