Jeff Curtis

Hey you lucky Turbo 3.6 owners, I have a question for you, maybe Cupcar can answer this one as well??

I have had BIG Red calipers on the front of my C2 for several years, just renewed the calipers last year and over the Winter I have purchased the correct BIG Red calipers for the rear.

Currently, thanks to Cupcar (if I remember correctly) I utilize a 60bar brake bias valve for the rear brakes...the new calipers for the rear take the same size pad, but have larger pistons...do I go back to a 45bar brake bias or lower like 33??

garrett376

On my track car I run Big Blacks up front, 993 rears, with NO bias valve - works fabulously! Brakes so hard I need to squint to keep my eyeballs in!

Jeff Curtis

Garrett, you're saying that you removed your factory 45bar bias valve for the rear brakes??

I have increased rear brake bias to 60bar due to the larger calipers up front, but the mindset is that I need to dumb it back down to 45bar or so being that my new rear calipers have larger pistons than the current ones, although they take the same pad.

garrett376

Hey Jeff, here's my link from a while back:
https://rennlist.com/forums/964-forum/204795-ever-wonder-how-the-proportioning-valve-works-and-what-its-innerds-look-like.html

The larger pistoned 993 calipers are the same as the 965 3.6; coupled with the Big's on the front, plus the 60 bar valve - that equals the same setup as the 965 3.6. But for a track car, having more rear bias is helpful, I think. That's why I removed the valve per my post above. It works really well, even on downhill sections under hard braking, I don't get rear lockup. Love it

Jeff Curtis

Well that certainly makes sense...leave the 60bar bias valve in because that's what the Turbo 3.6s had.

Thanks for clarifying, oh I am so out of it when it comes to my C2...haven't really paid attention to it for a couple of years except for fixing something here and there.

SO, being that I NOW will have the same setup as a Turbo 3.6, I'll keep my 60bar bias in...simple enough.

Bill Verburg

965 rear and 993 rear are the same size caliper(small) and use the same pad and have the same 30/34 pistons, the difference is in the throats wher the 965 accomodates a 28mm rotor while the 993 only accomodates a 24mm rotor

The stock 964 rear has the same size as the above, uses the same pad but has smaller 28/30 pistons.

I am guessing that Jeff means that he has a set of 965 calipers and hopefully some 28mm rotors to go w/ them(though last i looked there were none).

If you are still using 24mm rrear rotors you really want the 993 rear calipers(not the 965s)

Also w/ the bigger front and rear caliper pistons the bigger 993 m/c will give you a much better pedal.

As far as the bias goes I would at least try it w/ no p/v. You have increased the front bias by a lot and the 30/34 calipers only gets back a little of that.

On the 993tt and 993RS a whole bunch more rear bias was dialed in, it seems to work.

first pic is what is usually considered true Big Red front(large) and rear(medium)

Second is a 993ttrear(medium) and a 965rear(small)

Cupcar

The 964 Carrera Cup used essentially the same brakes that a Turbo used (w/thinner discs in the rear) and NO proportioning valve.

I installed the Cup proportioning valve bypass line on my car and the brakes work great.

I have the same brakes as Garrett does.

Bill Verburg

i.e 993calipers on stock 964 24mm rotor or the drilled 951 MO30 24mm rotor.

It really needs to be emphasized here, the 965 rear caliper wants a 28mm rotor, the 24 is too thin!

Jeff Curtis

Hmmmm, interesting, do you have a PN for the 993 rear caliper then?? ...in RED??

I'll double check what calipers I received, I haven't installed them yet but do believe they are of the 965 variety and I also bought a pair of the M030 968 rotor which is 24mm, just like the stock 964 rear rotors but they are cross-drilled.

Will the 993 rear caliper bolt right up then?

garrett376

Yep, direct fit. I got some used ones for $200 - they are quite easy to come by! what a deal!

Marc Shaw

These might be another option - floating rotors and all.

Marc

Bill Verburg

Unfortunately the 993 calipers(other than the Big Reds or special orders) only came in black or silver.

You could buy a pair and send them to Cris Walrad for powder painting.

993rear
993.352.421.00
993.352.422.00

yes they are readily available from all the 993 guys going to the 993RS setup.

and yes, the rear 964, 993, 965 928GT and 944 are all basicly thes ame caliper.

The 965r is the only one w/ the wide 28mm throat, the 964 front also has the wide 28mm throat and would bolt in but it's pistons are way too big for use on the back.

Cupcar

If you have the 965 calipers I believe there are machine shops who can machine the caliper for the thinner disc.

Bill Gregory

That would be VCI in NJ. Website is www.vehiclecraft.com

Jeff Curtis

Well, I think machining a BRAND NEW set of calipers is out of the question, if the "correct" ones are available. Bill, I ordered the PN you had emailed me...maybe I need to double check what they are? ...as far as mm spread.

Really, is 2mm a side going to make a difference?? - that's not a whole lot, I usually toss pads at 50% due to heat cycling/heat checking anyway, they're just like tires people.

BUT, you've all got me wondering...I paid about $700 shipped for these, if I could save $$$$$$ by getting a pair of used 993 rears, that would be swell! ...they are RED, correct? ...the 993 rears?

GOT to have red, been going too long with BIG Reds up front and the 964 4-piston black at the rear, many people ask, "WHY are your front brakes RED and the rears black...over that.

***Bill, just saw the post above where you say they are silver or black...maybe I'll just stick with what I've got for now...unless someone knows where I can source a pair of 993 rears?? ...and I will certainly get Chris to powdercoat them RED...gotta have that RED!