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kcoyle
Joined: 15 Jan 2011
Posts: 712
Location: Long Island, NY
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 Posted: Mon Nov 21, 2011 5:56 am Post subject: Warped rotor? |
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Decided to track down what feels like a warped rotor. I removed the front rotors to take them to be inspected and cut (they didn't seem to have too much runout) and while inspecting everything I saw this in the passenger side piston.
It looks like a piece of the piston broke off the very edge. Could this be part of the problem as well or nothing to worry about?
Thanks,
Kevin
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1982 931- Stock with MBC at 8psi
Relax, all right? My old man is a television repairman, he's got this ultimate set of tools. I can fix it. |
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9xx
Joined: 18 Jun 2006
Posts: 627
Location: Jarvenpaa, Finland
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| Posted: Mon Nov 21, 2011 6:21 am Post subject: |
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No, that is the way it should be. Nothing to worry about. But perhaps you could rebuild the calipers. The one in the picture looks... like it is 30 years old 
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Mikko
All gone: 931 '82 Alpine White, original option "220" G31 with LSD + 3 x 944 |
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Ozzie
Joined: 12 Mar 2005
Posts: 4448
Location: Townsville, Qld. Australia
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| Posted: Mon Nov 21, 2011 7:13 am Post subject: |
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thats the 20degree offset which is supposed to be set up like this.
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Porsche 924 1984 (UK import) NA
Its AUTO and its BLACK
Montego Black on black/red
Engineer of Electro/Mechanical Systems Maintenance |
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9xx
Joined: 18 Jun 2006
Posts: 627
Location: Jarvenpaa, Finland
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fiat22turbo
Joined: 18 Jan 2006
Posts: 4040
Location: Portland, OR
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| Posted: Mon Nov 21, 2011 12:49 pm Post subject: |
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Rotors rarely warp, usually it is uneven buildup of brake pad material. Proper bedding of t he pads and rotors helps prevent this from occurring.
Make sure the caliper parts are moving properly and that the pads are wearing evenly.
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Stefan
1979 924 Carrera GTS (clone-ish)
1988 944 Turbo S (Silver Rose) |
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kcoyle
Joined: 15 Jan 2011
Posts: 712
Location: Long Island, NY
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| Posted: Mon Nov 21, 2011 11:51 pm Post subject: |
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Ok, so i read up on the offset. I will check that when I get back to it.
I planned on rebuilding the calipers over the winter along with other things when the snow hits, I just wanted to address the shimmy under braking. I didnt want the car on jackstands for more than a day or 2 while the weather is still good, but if I have to rebuild it now I will.
So if the rotors didnt warp I should try new pads next?
Also can someone recommend a one man brake bleeding kit for a friendless wonder such as myself? Maybe the Motive powerbleed or something?
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1982 931- Stock with MBC at 8psi
Relax, all right? My old man is a television repairman, he's got this ultimate set of tools. I can fix it. |
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fiat22turbo
Joined: 18 Jan 2006
Posts: 4040
Location: Portland, OR
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| Posted: Tue Nov 22, 2011 2:46 am Post subject: |
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Google DIY Power Bleeding. Costs about $10 to build. $30 if you buy the special Motive cap.
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Stefan
1979 924 Carrera GTS (clone-ish)
1988 944 Turbo S (Silver Rose) |
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Ozzie
Joined: 12 Mar 2005
Posts: 4448
Location: Townsville, Qld. Australia
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| Posted: Tue Nov 22, 2011 10:34 am Post subject: |
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I had a very bad shimmy under braking.
This was just after I bought the car with a saftey inspection.
Turned out the front rotors were 9mm.
IIRC the minimum is 12mm.
Changed them and new bearings fixed the problem.
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Porsche 924 1984 (UK import) NA
Its AUTO and its BLACK
Montego Black on black/red
Engineer of Electro/Mechanical Systems Maintenance |
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emoore924
Joined: 13 Apr 2004
Posts: 2822
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| Posted: Tue Nov 22, 2011 1:00 pm Post subject: |
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| Quote: | | Rotors rarely warp, |
Rotors warp all the time..., on what do you base this statement? |
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fiat22turbo
Joined: 18 Jan 2006
Posts: 4040
Location: Portland, OR
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| Posted: Tue Nov 22, 2011 3:01 pm Post subject: |
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A Bendix Brake Engineer's statement.
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Stefan
1979 924 Carrera GTS (clone-ish)
1988 944 Turbo S (Silver Rose) |
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kcoyle
Joined: 15 Jan 2011
Posts: 712
Location: Long Island, NY
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| Posted: Tue Nov 22, 2011 11:33 pm Post subject: |
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| fiat22turbo wrote: | | Google DIY Power Bleeding. Costs about $10 to build. $30 if you buy the special Motive cap. |
Thanks, I'm going to make one of those.
I have my rotors back but i think I'll just leave the car dry-docked for now and rebuild the calipers and get new pads as well. It appears the PO put new pads on as window dressing but they wore unevenly especially on the side that had the most runout, so I'll do the whole job now. ($$)
Any special brake pad recommendo for street car?
Also, PET shows this as caliper rebuild kit
928-351-941-00
Do I need anything else?
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1982 931- Stock with MBC at 8psi
Relax, all right? My old man is a television repairman, he's got this ultimate set of tools. I can fix it. |
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emoore924
Joined: 13 Apr 2004
Posts: 2822
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| Posted: Tue Nov 22, 2011 11:55 pm Post subject: |
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| Quote: | | A Bendix Brake Engineer's statement |
Bah. Poppycock.  |
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!tom
Joined: 28 Aug 2006
Posts: 1941
Location: Victoria, BC Canada
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| Posted: Wed Nov 23, 2011 3:00 am Post subject: |
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There's several causes for brake shimmy. One is warped rotors, another is uneven deposits.
A cheaply made vented rotor may have the vented portion of the casting misaligned. As this rotor heats up with use, the rotor will warp due to the uneven thickness of the rotor. As the rotor cools, it will straighten. When it's hot, the rotor will wear unevenly as it is warped. This uneven wear is similar to warpage when the rotor is cool.
Solid rotors tend to warp less than vented rotors, as it's not possible to have a misaligned core.
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78 924 NA
5-lug |
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kcoyle
Joined: 15 Jan 2011
Posts: 712
Location: Long Island, NY
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| Posted: Fri Nov 25, 2011 1:13 am Post subject: |
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In the FWIW department, I slapped the car back together for a few errands this AM and all thing being equal except the newly cut rotors, the "shimmy" under braking is gone. I just had to check before I went and did the whole brake refresh.
KC
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1982 931- Stock with MBC at 8psi
Relax, all right? My old man is a television repairman, he's got this ultimate set of tools. I can fix it. |
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kcoyle
Joined: 15 Jan 2011
Posts: 712
Location: Long Island, NY
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| Posted: Tue Dec 20, 2011 10:42 pm Post subject: |
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| fiat22turbo wrote: | | Google DIY Power Bleeding. Costs about $10 to build. $30 if you buy the special Motive cap. |
Excellent advice, I built this one.
http://tinyurl.com/2e3nbgx
It cost me about $35.00 total as I had nothing laying around the garage to use except washers and O rings. I saved about $15 bucks over the real one, which was the cost of the Super Blue.
Pressure bleeding was so easy that I and my 6 year old helper were able to do it without any major catastrophes.
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1982 931- Stock with MBC at 8psi
Relax, all right? My old man is a television repairman, he's got this ultimate set of tools. I can fix it. |
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