Brake system questions - Specifically ABS module / controller

[roadsleeper]

Hi all,

Need to pick the Pelican Forums knowledge tree yet again...

I plan to upgrade the brakes on my MY90 C4 to 993 Big Reds (the car is also being converted to 2 wheel drive). As I am taking the entire car apart, I would like to rebuild it with as close to a modern day braking system as possible (i.e., vacuum powered, more advanced ABS brain, etc.).

How difficult is this to do?

My options are as follows, I'd appreciate it if someone could please tell me which of these are viable:

1. Transplant complete ABS system from a 993
2. Transplant complete ABS system from a 996 or 997

Again, I'd appreciate any help that can be shared!

[Bill Verburg]

first read through this thread

It contains a summary of what you need to do.

Neither the abs brain nor pump needs to be changed, on a '90 C4 the m/c and electro-hyd boost setup are great as is, you could go to a larger 25.4mm m/c for that last little bit of feel but it's not necessary.

[roadsleeper]

Hi Bill, as always, you are the Gold Standard when it comes to level of knowledge around here. I have read through that particular thread in the past while I was shopping for brakes, but I need some more information. As mentioned in previous threads, I am trying to build a track biased car and would like a lot more stopping power. Would a more modern ABS brain (i.e., 996 or 997) coupled with the Big Reds be able to better handle braking demands on track?

[Bill Verburg]

Originally Posted by roadsleeper

Hi Bill, as always, you are the Gold Standard when it comes to level of knowledge around here. I have read through that particular thread in the past while I was shopping for brakes, but I need some more information. As mentioned in previous threads, I am trying to build a track biased car and would like a lot more stopping power. Would a more modern ABS brain (i.e., 996 or 997) coupled with the Big Reds be able to better handle braking demands on track?

No, C2, C4, RS, T & TL all used the same abs, you are going to use the same brakes as the 3.6T

after that for 993 up they had versions w/ abd but you aren't interested in that

[roadsleeper]

Hi Bill,

I've spent the past week or so reading through your brake upgrade thread and the service books I have on the 964 to try and better understand the braking system.

However, I still have some questions which, admittedly, are going to sound really green, but I want to be sure of before I proceed with ordering parts.

Here is the set-up I hope to install in the car:

Front calipers: Big Reds on 2-piece 322 x 32 slotted rotors, 44 / 36 mm pistons, 132 x 58 mm Pagid Yellow pads (mounted on 993 GT2 Evo uprights, custom Moton struts and matched drop links)

Rear calipers: MY95+ 993s on 299 x 24 mm slotted rotors, 30 / 34 mm pistons, 98 x 44 mm Pagid Yellow pads

- 25.4 mm master cylinder (is this part #993.355.910.00 in your "parts needed" list?), with associated 993 electro-hydraulic brake booster parts (part # n/a)

- Master cylinder support (part #993.355.163.03)

- Vacuum canister (part #993.355.023.10)

- Gasket (part# 993.355.301.00)

- 12 mm stainless steel braided hoses and Castrol SRF go without saying.

The questions I have are:

1. ABD - Am I correct in understanding this as a rudimentary traction control system which uses the wheel sensors and ABS brain to brake individual calipers when slippage is detected?

If yes, then did the 964/5 Turbos have the most advanced 911 braking system available without ABD?

Now for my uber-green question: Is it, or is it not desirable to have a more advanced ABS brain (i.e., from a 993) installed to provide better braking control / feedback, even if it has something as undesirable as ABD? Or is the control / feedback really down to the individual parts listed above (i.e., M/C, 12mm lines, etc.)?

2. Proportioning valves - Is front / rear bias provided by the 55 bar P/V sufficient for the above set-up, or should I upgrade to the 60 bar? I am running under the assumption that 60 bar is the same pressure maintained in the 993’s brake system.

Would an adjustable brake bias control be worthwhile to install?

Thanks in advance for any insight you can provide!

[Bill Verburg]

Originally Posted by roadsleeper

Hi Bill,


Here is the set-up I hope to install in the car:

Front calipers: Big Reds on 2-piece 322 x 32 slotted rotors, 44 / 36 mm pistons, 132 x 58 mm Pagid Yellow pads (mounted on 993 GT2 Evo uprights, custom Moton struts and matched drop links)

good

Rear calipers: MY95+ 993s on 299 x 24 mm slotted rotors, 30 / 34 mm pistons, 98 x 44 mm Pagid Yellow pads

good

- 25.4 mm master cylinder (is this part #993.355.910.00 in your "parts needed" list?), with associated 993 electro-hydraulic brake booster parts (part # n/a)

This will be unbelievably expensive to purchase new, the usual plan is to purchase a complete setup from a 964turbo

- Master cylinder support (part #993.355.163.03)


- Vacuum canister (part #993.355.023.10)

- Gasket (part# 993.355.301.00)

this is not needed w/ the above m/c setup. But a 993 vacuum booster and 23.8mm m/c is often used to replace the 964 vacuum boosted setup as a much lower cost alternative to the electro-hydraulic setup


- 12 mm stainless steel braided hoses and Castrol SRF go without saying.

