Who has Dr. Diff 8 3/4 rear discs?

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plumkrazee70

plumkrazee70

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Did you have a problem bleeding them?

I have his stage 1 rear disc kit with the mustang calipers, his 15/16 MC and his 73+ A body front discs on my 70 Dart with a drum distribution valve.

When the car is jacked up in the rear, idling in gear, I cannot get the rear wheels to stop when I push on the brake pedal. The wheels will slow, but won't stop.

I have bled them all along with the master, but I am out of ideas. I don't have parking brake cables, but did actuate the lever about 2 dozen times before bleeding. I haven't tried holding the lever (applying the parking brake) while bleeding, yet. I am getting fluid to the rear and can NOT turn the wheels by hand, if either brake or park brake is applied.

When the car is in the ground, it will stop if the car is idling in drive, but haven't tried it at any kind if speed.

Any thoughts?
 
Do the rear mustang brake calipers use a drum inside the rotor or does it push the caliper piston for e brake.

IIRC when you replace pads on the push the piston type you have to reset the piston with a tool. I think you have to apply the brake or e brake some number times to adjust the piston
 
I have his 11.7” rear disks on my Duster. I had no issues bleeding them and they work great. My parking brake is hooked up and also works great. I use his 15/16” master cylinder, his 13” front disk set up and an aftermarket adjustable proportioning valve.

have you asked Cass? @DoctorDiff ?

Dana67Dart said:
Do the rear mustang brake calipers use a drum inside the caliper or does it push the caliper piston for e brake.

IIRC when you replace pads on the push the piston type you have to reset the piston with a tool. I think you have to apply the brake or e brake some number times to adjust the piston
Click to expand...

The e-brake moves the piston, no drum set up.
 
72bluNblu said:
I have his 11.7” rear disks on my Duster. I had no issues bleeding them and they work great. My parking brake is hooked up and also works great. I use his 15/16” master cylinder, his 13” front disk set up and an aftermarket adjustable proportioning valve.

have you asked Cass? @DoctorDiff ?



The e-brake moves the piston, no drum set up.
Click to expand...

I have reached out to Cass, we covered all the bases, so far. I'm just not sure how to tell if the ebrake is adjusted or not. Like I said I don't have a cable, just moving it by hand with a pry bar.
 
Technically, NO proportioning should be needed if the front caliper piston size and the rear caliper piston sizes are compatible. Drum/drum systems relied on wheel cylinder sizes to determine proportioning. The same applies with disc/disc systems.
I have a 2.75" single piston caliper up front and the 1.5" piston Dr Diff/Mustang Cobra rear caliper with just a drum brake combination valve. My front skids before the rear but just barely.

Ginger A.jpg
R T 27.JPG
 
Kern Dog said:
Technically, NO proportioning should be needed if the front caliper piston size and the rear caliper piston sizes are compatible. Drum/drum systems relied on wheel cylinder sizes to determine proportioning. The same applies with disc/disc systems.
I have a 2.75" single piston caliper up front and the 1.5" piston Dr Diff/Mustang Cobra rear caliper with just a drum brake combination valve. My front skids before the rear but just barely.

View attachment 1715561662 View attachment 1715561663
Click to expand...

Correct. I have no proprtioning valve, just the stock drum distribution block.
 
72bluNblu said:
I have his 11.7” rear disks on my Duster. I had no issues bleeding them and they work great. My parking brake is hooked up and also works great. I use his 15/16” master cylinder, his 13” front disk set up and an aftermarket adjustable proportioning valve.

have you asked Cass? @DoctorDiff ?



The e-brake moves the piston, no drum set up.
Click to expand...

Did you adjust your parking brake before bleeding them? Or did you have it applied while bleeding them?
 
plumkrazee70 said:
Here is how my lines are run, could it be the way the flex is routed?

View attachment 1715561667

View attachment 1715561669
Click to expand...

Possibly. In the second picture it looks like your might be just as high as the bleeder is. Hard to tell from a picture, but if the line is actually higher than the bleeder you could have an air bubble trapped in there.

Cass would know better than I do but I'm not a fan of the calipers being run without the emergency brake cables. Some rear calipers won't adjust without the parking brake. I don't think the mustang calipers fall into that category, but I wouldn't rule out the cable being unhooked as contributing to the issue either.
 
