BrokeAss

You may recall from a previous post, that my wife & I ran our C4 cab in back-to-back sessions at a driver's ed and basically cooked our brakes by the end of the day. I was looking for the cheap way out and wanted to get a better set of Pagid Orange pads and a brake ducting kit.

In the end, I've finally come to terms with the fact that that's just not going to be good enough. Next month we're going to drive at Sebring (notoriously brutal on brakes) for two days. New pads & some ducting just ain't gonna cut it.

We've decided that we don't really need to fund our IRA's this year and that new brakes would be much more fun! After reading several posts and consulting the Pelican Parts Brake Chart I'm considering a "Big Red" 3.6 turbo brake kit for the front.

I can barely believe what I've read, but it looks like I can actually SAVE $1,500 because it appears that C4's don't need to change their rear brakes. However, they do need a brake biasing valve. (of course you wind up with red calipers up front and black in back, but I don't care!) VehicleCraft says so here.

Somebody pinch me, is it really true!?!?!?

Ade - C4 91

Just get some cross-drilled disks and paint your front and rear calipers red,
no one will ever never notice the difference - including you.

Spend the remaining cash on your wife, a nice holiday and lots and lots of booze.



Ade

Bill Verburg

Actually that's my site , which is kindly hosted by Pelican,

If you do the Big Red on 322x32 front, then you should also;
1)use 993 rearcalipers(might as well paint to match before installation) and
2) the 968 sport rear rotors and
3) get rid of the p/v all together

Yes, I know that the 993tt and 993C4 use the hydraulicly forward biased smaller rear 30/28 pistons, but they compensate moving bias back because of their 322x28 rear rotors and 304 cm sq pads(vs. the smaller 172 cm sq pads of the 964 or 993 rear caliper)

BrokeAss

Good news - I ordered my "big red" brake kit from FVD last Friday afternoon and the parts should be in next week! I've already lined up a couple of PCA buddies to come over that weekend for some beer, pizza and brake fluid.

I'll snap some photos of the installation to share here.

BrokeAss

Bill, what about taking the cheap way out and moving the stock front setup to the rear? I am sooooo broke!

Looking at your brake chart, I see that moving my stock front setup with 298x28 rotors to the rear gets me really close the 3.6L turbo configuration with a 299x28 rear rotor. (I know there's a lot more to it than just rotor size) That will give me an additional 4mm of rotor thickness in the back and should really soak up a lot more heat.

91C2wrencher

WOW where did that brake link come from? great work! I'm toying with getting a brake up grade but never wanted the $$$$ of big reds. Now it looks like from the chart, a great combo for my C2 would be S4 in front, 2 piston rears from a C2 RS, a new master cylinder and a proportioning valve. Voila! not quite as effective as big reds but yikes it should still stop me better. Is this just as much $$$ as big reds? And could I use my current fronts in the rear as mentioned above?

Bill Gregory

Note on the new master cylinder, I believe you need the 993 vacuum booster, and adapters made to bridge the smaller 964 brake lines to the larger 993 brake line openings in the 993 MC.

I have S4's in front with 928 S4 (or can use 968 M030) rotors and 993/RS (RS rears are superceded by the 993 C2 rears) calipers on the stock 964 rear rotors, with a Turbo 60 bar bias valve. I haven't upgraded to the 993 MC, as I haven't noticed a large enough difference to bump the priority up over other projects.

I upgraded my brakes because I spend time at the track. For street usage, unless you do something like upgrade to 3.8L, or the like, the stock brakes are fine (although 90-91's may want to upgrade the rears to the quad piston calipers of 92-on).

91C2wrencher

Bill, when you say,

"I haven't upgraded to the 993 MC, as I haven't noticed a large enough difference to bump the priority up over other projects."

Are you talking about braking improvement or just that going to the 993 MC seems unneccessary?

