Brake Caliper Rebuild
12-21-2008, 02:04 PM
#16
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Dwayne, your S4 sounds like an early car. The seals are not available for the early calipers, the pistons are different and you end up needing new ones (!!). Then replacement starts making sense....
However, I was able to pull the pistons and seals out of mine with no damage, clean everything and put it back together with the same seals and dust boots. Cheapest way to go - it cost nothing!
However, I was able to pull the pistons and seals out of mine with no damage, clean everything and put it back together with the same seals and dust boots. Cheapest way to go - it cost nothing!
12-21-2008, 08:40 PM
#17
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Hi Glen,
I ordered them from zeckhausen and they were the wrong size. When you order they will tell you that they do not guarantee the fit.
Price was right but not if they won't work.
I have a box full of there seals and boots if anyone wants to try them.
Maybe we can find out what fits and what does not and come up with a compromize of some sort.
Roger
I ordered them from zeckhausen and they were the wrong size. When you order they will tell you that they do not guarantee the fit.
Price was right but not if they won't work.
I have a box full of there seals and boots if anyone wants to try them.
Maybe we can find out what fits and what does not and come up with a compromize of some sort.
Roger
12-21-2008, 08:57 PM
#18
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Nicole - maybe. Worth checking as they told me they would not fit.
Hopefully someone who knows more about these seals and covers will enlighten us.
Hopefully someone who knows more about these seals and covers will enlighten us.
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Does it have the "Do It Yourself" manual transmission, or the superior "Fully Equipped by Porsche" Automatic Transmission?
George Layton March 2014
928 Owners are ".....a secret sect of quietly assured Porsche pragmatists who in near anonymity appreciate the prodigious, easy going prowess of the 928."
Does it have the "Do It Yourself" manual transmission, or the superior "Fully Equipped by Porsche" Automatic Transmission?
George Layton March 2014928 Owners are ".....a secret sect of quietly assured Porsche pragmatists who in near anonymity appreciate the prodigious, easy going prowess of the 928."
12-21-2008, 09:18 PM
#19
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But wouldn't I see massive amounts of brake fluid leaking, if there was an issue with the seals? As it is, I don't see the fluid level decline, nor any fluid at the calipers.
12-21-2008, 10:35 PM
#20
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The caliper seals do two functions. They seal the piston and they return the piston, after the brake pressure is removed. That is the only thing that returns the piston. The "square" rubber o-ring turns into a parallel-o-gram when the piston moves. When you release the pressure, this parallel-o-gram tries to return to a square cross section, which pulls the piston away from the rotor. Get some corrosion between the piston and the bore and the piston will not return. Get the wrong size seal and the piston will not return properly. Don't assembly the caliper with the proper lubricant and the piston will not return properly.
Piston related "soft" pedal issues can be determined by pumping the pedal a few times quickly. If the pedal rises or gets firmer...you have an issue with the pistons.
12-21-2008, 10:52 PM
#21
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The "H-shpaed" pad guides can get enough crap in them to bind-up the pads and keep them in contact with the rotor. I've only found this to be true with the rear calipers and only when the rear calipers have been all but neglected since factory days.
12-21-2008, 11:02 PM
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Great info, Fraggle! I want to keep the original brakes but if no new seals/boots are available I may attempt to re-use as you suggest - hhmmm. I'll have to give it more thought. THANKS!
12-21-2008, 11:25 PM
#23
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Yes, you would, if they were leaking.
The caliper seals do two functions. They seal the piston and they return the piston, after the brake pressure is removed. That is the only thing that returns the piston. The "square" rubber o-ring turns into a parallel-o-gram when the piston moves. When you release the pressure, this parallel-o-gram tries to return to a square cross section, which pulls the piston away from the rotor. Get some corrosion between the piston and the bore and the piston will not return. Get the wrong size seal and the piston will not return properly. Don't assembly the caliper with the proper lubricant and the piston will not return properly.
Piston related "soft" pedal issues can be determined by pumping the pedal a few times quickly. If the pedal rises or gets firmer...you have an issue with the pistons.
