So a while back I read somewhere that someone said it was bad to run 12" rotors front and back. Because it messes with the ABS system. Is it because they are all the same size or just anything bigger in the back will mess with the ABS? I was considering running the fbodies with the GXP rears. Anyone doing this and is it worth it?

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First I've heard of this problem.

If all the wheels are reading the same speed, then there shouldn't be a problem.

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GreenBastardPerformance2000 GTP Coupe (the green bastard)
XP, Pacesetters, LS1 TB & MAF,MSD System, P&P LIM, P&P GenV w/ 3.2, 3.0, 2.8, Devil'sOwn Injected 100% Methanol,PowerTuned, TripleEdge Trans w/3.29's
12.92 @ 105mph

i cant see why there would be an issue, but rather at least until the GXP, there wasnt a viable alternative for bigger rear brakes. -- that being said, the rear brakes dont do much of the braking to stop the car, so you may not feel much benifit.

Toasty - True but I think that comes from people who upgrade the rear rotors and pads to better pads of the same size. I think that with a larger calipers and larger pad surface with good rotors there are nominal gains to be had. Especially if you can get the upgrade parts for the right price. Also with 18's it looks a little beefier which is cool.

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I've heard of the issue but to my recollection, it was because the proportioning was set for the rotors of different sizes so when you slam on the brakes, the bigger rear brakes, getting fluid ment for smaller brakes, could mess with the ABS. I'm not sure I'm saying that clearly but I'm sure someone can correct me.

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I think I know what you are saying, well since I got 04 comp-g I might just do the gxp upgrade myself.

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Steven Oliver
2004 GTP comp-g WS6. Gator and suede all around interior.
Advanced MECP certified installer, custom upholsterer.

97-03 had the same size rotor front and rear. The difference is the rears are not vented like the front. The GXP rears are though which is why it will mess with the ABS, by design, they will stop better than a non-vented rotor.

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2008 Greater Ohio Club Grand Prix President

My Mod List

Okay thanks Vinnie makes good sense. Has anyone ever tried running a different master cylinder?

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I will be running 12" front and rear soon..

F-body front and GXP rear.

Why not gxp brakes all around

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2002 Pontiac Grand Prix Gt Bone Stock Till Paid For
1992 Pontiac Grand Prix Se Sleeping To Be Re Born Soon