Black04Vert

Problem:
I have a Ridetech front end. It requires a GM A/F body hub which Wilwood sells. I want to use 15" repro rally wheels. There are two rotor options with the A/F body hub, an 11" rotor and a 12.19" rotor.
I know that a D8-4 caliper on a stock rotor typically fits a 15" wheel. I would like to use the Wilwood 12.19" rotor and not the 11" rotor but I think I read that this combo doesn't work with Wilwoods 12.19" rotor, with 1.25" thickness.

However:
In looking at the diagrams, the Wilwood A/F body hub uses a thinner 0.81" rotor (vs 1.25" stock) and a different Wilwood caliper. The Willwood caliper + 12.19" rotor appear to be shorter and narrower than a D8-4 caliper on a stock 11.75" rotor.

Can anyone confirm this? Or better yet, confirm the fit on a 15" wheel?



My calculations:

Wilwood D8-4 caliper on stock 11.75" rotor, 1.25" thick:
Minimum wheel radius = 7.0" per diagram
Overall caliper thickness = 5.84" per diagram
Inbound caliper thickness from center line of rotor = 2.3" + 1/2 rotor thickness = 2.3 + 1.25/2 = 2.925"
Inbound caliper thickness from caliper mount = caliper thickness - mount offset = 2.925 - 1.3 = 1.625" (meaningless since I don't know mount position difference between Ridetech and stock)

Wilwood 120-13846-RD Forged Dynalite caliper on Wilwood 12.19" rotor, 0.81" thick:
Minimum wheel radius = 6.93" per diagram
Overall caliper thickness = 1.83" + .81" + 1.68" = 4.32"
Inbound caliper thickness from center line of rotor = 1.83" + 1/2 rotor thickness = 1.83 + 0.81/2 = 2.235"
Inbound caliper thickness from caliper mount = caliper thickness - mount offset = 2.235 - .98 = 1.255" (meaningless since I don't know mount position difference between Ridetech and stock)


Wilwood D8-4 caliper used with 11.75" rotor:




Wilwood Forged Dynalite caliper with Wilwood 12.19" rotor 0.81" thickness:

0Todd TCE

Compare the two Dim E number times two as you have. Go to the hardware store and get a very small dowel rod (or welding rod) and cut to the dia spec (14" ex)

Put that down inside the barrel of your wheel. Then do it with the other spec. You'll need to evaluate WHERE that number is relative to the depth and the wheel pad and evaluate if you still have the room past the wheel pad if the caliper body sits in the spokes deeper.

Keep in mind you'll need to do this on both axles of you car and possibly go to a smaller bore MC with all this. The bias will be all out of whack and the large bore will make for a very hard pedal to push. Also you're losing about 15% clamp force with this design....just so you know. The added .250" of rotor won't bring back a lot of that.


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Black04Vert

I'm assuming that 15% clamping loss is due to caliper piston bore of the Wilwoods being 1.75" vs 1.875" from stock?

0Todd TCE

Correct, you're dropping from about 5.4 to 4.8 sq inches if my memory is correct.

naramlee

Dynalite calipers have quite abit of flex as well, get dynapros if this is for the street

Black04Vert

I never checked the DynaPros, they are even narrower than the DynaLite. Thanks

Black04Vert

I calculated:

Center of piston radius for Wilwood is 5.22"
Center of piston radius for stock is 4.9125"

As you said, the increase in rotor size only buys me 6% back of the 15% loss due to smaller caliper pistons.

I'm assuming I can go with a Wilwood tandem master with a 1" inch bore vs my stock 1.125" (power brakes) to even up the clamping force loss and use the built-in proportioning valve to solve the front to back ratio difference?

0Todd TCE

Maybe....I don't have a D8 pad on the shelf to measure block height, but the DL pad is 1.7" tall. My guess is the D8 is closer to 2" which would make the DL pad's ER higher on the 12.2" rotor as well both going to offset the clamp force loss we see.

If you do it I'd try the 1.125" you have now first and see if you find it's to hard to push to whoa it down. The booster may mask that change. If not and it works fine then let it go, there's no gain in the 1.0 other than less effort required. But because it's the same on each axle yes the bias will be shifted reward by X% and the prop valve may be your only hope if you find it's tail happy.

The DL caliper, while a fine part in its own right, doesn't belong in use here in my opinion. *The reason I am contributing to this thread. It's a lighter use part and has far smaller pads and mass for true spirited use in cars the weight and speed you may be looking to achieve.

0Todd TCE

The DP caliper I think he's speaking of is the DPR (or I would like it to be) and has a fatter pad but the same basic size footprint. The rear benefit is that it's radial mount making for a stiffer mount design. And more costly build.

69427

OP, what's the intended use of your car after these suspension/brake mods?

Black04Vert

Street light to street light. Maybe the occasional auto-cross.

69427

The Dynalites and 11.75" rotors will do just fine in that application.

I have that combination on my '69. I do a lot of track days with my car, but I also like having 15" wheels on it for street driving. I had to stay with 11.75" rotors to fit inside the stock wheels. There's enough brake torque capability to lock up the tires, so that combination isn't lacking in that regard. The only downside to the Dynalites is the small pad size, so they wear out quicker than a larger pad. But if you're just driving on the street and the occasional autocross, even the smaller Dynalite pads ought to last a long time.

naramlee

https://www.wilwood.com/Calipers/Cal...o=120-13433-RD


is actually what I was referring to, Dynapro 6, sorry, forgot the additional tag