mark my words

Some of you might have seen my 964 Lightweight build thread - now it's time to make the next step...

I want to convert my C4 into a C2 and i think i have pretty much solved every problem that comes around with the conversion.

But i hope this forum might help me with the last thing to sort out:

How do i keep the high pressure braking system without having the dual solenoid valve block.
Is there a trick to tell the C4 ABS computer that it is not a C4 anymore but keeping the ABS and high pressure brake system alive?

Maybe you can help me with my problem - that would be very nice!

Thanks, Mark

evanscott964

Hi Mark

What exactly are you wishing to remove in order to achieve the end result?

Cheers Simon

mark my words

Hi,

I want to change from c4 to c2 - so i want to swap all the parts needed to get me there. But i don't know what result the removal of the solenoid valve block( which is nicht longer needed with the c2 gearbox ) would have to the ABS and high pressure brake system.
I think just removing it would end up in a permanent PDAS error - but i really don't know.
So I hope to find someone who might had done a conversion from c4 to c2 and knows more about that solenoid valve block and the c4 ABS computer thing.

evanscott964

Ok
I did this quite a lot of years ago so its a little bit rusty RE the details!!
There are certain things you can remove but some things you cannot! With reference to the hydraulics all must stay but you just need to block the fluid supply to the two slave cylinders for Diff unit and front Power Take off.
Basically the system can be left to think it is proportioning drive to the front and rear without it actually doing so!,

cajonfan

Hi Mark,
It sounds like you will never be going back to a C4 -

Have you considered swapping over to a C2 ABS controller? You have all the signals needed, but would have to re-pin a 37 pin connector (vs. the 55 pin connector you currently have).

Advantages - no PDAS indications or issues at all.
Disadvantages - the C2 computer cannot provide error codes to the test port (but there is a test set for that!).

You could build a short adapter harness to make the wiring changes and leave the vehicle harness as is.

I could provide you with the pin to pin wiring changes if you are interested.

Cheers,
Michael

mark my words

Hi Michael and thank you for your reply - you're right I never gonna go back to c4 once i did the conversion!

So it seems your solution is the one I am looking for!
I want the car to be clean as possible.
And i'd rather change the wiring than build a adapter!

Again my question about the high pressure baking system - will the c2 computer support that system?

If that is the case you have the key to the solution i want and it would be very nice to get the changes in the pin wiring!!!


I think for testing purpose I might start with the solution evanscott964 did choose.

What Lines did you block of:

a)block of just the one the fluid line that comes from the pressure accumulator and leave all the rest( the lines an slave cylinders) in the car

b) block of the two lines from the solenoid valve block to the cylinders (and remove the lines and cylinders) but leave the connection to the pressure accumulator

c) block of all three lines connected to the solenoid valve block and throw all lines ans cylinders in the bin? ( I would very much like to do that )

evanscott964

Hi Mark
Yes I just removed the 2 lines from the lock control valve, 964 315 013 50, but left it connected and never had any issues!!
I need to look at a C4 again to jog my memory!! Been a long time since I looked at how it was!
Simon

kos11-12

Hi Mark , I hope this will help, I had saved this text long time ago , written by Garrett an active Rennlist member who is racing a C4 ,

Convert c4 to c2 From Garrett376
On a recent 5 hour plane flight I was bored and looked at the wiring issues of converting a C2 to C4, and it's neat that the process is actually quite simple thanks to Porsche's wiring. By purchasing a C2 ABS unit and the plug cut from a C2's harness, it is quite easy to remove the PDAS plug on the C4 and splice in the C2 ABS plug to the proper wires. That would permit the use of a C2 ABS brain with all functionality. After plugging off the hydraulic accumulator feed to the solenoid block, the extra C4 stuff can be removed: accelerometers, control unit, dash switch, PDAS solenoid block and all hydraulic lines to the transmission. Remove the tranny, drive shaft, front differential and CV's, and just plug in a 2wd 5 or 6 speed tranny and change the front axles - complete! It always seemed hard to manage the electronics, but it's not.

cajonfan

I would suggest that re-pining the 35 pin connector would be more reliable than cutting and splicing all the required connections. In principle, the contacts can be easily removed from the 55 pin connector, the tangs on the contacts cleaned up (straightened), then inserted into a 35 pin connector shell.

I'll admit I haven't found the right extractor tool yet in my efforts building test sets for ABS test sets, but my application is different.

You have lots of options on sourcing the 35 pin harness connector and its backshell, there are BMW cutoff harnesses available on ebay all the time for way less than a C2 part, all are originally Bosch parts.

Cheers,
Michael

cajonfan

I did a quick search for AMP Timer contacts to find the correct extraction tool. Looks like it is a part number 1-1579007-4 and is in stock ~ $50. The data sheet for the tool has a dimensioned drawing that may help fabricate a similar tool cheaply to test or for limited use.

