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Prior to this event I replaced the rear brake hoses because I saw that when I was bleeding the brakes the old fashion way(with a person working the brake pedal) the amount of fluid coming out is inconsistent from left rear to right rear calipers. But both rears seemed to have lower fluid pressure than what I have seen on other cars when the bleeder screw is open with pedal down. This was something I couldn't see using a power bleeder or vacuum pump to bleed brakes. Earlier this year I felt the car has way more front braking basis than I remember from the year before. I dismissed it as driver induced problem and adjusted my braking effort/reference points for it. Now I am happy to report after replacing the rear brake hoses problem is solved! Even bleeding the brakes the fluid pressure looks to be more even. The old hoses visible look fine but they must be swelling inside or something to reduce fluid pressure to the calipers. Other data points: 1) I replaced the front hoses last year because the caliper fell when I was changing rotors, 2) I have been using same pad compound front and rear, 3) using OEM hoses.
Moral of the story is change all four hoses at the same time on a track driven car. The difference it made for me was like changing rear pad compound to restore bias.
OEM rear hose superseded to same as front with plastic protective coil around the outside.
May I as why you went with OEM vs. aftermarket stainless ones?
Just personal preference on the pedal feel. I have installed aftermarket SS braided lines before, the ones I have installed(probably not all) have smaller ID(Inside Diameter), I think the difference was line size -3 versus -4. The smaller ID produced a firmer pedal which is nice for those wanting firmer pedal, but personally I felt there was a trade off on modulation and slightly harder to push. GT3 Cup use the same OEM hose so plenty good enough for me. Not to knock on the SS hoses, they just not my personal preference.
Just personal preference on the pedal feel. I have installed aftermarket SS braided lines before, the ones I have installed(probably not all) have smaller ID(Inside Diameter), I think the difference was line size -3 versus -4. The smaller ID produced a firmer pedal which is nice for those wanting firmer pedal, but personally I felt there was a trade off on modulation and slightly harder to push. GT3 Cup use the same OEM hose so plenty good enough for me. Not to knock on the SS hoses, they just not my personal preference.
Just personal preference on the pedal feel. I have installed aftermarket SS braided lines before, the ones I have installed(probably not all) have smaller ID(Inside Diameter), I think the difference was line size -3 versus -4. The smaller ID produced a firmer pedal which is nice for those wanting firmer pedal, but personally I felt there was a trade off on modulation and slightly harder to push. GT3 Cup use the same OEM hose so plenty good enough for me. Not to knock on the SS hoses, they just not my personal preference.
Let me rephrase myself here, I meant to write its not my personal preference for the 997 GT3 braking system. On other cars, such as 987 Cayman, which the braking system has higher ratio of power assist and different master cylinder piston size, the -3 size SS hoses can be beneficial.
I'll be exhibiting DSC/Tractive products at the SEMA show in Las Vegas all next week. If any one care to visit its exhibit # 50421.
After I return to the shop and get settled in, I'll seek the expert guidance of Mike Levitas to rebuild and setup my diff. I'm ecstatic to be using sloppy seconds from Mike's Cup cars.
Last edited by Tom@TPC Racing; 10-28-2016 at 05:03 PM.
After changing the rear brake hoses couple months ago my brakes have been working very well, for a .1 car with 350mm fronts. But of course, I can't just leave things well alone. So, 380mm front brakes is something that's been on my mind because who doesn't want 997GT3 Cup-size front brakes, right?? Plus they look badass filling up the wheels more. Basic function wise, do I need bigger front brakes? No, not really, as the front braking is limited by the tires not by the stock 350mm brakes. Besides the cool looking factor of the 380mm fronts, I have often felt there should be more modulation without losing braking torque on my car. I could easily just use lower torque rating brake pads for better modulation but not doing that. Also, with the 350 front/350 rear, there are times when I trail brake that I felt there's too much front braking bias and came close to spinning the car, such as at Watkins Glen T6. DSC system has been helping to prevent spinning the car by managing weight transfer but I want to improve the braking bias. You are probably thinking why do you want bigger front brakes to reduce front bias? Normally I wouldn't, but the case of OEM 997.2 GT3 calipers for 380mm rotors the piston sizes works out that way. The .1 non-PCCB calipers(for 350mm rotors) have 28-32-38mm pistons. The .1 PCCB and .2 calipers(for 380mm rotors) have 28-30-32mm pistons. While the 380mm rotors is larger diameter, the calipers that fit the larger rotors have smaller pistons to reduce the amount of pressure on the pads. Here's my rationale- larger diameter to increase available braking torque, smaller caliper pistons for better modulation, and looks badass. Trifecta!
Now the idea is set, what about the parts? There are number of options available for converting 350mm to 380mm front brakes at different price points. OEM and aftermarket, all are good quality. With my budget and preference, I decided on using OEM adapters, OEM .2 calipers, and AP Racing rotors by Essex Parts.
I have done 380mm upgrades on 997 Turbo using the OEM PCCB adapters(part # 997 351 505 02, with has been superseded to parts # 997 351 505 04) This adapter was used for 997 Turbo/Turbo S to radially space out the caliper and to provide mounting for the wide bolt spacing. I think the superseded part # is for 991 Turbo/Turbo S. Not sure what the difference on the adapter but the old part # not available so it doesn't matter. As I said, I have done this conversion on 997 Turbos as a bolt-on so it should be a weekend afternoon project for a GT3.
Here's my pile of parts.
I'm a big fan of the AP Racing J-Hook rotors by Essex. They are two-piece floating design with spring clips to prevent low speed knocking. I have using the same brand rotors in 350mm for a year and a half with excellent durability. Which is more the reason to go with the same brand for 380mm size.
Here's my 350mm AP Racing J-Hooks by Essex with 20 track days on them. Yes 20!
The new 380mm rotors weights 24.6 lbs. Obviously it weight more than the AP/Essex 350mm but the 380's are still lighter than the OEM 997.1 GT3 iron rotor which weight 27.xx lbs.
Here's the OEM adapter with OEM shallow head bolts.
10-25-2016, 03:33 PM
Observation on braking bias change
Not to knock on the SS hoses, they just not my personal preference.
