Myles Maycher

cjoenck

Just search here and on Pelicanparts. There are countless threads on this topic and I am sure you will find your answer.

Bill Verburg

You really want to change the rear calipers to 993 versions, even w/ those the system is heavily front biased, I'd remove the p/v totally as was done on the Cup cars.

C4 comes w/ a 23.8mm m/c oe this will be fine, though you will get much better feel from using a 25.4 from a 964RS

Goughary

Bill, can one run a 964 RS master on a C4 without modification? And are they available?

Achtung964

I'm running big reds up front and 993's in the rear, stock C2 MC and brake booster. Gutted the P/V. Pedal feel is pretty firm. Is it worth upgrading to 993 MC and booster?

Bill Verburg

yes

Bill Verburg

If you think that is good then you have an eye opening experience awaiting.
stock 964 w/ 4/4 calipers has a pedal ratio of 46 .159, this is already poor
964RS(essentially what you have) is 32.786 when a 25.4mm m/c us used. This is excellent and right where you want to be for sporting use

stock 964 20.6 w/ the 964RS calipers(again essentially what you have) is 49.651 again poor and borderline inadequate, issues will arise in panic stops @~50 or higher

the best you will be able to get w/ vacuum boost is to use the 993 booster and 23.8mm m/c, that will give you 37.342 ok but nowhere near as good as the true RS set up.

Achtung964

Thanks Bill. Just to confirm, I can't simply get the 964RS 25.4mm m/c and booster to achieve optimal braking as you mentioned? Is the limitation availability? price? compatibility?
Also, I see a couple of versions of the 993 mc and booster for sale from various internet outlets. Does buying from a place like Sunset Porsche ensure that I'm getting the best quality OE product? If not, where should I buy from?

Bill Verburg

the m/c used by the electro-hydraulic boost systems used in C4, RS & turbo are incompatible w/ the vacuum boosted systems used in the C2's

You'd have to t'p the whole setup, a non trivial task

tjb616

I'm still waiting for someone to do a DIY.... I'd like to do the conversion one day but I think if I tried to pioneer the effort I'd end up deterring more than Id encourage.

Sire

I'm curious al so. I just bought the Big reds for the front and back. So when I read it correctly the best setup is then an 964RS MC and booster.

porsche mania

I have big reds on the front of mine with a 993 mc, a gutted pv but still only the 964 4 pot rears. I know I need to get the early 993 rears to improve the bias as the car still has too much front bias. Rather than finding 993 rears is there another caliper that would bring the bias even closer to that of the rs. I know the 993tt will fit but at the expense of the handbrake which is a no go but could I get it to work with some custom made discs for the rear? I've found somewhere that can make whatever I ask for but that's the problem, I've no idea what I need!!

Bill Verburg

yes but the t/p is pretty involved

the 993 vacuum booster and 23.8mm m/c is a straight forward t/p
you need
993 355 910 00 m/c
993 355 023 10 vac can
993 355 301 00 gasket
993 355 163 03 m/c support
the hardest part is bridging the 12mm 993 fittings w/ the 10mm 964 lines
one way is to use Fedhill M6-3 - 12mm x 1.0 male steel nut with non-threaded lead - SAE flare or DIN flare
another is to have new lines fabricated 12mm on the m/c side 10mm on the chassis side
another is a BMW adaptor 34-32-6-752-405

Bill Verburg

993tt and 993RS are physically the same but use different pistons tt is 28/28 way to small, RS uses 30/36 this what you want, the regular 993 rears are 30/34 and use a smaller pad, this is the easiest compromise

and yes even w/ the 30/34 the p/v ought to be removed or gutted

Goughary

Bill. On the 964RS Brake MC...

You say they are available. I'm assuming only from Porsche directly?