The caliper seals do two functions. They seal the piston and they return the piston, after the brake pressure is removed. That is the only thing that returns the piston. The "square" rubber o-ring turns into a parallel-o-gram when the piston moves. When you release the pressure, this parallel-o-gram tries to return to a square cross section, which pulls the piston away from the rotor. Get some corrosion between the piston and the bore and the piston will not return. Get the wrong size seal and the piston will not return properly. Don't assembly the caliper with the proper lubricant and the piston will not return properly.
Piston related "soft" pedal issues can be determined by pumping the pedal a few times quickly. If the pedal rises or gets firmer...you have an issue with the pistons.
1. Pedal travel now is very long and soft, and when I hold the pedal down full force, it slowly sinks a bit more
2. Pumping quickly provides for a minor change in firmness, but not sensational, and not even close to how the brakes felt before this project.
Here is a summary of other things we observed:
During the first test after installing the rebuilt calipers, the rear brakes overheated. This tells me that the rears must work pretty well. Those were rebuilt with original Brembo parts, while the fronts got the Zeckenhausen seals and retained the old pistons.
No matter how much we bled, it never seemed to make much of a difference. There were incremental improvements, but we're still so far off, it's outright dangerous to drive the car. The system has been bled 10 times now; the last two times with high pressure at the Porsche dealer by a very senior technician who has worked on lots of 928s in his career. He also checked the whole system and could not find anything beyond a few small bubbles of air.
A new brake master cylinder did not make a hint of a difference.
The flex bake lines are new original Porsche - it should be unlikely they are soft or swollen - right?
So, what remains suspicious is the way the front calipers were rebuilt. Would you agree that this is the next thing to attack?
We could either:
- re-rebuild these calipers with original Porsche/Brembo parts
- rebuild my old calipers with original Porsche/Brembo parts, refinish them, and put them on.
Both should yield similar results.
What else could we try?
12-21-2008, 11:53 PM
#24
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Nicole, Two points:
1. The rear brakes overheating does not mean they are working correctly. They may be dragging, or instead they may have been doing all of the stopping because the rebuild on the fronts wasn't letting them do any of the braking.
2. Calipers may be done two at a time, same end of car or preferred diagonal. Start on the wheel with the most dust, or the one with the most resistance when spun by hand. Never rebuild more than two at a time. They need a break-in period, of about 100 city miles. If you do all at the same time, the car will have very poor brakes and will feel like there’s air in the system. This is normal, the brakes won’t feel right until 300-500 miles after all 4 are rebuilt. So you may just have to seat the seals in all four calipers.
1. The rear brakes overheating does not mean they are working correctly. They may be dragging, or instead they may have been doing all of the stopping because the rebuild on the fronts wasn't letting them do any of the braking.
2. Calipers may be done two at a time, same end of car or preferred diagonal. Start on the wheel with the most dust, or the one with the most resistance when spun by hand. Never rebuild more than two at a time. They need a break-in period, of about 100 city miles. If you do all at the same time, the car will have very poor brakes and will feel like there’s air in the system. This is normal, the brakes won’t feel right until 300-500 miles after all 4 are rebuilt. So you may just have to seat the seals in all four calipers.
12-22-2008, 12:56 AM
#25
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Hi Jim: If the rears had overheated from dragging, I would think they'd be hot all the time, and it would be hared to turn the rear wheels with the car lifted Both has been checked, and is not the case, though.
I have a bit of a hard time imagining that the lack of "seating" of the new seals can make a such drastic change in brake feel and performance.
This is not "a bit soft" - this is "friggin mushy", like stepping on a sponge that offers little resistance until you have almost stepped through it. It's frightening! My 15 year old waSAABi has a much better brake feel than that.
Yes, the ABS engages - but how do I know it engages both front and rear? I don't.
Based on all this and my gut feeling, I think there is something wrong in the front. But I'm not sure, if it's the caliper rebuild or something else. The caliper rebuild is one thing that has changed in the front - the only other thing being the brake lines.
I have a bit of a hard time imagining that the lack of "seating" of the new seals can make a such drastic change in brake feel and performance.