72bluNblu said:
Possibly. In the second picture it looks like your might be just as high as the bleeder is. Hard to tell from a picture, but if the line is actually higher than the bleeder you could have an air bubble trapped in there.

Cass would know better than I do but I'm not a fan of the calipers being run without the emergency brake cables. Some rear calipers won't adjust without the parking brake. I don't think the mustang calipers fall into that category, but I wouldn't rule out the cable being unhooked as contributing to the issue either.
Click to expand...

Somebody else mentioned that too, it's just the picture. So does his parking brake cables go from caliper to your existing parking brake cables, or is it all new to the handle?
 
If Parking Brake system not adjusted,sometime caliper piston barely will hit pads/rotor when pedal firm
I have had similar problem......


D.
 
It’s just the way the system works. It’s weird, I know. But it just works that way and no other way while other systems work in a different way and in just there way, not the other way.
 
plumkrazee70 said:
Somebody else mentioned that too, it's just the picture. So does his parking brake cables go from caliper to your existing parking brake cables, or is it all new to the handle?
Click to expand...

I just did this install (the stage 2, calipers are the same). The cables have a large (~0.53") and small (~0.49") end, so measure them to know which end is which. The small end goes to the caliper, the large end on the body. For me it was just the two cables to the equalizer on the main cable to the handle (just replaces that too, what a *****).

I have the parking brakes where the two cables route to the passenger side frame rail, so you have a short (drivers) and long (Passenger) cable. Cass will need to know what you have when you order cables, as I understand there were two types, not sure of what years or models that broke down too.

I still need to bleed the system.

One thing to note, how centered are the caliper frames to the rotor and how free does the caliper slide on its pins?
 
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mycuda said:
If Parking Brake system not adjusted,sometime caliper piston barely will hit pads/rotor when pedal firm
I have had similar problem......

That makes sense, why the wheels slow, but don't stop. My parking brake cable is completely missing. I may have the handle.

This could get interesting since th while car is assembled.
Click to expand...
 
dano said:
I just did this install. The cables have a large and small end, so measure them to know which end is which. The small end goes to the caliper, the large end on the body. For me it was just the two cables to the equalizer on the main cable to the handle (just replaces that too, what a *****).
I have the parking brakes where the two cables route to the passenger side frame rail, so you have a short (drivers) and long (Passenger) cable.
Click to expand...

so the doctor diff parking brake cables he sells attached to the factory cables at the equalizer?
 
plumkrazee70 said:
Ok, thank you. I'll have to see what I have and order the cables from him. And the adjustment just comes from the equalizer, right?
Click to expand...

On my car yes, right to the cable that runs from the hand brake to where the two cables split off. Just loosen the nut, move the equalizer back, pop the new cable heads through and tighten the nut and adjust accordingly, after the cables are routed and secured of course. It was easy and E Clips secure the cables on both ends.
 
This is how may car is. Red arrows are new from Dr Diff. Blue is the existing front cable.

upload_2020-7-15_7-31-58.png
 
Thanks @dano I ordered the cables from him just now, but he said the place that makes them got shut down, so the turn around in undetermined. In the mean time, I will see what I have as far as parking brake is concerned and placed a want ad.

Im just hoping I can install everything with the motor and such in place.
 
plumkrazee70 said:
Thanks @dano I ordered the cables from him just now, but he said the place that makes them got shut down, so the turn around in undetermined. In the mean time, I will see what I have as far as parking brake is concerned and placed a want ad.

Im just hoping I can install everything with the motor and such in place.
Click to expand...

Dano covered it, the cables I got from DoctorDiff just go from the caliper back to the first clip where the old cables tied into the rest of the system, so they’re only a couple feet long and utilize the stock cables back to the parking brake lever. But that’s dependent on the year.

I installed the whole rear brake conversion with my car fully assembled, I drove it into my shop, pulled the wheels, removed the old drums and installed the whole conversion including the parking brake cables. Whole thing was done in a day and right back on the road as my daily.

My install is on the last page of my build thread, although the pictures there don’t show the parking brake cables very well. I’ll see if I have any others

My "new" '74 Duster- or why I need a project like a hole in the head
 
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