A few brake caliper refinishing questions
09-30-2008, 12:58 PM
#61
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As another helpful hint. While bleeding the Brembo style calipers, if they have been off the car and open, you should try lightly taping on the body of the caliper behind where the pistons are. The tapping helps loosen any bubbles lodged in the nooks and crannies of the caliper bores.
See the ancient thread Those Bloody Brakes and, in particular, post #9 in that thread where I finally got it resolved.
09-30-2008, 01:08 PM
#62
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Nicole:
A key question in all this is whether or not you let the system drain when the calipers were removed.
If your system was let go to all air, it is not a matter of getting some bubbles removed but instead an issue of getting new fluid back into all areas of the system. If you look at all of the line junctions as well as the ABS, there needs to be lots of fluid movement with disturbance to get everything bled. If you can get a pressure bleeder to hold pressure and not leak around 10+ psi, the bubble removal goes much better.
Patience is much needed when doing this task...
A key question in all this is whether or not you let the system drain when the calipers were removed.
If your system was let go to all air, it is not a matter of getting some bubbles removed but instead an issue of getting new fluid back into all areas of the system. If you look at all of the line junctions as well as the ABS, there needs to be lots of fluid movement with disturbance to get everything bled. If you can get a pressure bleeder to hold pressure and not leak around 10+ psi, the bubble removal goes much better.
Patience is much needed when doing this task...
I am intrigued by the power bleeder method.
10-02-2008, 06:05 AM
#63
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I spoke with the service manager at the local Porsche dealer today, and he told me there is no way to bleed an ABS system at home without some pressure system like the PowerBleeder. He also said it takes a while until even the small bubbles are out, and that we probably haven't bled enough.
Another interesting tidbit I gathered: The original PORSCHE brake fluid they use has a 15 Degrees higher boiling point than Super Blue. One might argue whether that's necessary for street driving, but there might be situations on the track where this provides for some additional margin of safety.
Another interesting tidbit I gathered: The original PORSCHE brake fluid they use has a 15 Degrees higher boiling point than Super Blue. One might argue whether that's necessary for street driving, but there might be situations on the track where this provides for some additional margin of safety.
10-02-2008, 02:29 PM
#64
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Something we may get to someday: The silicone brake fluid requires a vacuum de-gas to get the bubbles out. I wonder how hard it would be to vacuum the system from the reservoir, and whether we would draw air in through the rear master cylinder seals. The procedure would be to do a 'normal' fluid swap and pressure bleed, then use vacuum to draw out any remaining bubbles. I guess if there's a path for air to be drawn in, I'd have to have a separate reservoir to see any gas bubbles coming through. Gotta work on that a bit...
I also think there may be some value in operating the ABS pump for a few seconds at a time to make sure there are no remaining spaces in there to harbor air.
My car is due for its annual fluid replacement, so I may have a chance to polish up a procedure for both of these options. Another reason to get a lift installed soon.
I also think there may be some value in operating the ABS pump for a few seconds at a time to make sure there are no remaining spaces in there to harbor air.
My car is due for its annual fluid replacement, so I may have a chance to polish up a procedure for both of these options. Another reason to get a lift installed soon.
10-03-2008, 02:26 AM
#65
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Just a brief update... I don't have much time to deal with this these days, but Christoph was nice enough to come over and bleed the brakes again with the PowerBleeder.
He started with the Master Cylinder, and then did the usual sequence of left rear, right rear, left front, right front - first the inner than the outer bleeder.
There were a few very small bubbles coming from the rear calipers. Tapping those did not make any difference in the bubbles.
There were a few larger bubbles in the front, but that was it.
We used about a quart of brake fluid tonight.
The pedal feel only changend minimally; the pressure point is still lower than the gas pedal. The pedal does not fall to the floor.
We did go on a test drive and I tried to bed-in the new rear pads - which I'm happy to report have not made one squeak (without Porsche silencers, but lots of copper paste on their backs).
The brakes appeared to decelerate the car quite well, after the long pedal trave.
However, once the ABS had to kick-in, all hell broke lose. Instead of the vibrating pulse, I got a "hoppedi-boppedi-hop-bop-di hoppedi" and-so-on type of pulsing - and the stopping power then seemed rather disappointing (if not outright weak). We tried this four times (in a quiet industrial area), with no significant change.
When we arrived back at the house, all wheels where hot, and both rear discs showed some discoloration (probably from the bedding-in).
What can we do short of bleeding again?
He started with the Master Cylinder, and then did the usual sequence of left rear, right rear, left front, right front - first the inner than the outer bleeder.
There were a few very small bubbles coming from the rear calipers. Tapping those did not make any difference in the bubbles.
There were a few larger bubbles in the front, but that was it.
We used about a quart of brake fluid tonight.
The pedal feel only changend minimally; the pressure point is still lower than the gas pedal. The pedal does not fall to the floor.
We did go on a test drive and I tried to bed-in the new rear pads - which I'm happy to report have not made one squeak (without Porsche silencers, but lots of copper paste on their backs).
The brakes appeared to decelerate the car quite well, after the long pedal trave.
However, once the ABS had to kick-in, all hell broke lose. Instead of the vibrating pulse, I got a "hoppedi-boppedi-hop-bop-di hoppedi" and-so-on type of pulsing - and the stopping power then seemed rather disappointing (if not outright weak). We tried this four times (in a quiet industrial area), with no significant change.
When we arrived back at the house, all wheels where hot, and both rear discs showed some discoloration (probably from the bedding-in).
What can we do short of bleeding again?