Jan911

Hi All,

I am in the middle of a 1989 964 C4 to C2 conversion and I am struggling with the PDAS/ABS
What have I done so far:
Removed front diff and axle tube with shifter.
Purchased a complete C2 gearbox including drive shafts
removed front drive shafts and grided of the wheel end close to the dust cap, then put it on a lathe to smoothen it and put it back in the axle. This enables the ABS.
I blocked off the PDAS supply line at the hydraulic accumulator. Removed all the hydraulics after that (solenoid block, lines to the gearbox).
Blocked off the solenoid return line to the break oil tank.
Gear shifter from Numeric will be mounted which does not need a housing. (waiting for delivery)


I intend to keep the front sub frame.
I intend to keep the hydraulic break booster pump, (so no vacuum powered brake system)

Now I need to do the electrics. Please correct me where I am wrong:

A
With the above it means: - Pressure switch incl. warning switch remains
- Brake booster pump remains
-Relay 51 remains



The brake booster pump seems to operate quite independent looking at the electrical schematics.

It can only give alarms trough the pressure warning switch. It is all not connected to PDAS/ABS.

Warning light at the instrument light (YE/BK) and Central Informer (YE/BK).

Switching signal to Relay 51 (GR/YE) for pump switching on/off.



B

I plan to remove the PDAS electrics as follows:

-remove locking valves (solenoids) wiring up to connection points.

-remove the 2 lights (1 and 4) from instrument cluster for Diff on and diff alarm.

-remove wire for light 4 (WT/BK)

-remove wire for light 1 (PDAS warning) cables (0,5 BL/BR) from the instrument to the central unit and to the central informer.

- remove Diff switch central console and its cables ( BR + RD/GR + GR/BL) up to the central box.

-remove diff light in central console and its 2 wires (WT/BK) up to instrument and up to central box.

- remove plug for bridging Diff switch and its wiring.



C

I would like to remove the 2 accelerator sensors in the central console, but I read somewhere that they have a function for the ABS as well. Does anybody know?



D

The PDAS/ABS has a connection to the diagnose plug and it might give error signals there, but that is no problem for me.

I only need to make sure that the ABS works, and that it has no effect on the Motor ECU.

Or should I disconnect the diagnose cables as well? L and K (OR/BL and OR/WT).



E

Could a C2 ABS work with the hydraulic booster as well?

If I would choose a C2 ABS, I assume, that I do not need to connect pin 17 and 23. Right?



Cheers,

Jan

koenig_roland

did this some years ago at my blue car. Got a list to adapt a C2 ABS unit to the C4 wiring loom and started the conversion with that. So first i changed the ABS Unit to a C2 unit via adaptor (selfmade with and old Audi/BMW Plug, i can name you that stuff if you need this) and drove the car with high-pressure brake and C4 but with C2 ABS for 100km... The car forgot completely, that is has had a C4 drivetrain with active locks installed.. No warning light nor other issues... but ABS was working properly.. the high-pressure system works independent from the C4 ABS ECU, because RS and turbo have the same system but with a C2 brain...

After i did this, i did the mechanical C2 conversion with a short geared fresh G50 box and the front ABS-triggers from a C2 - your way with the C4 axles modified does also work. I used an CAE shifter. Works plug&play.
First, i did nothing further and left all the hydraulics to the PDAS valve block as it was as a C4 and left the center console stuff from the C4... i just disconnected/removed the two pressure lines to the slave cylinders.

After several kilometers of test-driving, i started to remove the unnecessarry C4 stuff like the switches in the center console, the acceleration sensors, the PDAS valve block - but left the high-pressure brake system.

In this state, i drove the car roughly 15kKM until last autumn, mostly at the Nordschleife. Now i convert the car to a 993 vaccum brake system, parallel to other upgrades and further lightweight stuff.

You NEED TO adapt the C2 ABS brain first to your car, OR you have to leave everything from the C4 system except the two hydraulic connections to the previous G64 diff-cylinders as it was... I would prefer doing the switch to C2 ABS brain, because a good C4 ABS brain is a lot more seldom than the C2 ABS ecu...

contact me via mail (thilo.vaeth AT googlemail . com) if you need the mapping for the C2 ABS to the C4 and infos how to do this plug&play...

Jan911

Thanks Roland,
It looks like I have to switch over to a C2 ABS Unit.
For me it is on the other hand hard to believe that Porsche did not seperate the brain for PDAS from ABS for safety reasons. If the PDAS fails it should not cause a failure in the ABS.
I wil send you a mail

Regards, Jan

koenig_roland

you have mail...

Jan911

Roland has provided me with info for an adapter cable piece between C4 connector and C2 ABS unit. Thanks!
Is it also possible to unpin the C4 connector and use the same pins to put it back into a C2 connector?
Has anybody experience with that?
It would look neater