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First, some basics: OE Brembo 4 piston 951 front calipers, with scraper rings, were rebuilt at one time but it's been awhile. I'm replacing front pads and rotors and I noticed that 1 pad is nearly worn completely down while the other three have a lot of life left. I also noticed that some of the pistons are quite difficult to press back in the caliper, with two pistons (on the same pad) that are extremely difficult, so much that I couldn't even get them completely depressed.
So, is this a sign of a needed rebuild? Bad pistons or scraper rings? Or just inner seals?
Some pics. You can see in the first pic that the left outer pad is worn down while all the other pads are evenly worn with much more life left:
I'm no expert, but if the pistons won't go back in, I would say that is more than just seals. Mine were doing the same thing last year and I sent them out to be rebuilt. Although I assume mine have never been rebuilt, or at least I know they hadn't in the past 12 or so years I have owned the car. I did some research into rebuilding them myself and the scraper rings were more than I wanted to deal with. It seems that newer style calipers are relatively straight forward as far as rebuilding goes. Which side has the pistons that wouldn't retract?
I'm no expert, but if the pistons won't go back in, I would say that is more than just seals. Mine were doing the same thing last year and I sent them out to be rebuilt. Although I assume mine have never been rebuilt, or at least I know they hadn't in the past 12 or so years I have owned the car. I did some research into rebuilding them myself and the scraper rings were more than I wanted to deal with. It seems that newer style calipers are relatively straight forward as far as rebuilding goes. Which side has the pistons that wouldn't retract?
Right passenger side, inner pistons
(Second picture, left side of caliper)
Oh, and I haven't noticed anything weird in the braking such as pulling to one side.
I had a similar problem in my Scirocco where one of the pads was hanging up in the caliper but in that car, I could feel that braking was not good. Also, all the pads in the VW were worn down evenly except for the one pad that was hanging up.
So with the Porsche, does that mean that 3x2 pistons are sticking? And what exactly sticks in the Brembo calipers, the piston on the scraper ring? Or somewhere else?
Oh, and no leaking or other strange signs and brake fluid has been changed fairly frequently through the years with ATE superblue or Typ 200.
The pad wear should be fairly consistent across all four pads at one end. There are a bunch of mechanical forces that will induce some amount of taper wear, but the difference would not be to the degree seen in your pictures. The fact that one pad is so much more worn than the others, could be a few things causing that. Checking the pistons, bores, and seals is a good place to start. Check the wheel bearing also, make sure it's adjusted to spec and not letting the rotor "lean" on one pad, so to speak. Good luck!
The pad wear should be fairly consistent across all four pads at one end. There are a bunch of mechanical forces that will induce some amount of taper wear, but the difference would not be to the degree seen in your pictures. The fact that one pad is so much more worn than the others, could be a few things causing that. Checking the pistons, bores, and seals is a good place to start. Check the wheel bearing also, make sure it's adjusted to spec and not letting the rotor "lean" on one pad, so to speak. Good luck!
Bearings are good, nothing unusual that would seem to be causing this. I was able to push all the pistons back in and they seemed to eventually loosen up; I think just by design these pistons get grubby and then when installing new pads, the scraper ring has to scrape off the old build-up when depressing the pistons. I suppose that's why Brembo changed to the rubber boot instead of the scraper ring.
But still not sure of what caused the uneven wear....
Another question about rebuilding: Do the caliper bores usually require honing? And if so, is this procedure fairly straight forward: just buy one of those brake honers at AutoZone and hone away a little bit until smooth? I suppose it's not as critical as an engine bore in that the piston just has to move smoothly and the rubber seal is mostly responsible for keeping the fluid in the caliper.
The bores do not usually require honing. If they don't look clean, you may want to clean them with some 000 synthetic steel wool just to brighten. I would certainly use this to clean up the operating surfaces of the pistons in your calipers, judging from your photos. Or get the Porsche kits that come with new pistons and seals. If there is heavy corrosion or pitting in the bores, I would take the calipers to a shop for inspection and attention from someone with experience.
With the pistons as far out as yours are, if you don't R&R them and decide just to push them back in (not my recommendation), be careful not to **** them. Kukko makes a very nice tool, 126-00, for pressing pistons in. Pricey but it works well.
I finally got one caliper rebuilt but the new scraper rings slipped in very easily so I'm worried about them staying put. I bent the metal a tiny bit to make them fit tighter as they pretty much just fell into the bores. I know they can't really go anywhere but seems like they should fit better. Anyone else experience this? I'm using the Centric rebuild kits.
The hardest bit of this whole rebuild is getting the pistons out. They just don't want to come out! I don't have a compressor so I used a Motive brake bleeder to pressurize the caliper which did the trick but it took quite awhile. Also, pb blaster and WD40 helped also. I did slightly damage the pistons, thinking I could pull them out from the leading edge which never touches the seal but I ended up putting some scratches and dings. Not sure how perfect they need to be but hopefully they won't leak and will perform ok. Those replacement pistons are way too expensive.
My old seals were in good shape, scraper rings were showing wear though. The pistons were hanging up and the pads were wearing unevenly so hopefully they just needed a cleaning.
One more caliper to go and a lot of reassembly of my timing belt/water pump/front end reseal project so no word on if they will improve my braking yet.
As for the scraper rings, mine is an 86. If memory is correct, the rings were either NLA or crazy expensive. The kits I got didn't have a usable option included.
As for the scraper rings, mine is an 86. If memory is correct, the rings were either NLA or crazy expensive. The kits I got didn't have a usable option included.
Scraper rings are available from Centric for very little money, $5-20 for a whole kit which rebuilds one caliper, including the sealing rings too. They seem well made but the scraper rings were a bit loose in the caliper but I have never used the Brembo parts so I don't know if that's the norm.
I see. Mine were Stoptech, but the centric scrapers look legit. Are they so loose you can't stake them? That will be my next move, down the road. I figure I'll be 85 years old before they'd have to come out..
I see. Mine were Stoptech, but the centric scrapers look legit. Are they so loose you can't stake them? That will be my next move, down the road. I figure I'll be 85 years old before they'd have to come out..
Ha, 85....i doubt that.... Never underestimate the ability of the 944 to throw an unexpected curve ball!
They were loose but no one has come forward saying that the Brembos are any different so not sure really. I bent them slightly so they would have some friction but I really thought I would have to pound them in.
Would love to hear from people who have rebuilt their calipers.....
04-20-2018, 03:56 PM
OE Brembo Caliper Rebuild Questions
