If there is air in the system, it might be hard to get it out of the ABS pump. The easiest way would be the use of the Hammer tool to move the pump while bleeding. When I had this issue, I moved the pump by putting the ignition on/off which mooves the pump slightly and after 4 rounds of bleeding, I had a stiff pedal again. GL.

 

I used the Motive power bleeder dry today. I added fluid to the reservoir and pumped that little sucker up to 20 psi (90 strokes, jeez) and bled about 6 ounces through a caliper. After repeating this procedure at each wheel, I then bled the accumulator.

When I bled the accumulator, FOAMY brake fluid came out. After the catch bottle sat for a while, the bubbles dissipated and I could see small black chunks of metal in the bottom of the catch bottle. The foam was a surprise, the chunks were not. I bled the accumulator again and clean fluid without air comes out now. The metal chunks were not a surprise because the bleed procedure starts with bleeding the acccumulator and when I did this on Saturday, the same amount of metal chunks came out of there.

The pedal is better after bleeding today. It is still squishy. It does not get rock hard. But, I can't push it all the way to the floor now. I should have paid more attention to the pedal before the procedure so I could compare better. It's just that I've not spent a lot of time pressing on the pedal without the car running and/or moving.

Can anyone tell me where these metal flecks are coming from (the accumulator itself or something else) and what this indicates?

 

I am preparing to do a brake job on the C4 Cab. Any closure on soft brake pedal or metal flecks?

(*Yes I know it is a 13 year old thread)

 

Blam! This is a blast from the past.
The soft brake pedal was resolved after my 2nd round of bleeding.
I never did find the source of the small metal flecks and wrote it off as something generated during the manufacturing process.
Whatever the case, the brake system was still performing flawlessly when I sold the car in 2020.
Chuck, I don't think you will have any issues if you follow the workshop manual procedure.
BTB

 

Hi Chuck,
Are you referring to the "small black chunks of metal in the bottom of the catch bottle"
Black in color suggests to me it isn't metal but bits of rubber from the brake hose.
If your brake hoses are original to your car, replacing them with fresh braided lines will profoundly improve brake feel.
I do not know if replacing them with regular rubber hoses will improve the feel equally, but it is entirely likely that it will.
Also, the caliper internals are just iron castings that may exhibit some flashing, or when the castings' bleeder ports threads were tapped (cut), it may have released some cuttings into the casting.
None of which will influence the performance or reliability of the system.
Any corrosion in the master cylinder would immediately cause gross operating symptoms, something you do not appear to be seeing.
If the ABD/ABS valves were the source, that system would also exhibit operating symptoms when activated or not work at all.

Also:
The brakes can bleed slowly at the caliper with the power bleeder, even with increased pressure.
I wait and take my time. I let 3~4 oz. bleed out from the first and most distant caliper bleeder screw to ensure the longest path was fully bled. In the old days, one could purchase an alternate color fluid that made it obvious when the fresh fluid was beginning to bleed out. It is no longer available as the DOT specification includes the color of the fluid, go figure.
Also, slightly spongy brakes can be from air bubbles clinging to the inside of a caliper. As a best practice, I tap the body of the caliper with a wrench when bleeding each of the screws on each caliper to release these bubbles. This procedure is only needed if spongy brakes were a symptom before bleeding the brakes, if the reservoir was fully drained, introducing air into the system, or if one of the hoses or lines was opened previously to the bleeding.


Andy

 

From what I remember, 993s equipped with ABD (C4S and Turbos specifically) will require a Bosch Hammer tool to fully bleed your 5 channel ABS. You can bleed your brakes conventionally with a Motive Power Bleeder, but there will be fluid that you won't be able to take out of the system without the Hammer procedure.



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Hi Boman,
Or an aftermarket OBD Code reader that sees the ABS/ABD module and supports manual actuation.
Some use the force to activate the system while driving approach, but then it is unclear to me what the procedure is to make this work. Or even how to tell if the system is fully bled.
Andy

 

A Hammer tool or the UDT999 were the only 2 tools I could get to activate the ABS/ABD module on my ‘95. I did also try and PIWIS3 and was unable to activate it. My understanding is that PIWIS2 should be able to activate reliably, but I wasn’t able to find anyone who still has one.