Bill Verburg

993 standard front calipers are the same as 964RS/t front calipers except for 1 feature, the 964RS/t have built in raised mounting bosses. They both want a 32mm thick rotor, the 993 wants 304mm and the 964RS/t wants a 322mm. The 993 can be adapted to 322mm rotors by using shims that emulate the mounting bosses on the 964RS/t calipers

orp73

Bill this most interesting, thank you, my car is an early one so only had the 2 pot rear brakes, guessing i could fit a brake bias valve to correct any front to rear discrepancy ?

KaiB

Should you do this, you should certainly install a manual bias valve (it'll fit just fine up front). A day spent carefully finding the proper rear bias is a good thing.

Note the caveat regarding the 24mm rotors beneath calipers designed to accomodate 28's....you'll need to replace pads more often. The money you save by transferring the front calipers to the rear will then be offset by the cost of the bias valve and additional pad changes.

Paul284pt

Hi Bill/KaiB,

If I use the 964t front with 322 x 32 rotors for the fronts and rear set-up as per your suggestion:

[QUOTE]in back you will want to use 993 rear calipers which bolt up to the stock 964 trailing arms and...... use 968 M030 rear rotors as was done on 964RS.

To use the above brakes you will also want to install a 993 brake booster and m/c and remove the stock p/v./QUOTE]

....do you have any suggestions as to part nos. for the 993 brake booster and which m/c please?

Also am I likely to encounter any problems fitting them and then setting up?

Thanks again,
Paul

KaiB

IMHO you don't need the 993 brake booster along with the cost and installation it requires.

I race my car without it (i.e., the stock booster) and LIKE my brakes. A lot, actually. I can go deeper than most drivers in their Cup cars and have never felt that my brakes were limiting me.

Why not go without for a year and see how you feel about it.

Paul284pt

Hi KaiB,

Thanks for your speedy response.

That's good news! Will I still need the 993 m/c, or can I get away without that too?

Cheers,
Paul

PS any more pics of your car, it's beautiful?

KaiB

Thanks, hereya...

I'd save the money and go with the stock m/c - I do and again, my car works very well.

Bill Verburg

here are the 993 booster/mc #s
964 to 993
m/c 993.355.910.00
vac can 993.355.023.10
gasket 993.355.301.00
support 993.355.163.03
you also need to convert between the smaller 964 brake lines and the larger 993, the easiest thing to do is to have some brake lines made up w/ 964 10mm fittings on one end and 12mm 993 fittings on the other end, Classic Tube can do this or you can use some 10/12mm fittings BMW pat #34-32-6-752-405

The reason you want to use the bigger 23.8mm m/c is the hydraulic ratio between the slave and master cylinders, ideally for track/performance use you want this to be in the low 30s, a stock 964 is 43 which is at the high end of acceptable, go much further and the m/c is too small to service the brakes. A 993 is 37.311. Your car w/ the big brakes and stock 964 m/c is 49.796 this is too high. Do use the 993 booster and m/c.

KaiB

Hopefully Bill, someday you'll drive my car.

I see no need for the boost and m/c. Neither does my pro coach, nor does the tremendously experienced/accomplished builder of my car - a top level racer and pro crew chief himself.

Paul284pt

Fantastic! Love your car and advice

I'm going with that and see what the brakes are like, if they're good enough for you on the track then suspect I won't have too much to worry about.

Your car reminds me of the famous Bob Akin cars, my favourite was the 1981 935 in Coca-Cola livery...mint! I saw it race at Le Mans 1981. Got some nice photos of it somewhere. The red & white is my favourite for 911 race cars, it just looks so right.

Here's my 964 which this month is going to Nick Fuljames of Redtek. Similar engine job to Frank's beautiful Black Betty although not quite as highly spec'd.

Mine's only done 75k and doesn't really warrant a full top & bottom rebuild but I thought what the hell! I may as well enjoy it now! I originally bought her to back-date but she's such a beautiful car I didn't have the heart to tear her up.



Cheers,
Paul

Paul284pt

Hi Bill,

That's much appreciated! I'll give it a try without first and I'm due a freebie with Porsche at Silverstone so I'll maybe try it out there and also see what the instructors think, they like thrashing a different car

If there's any issue I'll go ahead and change to your suggestions.

You've been a great help guys and even though there are pages of this stuff on previous posts, I'm sure there are others who have learnt something like me by having it spelled out for them

Thanks again,
Paul

Bill Verburg

look, you like what you like and no one else could care less

I post the engineering facts and compare what people have or propose to use and can compare that w/ what the factory has done. Believe it or not, it's you call. As we all know the internet is full of bad advice and it's up to you to do your due diligence.

here are a few more facts concerning the ratios
911 thru '76 41.311
911 '77-83 35.328
911 '84- 89 38.345
911SC/RS 33.077 w/ 23.8mm, 33.181 w/ dual masters race setup
964 2pot rear 45.456
964 4pot rear 43.004
964 C4 32.342
964RS 32.786
964RS C4/lw 30.346 w/ dual masters
993 37.311
993RS 33.654
993 Gt2 Evo 27.826
996 Gt3 30.479
Boxster 32.615
Cayman S 32.342
Cayman S PCCB 30.603
997 GT3 30.603
997 GT3 Cup(early) 30.603 late 29.470

993 brakes w/ 964 m/c 49.796

cars that I have personally seen have insufficient m/c volume 50.2

Enjoy

KaiB

Bill is the BEST resource we have on our cars, bar none.

He and I have gone back and forth regarding my braking system for two years now - please don't let it bother anyone...I actually think we enjoy it.

I value his work; it was his stuff that got my build started back when Claudia was to be a dual purpose car.