This is not "a bit soft" - this is "friggin mushy", like stepping on a sponge that offers little resistance until you have almost stepped through it. It's frightening! My 15 year old waSAABi has a much better brake feel than that.
Yes, the ABS engages - but how do I know it engages both front and rear? I don't.
Based on all this and my gut feeling, I think there is something wrong in the front. But I'm not sure, if it's the caliper rebuild or something else. The caliper rebuild is one thing that has changed in the front - the only other thing being the brake lines.
12-22-2008, 12:56 AM
#26
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Thank you very much for explaining this! I went down to the garage and tried this immediately, and here are my findings (with the car sitting in the garage, engine running):
1. Pedal travel now is very long and soft, and when I hold the pedal down full force, it slowly sinks a bit more
2. Pumping quickly provides for a minor change in firmness, but not sensational, and not even close to how the brakes felt before this project.
Here is a summary of other things we observed:
During the first test after installing the rebuilt calipers, the rear brakes overheated. This tells me that the rears must work pretty well. Those were rebuilt with original Brembo parts, while the fronts got the Zeckenhausen seals and retained the old pistons.
No matter how much we bled, it never seemed to make much of a difference. There were incremental improvements, but we're still so far off, it's outright dangerous to drive the car. The system has been bled 10 times now; the last two times with high pressure at the Porsche dealer by a very senior technician who has worked on lots of 928s in his career. He also checked the whole system and could not find anything beyond a few small bubbles of air.
A new brake master cylinder did not make a hint of a difference.
The flex bake lines are new original Porsche - it should be unlikely they are soft or swollen - right?
So, what remains suspicious is the way the front calipers were rebuilt. Would you agree that this is the next thing to attack?
We could either:
- re-rebuild these calipers with original Porsche/Brembo parts
- rebuild my old calipers with original Porsche/Brembo parts, refinish them, and put them on.
Both should yield similar results.
What else could we try?
1. Pedal travel now is very long and soft, and when I hold the pedal down full force, it slowly sinks a bit more
2. Pumping quickly provides for a minor change in firmness, but not sensational, and not even close to how the brakes felt before this project.
Here is a summary of other things we observed:
During the first test after installing the rebuilt calipers, the rear brakes overheated. This tells me that the rears must work pretty well. Those were rebuilt with original Brembo parts, while the fronts got the Zeckenhausen seals and retained the old pistons.
No matter how much we bled, it never seemed to make much of a difference. There were incremental improvements, but we're still so far off, it's outright dangerous to drive the car. The system has been bled 10 times now; the last two times with high pressure at the Porsche dealer by a very senior technician who has worked on lots of 928s in his career. He also checked the whole system and could not find anything beyond a few small bubbles of air.
A new brake master cylinder did not make a hint of a difference.
The flex bake lines are new original Porsche - it should be unlikely they are soft or swollen - right?
So, what remains suspicious is the way the front calipers were rebuilt. Would you agree that this is the next thing to attack?
We could either:
- re-rebuild these calipers with original Porsche/Brembo parts
- rebuild my old calipers with original Porsche/Brembo parts, refinish them, and put them on.
Both should yield similar results.
What else could we try?
Start with the simple stuff, first.
Make sure all of the calipers are installed in the proper positions....I know this is going to seem obvious, but make sure that all of the bleeders are at the top of the calipers. (Don't laugh...I've had more than one car towed to my shop that had been looked at by every expert around and it dawned on no one that the calipers were upside down!)
If the calipers are installed correctly and bled, we need to explore your brake pedal a bit more. If the brake pedal slowly sinks, with constant pressure, there can only be two sources. You either have a leak....or the master cylinder is bad. There has to be a loss of pressure for the pedal to sink, with constant pressure.
Take a look at the calipers and go try the brake pedal again. Let me know.
12-22-2008, 01:04 AM
#27
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Nicole, what you described with the pedal continuing to sink when you hold pressure is indicative of a leak in the system, normally from the brake master cylinder. I know you say that it has been replaced, but I know ALOT of people who have had this issue with replacement master brake cylinders on other models and replacing the master cylinder a second time has always fixed it. That said, ensure that the shop that replaces the MC DOES NOT touch the brake pedal in any way shape or form until the master cylinder resevior is filled, and the bleeder is opened on the MC to allow the air to leave the MC. The fluid acts as a lubricant for the seals, and if run dry on the walls they tend to leak slowly.
