apanossi

Having trouble getting my brake upgrade right. I wanted to upgrade to the 993TT big red brake kit for my '94 C4 widebody. So far what I have for parts needed are:

Front Calipers (red):
993.351.425.10 (993TT)
993.351.426.10 (993TT)

Front Rotors:
965-351-045-00
965-351-046-00

Rennline caliper adapter


The rears get a bit interesting. Not sure of the rotor size and caliper that a C4 widebody can handle with its turbo trailing arms. Currently, it has a 965 rotor that is specific to the C4 TL. The 3.6 turbo rotor part number is off by one trailing number. The question is what rotor and caliper combo will fit with the best bias using the 993TT big reds?

Bill Verburg

In back you will use the stock 964t caliper and rotor

not sure why you want to change the fronts, the stock 964t setup is actually better in most respects

apanossi

Thanks Bill. I was hoping you would chime in. The 1994 C4 widebody has a different caliper/rotor configuration than the 1994 3.6 964T. The 3.6 has 322mm rotors w/ larger calipers (similar to 993tt) up front (pistons 44/36). The C4 widebody has standard C4 calipers/rotors in the front (pistons 40/36).

For the rears, the brake setup is nearly identical between the 2 models. The question is, in order to balance f/r bias with 993tt front big red brakes, is it advantageous to get the slightly larger 3.6 rear caliper or is it better to make the leap to the 993RS rears? I don't know if anyone has conclusive evidence that you would lose the parking brake with 993rs rear rotor/caliper combo on a 964 turbo trailing arm. I know that you would lose it on a n/a 964.

Bill Verburg

So you have regular 964 brakes now, and the trailing arms are 964t

and you are changing to the Big reds from 993tt

ok then that is basically what a 964 3.6t used, to match the big red fronts use the 964t rear rotors and calipers, these have the bigger 30/34 pistons(same as 993 or 964RS rear) but use the thicker 964t 28x299 rotors(993 and 964RS use 24x299) the pad is the same as you have now front and rear. the 964t rear calipers come in black 965.351.423.01 /L 965.351.424.01 /R or red 993.351.425.10 /L 993.351.426.10 /R

another option is to just leave the rear alone, the 964tl comes w/ 30/34 rears already, the only thing you are giving up is the slightly thicker 964t rear rotors.

As I said I don't think that the larger 993RS/tt rear 322x28mm rotors will work w/ the existing parking brake.


if you want black front 993tt/RS calipers use the 928GTS front calipers, just swap the bleeds and feeds.

apanossi

Bill, thanks again for lending your extensive knowledge on this. I have since confirmed for myself that which you just stated: 993RS/tt rear rotors will NOT fit a 964t rear trailing arm without sacrificing the parking brake. The reason is the height of the hat (73mm for 964t vs 68mm for 993RS). This translates to different offsets.



I could not find a similar blueprint for the 964t rear rotor, but I did pull out my rear rotor to get some dimensions.

Overall height = 73mm
Centering dia = 103mm
Thickness = 28mm
Overall dia = 299mm or 11.75in
offset (back of hat to furthest back surface of rotor) = 68mm

For the few people who do have my configuration (ie, stock C4 TL), let me summarize.

Fronts: you can upgrade to the 993tt big red caliper with a 964t front caliper 322x28 and Rennline/FVD caliper adapter.
Rears: you CANNOT upgrade to 993RS rear caliper and rotor without modifying the stock configuration or risk losing your parking brake. Best option would be to keep the 964t rear rotors (299x28) AND the stock C4TL rear caliper (BLACK) or switch to the 964t rear caliper (RED). Both options accommodate the 28mm rotor thickness with good braking bias. Additional adjustments for bias will need to be done with PV changes.

Bill, please feel free to adjust this recommendation if you see anything incorrect or add info as necessary.

cobalt

Why they used the turbo front brakes on the America Roadster but the stock front brakes on the 94 c4 widebody doesn't make sense. Although it appears you figured this out the rear calipers are the same as the turbo just painted black like the 3.3l Turbos or optional on the 3.6T in black. So you don't need to make any changes there.

The calipers for the front are identical 964 turbo or 993TT it is your choice whether you want to us the 993TT adaptor and rotors or a 964T adaptors and rotors. (5mm offset difference)You have many more rotor options if you go 993TT since they already are two piece and can save some money if you choose to go slotted vs cast hole. You can also find aluminum hats more readily if you want to go that direction. Although I had a set that fit the 964C2/turbo they are hard to come by or need to be custom made.

