Abe Anderson

I have big reds on my 92C2 and would like to install the front calipers on the rear. To do this correctly one should use thicker rotors for the wider calipers. I understand that the cup cars or RS models had this thicker rotor.

Has anyone done this upgrade and if so do you know the part number of the rotor.

Thanks
Abe

Bill Gregory

Hi Abe,

The Carrera Cup US (cup version specs I have in hand) and Carrera RS had the same size rear rotor as the C2. Both 24mm thick and 299mm diameter. Only difference there is that the Cup/RS rear rotor has cast-in holes. Turbo rotors would be 28mm thick. This 4mm difference is the same as the delta on the front: C2 thickness is 28mm and Cup/RS is 32mm, which is the Turbo rotor. The rear 91-93 Turbo is 299mm diameter. So, perhaps that's the rotor you want to consider? (wonder if the rear Turbo hub is deeper than the C2 rear hub?)

Abe Anderson

Hi Bill

My 964 spec book and parts fiche agrees with what you said, the 92 Turbo and the 3.6 Turbo use the same rear rotor at 28mm x 299mm. I've always heard that to use the front calipers on the rear that one had to get special rotors, so I'm guessing that the Turbo's do not fit.

GeoC2cab

High,
I have done this upgrade to my 1991 cab, Big blacks on the front and moved the fronts to the rear, I did have to change the pressure bias valve because of early lock up in the left rear, I did use OEM cross drilled rear rotors from AJR. Everything feels very nice now, though I have thought if it was neccesary to use a thicker rotor, but my shops says no, is that right?,I kinda agree just because they feel real nice(the whole set up).

Bill Gregory

Abe,

Sorry, I misunderstood. You want to move the old stock C2 front calipers to the rear. The stock calipers use a 28mm wide rotor. I just took a look at the VCI website, and under 964 brake upgrades they talk about narrowing a rear turbo caliper to handle the stock 24mm width, as the factory did on the cup and RS's. Maybe that's another option for the C2 front calipers if you can't nail the right rear rotor. They do say not to use the Turbo rotor in the rear as it's the wrong offset.

George, VCI does suggest not to use a caliper made for a 28mm rotor on a 24mm rotor, as the pistons can pop out if the pads get way low.

VCI page is at <a href="http://www.vehiclecraft.com/Brakes/vciweb7.htm" target="_blank">http://www.vehiclecraft.com/Brakes/vciweb7.htm</a>

Bill Verburg

The 964T(both 3.3 and 3.6) used the wider 299x28mm rotor in the back. The 993RS and 993TT used a 322x28mm rotor in the back. These are the widest available for that application.

To complement the front Big Reds you should use the 34/30mm rear calipers from a 993 or 964T.

If the oem fronts are moved to the rear there will be way too much rear bias, necessitating a more aggressive p/v.

GeoC2cab

High,
I can get my hands on 993 rear calipers, so I then would be able to keep the 24mm rear rotors? but will i have to change the pressure valve bk to the stock one(still have). Anyone have a part# for that 34/30 mm rear 993 caliper, thanx.
Or, how do i narrow my stock front calipers to keep them on the rear? thanx for help.

Abe Anderson

I am currently running big reds in front with the stock rear calipers. I have removed the brake bias valve. I use my car for 20 - 25 track days per year and some street use and I drive to the track pulling a track trailer with eight track wheels and tires. I found that running with the bias valve, I didn't have enough rear brake at the end of high speed straights (unstable), removing the bias valve helped considerably. To further improve braking I replaced the rear Pagid Orange pads with Pagid black. I will pursue the elusive 28mm correct rotor for this application. If the front C2 calipers on the rear give too much braking then I will re-install the bias valve. Running the stock 24mm rotor with the C2 front caliper is not an option as you would have to throw away perfectly good pads.

AES

Check Bill Vs brake page. there is lots of info there that you may find usefull.
<a href="http://www.pelicanparts.com/MotorCity/wmv/brakes.htm" target="_blank">Brake Info</a>

GeoC2cab

High,
Thanx for that link very helpful and helped me understand alot more about brake applications. I have a set of factory 993 rear calipers and rotors I plan to put on the rear of my car (instead of the original front calipers) w/ the big blacks on the front, according to the chart on Bill V.'s page I should use a 40 bar prop. valve? can anyone confirm if I'm right.
Is it neccesary to change master/slave cylinder sizes w/ this larger brake set up? Thanx for important information, I feel brakes are probablly the most critical component in the car to have "exactly right". <img src="graemlins/burnout.gif" border="0" alt="[burnout]" />

Bill Verburg

GeoC2cab-there are several different 993 rear calipers the 94-95 C2 rear have the correct 30/34 pistons but are narrower for the 24 mm rotors, they can be used on the 28mm 964t rotors if the pads are shaved. The best Are the 964T rear 30/34 which are designed for the 28mm rotor(they are a few mm wider). The master cylinder should be changed to the turbo 23.3 vacuum boosted mc if any of the larger piston calipers are added, it is a straight swap. The 25mm hydraulicly boosted mc won't work without a great deal of extra effort.

Personally the effeort involved in putting the wider rotors seems to have little return for all the expense and trouble involved. The Big Red or 993/S4 on 322mm rotors with a 993 30/34 rear on the 24x299mm rotors is a very nice setup

Cupcar

I have to second Bill Verburgs recommendation since I just spent yesterday afternoon installing it. One thing of interest to anyone, like me, not wanting red colored "Big Red" calipers is to use late 928 front calipers (part #'s 928.351.423.03 and 928.351.424.03) which are identical to "Big Reds" except they are black painted and have the bleeders and crossover pipes flipped. The bleeders and pipes are flipped because the 928 mounts the left caliper at the 2 o'clock position and the right at the 10 o'clock postion and the 964 is the opposite side to side. The parts are easy to move, I did replace the crossover pipe with an unpainted new one (part # 928.351.971.01) since the paint gets chipped during removal.

GeoC2cab

High,
Just in case anyone is interested I have a connection to two sets of the 993 rear calipers
34/30, should u want to use them w/ ur big reds or S4's, make that 1 set, 1 is taken; by me
The other set is in good shape w/ only 15000 miles on them. E-mail me if ur interested.