Why won't these LS400 rotors fit on my Gs430. This is a typical upgrade for this model and my mechanic says the LS400 rotors won't fit. I've tried 1 different sets of rotors...any help is appreciated.

 

Are you trying to put the LS rotors on with the stock GS calipers? For the larger LS rotors you'll need the larger LS calipers. The larger LS calipers require a spacer, also known as a RCA, which will lower the front suspension to fit the larger caliper. Once you have the larger caliper on, you'll need to both cut and bend the dust shield to fit the larger rotor.

 

If you do the calipers as well you must do the rears also. If you do only the front rotors/calipers you will seriously mess up the brake bias. By default these cars already have a largely front brake bias (around 74-76% braking torque at the front wheels), so adding larger front calipers only would bring that number up to around 80ish percent.

Keep in mind, it is a common misconception that larger brakes = shorter stopping distance. This is only true if the stock braking system is weak to the point where wheel lockup doesn't exist. These brakes on these cars are fairly strong, not ultimately strong but fairly. What really determines stopping distance on most cars is tire size/compound.

 

yes I have new rotors, calipers, pads, I also know about removing the dust cover and yes I have Megan rca's installed. I didn't realize I'd have to do the rear brakes also, but that can't be why the caliper isn't sitting flush on the hood like it should is it?