Bill Verburg

For completeness I'll add some info that was in the separate PMs
So you already have the biggest pistons that can be t/ped to that car from a 964 or 993. These calipers still use the same 930 size pads as stock 964 use front and rear, the rotor is still the narrow 24x299 as used on 964RS or stock 964 or stock 993

The only advantage here is the slightly thicker rotor, stock 964 is 24mm and the 964t are 28mm, both are still 299mm diameter. For this option he 964t rear calipers come in black 965.351.423.01 /L 965.351.424.01 /R or red 993.351.425.10 /L 993.351.426.10 /R

As Cobalt says in front the same caliper adapter is used for either the red 993RS/tt, red 964 3.6t or black 964 3.3t calipers on the 964t 1 piece 322x32mm rotors. A different caliper adapter is needed if any of those calipers are used on the 2 piece 993 322x32mm rotors because the 964 and 993 have different rotor o/s in front as well as in back.

all of these 964 combos have a lot of front bias

blackbull

In total ignorance I ask......what is the performance improvement or advantage gained by doing this mod???

apanossi

Thank you Bill and Anthony for your wisdom on this. The C4TL braking system is a bit of a head scratcher.

This is done to very simply refresh my 22 year old braking system that needs new rotors and paint. In the process, I figured I would get a little added benefit of improved braking (albeit marginal for my purposes as a daily driver) with a cosmetic upgrade. It looks great on widebody Porsches.

apanossi

Bill, just a quick clarification... the stock 1994 C4TL rear rotors are 28mm thick, not 24mm. Same as the stock 964t. So, I essentially have a rear caliper/rotor combination that is nearly identical to the stock 3.6 964t in the back (except my calipers are black and the rotor is solid). In fact, the part numbers of the C4TL and 3.6 964T rear rotors are almost identical, except for the last number. I believe the only difference is that stock rear C4TL rotors are solid and the stock 3.6 964T rotors are drilled.

Bill Verburg

Ok, I did not know that

then your stock rear is the same as was used on the turbos

another upgrade is to use the 25.4mm master cylinder, this was used on the turbos and RS's, yours is 23.8mm which is ok but the bigger m/c gives a better pedal

according to the docs I have the tl used the perforated rear rotors through '92 then the solids face ones from '93 on
rear 964tl rotors
perforated 965.352.041.00 & .042.00
non perf. 965.352.041.01 & .042.01

apanossi

The 1994 C4TL is certainly an odd bird in this department. Not sure what Porsche was thinking with this one. Why 2 versions of the same turbo rear rotors with the exception of perforated or not? Why not complete the front end with a turbo setup as well? Why C4 and not a C2 widebody, which would have been cheaper to build and possibly more desirable? Not sure if the C4TL was the result of desperation marketing/product diversification during the troubled years of Porsche. Or was it a legitimate R&D effort for the later 993 4S and AWD 993RS/TT?

Not to beat this one to death, but is it possible (or, is it not recommended) to put a 24mm thick rotor on a rear turbo trailing arm in order to use a 993 n/b rear caliper? Not that I would this, but given all of the data I have come across, it seems that this would not be compatible. I only bring this up to archive this knowledge for those few such as myself who would otherwise spend hours researching this information.

I'm in agreement with you also on the m/c. Although, I don't think I will need the upgrade for my use as a daily driver/canyon carver.

cobalt

You could say they were in panic mode. 1994 was the year of very little sales across the board. Any 94 MY is a rarity especially US spec cars. There are many ways to look at it but in essence they bins built cars to try to come up with something unique that might sell off their inventory of parts. The 993 was a go and they had sold far less turbos than expected. US sales were limited to 335 turbos 160 C2's, 76 928GTS's and a rather small number of 968's which I would need to look up. A handful of cars were built for Canada. ROW saw higher numbers but still quite low.

No doubt they had enough parts remaining from the ROW 911 Jubilee left over to market this in the US with whatever did not sell the prior year there. IIRC Norbert states 267 C4 widebodies for the US. They focused on high end customers with the turbo S's which were shuffled off to the exclusive department to be finished up while they retooled for the 993.

As far as using 993 rears on your car I don't see the point you have the same caliper on your car but setup for the 28mm rotor which works with your handbrake perfectly. There is 0 gain. they only difference between 3.3 rears and 3,6 rears is the color and you could special order them in black in 94 on the turbo or any color in fact at a cost if you chose.

Your master cylinder is the same as used on the turbo. You have the electro hydraulic brakes already. The only cost effective gain is going either 3.3 or 3.6 turbo calipers and rotors. For the street the 3.3's are more than good enough give the same big brake appearance and larger rotor offer the same clamping force but 10mm less swept area. I have run the big red setup on many cars with varying HP. My turbo has 450bhp and the 3.6 brakes are more than capable. I am using the 993 RS on my track car which I have to thank Bill for. For my dedicated track car they are amazing but would IMO be overkill on a less powered car.

These are pretty simple cars so less is more so to speak.

Good luck and most of all enjoy the car it is a unique piece and worth being able to revert back to stock if you choose to someday.

Turbohead

If need them
I have a set of rear 964T 3.6 rotors.
used but nice condition and no cracks .
P M me if you need them
Elliot

cobalt

There you go take these off Elliot's hands to go with the fronts or use the 928 GTS front rotors to go with your rears. I am using the big blacks with 993 rears on my C2 with cast hole rotors a bit more aggressive looking than the sold faced rotors.