swftiii

All,

I have been trying to solve a soft brake pedal on my C2 for a while and need your expert advice on the next steps.

Symptoms: soft brake when the car is running and or when it is off. Pumping doesn't produce a hard pedal like it should. There is no leaking.

Following is what I have already done:

1. Brake lines are braided
2. Replaced Master Cylinder
3. Replaced Booster
4. Each of these steps has had significant fluid bleeding to remove any air from the lines, but the pedal is still soft.

So, what is the next step. I've read so many threads I'm not sure of the next step.

Is the next step to replace the ABS Pump (964 355 901 01 or 993 355 953 01) or the ABS Hydraulic unit (964 355 955 00)?

Follow-up questions:
- Is replacing either of them a DIY job or should I have the shop do it?
- Do these parts fail often, where a new one is the right answer, or are they pretty reliable and a used one would be a viable alternative?
- What about the relays that are on top of hydraulic unit...could these be a culpret?

Other ideas...I really want to get my car back on the street and ready for my track season that starts next month.

Thanks,

Skip

Rocket Rob

A soft pedal sounds like you still have air in the system somewhere. How are you bleeding? I use a power bleeder.

Laker

+1

swftiii

The shop typically does vacuum bleeding, but I had them do some additional pressure bleeding when the vaccuum approach didn't work. Same result, so yes it could be air in the lines and I'll work through that somewhat, but what is the next step when that doesn't solve the problem (low level of confidence)?

Thanks,

-Skip

Laker

I had the same problem (my own fault, don't ask) so I completely re-bled the brakes, accumulator, clutch (step by step in Adrian's book) and it firmed right up. Pressure bleeder is the only recommended approach (per the book)

swftiii

I hear you and the pressure bleeder is all that I have ever used. I agree - when I asked my shop how they bled it he told me the approach he used and I kinda flinched and had him re-do it with the pressure bleeder.

I'll give it another shot myself tonight if I can get the wife to help me pick up the car.

Pray for me as I'm going to lose my mind on this. Still would like to know the next step as the track season starts in just about a month.

-Skip

wagonface

Apologies if this is obvious but I think I read in Adrian's book and on here that the clutch slave is tricky to get to, so some people dont bother bleeding it after doing bakes (me included). Maybe check they have done that too?

campoj2

Re-bleed and all hydraulic check connections. Either the bleeding was not accomplished properly (maybe it was) or air is entering the system after you have bled. Frustrating!

When did you replace all of your brake components?
When did you get a soft pedal? Did it happen at once or was it a slow progression?

swftiii

More information...I have bled the system many times and think I need to take the next step and replace what the experts call the 'ABS Pump'. I understand from many threads that the C2 doesn't actually have an ABS pump, but wanted to make sure I'm not mis-understanding everything and the reason I'm getting confused is that the Porsche Parts PET does list a 'Pump' for the C2. I have looked and cannot find this 'Pump' on my C2, so am coming to the conclusion that the Porsche PET is incorrectly listing this part and I believe it is the Pump that goes with the PDAS that came on the C4 only...Someone please confirm or correct me with this...

Here are the parts from the PET for the C2:
Controller: 964 618 119 00
Hydraulic Unit: 964 355 955 00 (supersedes 965 355 755 01)
Pump: 964 355 901 01 or 993 355 953 01

So, I believe the part I need is the 'Hydraulic Unit' - 964.355.955.00, but please confirm for me.

Thanks for the ongoing help of this forum.

-Skip

Crystal Cranks

A faulty hydraulic pump on a c2 should not give you a soft pedal unless it's leaking it also cost $$$$$. Check all the connections especially anything you have changed then pressure bleed bleed bleed.

Rocket Rob

I had the ABS pump on my C4 fail and the brake pedal went very hard, not soft.

Note: The failure was caused by a pressure sensor and relay. The replacement was very expensive. I your problem is less expensive than this.