10-03-2008, 03:17 AM
#66
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Nicole, in your bleeding sequence, is the left rear the passenger side rear, or the driver side rear? It seems to me that the left rear should be relative to the driver's side, and that would explain some difficulty removing all the bubbles. On my car, the reservoir is on the driver's side and the rear most wheel is the passenger side rear. Is that how you bled your system?
10-03-2008, 03:24 AM
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Yep - left and right are always in the direction of travel. But passengers might be on differnet sides, based on where the steering wheel is...
We always start at the end opposite from the master cylinder, which is the passenger side rear on our LHD cars. Then we move to the rear drivers side, then the passenger front, then the driver front.
I'm majorly bummed right now. I thought I could maybe I could get away from the computer and go on a short fun drive this weekend - but not with these brakes...
We always start at the end opposite from the master cylinder, which is the passenger side rear on our LHD cars. Then we move to the rear drivers side, then the passenger front, then the driver front.
I'm majorly bummed right now. I thought I could maybe I could get away from the computer and go on a short fun drive this weekend - but not with these brakes...
10-03-2008, 07:27 AM
#68
Instructor
....
However, once the ABS had to kick-in, all hell broke lose. Instead of the vibrating pulse, I got a "hoppedi-boppedi-hop-bop-di hoppedi" and-so-on type of pulsing - and the stopping power then seemed rather disappointing (if not outright weak). We tried this four times (in a quiet industrial area), with no significant change.
When we arrived back at the house, all wheels where hot, and both rear discs showed some discoloration (probably from the bedding-in).
....
However, once the ABS had to kick-in, all hell broke lose. Instead of the vibrating pulse, I got a "hoppedi-boppedi-hop-bop-di hoppedi" and-so-on type of pulsing - and the stopping power then seemed rather disappointing (if not outright weak). We tried this four times (in a quiet industrial area), with no significant change.
When we arrived back at the house, all wheels where hot, and both rear discs showed some discoloration (probably from the bedding-in).
....
Hi Nicole,
did the rear brake pads slide easily into the calipers ?
If not , they cannot be pulled back slightly after braking and block the disk permanently . Another possibility is that the handbrake pads aren't adjusted correctly.
Often the brake pads do not fit exact into the calipers cause of alu corrosion between the caliper and the two small guide plates .
Fast "russian" solution : Do some grinding to the brake pads til they slide in without resistance.
Optimal solution : Remove all calipers and brake pads , then the guide plates . Caution : mostly the torx (?) screws are worn out or rusted .
Clean the caliper bay with a steel brush or better sand blast them .
After that , use new guide plates and screws :
993 351 929 02 for GTS caliper front ( 4x )
993 351 929 00 for S4 caliper front ( 4x )
993 352 929 00 for S4/GT/GTS caliper rear ( 4x)
Greetz,
Thommy
10-03-2008, 07:40 AM
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Hi Thommy:
The rear calipers have been rebuilt with new pistons and seals, and the guides have been cleaned from all baked-on residue. The pads slid in easily, and move rather freely, thanks in part to lots of copper paste...
We actually lifted the wheel and tried turning it - it was pretty easy going back and forth a little, until the resistance form the transmission kicked-in. I don't think the brakes are dragging in any way, but I'm wondering why they had to work quite that hard.
The S4 and later car have a brake bias that is very much slanted towards the front, so the fronts should have gotten much hotter, I would think.
The guys on the German message board say you cannot run the ABS pump on our cars with the Hammer. If that's where the air is, we have some fun carved out for us...
The rear calipers have been rebuilt with new pistons and seals, and the guides have been cleaned from all baked-on residue. The pads slid in easily, and move rather freely, thanks in part to lots of copper paste...
We actually lifted the wheel and tried turning it - it was pretty easy going back and forth a little, until the resistance form the transmission kicked-in. I don't think the brakes are dragging in any way, but I'm wondering why they had to work quite that hard.
The S4 and later car have a brake bias that is very much slanted towards the front, so the fronts should have gotten much hotter, I would think.
The guys on the German message board say you cannot run the ABS pump on our cars with the Hammer. If that's where the air is, we have some fun carved out for us...
10-03-2008, 08:52 AM
#70
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Hi Nicole,
the factory repair manual says nothing useful for bleeding the brakes with ABS.
Its says : No diffences to cars with ABS . Normal bleeding procedure with an electrical power bleeder from ATE . In order to get all air out of the master cylinder you must first push the brake pedal several times when all bleeder valves open . Begin the bleeding procedure at the valve on the master cylinder , then on the calipers .
Doesn't help very much ....
Greetz,
Thommy
Edit : replace the powerbleeder valves with the stock ones. The flow-through of the speedbleeder valves is probably too small. If the brake fluid doesn't go really fast through the brake lines and calipers when bleeding , you will always have air bubbles inside them. The air bubbles are also the reason for the strange ABS behaviour .
the factory repair manual says nothing useful for bleeding the brakes with ABS.
Its says : No diffences to cars with ABS . Normal bleeding procedure with an electrical power bleeder from ATE . In order to get all air out of the master cylinder you must first push the brake pedal several times when all bleeder valves open . Begin the bleeding procedure at the valve on the master cylinder , then on the calipers .
Doesn't help very much ....
Greetz,
Thommy
Edit : replace the powerbleeder valves with the stock ones. The flow-through of the speedbleeder valves is probably too small. If the brake fluid doesn't go really fast through the brake lines and calipers when bleeding , you will always have air bubbles inside them. The air bubbles are also the reason for the strange ABS behaviour .
Last edited by 928@AMG; 10-04-2008 at 09:32 AM.
