924Board.org

BionicBalls · Joined: 05 Jan 2009 Posts: 642 Location: Charlotte, NC

So I am in the midst of doing my five lug conversion. ATM I am pulling the parts off of my '83 944 parts car. All of the rotors are shot. So I'm looking to buy 4 new ones off Ebay. It seems that I can get 4 drilled/slotted ones for about the same price as 4 regular rotors. I'm not planning on racing the car, and am really just looking at this decision from a monetary perspective. Comments?

http://cgi.ebay.com/ebaymotors/PORSCHE-944-83-84-85-86-F-R-Drill-Slot-Brake-Rotors_W0QQitemZ120539991343QQcmdZViewItemQQptZMotors_Car_Truck_Parts_Accessories?hash=item1c10be4d2f#shId

I only spent $250 on the parts car, so I'm really not wanting to more than that on rotors. One good thing about the parts car though is that it has koni shocks in the rear!

BTW, if anybody needs any parts send me a PM, I'll be selling them cheap considering the price I paid for the car. It's a complete car other than the parts I'll be using for my swap.
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1980 924 NA
1982 931

!tom · Posted: Fri Mar 12, 2010 5:26 pm Post subject:

Drilled rotors are a gimmick. Just go for plain jane ones, and you won't be disappointed.
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78 924 NA
5-lug

Fifty50Plus · Posted: Sat Mar 13, 2010 12:02 am Post subject:

+1 ^
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1979 924 NA race car H-Prod SCCA
1982 924 NA race car - Sold
1981 924 Turbo sold
1982 924 Turbo sold
1972 911 E race car - traded for Cayenne Diesel
1975 914 1.8 Building for H-Prod SCCA

BionicBalls · Joined: 05 Jan 2009 Posts: 642 Location: Charlotte, NC

I don't really care if they are a gimmick if they are cheaper... Is there any disadvantage to them?
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1980 924 NA
1982 931

Cedric · Joined: 27 Aug 2004 Posts: 2810 Location: Sweden

CorsePerVita · Joined: 25 Jul 2008 Posts: 1992 Location: Redmond, Oregon

Rasta Monsta · Joined: 12 Jul 2006 Posts: 11733 Location: PacNW

Cheaper is a problem here. Drilled rotor "Brand X" started as plain rotor "Brand X." Then the cost of the machine work was added. If the result is cheaper than a name brand, plain rotor, this means the Brand X process started with a REALLY cheap rotor.

It's your brakes, eh?
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Toofah King Bad

WeiBe (1987 924S 2.5t) - 931 S3

BionicBalls · Joined: 05 Jan 2009 Posts: 642 Location: Charlotte, NC

I like Rasta's line of thinking. I Guess I'll be looking into some plain-jane rotors.
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1980 924 NA
1982 931

CorsePerVita · Joined: 25 Jul 2008 Posts: 1992 Location: Redmond, Oregon

If you look at the above threads as well, bionic balls, you've got more surface area to make contact with for friction and stopping on OEM rotors over drilled/slotted.
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- 1977 Porsche 924 2.0 N/A (Trackday Project)
- 1979 Porsche 924 2.0 N/A (The other daily)
- 1980 Porsche 931 (Daily)
- 1987 Lamborghini Jalpa
- 1999 Ducati 900SS

mikebola · Joined: 07 Sep 2009 Posts: 361 Location: Parkside, PA

When picking up rotors for my jeep, I found that companies drilled the cheapest rotors (no doubt in a sweat shop) to sell them for more money. and most of the time they were drilled improperly, which could lead to a shattered rotor. I ended up getting brembo drilled rotors as I warped 2 sets of OEM ones. they didn't crack in 60k miles. but they were like, $400 or something on special.
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proud owner of a 1979 924 Sebring Edition with a 931 trans that looks horrible but somehow runs...

fiat22turbo · Joined: 18 Jan 2006 Posts: 4040 Location: Portland, OR

Were they really warped or did you not bed the brake pads properly?

Just curious.
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Stefan
1979 924 Carrera GTS (clone-ish)
1988 944 Turbo S (Silver Rose)

931Owner · Joined: 14 Feb 2009 Posts: 352 Location: Chicago NW Suburbs

I agree that drilled rotors will eventually crack between the holes.

I had ATE PremiumOne Slotted Rotor on my A6 which was not babied at all and had good pad and rotor wear with over 80k miles on them. The slot is a
oblong star shape which did a great job at removing the pad dust and had very little brake fade.

I am looking at getting the same type of rotors for the 931 and are readily available from tirerack.

http://www.tirerack.com/brakes/results.jsp?autoMake=Porsche&autoModel=924&autoYear=1980&autoModClar=
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1980 Turbo
-too many cars and too many motobikes

Vince Ponz · Joined: 02 Nov 2002 Posts: 3581 Location: Florida

Mine are slotted and no problems exist.
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"Never let them see you sweat"
77.5 924 modified track car
79 931 Euro stock
88 924S SE
87 911 Targa stock

Mike9311 · Joined: 14 Dec 2004 Posts: 1798 Location: Chicago-ish

They crack because there is stresses imparted into the material when drilled. Are we talking about actual drilled rotors or the term drilled rotors?...huge difference. There are also as-cast holes in rotors that are called drilled rotors when marketed. Holes and slots help release the gas that forms between the pad and rotor as things get hot under braking. The brake pads outgas and leave a cushion of gas between the pad and disc and the holes and/or slots help vent the gas at a slight loss on contact area of course. This help in venting gas includes rain conditions as well when water gets between on the discs and pads. Might as well throw in the slight improvement in MOI (moment of inertia) from the rotational mass loss too with drilled/cast and/or slotted rotors oh and and the tiny bit of loss in unsprung mass (I am covering my bases here)

My guess is the Brembo units have cast in holes which are formed when the disc is made.

Cheap drilled discs with holes drilled without any attention paid to heat buildup and little to no proper chamfering of these holes are garbage and will crack at the holes once stressed by braking.
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1980 931 since 1989
1981 Ideola 931 Club Sport
1982 931 Entwicklungsfahrzeug
1979 924 NA ohne 650 mit 471
1982 931 Red Resurrection - 951 IC
1982 931 parts car / resurrection?
1980 924 NA (R&D lightweight)
1982 931 wana-be GTR race car

fiat22turbo · Joined: 18 Jan 2006 Posts: 4040 Location: Portland, OR

Mike,

Modern brake pads do not "outgas" like older style pad compounds that many are used to. This has been confirmed by multiple brake engineers (both OEM and aftermarket/racing)

There may be an advantage to drilled rotors in wet conditions by providing a path for the water to leave the face of the rotor (since water doesn't compress well at all) and an advantage to brake pad/caliper piston cooling, but if you are running into issues like that then perhaps a set of proper cooling ducts.

Drilled rotors appear to be mostly used for marketing and to help give performance cars a chance of having the large rotor diameters needed to provide good leverage (and to make them legal for certain racing classes) while reducing the surface area to allow them to work at the slow speeds that the cars will typically see since brakes need to be within their working temperature to work properly.

Bottom line, I wouldn't use them as they offer too many disadvantages compared to a properly engineered and built brake system.
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Stefan
1979 924 Carrera GTS (clone-ish)
1988 944 Turbo S (Silver Rose)