Adrian

I also provide another warning. Watch your brake pad wear very carefully. Why? at a certain point you will suddenly run out of brake fluid. This problem has occurred a number of times. A lot of people do not believe this until it happens to them. If you run big reds on a 964 C2 you have to be super super careful and on a C4 or Turbo you need to be super careful. The proven (by RUF research not me) is around 75% pad wear and you had better change them to avoid the brake fluid warn light and possibly no brakes. The reason for this is fairly easy to understand. As the brake pad wears the amount of fluid required behind each piston increases because it has to move the pad further. Eventually the contents of the individual brake system chambers in the reservior runs out and well you know the rest. The Carrera 2 has half the brake fluid available as compared to a C4 and Turbo.
Bill also makes a good point about the other items. I also recommend a 25 mm master cylinder from the Carrera RS as well. The C4 and Turbo are smaller. The C2 is the smallest.
Ciao,
Adrian
964C4

91C2wrencher

Thank you Adrian. Once again you provide vital information to protect us weekend wrenchers from sure diasaster. I knew there was reason to have a correctly sized MC, I just didn't make all the neural connects to have it mean anything......

Bill Verburg

Absolutly not! Your '91 C4 has 40/36 front calipers and needs 28mm thick rotors. The big issue is that w/ the front calipers on the rear, bias is terrible. The front rotors cannot be moved to the back either

The rear calipers needed w/ Big Red fronts are in order of increasing cost; the small 30/34 993 calipers which will work fine w/ your existing rear rotors, small 30/34 965 rears which also need the wider 28mm rear rotors or the big 30/28 993tt/993C4 rear calipers on 322x28 rear rotors.

Not in my chart!! Yes, for a 964 the 993/S4 front caliper on 2 piece 304x32 rotors(or BGs 928rotors), w/ 993 rears on the stock rear rotors is a good setup, Yes, the 993 M/C change is desirable for a higher harder pedal and the stock one is too small to properly move the large amount of fluid used in the bigger calipers quickly enough under all conditions, it's right on the edge so under normal use isn't an issue.

91C2wrencher

Thanks Bill, yeah my bad, I meant 993 4 piston units. Judging from both your and Adrian's comments it would be best to upgrade to the 993 MC and all that entails for a fool proof set up. ( i don't need the worry of no pedal at some point). Then question becomes if I go to a big red set up the MC would still need to be changed? Ya know why do all this if the big reds are a bolt on w/o an MC change?

Bill Verburg

The hydraulic requirements of the Big Red and 993/S4 are identical. They both use 44/36 pistons. The difference between them is their height. The Big Red is ~10mm taller and thus will require a larger rotor than the 304 that is used with most 993/S4 setups, 315 would do but 322 is the commonly available one.

The Big Red will move bias even further forward due to the increased leverage of the bigger rotor and the increased pad area.

The larger 23.8mm 993 m/c will give a nice high, hard pedal. It's not that the 20.64 will give you no pedal, but it is the inability of the smaller m/c to move enough fluid in a short enough period of time to properly service all 16 larger pistons. Some(the largest ones) can be shortchanged, meaning that the smallest will engage, usually locking the rear wheels prematurely.

Why do people sell only the Big Red fronts? because people will buy them for looks and never be bothered by problems at the limits of the performance envelope.

An optimal setup will include front, rear, m/c and p/v changes. As well as suspension, wheel and tire upgrades to go w/ them and if you really want the best bigger brake lines through out as well.. Just like an engine, you can't expect the most performance from changing only a single component.

91C2wrencher

Wow, thanks Bill. This has been a very enlightening thread for me. You seem to have a keen understanding of how the mechanics of these different componenets go together. Interesting that none of the vendors selling big reds mention the MC issue. Seems to me they'd want to cover their **** and possibly sell MC's as well. With all the options and expense involved with a brake upgrade it would seem silly to do half the job. Thanx again.

91C2wrencher

Adrian / Bill, Between the two of you there is some disagreement on the proper MC? Adrian you call out a Carrera RS (25mm) MC and Bill your leaning towards the 993 MC? Silly question? are they the same? My inclination at this point is to do as Bill has suggested, S4 up front and 993 rears. So which MC is it?

What concerns should I have regarding the ABS and related tubing? do these lines need to been changed? Can the internals of the ABS manifold handle the increased volume of a larger MC?