Re-Rebuilding the 440-493 in a 1970 Charger

[Kern Dog]

The fronts only locked on a section of road that was wet and on dirt in my back yard. On dry roads, I can't get them to lock at either end.
The front pads are new, the rears are 16 years old. The entire front brake setup is new. The only thing new on the rear are the rotors. The pads had 35-40% of the material left so I thought they would be okay. Who knows...maybe they are not the problem but with how they chipped on the edges, I thought they should be replaced.

 

[PeteBell68]

wow just read your entire post , you in there for a complete rebuild excellent detailed thread very nice ..

 

[ckessel]

Before I hang my stuff on, have the same Dr Diff package as you, I'll upgrade the pads for all 4 wheels. Pretty good chance that what you got and me too, were the cheapest thing possible to put the package together and keep the cost down. Thanks for being the neighborhood guinea pig.

 

[Boris7K]

I am also getting ready to run this setup, but the rear calipers I have are different. I'll have to look at the pads but the calipers I have are aluminum and finned. A pad upgrade might be in my future if this works out for you. Thanks for detailing your progress!

 

[Boris7K]

Sorry, just looked at Dr Diff's page, the calipers might be the same, just powder coated.

 

[Cheapsunglasses]

Wow they make a tool for that, I thought you use a screwdriver and and stab your hand a couple times

 

[Kern Dog]

There are some mechanical things that are difficult but you accept that it had to be that way to get the system to work.
These rear calipers with “screw in pistons” may fall into that category. What the f*** ?
The pistons have these small notches.

To retract the pistons, they have to be cranked back in.
To do so, you need something to grab the piston face.

This cube has 6 sides with patterns for other cars… which makes me sad that at least six other engineers were stupid enough to also use this design.

Here is the problem…
You have to hold the caliper with one hand and screw the piston back in WHILE PRESSING IN. Do these calipers have 300 threads per inch? My hands are sore and the piston still needs to retract another 1/4” to fit over the pads. There is another tool that one can rent that serves as a clamp and twisting implement but Auto Zone isn’t right down the road.
Torsion bars are a pisser but I understand their purpose. The weight is low and to the rear compared to a coil spring setup.
Rear mounted steering linkage makes header fitment difficult but in stock form, the components could be made smaller, lighter and again, moving weight to the rear for better handling.
Screw in caliper pistons??? WTF?
This sucks.

 

[NoCar2023]

This set works great.

https://www.autozone.com/test-scan-and-specialty-tools/brake-tool/p/oem-loaner-disc-brake-caliper-tool-57111/298604_0_0

 

[Cheapsunglasses]

I agree with your screw in pistons, screw then up the person that invited thems’ a$$!

My 82 Datsun 280zx has them, I didn’t have the right tool, so I started out with a screw driver, which worked ok…until it slipped and went right into my thumb! I eventually got it done with vice grips.

 

[Kern Dog]

When I am cold and sore, my tolerance level is very low. Same goes with extremely hot weather. The only difference now is that I’m not getting sweat in my eyes.
I was cranking the LH piston clockwise but then suddenly wondered if I was turning it the wrong way. I checked a YouTube video and saw that I was doing it right.
I have spun this piston maybe 40-50 turns. Who knows, I was tired, sore and pissed.
Out of the blue, it started retracting and it finally seated. The RH side screwed in easy as can be.
The calipers are on with the anti-rattle clips in place.

I’ll save the test drive for tomorrow. Next week I am getting it aligned.

 

[67MPRFAN]

suddenly wondered if I was turning it the wrong way. I checked a YouTube video and saw that I was doing it right.
I have spun this piston maybe 40-50 turns. Who knows, I was tired, sore and pissed.
Out of the blue, it started retracting and it finally seated

Do the pads look to have about the same wear thickness on them. I only mention this because on my DD that's the side that starts grinding first. I have since changed that caliper. Btw good thread

 

[Kern Dog]

Thank you for the kind words.
The old pads do look like they wore evenly.
I suspected that the LH caliper may have been "frozen" in place since the piston was stubborn to retract but since it had even wear, the chance of that was slim.

 

[Kern Dog]

The brakes WORK great! Hard stops from 60-70 mph are finally impressive.
Low speed operation is still excellent. The brakes grip and slow the car down nicely. Higher speed, they are working much better with these new rear pads BUT the boost assist starts to drop off after one good hard stop or a couple medium rate stops. I think this vacuum pump isn't keeping up. It feels like a car with power brakes that allows one good stop after the engine stalls.
I still can only get the front tires to skid. I don't know if I have skidded the rear tires on pavement. In fact, I don't know that I have ever skidded the rear tires since I switched to these disc brakes.
I'll look at vacuum pumps and decide how to proceed there. Driving casually, this setup is okay and would be enough for many people. Replacing the pump at this time isn't necessary but it would allow me to close the book on the brakes.
It has me curious though....
IF the brake force is excellent with the booster at full vacuum, that tells me that the calipers and pads are working right.
This makes me wonder if these pads were in place when I had the manual master cylinder, if I would have just stayed with that.
The manual setup is obviously lighter, simpler and looks more tidy.

Old picture below but it shows the additional complexity and bulk of the booster and brackets.

 

[Cheapsunglasses]

Awesome, glad you got it working!

 

[Kern Dog]

Awesome, glad you got it working!

Well, it has been a journey to get here.
This project was initially about rebuilding the engine due to a cam going flat. Brakes were supposed to be a simple change.
The Snowball Effect changed all of that.
To recap:
Before the project started, I had this 1975 Dart power booster and iron 15/16" master cylinder. The front brakes were the popular 11.75" Cordoba discs with the 2.75" iron calipers. The car stopped pretty good with this setup.
I saw that video with the red Pro Street '64 Mercury Comet....the one where the guy drove it despite a sticky throttle. The brakes overheated from riding them the whole time and he ended up rear ending a minivan at 40+ mph. He had small brakes and over 1000 HP.
This inspired me to improve my brakes and that set off a whole series of mistakes, trials, parts swapping, disappointments, cuss words and regrets.
I still need to solder in that diode in the tachometer wire to stop the tach needle from bouncing.

 

[Cheapsunglasses]

It always snowballs

 

[moparedtn]

AKA "making a career out of it"....

 

[OKDart]

I'd try a vacuum reservoir before anything else.

power brake vacuum reservoir - Google Search

The late 50's Mopars used large reservoirs and large diameter vacuum hose. Every time the throttle closes, vacuum spikes whether a big or small cam, then that vacuum is stored for a few brake actuations.

 

[Kern Dog]

Do you mean that in addition to the pump? Something like a reserve cannister?

Several years ago when I used this cam before, I had low vacuum so I first tried this tank in between the intake vacuum fitting and the booster. It helped some but more was needed. I changed to the vacuum pump and braking performance was a lot better.
If I plumbed this tank between the pump and the booster, it could add a measure of reserve. The photo on the box shows a check valve in one hole.

 

[OKDart]

Yes, in between the pump and the booster. As close to the booster as possible to keep the 3/8" vacuum hose from being a restriction. Right now the front half of your booster is your only reservoir. You say you get one brake application before it gives out, just eyeballing the size of your reservoir, I'd say adding it should give you 2 quick brake applications.
Full disclosure: I've never had the need to use one myself, but the theory is sound. But if your pump is weak, it'll take longer to build the vacuum back after use.