Brake Upgrade

I have solid rotors front and rear which I wish to upgrade to vented, cross drilled. Can I upgrade the rotors without changing over the calipers, or am I in for a full change over?

As usual your collective advice is appreciated.


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Paul
911T'69

I can't say for sure about your specific car, but I swaped my old rotors for a set of new cross drilled ones for approx. $500.00 I think. Not really too tough. The front rotors are a little trickier because the rotor is mated to the hub...(bearings etc.) I just made sure I checked the amount of free play before I removed the hubs so I didn't over tighten them and repacked the bearings.

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Leland Pate

___79 SC Targa

Actually, it is possible to rebuilt your calipers with longer Allen bolts, a spacer machined flat in a mill, four new VW 'Type 3' 311.615.277 'O' rings (with rectangular cross-section) ... since that is precisely what Ate did for the cars with vented-rotors! You would have a bit of trouble getting those old bolts out, as they are properly called a 'Ribe' fastener, not an Allen, not a 'Polygon,' not a 'Torx' ... but Torx is close, maybe good enough fit if the rust after 31 years is not TOO bad! You could just have some 3/8 " or 8 mm steel bar stock milled flat and to a finished thickness of 0.287 " or 7.3 mm after it was cut to shape and drilled for the bolts and fluid holes. The 'new' thickness of the solid rotors was 0.5 in. or 12.7 mm, and the '69-'83 vented rotors was 20 mm. I think I would assure myself that the calipers were in good enough shape to rebuild before I had those spacers made, though! Used calipers are readily available, and a LOT less trouble. Good luck!

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Warren Hall
1973 911S Targa

Thanks for the advice guys.

Warren, sounds like replacement calipers are the go. Any recommendations? Should I start keeping an eye out for used "S" alloy versions (for the front) '70 - 73?


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Paul
911T'69

Paul, I kind of figured you wouldn't want to mess with making new machined parts, but I would throw it out there just in case any budding machinist's out there needed something to think about! If you run across any bargains down under on 'S' or 'A' calipers, by all means give it a shot, but be aware that you have to find a pair of used/new struts to mount them on, because the mounting 'ears' spacing is wider than those for your 'M' calipers!

In my opinion, 'M' front calipers are quite adequate for any street driving conditions, because those are what the first vented rotor application, the '67 911S, had! That was the first 911 model I ever drove, and it had simply amazing braking performance from 140 mph on 4.5" wheels and 165VR-15 Dunlop CB-57 'dogbone' tires!!! The latest Japanese multi-valve wonders can only dream of braking performance that good, even on 21st century, state-of-the-art tires!

Just for the record, I did my own cross-drilled rotors back in '84, long before they were available commercially, and they do look neat! But, no measurable improvement in braking performance was to be found ... overheating of rotors or pads just is NOT a problem on 911 brakes on the street! They do get their share of compliments, though! I'm not saying to forget them, but other than helping under downpour conditions (doubtful you see much of that) they are just a visual treat!

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Warren Hall
1973 911S Targa

Hi Warren

Why am I not surprised you were upgrading your brakes with cross drilling before it was a “standard” upgrade?

Anyway, might start keeping an eye out for some “M” calipers to suit, which will become the subject of my first attempt of brake rebuilding. Changing from solid to vented rotors appeals but if there is substantial $ difference in going to cross-drilled I might give that a miss. I think my stock bodied car looks sexy enough as it is (photo to appear soon). Powder coating or bake enamelling the calipers could be a nice touch though.

Regards,


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Paul
911T'69

An additional thought. Would I have to change hubs due to the increased thickness of the rotors? I assume the bolt studs are mounted on the hubs that the rotors bolt onto.

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Paul
911T'69

No change in the hubs necessary.

Paul Frere's book 'Porsche 911 Story' is probably the best technical description from an engineer's viewpoint of the evolution of the 911 since the prototypes. He has chapters on the various systems: body, engine, suspension and tires, brakes, racing developments, etc. A really fascinating book with plenty of great factory pictures over the years! Great info on upgrades over the past 35 years!

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Warren Hall
1973 911S Targa