trebor_quitman

Hello all,

I'm looking for some of the more tech inclined people to chime in here. I have never gotten into my brakes before other than to change pads, but I just recently scored some Big red callipers cheap and ordered the adapters from Paragon, Their here allready! wow! In a week or two I'll blow the bank and get the rotors/pads. Here's my question. I was told that 968 front and rear callipers are interchangable, true? When I put the big reds on I'm thinking about putting the old fronts on the rear since the pistons are bigger. But I was also told that even though the reds are bigger, I might still have an issue with the rear locking up to easily. Is there some kind of proportioning valve I can use to keep the reds balanced against the rear/old fronts? Probably in over my head and should just put the reds on and be happy. It just seems like It would be better to have that extra amount of fource to help slow/stop the car. I would still like to hear some of the pro's/con's behind my logic simply for the learning experience. Thanks

trebor_quitman

C'mon, there has to be SOMEbody up at 2:00am. Can you tell work is boring tonight...

FSTPRSH

At this time in the morning, I got lost after you said "inclined". From what I know of the 968s, the ABS should keep the tires from locking, and yes there is a proportioning valve to adjust brake bias. I don't have ABS on my car nor do I want it, so I can't tell you definitely the system will keep the back tires rolling. Someone else may know more about the caliper/pad/rotor/interchange issues.

marksportcts

Well I am running Big Reds up front and stock 951 rears with a 5/33 proportioning valve. I have talked to many shops/specialists and they all do not recommend moving the front calipers to the rear. Also keep in mind that the front rotors are thicker, and tho it is unlikely, the pistons can pop off is the pad it worn out too much.

Robby

I know that lot's of people have done this & I really wanted to at one time, but, now I think it's probably best to just use a p-valve w/stock sized calipers- I have Turbo S calipers & a 5/33- IF you went w/BR's (OR stock Turbo S fronts- the dif isn't THAT much) & used regular FRONT calipers on the REAR, then you would probably want the opposite proportion- stock would probably do just fine- I've never heard of anyone finding a LESS aggressive p-valve than 5/18 (stock) anyway- I doubt one is made...

ABS will help, but, is NOT what is supposed to be used for propotioning- just side to side metering....

I think I'd stay w/stock rear & use either a 5/33 or a 5/44 bias valve w/your BR's. - maybe an adjustable(?)- you will have the lighter rotors & calipers in the rear this way- weight reduction's worth something- & I've never heard of anyone overheating the rears anyway- I used to think it would be worth it to upgrade, but, in all honesty (& lot's of people tried to tell me, but I was too hard headed & had to find out on my own) that the rears hardly contribute anything comparably anyway...

Robby

IceShark

A couple things to keep in mind which end up pushing you down Robby's chain of thought. And he has gone through the facts and figures and talked to about everyone in the world for at least 2 years, that I know of.

The fronts do 85% of the braking work in hard stops. Just go to Brembo's web site and read a few of the papers if you don't believe me. So fronts are where you want to put your effort and money. If you put big reds on front and something bigger on back you will probably need a bigger master cylinder because the stock one doesn't have enough volume. But with stock rears and big red fronts you will be fine with your current MC. Then there is the issue of a parking brake. If you move your current fronts to the rear, kiss goodbye the parking brake. Not exactly the end of the world but it is nice to have.

I think I would look at getting larger diameter front discs before I would consider messing with the rear. I believe the big reds are about maxed out on disc diameter which means going to some new racing calipers like some 6 or 8 piston jobs that can take on a monster disc up towards 14 or 15".

Robby

Yes, the MC is another excellent point- Chris Cervelli mentioned this to me a long time ago- the pedal travel will increase GREATLY b/c of increased piston size- the BR & Turbo S calipers have the same piston size (unless the Turbo S has slightly larger front pistons like many people say, but, Porsche literature shows them as exactly the same)- therefore, if stock MC works for Turbo S fronts w/regular rears, then it will work for BR fronts w/regular rears, but w/regular fronts in the rear, it becomes a little much from what I understand- the best for the rear are the BR rears- they have the same pad size but much smaller pistons- this is what I've been told, anyway...

I had never thought of the parking brake thing- couldn't you just use dif rear rotors w/the parking drum in there & keep it? I'm not sure- I DID speak w/KVR long ago about custom two-piece rotors for the rear to use w/larger calipers, etc & they said they regularly make them w/the p-brake still in place, but, it get's sort of expensive- there was a guy who owned a 968 parts place- Prospeed maybe?- who said he had parking brakes in the rear too, but I think he normally used a BR REAR w/12.7" rotor (needs 17's or larger of course)- that's a good point though & one to look into if considering this- I wouldn't want to lose my p-brake on a street car...

BTW- Dan here is one of the ones who tried to tell me about how modding the rears wouldn't help- STILL bugs me, as I thought it would make a LITTLE more dif than it did I guess I was wrong I'm thinking that PART of my prob is worn out susp though better shocks & MAYBE SLIGHTLY stiffer springs (front especially) should help reduce nose dive & posibly keep the rears down a bit more, thus helping the rears do a tiny bit more- maybe 2-3%? Not sure, but will find out soon enough... I'm STILL trying to decide on what to do, but have narrowed it down to: 225lb - 250lbs front springs w/27mm or 28mm rear HOLLOW T-bars & Bilsteins all around- will mess w/sways later when I get closer to the end- I understand that SOME cars have done better w/SMALLER sways (Lindsey Racing did) b/c they have been lighter- I'm hoping to lose ~250lbs total- might not be enough to matter, but well see- Lindsey's wasn't too much lighter (I THINK ~2800) & they realized that 944Turbo S sways were better for them than 968 M030... who knows?