12-22-2008, 01:06 AM
#28
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All calipers are installed correctly - with the bleeder nipples up.
I also tried the pressure on the pedal again. Here is a more precise description:
The pedal has a long travel before it builds-up back pressure. As I hold the pedal against this pressure, the pedal sinks a bit more but not all the way to the end of its travel. There is still travel left when I can't push it down anymore.
The difference in firmness from pumping is very little.
I also tried the pressure on the pedal again. Here is a more precise description:
The pedal has a long travel before it builds-up back pressure. As I hold the pedal against this pressure, the pedal sinks a bit more but not all the way to the end of its travel. There is still travel left when I can't push it down anymore.
The difference in firmness from pumping is very little.
12-22-2008, 01:08 AM
#29
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This is a very timely thread, as one of my holiday To-Do's is to rebuild the stock calipers on my '90. I was going to pull all 4 and do them all at once, but perhaps that's not such a good idea? (And why don't the new brakes on all new cars suck, then?)
Regarding parts, after a bunch of reading, trying to understand PET and searching archives, I came up with the following parts list. Each kit contains a new piston, seal, and dust seal:
brake caliper bleeders (pairs, with dust cap)- need 6 (3 pairs) 930.351.919.00
brake cylinder paste/sliding lubricant 000.043.117.00
36 mm piston front repair kit 951.351.919.10
44 mm piston front repair kit 928.351.919.10
28 mm piston rear repair kit 951.352.919.10
30 mm piston rear repair kit 951.352.919.11
Total cost from Sunset for these bits was $328.
Now would be a good time to tell me I got the wrong parts, if indeed I have....
The items:
Regarding parts, after a bunch of reading, trying to understand PET and searching archives, I came up with the following parts list. Each kit contains a new piston, seal, and dust seal:
brake caliper bleeders (pairs, with dust cap)- need 6 (3 pairs) 930.351.919.00
brake cylinder paste/sliding lubricant 000.043.117.00
36 mm piston front repair kit 951.351.919.10
44 mm piston front repair kit 928.351.919.10
28 mm piston rear repair kit 951.352.919.10
30 mm piston rear repair kit 951.352.919.11
Total cost from Sunset for these bits was $328.
Now would be a good time to tell me I got the wrong parts, if indeed I have....
The items:
12-22-2008, 01:10 AM
#30
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Greg, I am really keen as to why you say this as I have found numorous times that if the pedal has far travel and that pumping it (4 wheel discs here) there has ALWAYS been air in the brake lines and that a proper bleeding gets them back to a proper firmness.
Nicole, what you described with the pedal continuing to sink when you hold pressure is indicative of a leak in the system, normally from the brake master cylinder. I know you say that it has been replaced, but I know ALOT of people who have had this issue with replacement master brake cylinders on other models and replacing the master cylinder a second time has always fixed it. That said, ensure that the shop that replaces the MC DOES NOT touch the brake pedal in any way shape or form until the master cylinder resevior is filled, and the bleeder is opened on the MC to allow the air to leave the MC. The fluid acts as a lubricant for the seals, and if run dry on the walls they tend to leak slowly.
Nicole, what you described with the pedal continuing to sink when you hold pressure is indicative of a leak in the system, normally from the brake master cylinder. I know you say that it has been replaced, but I know ALOT of people who have had this issue with replacement master brake cylinders on other models and replacing the master cylinder a second time has always fixed it. That said, ensure that the shop that replaces the MC DOES NOT touch the brake pedal in any way shape or form until the master cylinder resevior is filled, and the bleeder is opened on the MC to allow the air to leave the MC. The fluid acts as a lubricant for the seals, and if run dry on the walls they tend to leak slowly.
There was no fluid leaking at the back of the old master, and no noticeable difference in pedal feel after the replacement.
Last edited by Nicole; 12-22-2008 at 01:32 AM.