Rotor size inquiry

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Mikey Yoh

Mikey Yoh

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Treasure Coast, FL
I am about to purchase a disc brake conversion kit from Dr. Diff. My question is whether the 10.95" rotor kit will suffice, or should I order the 11.75" kit? My '74 Duster has manual drum brakes now. The car will be street driven most of the time, with a monthly trip to the dragstrip to run in no box bracket races.
 
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What size wheels you running? IMO get the best/biggest that will fit and you can afford...
 
If running 15's steels the 10.75" will work. the larger rims have an interface problem with the calipers.
 
Mopar Tim said:
What size wheels you running? IMO get the best/biggest that will fit and you can afford...
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15" rims. I was thinking the same thing that bigger is better, but how big is too big for my application? I mean, ANTHING is better than the manual drums that are on there now. Some guys will tell me 13" Wilwoods or Brembos are the way to go, and other will say that drums are okay. Just looking for advice from others that have done these swaps.
 
I am running the 10.75 from Dr. Diff on the back of my Dart, on the rears, I have the Mopar disc's on the front. I ran this combo on the 69 Pro Street with manual brakes and they work fine. In fact I have this combination on the 69 Dart I now have with power booster, from Dr. Diff. Have no issues at all with it.
This is just my application and you will get other ideas.
 
Steven190 said:
I am running the 10.75 from Dr. Diff on the back of my Dart, on the rears, I have the Mopar disc's on the front. I ran this combo on the 69 Pro Street with manual brakes and they work fine. In fact I have this combination on the 69 Dart I now have with power booster, from Dr. Diff. Have no issues at all with it.
This is just my application and you will get other ideas.
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Okay thanks. I have 10x1.75" drum rears for now, will upgrade them to discs later. Just REALLY need to get rid of these front drums!!
 
Don’t know if this helps you. I put 11.75” from a 75 Córdoba on my Demon. The wheels are summit racing aluminum 15x7 4” BS. They’re very snug to the caliper but do fit. I used all factory parts so I don’t know if there’s a difference. You could also talk to Cass at Dr Diff. He’s very knowledgeable.

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The 11.75 discs will be slower on the strip than the 10.95 because of the larger inertial mass. Everything else being equal.

My 2 cents....unless you are roadracing or commute down Grapevine Hill, the smaller will be fine.
 
For street duty, I have never needed more than the factory KH 4-piston set-up, and I think those are right around 11. And the Bonus is I can run any factory wheel 14" and over, and probably anything except an old steel chrome reverse with the flat dinner-plate spiders.
I have been to different tracks on two just separate occasions, and both had plenty of shut-down area.
With a manual trans and 11/1 compression, I hardly need brakes.
 
KosmicKuda said:
The 11.75 discs will be slower on the strip than the 10.95 because of the larger inertial mass. Everything else being equal.

My 2 cents....unless you are roadracing or commute down Grapevine Hill, the smaller will be fine.
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Yeah, my problems at the strip won't be with the car; it's been awhile since I've driven there and some things don't get better with age. I'll be first round fodder for awhile.
 
Thanks to all that replied. After weighing options, I realized that the larger brakes were only $155 more, so that's what I ordered. Better safe than sorry.
 
Just an update. Got the Dr. Diff 11.75" disc kit installed. Almost too easy. Had to get new rims with a 5x4.5" bolt pattern. Only bad part was the discovery that all the hard lines were rusted crap. Just ordered the OEM steel front and rear line kits from Dr. Diff.
 
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