The questions I have are:

1. ABD - Am I correct in understanding this as a rudimentary traction control system which uses the wheel sensors and ABS brain to brake individual calipers when slippage is detected?

yes, abd was an option on 993(M220 lsd/abd) you will be leaving your stock 964 ABS pump which won't have that. The abs/abd pumps have 2 outlets to the rear(4 channel abs) all the other only have 1 outlet to the back(3 channel abs)

If yes, then did the 964/5 Turbos have the most advanced 911 braking system available without ABD?

yes

Now for my uber-green question: Is it, or is it not desirable to have a more advanced ABS brain (i.e., from a 993) installed to provide better braking control / feedback, even if it has something as undesirable as ABD? Or is the control / feedback really down to the individual parts listed above (i.e., M/C, 12mm lines, etc.)?

No, you could go to the extremly expensive 993RS brain i suppose but than you need to redo everything, electronics as well as hydraulics and mechanicals. It can be done but the cost benefit just isn't there

2. Proportioning valves - Is front / rear bias provided by the 55 bar P/V sufficient for the above set-up, or should I upgrade to the 60 bar? I am running under the assumption that 60 bar is the same pressure maintained in the 993’s brake system.

W/ the proposed rotors and calipers I would take off the p/v as they did on the 964 Cup cars. Some have mounted an adjustable one and some have the 55 or 60

Would an adjustable brake bias control be worthwhile to install?

not in MO

Thanks in advance for any insight you can provide!

My comments in blue

My comments in red are alternatives

[roadsleeper]

Fantastic, thanks a bunch for your in-depth reply, Bill! I am going to read through and absorb your responses. Although I might have a couple more questions, I'm feeling pretty comfortable as to what set-up I want now. Thanks again!

[roadsleeper]

We've gotten to the brake system and related wiring on my project car, so I need to resurrect this thread...

Whilst my tech has been sorting through the wiring harness, it's become clear that some of the connecters and wiring need replacing, so we got into the discussion of laying the ground work for a full upgrade to a 964 RS brake setup in the future. This means that we are going to:

1. Change the ABS brain from the C4 (as it has PDAS built in) and replace it with the ABS brain from a C2 (which is the same as the 964 RS's brain, according to PET). This will also allow us to ditch the differential solenoid valve from the 4WD system; and,

2. remove the ABS/PDAS related wiring from the wiring harness.

My question centers around point 2, which is that we intend to replace the ABS/PDAS related wiring with the ABS wiring harness from the 944 Turbo. Apparenty, ABS was an option on the 944 Turbo, and Porsche supplied a separate harness for cars with that option, instead of bundling everything into a generic harness like in the 911s.

My tech has checked against the wiring schematics for both the C2 and the 944 Turbo, as well as on actual cars themselves, and it looks like the plug for the ABS brain in a 944 Turbo is the same as that of a C2. However, there is no substitute for experience, so I'm curious to know whether anyone else has done the above, and whether they can confirm our findings to be correct?

[38D]

Originally Posted by roadsleeper

We've gotten to the brake system and related wiring on my project car, so I need to resurrect this thread...

Whilst my tech has been sorting through the wiring harness, it's become clear that some of the connecters and wiring need replacing, so we got into the discussion of laying the ground work for a full upgrade to a 964 RS brake setup in the future. This means that we are going to:

1. Change the ABS brain from the C4 (as it has PDAS built in) and replace it with the ABS brain from a C2 (which is the same as the 964 RS's brain, according to PET). This will also allow us to ditch the differential solenoid valve from the 4WD system; and,

2. remove the ABS/PDAS related wiring from the wiring harness.

My question centers around point 2, which is that we intend to replace the ABS/PDAS related wiring with the ABS wiring harness from the 944 Turbo. Apparenty, ABS was an option on the 944 Turbo, and Porsche supplied a separate harness for cars with that option, instead of bundling everything into a generic harness like in the 911s.

My tech has checked against the wiring schematics for both the C2 and the 944 Turbo, as well as on actual cars themselves, and it looks like the plug for the ABS brain in a 944 Turbo is the same as that of a C2. However, there is no substitute for experience, so I'm curious to know whether anyone else has done the above, and whether they can confirm our findings to be correct?

For #2, another option is the front harness from a 91-92/94 turbo, as this had ABS without the PDAS. When mine 964 turbo melted the front harness at a race some years ago, it was ~an $800 part.

[roadsleeper]

Originally Posted by 38D

For #2, another option is the front harness from a 91-92/94 turbo, as this had ABS without the PDAS. When mine 964 turbo melted the front harness at a race some years ago, it was ~an $800 part.

Yeah, we looked into that as one of the options, but the 944T harness is something like US$400, and it includes all new connectors for both front and rear ABS / brake pad wear sensors. Thanks though!