Gretch

Joe, I installed the drilled Zimmermans on my 89 GT and they have been excellent.

I have tried "cleaning up" deposits on rotors with fine abrasive and have never had any luck doing it. When I do replace rotors and pads on ANY car in my fleet I get the best rotors and the high metallic pads. The cheaper, soft pads do leave deposits.

dr bob

I think they all leave deposits on the rotor. Cheaper pads work harder and hotter it seems, at least higher in their temperature range, so there's more chance of uneven material transfer. I've never come close to stretching the capability of the brakes on my 928. On the other car that had pulsing pedal syndrome with the soft OEM pads, a modification of stopping technique eliminated the symptoms. When rolling to a stop, I let off the pedal pressure for the last couple car-lengths, and roll the last couple yards with absolute minimum pedal pressure. Maintain that minimum pressure while stopped, and eliminate that big glob of hot pad material at that spot on the rotors.

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There are varying schools of thought on turning rotors. Some just replace pads when they are worn, with nothing done to the rotor, Some advocate a little casual glaze-breaking with sandpaper, which also removes any existing pad material deposits. Most 'pro' shops will turn the rotors on a brake lathe to guarantee a consistent surface for new pads to bed in to. I waffle among those options, usually depending on how the car was stopping prior to the service, and how the rotors look. On the few occasions when I find friction surfaces with noticeable grooving, I'm open to resurfacing options. I had a pretty good shop near my last home, and I'd measure the rotors at home for both thickness and runout before I took them in. On each I'd mark the current thickness, measured with a brake micrometer. At the shop, we'd measure again with his micrometer, and decide in advance what the minimum finished thickness should be and also the finish quality. They were in the machine-shop business, not the rotor sales business, so this wasn't too tough.

For the OP, this might be a good option to consider if the existing rotors aren't too worn; It takes care of runout, thickness variations, and obviously any pad deposits. It also gives you a nice consistent surface quality that helps with bedding the new pads correctly.

For cars that didn't have this done already, the machine shop would run the rotors through their hot-tank parts cleaner as part of the process. This takes off any surface corrosion along with old dust and other deposits. The refreshed rotors then get a little CRC Instant Cold Galvanizing spray on the non-friction surfaces including the cooling fins, to help avoid future surface rusting. The visible part of the hats then get some paint in the wheel color, in my case with some Duplicolor "Wheel Silver" with half a dozen topcoats of High-Temp Clear. The regular paint sealant or Rejex after it's all thoroughly dried and the pads have been bedded the first time. They look a lot better, and are a LOT easier to keep clean.

polecat702

I bought a set of ceramic pads from Mark, but never used them because I needed to replace all the ABS looms in my car. The originals were rotted out. Any way that's all done, but I'm getting a pulsation when I apply the brakes, and my pads are like new. I figured my rotors are warped, then I read the article that Jim provided, and it makes sense to me. I really don't drive my 928 that often it sits a lot.

Anyway I'm going to take to the Sniper Association meeting at the Leatherneck Club tonight, run her up on the freeway, and do some spirited stops out side of town. If it still persists I'll order a new set of Zimmerman's slotted and drilled cryogenic rotors, and try out the pads I got from 928 Int.

Thanks guys for all the great advice!
joe

Jim Devine

A couple of quick videos on the proper way to bed in new pads -

Gary Knox

Joe,

After having used solid and holed rotors for track driving, I settled on solids as I thought the added metal was better for absorbing brake heat than the open holes (sometimes the holes become plugged with dust, minimizing any cooling effect). The holed rotors actually microcracked sooner than the solids. I always replaced either when significant microcracking was present. Both types or rotors in my comparisons were Zimmerman.

I have holed rotors on my '94 F & R, but they are the for 'show', not for better 'slow'.

So, in my opinion: 'Spend more dough for holed rotors to get more show', Spend less dough on solid rotors for better slow'.

