996 brakes and master cylinder

[HorstP]

Dear all,

I now have 996 brakes front and rear on my 1987 Carrera. Pretty happy with it, better balance than I expected, no more temperature issues and a failing brake at the track. I am using slightly turned down stock front 996 rotors and as such being able to move the caliper very close to the center, that probably helped a little to balance better. I am using a 55bar proportioning valve for the rear. And most of all the stock 3.2l master brake cylinder.

As said, everything is cool but I think I could love a little harder and more defined pedal. Would be using the Turbo master make things better in this direction and is there any ill side effect possible?

Short clip from yesterday having fun at the track..

https://youtu.be/M2ut1rfDvfQ

[Bill Verburg]

Originally Posted by HorstP

Dear all,

I now have 996 brakes front and rear on my 1987 Carrera. Pretty happy with it, better balance than I expected, no more temperature issues and a failing brake at the track. I am using slightly turned down stock front 996 rotors and as such being able to move the caliper very close to the center, that probably helped a little to balance better. I am using a 55bar proportioning valve for the rear. And most of all the stock 3.2l master brake cylinder.

As said, everything is cool but I think I could love a little harder and more defined pedal. Would be using the Turbo master make things better in this direction and is there any ill side effect possible?

Short clip from yesterday having fun at the track..

https://youtu.be/M2ut1rfDvfQ

first you still have a huge amount of front bias, that' safe but makes the front do more work than necessary, it's much better for performance and longevity to take as much of the load off the front as you can get away w//

to that end, ditch the p/v, the stock '87 911 had a 33 bar p./v which was necessary because they had to much rear brake. You have the opposite issue.

the pedal is soft because you went from a pedal ratio of 38.3 to 43.2. You are on the ragged edge of what works. install a 23.8mm m/c from a 930. You will now have a pedal ratio of 32.3. ie what a stock 996 has. Right ~30 is a very nice place top be.

[wildcat077]

Listen to Bill's advice ... i asked a lot of questions many years ago when i was a newbie ... lol

Without a 23.8 mm master and a bias adjuster , which means you also need a dual master setup , you're not achieving the full benefits of the 996 brakes.

I ended up going all out with a Fabcar dual master setup and Titlton bias adjuster , it was crazy as i was outbraking most 996 GT3's on the track, those guys couldn't believe an "old" 911 could brake so deep into corners !

[HorstP]

Bill, Phil,

No worries. I am listening. That's why I posted here and hoped for replies from folks like you. I had of course been reading older threads so moving to the 930 M/C is nothing new to me. I just wanted to double check if there could be any negative effect, sounds like there isn't any. I will go right away to change it!

On the p/v, I am also aware that I probably don't need it. Reason why it is there that I wanted to start on the safe side and not being surprised by the rear end first time on the track with that set-up. I actually wanted an adjustable valve to slowly approach more rears, but for whatever reason that did not seem to work. Maybe I should try again after the new master.

Thanks again, I will report back.

[Elombard]

My experience with an SCCA GT3 datsun 510 - full race car, was that the rears lock so easy because they are unloaded and maintaining control was not difficult (and I aint any kind of gifted). You just crank the adjustable P/V until they stop locking. On that car once I had the PV set right it made a huge difference in how planted the car felt under braking. Made me feel like a superhero!

With the ratio Bill is describing I don't think you will have any issues. I think you will want more rear brake possibly.

[Bill Verburg]

Originally Posted by Elombard

My experience with an SCCA GT3 datsun 510 - full race car, was that the rears lock so easy because they are unloaded and maintaining control was not difficult (and I aint any kind of gifted). You just crank the adjustable P/V until they stop locking. On that car once I had the PV set right it made a huge difference in how planted the car felt under braking. Made me feel like a superhero!

With the ratio Bill is describing I don't think you will have any issues. I think you will want more rear brake possibly.

Any front engine car has very different brake needs compared to a 911


Stock 911 thru '83 had just about perfect bias for a 911 @ 1.491. The pedal ratio could be a bit lower but was still fine @ 35.3. The only short coming was thermal capacity as the cars got heavier and faster. W/ the the right setup even more rear could be used on a race car.

the next air cooled to have great bias was 993RS/Cup w/ 1.426 an a pedal ratio 33.6

After that you needed a Cup or RSR to get decent bias in the 1.2 to 1.8 range due to the twin master setup used on those cars

[Elombard]

Bill what does the bias end up being on the OPs car?

I guess its same as a 996.

[Elombard]

Bill what does the bias end up being on the OPs car?

I guess its about the same as a 996 except for the change from cutting down the front rotor.

[Bill Verburg]

Originally Posted by Elombard

Bill what does the bias end up being on the OPs car?

I guess its same as a 996.

w/ 996 calipers and rotors you have 996 bias which is 1.811, when a 55bar p/v is used that goes to 3.071 above 55bar line pressure( a fairly hard stop)

again 1.49 to 1.426 is where the sweet spot is, you can go as low as 1.2 in special circumstances w/ the right set up and driver

factory race cars are set up w/ adjustable bias in the 1.2 to 1.6 range.

[Maxhouse97]

OP - how did you get the caliper closer to the center of the hub on the front? Did you file down your caliper adapter? I too have this setup on my 87 and have a front lock up issue, and am trying to reduce front bias.

[HorstP]

Rotors were turned down and the adapters milled to move the caliper as close as possible to the hub. Mind you, the reason why we did it was to fit the 996 brake under 16" Maxilite which give significant less room than a same size Fuchs rim. As a bonus even my 15" Fuchs spare with spacesaver still fits!
I am just speculating that theoretical it reduces the front bias a little, not knowing if that is large enough to be noticed.
I would assume you could also play with different pads and have a more aggressive pad in the rear. I am running stock 996 break pads, only those little weights had to be cut off from the out front ones.

[HorstP]

[HorstP]

the spare still fitting over 996 caliper. If you look close enough on above picture, some minor machining was required on the caliper itself

[Flojo]

Originally Posted by HorstP

Rotors were turned down and the adapters milled ....

when I read this it makes me shiver.
I'm ready to learn, but the idea of fiddling with brakes in terms of removing material seem crutial.
no?

[HorstP]

I understand fully that you have a critical view on this but:
- tell me what removing 5mm on the outside of a rotor should make as a difference?
- The adapter is a very heavy piece of metal if you ever looked at one

My car has around 300hp now and I feel very comfortable with every modification done. Still needs some minor tweaks on the suspension, too much body roll in hard corners and a final mapping on the engine.

[Flojo]

obviously it works. I'm just very careful in matter of brakes and the heat/force they must cope with.

maybe you can detail out more as to what, how and exactly where you reduced/removed materail (pictures).
might be interesting for others In case they plan to copy your setupt.

[Maxhouse97]

I really like this idea. I was going to ask about pad clearance to the center bore of the disc, but the pic clears that. So was the total amount removed from the disc 5mm in radius or diameter?

5mm radius would turn a stock 318mm rotor into 308. Interesting that it fits under 15s. I assume you removed 5mm from the adapter bracket as well?

Bill V - what do you think about this mod? Any downsides?

[MAH77]

What caliper adapters did you use?

[Maxhouse97]

To the OP, did you have to machine the inner circumference of the disc (where the pad gets close to the bore)? I went and looked at mine (stock) and there seems to be a inner lip.

[Maxhouse97]

Or maybe my rotors are worn and I need new ones!