LexLuger06

I have a 2006 GS300 with 17 in stock rims. I'm upgrading my rotors/calipers to the larger ones that come standard on the 2006 GS430/2007-2012 GS350/IS350. My question is if anyone who has done this mod needed to also upgrade their master cylinder? I can get no help from lexus service technicians/advisors because I am "modifying my vehicle". I would appreciate any information on the subject because the remaining parts needed to do mod are in the mail and will be arriving shortly.

mitsuguy

iTrader: (2)

chances are you will be fine, however, if you are only doing the fronts, you could potentially throw off the brake bias... the only way to really fix that is to upgrade to the same model rear brakes as well...

LexLuger06

I have ordered front pads for 07 gs350 if that's what you mean. I talked to a mechanic and he mentioned something about a proportioner valve or something that I may need to change?? that distributes brake fluid/pressure to the front/rear brakes...any more help/info please? thanks

mitsuguy

iTrader: (2)

no, I didn't mean the front pads...

When a braking system is engineered, a certain brake bias is engineered into the system... if you upgrade the fronts without upgrading the rears as well, you will have increased stopping power in the front, but the rear will be lagging behind - basically adding too much stopping power to the fronts, but none to the rears, causing the fronts to lock up much sooner than they should because you have effectively changed the bias... many people do this without too bad of issues, however, keep in mind, if you are looking for additional braking performance, this may or not make things much better without doing the rears as well...

LexLuger06

I'm replicating the same braking system that is on a 07-12 gs350/is350. the rear brakes are essentially the same, no disrespect but I would like people who have actually done this mod to chime in and provide accurate information. the parts are bought and I would hate to be unable to accomplish this mod for the lack of exact info. CL is good at posting the what ifs, and supposes, but not the specifics. I learned of this mod here on CL, but have yet to get a concise answer to my specific question. once again I mean no disrespect to those who have answered or to those that have any info, but I do need exact, concise information. thanks

mitsuguy

iTrader: (2)

I am trying to help you, and, chances are, even if someone here has done it, they didn't do it properly...

here is the important part - brake bias... even if the rears are "essentially" the same, if there are any differences in the piston diameters, then you will have a brake bias issue...

There is no proportioning valve, aside from anything that is built in to the master cylinder. Your GS has a somewhat unique master cylinder, in that it also has an ABS modulator built in to it, so, you will not be changing that out for anything else.

That means that what I have been trying to tell you is of utmost importance... I'll try and help, but, I'm really just trying to show you the way... basically, you need to have the right proportion of piston surface area from front to rear as the car you are taking the parts off of... I can't find those specs easily, perhaps I'll look tomorrow, but it is very important the correct ratios are maintained...

if you can locate the factory piston diameters for the brakes you are going to and the brakes you are coming from, I would be more than happy to tell you exactly what you need...

the alternative is to just buy front and rear brakes from the car you are wanting, that way there is no question if it is correct or not...

Anyone that tells you it doesn't matter doesn't fully understand the braking system...

LexLuger06

ok, so I think I understand brake bias. essentially I'm changing the front rotors diameter + 2in to 13in and the calipers are increasing +2 to 4piston. so I believe the actual braking surface may increase somewhat.

LexLuger06

@ mitsuguy I really do appreciate your help! I meant no disrespect and I do apologize if I came off as ungrateful or condescending.

jaguar_83

Hey LexLuger06, just curious as to what the end results were on your brake upgrade? I'm thinking of doing the same especially since it adds more stopping force because of the extra pistons on the 07-12 calipers.

gt6

Hi guys
Did you ever do this upgrade? I'm interested in doing the same but no one at the dealer is willing to help me out. If you have pics and/or part numbers for this conversion that would be helpful....