In the final analysis, I think slotted solids are probably the best for good 'slow', but they are hard to find for 87+ 928's. A local Porsche indy had them custom made by a machine shop in the area, at an added cost of about $100 per pair.

polecat702

Thanks Gary, great advice. BTW, those sheep skin seat covers I got from you a couple of years ago really make a difference! Dee loves them, she sleeps like a baby on a trip. Great protection for my leather seats too.

mark kibort

bedding is not transferring an material, its cooking the resins out and making the surfaces have maximizing contact areas. the smiring of the pad material doesn't happen but with a few pads. I can change rotors with used pads and not notice a bit of difference , on a race lap with absolutely no bed or brake in period.. (if the pads are almost new and were only used on new'ish rotors before)
100 to 60 repeats til brake fade is felt , repeat after cool down, about 4-5 times) is the best way.

JWise

I have relatively new drilled rotors and Hawk ceramic pads on all four wheels. As such, I've been curious as to why I also have a front pulsation through the steering wheel and brake pedal under heaving braking. After reading the Stop-Tech article, I think I now know.

My front left caliper is "sticking" very slightly, not enough to be noticeable while driving, but enough that you see increased brake dust on that wheel and the rotor is slightly more worn than the right side. However, I never put 2 + 2 together. After reading the article, I believe when stopped the contact between pad and rotor has led to '"imprinting" and an uneven layer of pad material and resultant pulsing - in fact I've seen the imprint but didn't realize the significance of it. So, if you have brake pulsing, make sure you don't have a sticking caliper in addition to the other items mentioned in the article.

EDIT - Does anyone have a recommendation for a quality dial indicator?

Fogey1

http://www.harborfreight.com/catalog...dial+indicator

Not a recommendation, per se, but a dial indicator need not be as precise as a micrometer. Smooth motion, ease of secure mounting, and repeatability are the most important elements.

Will

dr bob

For the axial runout indication you are looking for, almost any decent dial indicator will do fine.

The fun part is getting holders that will keep the indicators in the right position on both inside and outside faces to get all the readings at once. I've jury-rigged a set-up using a magnetic base, but remember that things like the front fender and the control arms are aluminum. There are some magnetic 'goosneck' holders that work OK if you can stick them to the steel dust shield/backing plate. Otherwise, a woodworkers' spring clamp will hold a mag base to the aluminum control arms.

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Part of my 'fun work' includes analysis of vibration patterns in large rotating machinery. Modern laser alignment tools and calculators make the basic alignment setups amazingly simple. Still, when I have a problem with some stubborn misalignment signatures even after the laser alignment, I invite one of my old-school millright friends to consult. He's certainly fluent in the most modern methods, but we often end up doing some final tweaking using simple tools like dial indicators, and feeler gauges with gauge blocks. At a recent project, I watched him pull out a kit of Harbor Freight dial indicators and bases. Bob's eyebrows went up a little, until he explained that the ones he was using from Harbor Freight were easily comparable to his prized Starrett and Mitutoya instruments. And he doesn't feel as guilty when one gets dropped or damaged, since they are less than 20% of the replacement costs of the name brands. Ditto on the micrometer set, although he does use third-party calibration bars for those. And for the record, he does all the setups, measurements and calculations for this stuff. I'm allowed to watch, but don't touch his tools. I get the readings from him, and plug them into a model with the "orbits" from the proximity sensors, to make the final diagnosis and recommendation.

bills928

+1

Sent from my iPad using Rennlist

JWise

Thanks guys. I'll stop by Harbor Freight and pick one up.

M. Requin

A good source of machine tools and measuring instruments with a wide range of quality/price is Enco www.use-enco.com . No affiliation, but I have used them for over 30 years, and they carry everything from inexpensive imports to Brown & Sharpe and Starrett.

bills928

Here is a 20% coupon, in case you don't have one.

JWise

Thanks Bill. Pulled a coupon up online and went shopping - got the Pittsburgh unit for $28 with tax, out the door! The same one on Amazon.com is $57