Robby

Yeah, the disc size is getting close to maxing out I think- I've heard of people machining BR's to take larger discs- up to ~14"- KVR says that Turbo S can actually take larger ones than BR's- doesn't make too much sense- should be the same really, but maybe it has something to do w/the curve, etc(?)... I agree, though, that the larger rotor's added leverage would probably benefit you more than messing w/the rears- I just don't think they'll ever get overwhelmed w/out SERIOUS racing. The prob w/using BR's w/say, 14" rotors is: the BR works perfectly for that extra .68" of rotor, over the 12" rotors- the extra pads size is the height (I mean measured as in extra diamter of rotor- that's the direction of extra pad size)- so, the BR's can easily be mounted in the same exact position & they stick up further so the extra diam of rotor can be gripped by the extra height of the pad- the same reason for needing larger rims of course. W/14" rotors & machined BR's, I'm not sure that the extra part of the rotor wouldn't be just sticking out of the top of the caliper & not really even be being used- anyone know? I've never really seen anything about it- otherwise, you'd have to change the mounting position of the BR to further out, to grab the outermost edge- does that make sense? Anyway, the simplest way is to just throw the 12.7" rotors w/BR's & be done, UNLESS other rotors are made to work w/larger rotors, just right, etc- plus, from what I understand, rotors above ~13" really don't help as much- law of diminishing returns- the ceramics are 14" & 15" but this is for dif reasons IIRC- plus, the ceramics don't add as much weight- they're ~7lbs each from what I understand & that's for 14"-15"- my Turbo S rotors- cast drilled zimmermans, weogh ~15.5lbs each. A regular 14" rotor would weigh a TON- probably >25lbs- would hurt you in all kinds of other areas b/c of this- accel, mileage, handling & ride quality, etc...

Not sure the trade-off's worth it- it's not to me anyway- I gave up on all that b/c I see how the M3's, etc stop & they have much less brake than we do- EXCEPT for slightly larger rotors (& possibly their longer WB helps?)- they have the same 12.7' of BR's, so, if you had BR's w/12.7's, etc, & had them pretty much maxed out (right bias valve, good pads, lines, fluid, especially tires, etc) then you should be much better off than even the short-*** stopping newer cars, like M3's, etc...PLUS, be able to SUSTAIN this braking ability better....

I've just come to believe that our cars have really been given about the best base they can have, to start with- if you can optimize them, then you shold have better brakes than many track cars- plus, many of the BIG 6 & 8-piston racing calipers have a lot more maintenance to deal with & are noisy, etc...

trebor_quitman

Chris Cervelli was the one who told me it wouldn't work. I guess I was stuborn and wanted to hear more of the facts before I gave up the ghost. In fact, he's the one that sold me the BR calipers. Sucks that he's moving It was nice to have one of the best wrenchs within limp home distance. Sure there are other shops locally, Powerhaus etc... but it'll be hard to find someone I trust as much as Technodyne. Thats why I'm in such a hurry to start doing all my own work.

Robby

WHAT? MOVING? Is HE moving or Technodyne moving or what? Any details? I'm trying to get a lot done to my car & was planning to order some of the stuff from him- is he still going to own a shop at all?

Garrity Repta used to use the front turbo calipers on the rear w/BR's up front, but, I never saw any of his cars or talked w/any of his customers about it to find out how they liked it. I doubt it would kill you, but, the overall consensus is that it really doesn't help & can potentially have a few cons to it... If I had 18's, though, I'd have to find something to give the rear a little larger rotor, if for not other reason than for looks- I LOVE the way it looks to have wheels really filled out w/rotors- the 12" rotor's on the stock 16" CS's are pretty maxed out- going to BR's w/12.7's w/17's is pretty close to the same, but w/18's, even though it would look fine, would still not be the same by comparison.

Chris uses a dif MC for his car- not sure what he's using now, but he's experimented w/a FEW dif ones- seems to know what he's talking about- hell, he's one of the best 951 drivers in the world- he has the 951 record at WS- low 1:20's... Stock GTSR VIPERS run mid 1:30's w/pros driving, so that tells you something... ALso, I THINK he ran that time w/just under 400HP & from what I understand, WS is a real power track, so the extra HP helps more than susp stuff- of course, I'm across the country, so I've never been on it...

any input on his situation would be appreciated...

Thanks...

trebor_quitman

Technodyne is closing it's doors at the end of the month, and moving to Denver. He is basically going to be working for someone else. From what I understand they will still do prep stuff for some of the big race teams, but thats about it. Thats what I got from Chris and Tiara.

Alan C.

I run Big Reds in front with stock rears. I use a manual bias valve. Works fine. I also use 94 3.6 turbo front rotors. Those do have an issue with being very close to the ball joints. The 933 TT has a shorter hat and moves the rotor to the outboard and away from the ball joint.

One guy here in Cincy runs the full 993 TT package on his 951 and another uses the Big Reds in front with the stock fronts moved to the rear. Neither seems to have an issue.

Alan C.