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Question upgrading brakes/rotors

I have a 1975 chassis that I am converting to a /6. I am also converting to 911 5 lug bolt pattern front and rear. I have purchased 1972 911 front Boge strut housings,struts,hubs etc. This uses a M caliper with 3 inch mounts and 20mm rotors. My question is what to do in the rear? I can go with M rear calipers but then I lose emergency brake unless I do more work? Or I can go with a setup like Eric Shea produces which modifies existing 914 rear calipers to use 20mm rear 911 rotors but you have to have a machine shop take off 8mm of the outer rotor for clearance. I will install a adjustable proportioning valve to help dial in front/rear balance. Any other suggestions on what to use in the rear? Car will be street/autocross with a occasional DE.
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Old 04-07-2007, 03:31 AM
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In my first 5-lug conversion....I spaced out my rear calipers and had the 911 rotors shaved. It only cost about 30 bucks to have that done at a racing/engine machine shop.

However, I'm now putting in a 3.2l engine...so I am upgrading my entire system with a matched set of carrera brakes. I'll be adding the 911 parking brake setup...it's alot of work but several have done it in the past....it's doable.

With the matched front/rears I'm going to first try it with the proportioning valve in and then second try it with the 911 matched prpportioning valve.
Jim
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Old 04-07-2007, 06:01 AM
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Or you can have the rear hubs drilled and studs pressed in. Have this done by someone who knows WTF they are doing!! Use 914-6 rear rotors, and stock 914-4 rear calipers.

The fronts do most of the braking work, so using the stock rears is not really a problem.

--DD
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Old 04-07-2007, 03:21 PM
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I would stay with stock rears and spend money on other things. Vented fronts, or at least brake fluid that is a little harder to boil sounded nice to me the first time I auto crossed it.
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Old 04-07-2007, 03:32 PM
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Guys,
I just used a pretty trick set up for my race car this past weekend at Road Atlanta, and I was extremely pleased....

Previously, I had the typical Carrera front and rear rotors and calipers. Nice, but in a long weekend at the track, i kept warping my rotors and boiling the fluid (yes, I use race fluid, the stuff just above Super blue called Motol or something like that). Anyway, it was getting annoying....

I had a set of 993 calipers that I was determined to figure out how to use. I couldn't use the front because they mount different, but the rears looked promising.

So, with slight modifications to the 993 rear caliper mount holes, they fit on the front of the Carrera suspension, then I moved the Carrera fronts to the rear, and Viola, much better braking!! I already had a proportioning valve and it turns out I didn't need to adjust it at all. And I kept the Carrera rotors on the car mainly because I couldn't get a set of 993 crossed drilled rotors in time, but I htink I'll just keep it this way for now. Worked fine.

I tested it out for a full Club Race weekend at Road Atlanta had was very happy with the results. No brake fade, no warping of rotors, nothing. Perfect straight line braking. Pedal feel is just like a 993, very stiff.

Keep in mind, though, that I run 16" very wide wheels, so clearance may be an issue with 15"....not sure.

Anyway, just my .02 on the subject.
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Old 04-08-2007, 04:11 AM
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Quote:
Originally posted by Dave at Pelican Parts
Or you can have the rear hubs drilled and studs pressed in. Have this done by someone who knows WTF they are doing!! Use 914-6 rear rotors, and stock 914-4 rear calipers.

The fronts do most of the braking work, so using the stock rears is not really a problem.

--DD
Is a stock 914-6 rear rotor solid or vented? What width is it? I will have Eric Shea modify the rear stubs to the 911 bolt pattern, I like the way he adds ring bosses to make the flange thicker.
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Old 04-08-2007, 07:39 AM
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stock 6 rotor is solid
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Old 04-08-2007, 08:06 AM
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It's solid, and just a little bit (1mm?) thicker than the -four rear rotor. The diameter is very very slightly larger, and some people have reported the rotor rubbing on the bridge of the caliper. If you have that problem, I recommend pushing the caliper out as far as you can when tightening the mounting bolts (loosen them first of course) to try to move the calipers out a bit. You might even want to oval the mounting holes if that doesn't give you enough space.

--DD
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Old 04-08-2007, 08:19 AM
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Quote:
Originally posted by jim912928
In my first 5-lug conversion....I spaced out my rear calipers and had the 911 rotors shaved. It only cost about 30 bucks to have that done at a racing/engine machine shop.

However, I'm now putting in a 3.2l engine...so I am upgrading my entire system with a matched set of carrera brakes. I'll be adding the 911 parking brake setup...it's alot of work but several have done it in the past....it's doable.

With the matched front/rears I'm going to first try it with the proportioning valve in and then second try it with the 911 matched prpportioning valve.
Jim
When useing spacers to make the stock 914 rear caliper work with a 911 rotor why does the rotor have to be machined 4mm on each edge? Can the caliper mounting holes be elongated to push the caliper "up" to a point that the rotor can be used without machining? Or can the inside of the caliper be "massaged" with a die grinder to provide clearance? I just don't like the idea of engineering a rear brake setup that has to have additional machining done to the rotor every time you change it. But I guess the question is how many times are you going to replace the rotor?
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Old 04-08-2007, 12:12 PM
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First thing is, you never oval the mounting holes on such a critical system. You do not have enough meat on the caliper to modify it. You are only likely to have to modify one set of rotors unless you do long distance races for a living. Cryo the rotors for extra long life. It is cheap and easy enough to do the job correctly the first time.

The 911 rotor has to be reduced to the same diameter as the 914/4 rotor it is replacing. Otherwise it will not fit into the caliper without rubbing, and the rotor would extend too far past the pads. By reducing the rotor to the correct size, you reduce rotating weight (the flywheel effect) for faster acceleration and deceleration, while still keeping the advantage of thermal mass and better cooling with the vented rotor.
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Old 04-09-2007, 09:04 AM
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djpateman excellent feedback. Thanks
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Old 04-09-2007, 12:36 PM
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