C2 Brake Bleed Question
05-01-2012 | 04:54 PM
#1
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C2 Brake Bleed Question
I'm reading the Porsche manual for the C2 brake bleed procedure and it says the following:
"Caution: As opposed to other bleeding operations, the brake pedal must be actuated with sufficient force at least 4 times when the respective bleeder valves are opened. It is important to release the pedal fully before and after it is actuated and to depress it fully to the stop."
I must be interpreting this wrong, because to me it looks like they're saying to depress and release the pedal while the bleeder valve is open? This is contradictory to everything that I've ever been taught about bleeding brakes and I would think it would end in a lot of air in the system. Does anyone have any insight that they can share?
Thanks!
Hal
"Caution: As opposed to other bleeding operations, the brake pedal must be actuated with sufficient force at least 4 times when the respective bleeder valves are opened. It is important to release the pedal fully before and after it is actuated and to depress it fully to the stop."
I must be interpreting this wrong, because to me it looks like they're saying to depress and release the pedal while the bleeder valve is open? This is contradictory to everything that I've ever been taught about bleeding brakes and I would think it would end in a lot of air in the system. Does anyone have any insight that they can share?
Thanks!
Hal
05-01-2012 | 05:30 PM
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05-01-2012 | 06:29 PM
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What's odd is that Porsche states the above "Caution" while the "Bleeder Unit" is connected to the reservoir at about 2 Bar. The "Bleeder Unit" seems to be an electronic version of a Motive Power Bleeder.
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05-01-2012 | 06:46 PM
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for more detail, here are the first three steps from the Porsche Manual
1 Top up reservoir with fresh brake fluid up to upper edge. Connect Bleeder unit to reservoir. Block overflow (vent) hose using hose clamp. Switch on bleeder unit. Bleeding pressure approx. 2 bar.
2. The Quickfill brake master cylinder is fitted with a bleeder valve (arrow) for bleeding the filling chamber. Start by bleeding the filling chamber. "Caution: As opposed to other bleeding operations, the brake pedal must be actuated with sufficient force at least 4 times when the respective bleeder valves are opened. It is important to release the pedal fully before and after it is actuated and to depress it fully to the stop.
3. Proceed by bleeding or changing the brake fluid, respectively, at the calipers (no specific sequence needs to be observed). Open each bleeder valve only until the respective fluid change quantity per brake caliper is reached. Make sure that both bleeder valves of the four piston fixed calipers are bled and that the brake pedal is actuated with sufficient force 4 times of the valves (as described under caution in para 2. above)"
2. The Quickfill brake master cylinder is fitted with a bleeder valve (arrow) for bleeding the filling chamber. Start by bleeding the filling chamber. "Caution: As opposed to other bleeding operations, the brake pedal must be actuated with sufficient force at least 4 times when the respective bleeder valves are opened. It is important to release the pedal fully before and after it is actuated and to depress it fully to the stop.
3. Proceed by bleeding or changing the brake fluid, respectively, at the calipers (no specific sequence needs to be observed). Open each bleeder valve only until the respective fluid change quantity per brake caliper is reached. Make sure that both bleeder valves of the four piston fixed calipers are bled and that the brake pedal is actuated with sufficient force 4 times of the valves (as described under caution in para 2. above)"
05-02-2012 | 02:20 AM
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Huh... not sure what to make of that language. I suspect you might be over-thinking this part. The rest of us just connect the Motiv Bleeder, and make sure that the reservoir doesn't go dry.... and simply open the bleed screws til the new fluid comes out.
BUT I'd defer to someone more knowledgeable than I am for a final word on that language.
BUT I'd defer to someone more knowledgeable than I am for a final word on that language.
05-02-2012 | 11:45 AM
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I wasn't sure either when I read it, and re-read, re-read, etc... I've flushed/bleed plenty of cars and have never seen this type of "Caution". I read most of the posts about bleeding the brakes on a C2 and this has not come up. Until someone with more knowledge about the intent of the "Caution" chimes in, I'll continue to flush the system with the process suggested in other threads.
Thanks to all that responded so far.
Thanks to all that responded so far.
05-02-2012 | 12:06 PM
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It has to do with some sort of postive pressure on the system to preserve the seals in the master cylinder. Any negative pressure i.e. vaccum or suction can ruin the seals in the master. At least that is my understanding.
There is some other precautions. like never turn the car on with the Motive power bleeder hooked up with pressure. I am not sure why it is but there apparently is something very sensitive in the master cylinder/ABS system, and you never want the pressure or fluid going in the opposite direction it was intended to go.
It's not anything hard to do, but you do want to pay attention and not nut it up because you can cause serious damage to the brake system.
There is some other precautions. like never turn the car on with the Motive power bleeder hooked up with pressure. I am not sure why it is but there apparently is something very sensitive in the master cylinder/ABS system, and you never want the pressure or fluid going in the opposite direction it was intended to go.
It's not anything hard to do, but you do want to pay attention and not nut it up because you can cause serious damage to the brake system.
05-07-2012 | 06:17 PM
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Thanks again to all those that responded. I bought a Motive Power Bleeder and flushed the brake/clutch lines with new fluid as suggested. It didn't look like the clutch had ever been touched!
I can see why with the way you need to contort your arm to get the wrench and hose on the bleeder valve. It was well worth the dislocation of my shoulder, though. The clutch pedal has never felt better. And no brake fade at this weekend's DE event.
I can see why with the way you need to contort your arm to get the wrench and hose on the bleeder valve. It was well worth the dislocation of my shoulder, though. The clutch pedal has never felt better. And no brake fade at this weekend's DE event.
