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I have not seen this mentioned yet- 'for what it's worth' concerning brake calipers for the slip-on Astro rotors on stock B-body suspension- 1980-1987ish 3/4 ton 'heavy duty' JB7 calipers have the same mounting points as the light duty calipers (same as our cars), fit a 1.25 rotor thick rotor and have a 3.15 inch piston. If I ever get enough 'want to' to put the Astro rotors on the wagon, I'll use those calipers and larger bore rear wheel cylinders to keep the front/rear bias similar to original.
 

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Looks like they might be the same as the caddy J55 ones mentioned in the beginning.
 

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Even if the JB7 caliper/pad may fit, I think you'd be dealing with pad overhang on the J55 rotor OD and definitely on the Astro rotor, which is smaller (overhang is not good), and the larger 80mm caliper piston (vs 74.5mm for J55) may present a fluid displacement issue with the master cylinder. Pedal stroke would likely increase with stock MC. A larger piston does not present a solution unless it's tailored to the application, with corresponding MC sizing. Most performance & multi-piston calipers for car applications actually have LESS calculated piston area than the GM single-piston (2.9375" or 74.5mm) caliper used from 1969 to 1996 on millions of cars & trucks.

Rotor spec - 12.5" OD x 1.29" (JB7)
pad - More Information for CENTRIC 10401530
JB7 caliper - More Information for NUGEON 9717240B

Rotor spec - 11.88" OD x 1.29" (J55)
pad - More Information for CENTRIC 10300520
J55 caliper - More Information for CARDONE 18P4126
 

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These cars/trucks all use the J55 caliper according to RockAuto:

CADILLACBROUGHAM1987-1990
CADILLACCOMMERCIAL CHASSIS1979-1984
CADILLACFLEETWOOD1980-1996
CHECKERMARATHON1980
CHEVROLETC10 PICKUP1979-1986
CHEVROLETC10 SUBURBAN1979-1986
CHEVROLETC20 PICKUP1979-1986
CHEVROLETC20 SUBURBAN1979-1986
CHEVROLETG101979-1995
CHEVROLETG201979-1995
CHEVROLETG301979-1984
CHEVROLETK10 PICKUP1981-1983
CHEVROLETK10 SUBURBAN1981-1983
CHEVROLETK5 BLAZER1979-1984
CHEVROLETP101979
CHEVROLETP201979-1989
CHEVROLETR10 PICKUP1987
CHEVROLETR10 SUBURBAN1987-1988
CHEVROLETR1500 SUBURBAN1989-1991
CHEVROLETR20 PICKUP1987
CHEVROLETR20 SUBURBAN1987-1988
CHEVROLETR2500 SUBURBAN1989
GMCC1500 PICKUP1979-1986
GMCC1500 SUBURBAN1979-1986
GMCC2500 PICKUP1979-1986
GMCC2500 SUBURBAN1979-1986
GMCG15001979-1995
GMCG25001979-1995
GMCG35001979
GMCJIMMY1979-1984
GMCK1500 PICKUP1981-1986
GMCK1500 SUBURBAN1981-1986
GMCP15001979
GMCP25001979-1986
GMCR1500 PICKUP1987
GMCR1500 SUBURBAN1987-1991
GMCR2500 PICKUP1987
GMCR2500 SUBURBAN1987-1989
 

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J55 caliper - same piston area as JA9, JB9, JM4, JA1, JA2 - only difference is JA9 (for 94-96 9C1) uses the same wider caliper body/casting as J55, but JA9 also uses a specific piston to work with the thinner (26mm or 1.04") B-body standard rotor & thicker pad on the 9C1's. J55 was made to work with thinner D52 pads on 1.29" rotors (compared to JA9 spec pads).

The first problem with the JB7 idea is that it will leave piston & pad "pushing on air" beyond the diameter of the standard B-body rotor--and even more so with the Astro rotor. The increased piston area, as mentioned above, would not be any advantage without some other changes.

A rotor larger than 12" OD will not mount on the standard ABS-capable B-body knuckle/spindle - doing anything larger requires permanent knuckle modification.
 

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The JB7 caliper is made to mount further out radially, even if it's less than 1/2" (difference in 11.88 B rotor and 12.5 truck rotor) - putting JB7 caliper over a 12" rotor means a portion of the piston & pad is outside the OD of the B rotor. Plus the other issues with piston size & fluid volume mentioned already.
 

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1995 Cadillac Fleetwood Brougham
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Is it just me, or are the pads on those Wilwood calipers smaller than the OEM pads shown on that page?
 

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Is it just me, or are the pads on those Wilwood calipers smaller than the OEM pads shown on that page?
Looking at the difference in size of the calipers, I would say the swept area is at least the same.

Mark: Snowman-33
 

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1995 Cadillac Fleetwood Brougham
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Looking at the difference in size of the calipers, I would say the swept area is at least the same.

Mark: Snowman-33
I'm not sure the size of the body of the caliper is relevant. It looks like wilwood is being intentionally deceitful in that regard.
 

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Hey Matt, I think an actual side X side as this shows more.
193169


Mark: Snowman-33
 

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From that angle they do look pretty similar in size.
 
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