ThomasC2

On page 540 Adrian says that if you have a C2 and put on bigger calipers you should change your mastercylinder to a bigger one. First go for the C4, Turbo or RS version. If 993TT calipers then go for the 993 cylinder.

My question is if the Turbo or RS is a bolt on solution, I thought they didn't fit and that the only option is 993 version were you also have to make adapters for the thicker pipes.

And if a RS cylinder version fits, is it worth the money/effort or is the 993 cylinder the best/only way to go?

Adrian also says that you should use a larger brake fluid reservoir. Which ones are larger? Is the, lets say, RS-reservoir bigger and would it be a bolt on replacement?

ian c - u.k

turbo and rs use electronic boost rather than normal servo to inlet manifold

Tom W

The other models use a differnt style of boost and are far from a simple "bolt on" change. The closest that you get for a C2 is the vacum assist of the stock 993 C2.

I had my brakes changed to big reds on Saturday. I have not had a chance to test the new brakes at the track, but I was not dissapointed by the pedal feel leaving the stock MS and reservoir alone. I know of one other guy in SF that has also added big reds and did not change the MC and have no issues at the track. This car is used to support two drivers and the brake change was done for the extra cooling. The rationale for my change is the same - mostly cooling.

robmug

Rennlister Bill Verburg has a website dedicated to 911 brakes...

I'm sure he won't mind me posting the link.

http://www.pelicanparts.com/MotorCity/wmv/brakes.htm

Adrian

Dear Thomas,
The rationale for changing the brake fluid reservoir size and or the master cylinder is; If you install brake callipers with larger pistons which have a larger surface area to cover with brake fluid and you do not increase the supply of brake fluid you may run into a problem as the brake pads wear.
If the callipers you install do not have a total front and rear (remember two separate circuits) physically larger piston surface area than original then you will be okay.
If you want the larger master cylinder assembly the Turbo 23.1 mm version from the 1978 and up models may be worth looking at.
For the record this data and some testing was done by RUF and myself. RUF first came up with this problem during one of their own conversions. The consensus was that the brake pad wear limit was reduced to 75% if you install larger pistons surface area. If you allow the brake pad to get slimmer than this amount there is insufficient brake fluid supplied to the pistons. However again this is a hard use issue, racing issue more than anything. For road use you need not do anything except paint your callipers red because you will gain no benefits from installing larger anything.
Ciao,
Adrian
964C4

Bill Gregory

I know a number of people who have upgraded their brakes to either S4's or big reds, and have not upgraded the MC's or reservoirs, and everything works just fine at the track. I also know one or two who have noticed a lower pedal, but that seems, generally, to be the exception and not the rule.

Bill Verburg

The 20.64mm 964 C2 m/c is at the small end of acceptable. the issue that Adrian referred to will only arise if the fluid level isn't kept topped off as the pads wear(i.e. generally not an issue for a mechanically sensitive owner)

There is absolutly no question that the pedal will have more travel, whether it is objectionable is a matter of personal taste.

The 23.8mm 993 C2 vac boosted m/c can be installed relatively easily for a higher/harder more easily modulated pedal.

Bill Gregory

The 993 C2 MC requires custom adaptors for the 964 brake lines to fit. If I recall, on the order of 6mm to 10mm adaptors.

Bill Verburg

Yup, that's the hardest part

Adrian

Dear Bill,
You wrote "(i.e. generally not an issue for a mechanically sensitive owner)"
and whilst I agree with your statement the fact is when you write anything in the form of information such as a book or a technical article you must assume that people reading it are not mechanics.
The fact is that the vast majority of car owners including Porsche owners are not "mechanically sensitive". Many will take their Porsche to a mechanic to have this work done and accept/trust that it is correct.
There are currently 2 cases of unlawful death cases in Germany before the courts directly related to this matter.
On rennlist and all other forums nobody is legally liable for the advice or information they give so I always hold to a full and accurate explanation and then leave it up to the reader to decide whether to take any notice or not.
Ciao,
Adrian
964C4

garrett376

There are laws on how you're permitted to die in Germany...? Yikes!!!

Adrian

No, just laws against the incorrect an unapproved modifications to automobiles which are suspected or proven to have played a role in the death of somebody. Like running out of brakes and crashing. All accidents involving serious injuries and death are extensively investigated in Germany and other countries in the region.
Ciao,
Adrian
964C4