everything bolted right up, but, now rear rotors are 11.66" and fronts are 10.50", so what new problems have I created for myself?

 

Did you originally have rear rotors?

 

YES!

 

Shouldn't be any problems. It depends on the size of the piston in the new rear caliper compared to the size of the piston in the old style caliper. A larger piston will produce more force and more braking. There's a slight possibility of the rear brakes doing more braking now than the front but I doubt you'd notice any difference. The size of the rotor means nothing. It's the surface area of the piston that will determine if you have any problems or not.

 

First, 91 uses a 10-bolt, not a 9-bolt, and second, thats normal for 89-92 4-wheel disc brake cars to have the rear larger than the front.

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1991 Camaro Z28
5.7L 5-Speed (originally 305)
317 RWHP, 418 RWTQ
13.23 @ 107.62 MPH (2.10 60')
Southern California
Member: SoCal 3rd Gen F-Bodies
Member: SoCal F-Bodies
-=ICON Motorsports=-

 

Well, I guess the boneyard mis-identified the year of this 9 bolt I installed.

Anyway, the disks that came with this 87 IROC were 10.50 front & rear, and after I installed this newer(?)rear I ran into braking problems "hard braking", then noticed the rotor sizes were different.

I did some research and found a note on Bear Brakes web site, to which, they made note; "that larger rotors on the rear will cause problems with too much brake in rear."

 

i wish i had that problem when i changed over to 89+ Setup. instead i hardly have any rear brake bias.......LOL



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86',88',89' IROC-Z, 350 TPI, 700-R4

94' Formula, LT1, 6spd

 

I did that swap, 1989 9-bolt onto my 1987.
No problems with the 10.5 ft & 11.655 rears,
mine work great. One question did you use the Proportioning Valve from the 89 disc set-up??? The 87 and 89 valve may be different,
I would check that out.

 

I did check out the actual rotor area on both disks and found the fronts while smaller do have more surface area under the pads than the larger rears do!

I have never changed the valve, which one should I look for?

 

Palm beach
If you did not use the 1989 Proportioning
valve that could be your problem. All the posts I have read "said use the prop valve
from 89 rear set up" . Ask that question and see what replies you get. There is nothing wrong with the sizes of the front &
rear rotors.