Disk Brake Rotors, Slots, Holes, Zinc Plating, Painting

The VW Beetle. Everything about bugs!

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Scott Novak
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Disk Brake Rotors, Slots, Holes, Zinc Plating, Painting

Post by Scott Novak » Sun Mar 16, 2008 8:12 am

I need to buy a new pair of 4 bolt solid rotors for the front of my 1972 Beetle.

I'd like to hear some recommendations on good brands of rotors to buy, and brands of rotors not to buy.

What are your opinions on slotted, versus grooved, versus drilled rotors?

What are your opinions on Plain rotors versus Zinc Plated rotors versus Painted rotors?

What are your opinions on plain rotors, versus the rotors with the wheel centering ring?

Scott Novak

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Marc
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Post by Marc » Sun Mar 16, 2008 11:21 am

The "hub-centric" rotors with the ring are fine IF you are using rims that are compatible with them. The plain "lug-centric" rotors will accept any rim that'll bolt up.
VW went hub-centric to remove one potential cause of shimmying with the McPherson strut front suspension. If yours is a Standard Beetle it's not likely to be an issue.
Holes and slots are put into rotor friction surfaces to allow for the escape of gases which can form when the pads are super-hot. It's debatable whether they aid in cooling - IMO you're better off having more material there to act as a heat-sink. It's mostly a cosmetic choice anyway, since it'd be a rare occurrence for pads to gassify in normal driving.
As for painting/plating, I've always felt that it might impede heat transfer and so have run them "raw" - but it's probably not going to hurt anything so long as it's kept off the friction surface.
For a street car you should be fine with the basic Brazilian TRW or Varga rotors - Brembos are available but I doubt they're worth paying nearly twice the price for unless bragging rights are that important to you.
In my experience it's more important to upgrade the rear brakes when converting the fronts to disc - the larger Type III assemblies bolt right on, or at least fit larger "front" wheel cylinders to the Type I rear brakes.

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Post by Bruce2 » Sun Mar 16, 2008 12:10 pm

I've got a pair of drilled rotors and a pair of solid rotors. I have seen no benefit whatsoever with the drilled rotors. During heavy rain, the pads hydroplane just as bad as solids. Even with the stock dust/rain shields. The BIG change is the noise. They create a loud wooshing sound with just the slightest application. I will never again drill rotors. I've never tried slotted rotors.

I paint the rotors with cheap flat black spray can paint. I don't like rusty things. I doubt there's much difference in the radiation of heat between a clean flat black surface and a rusty surface. One could argue that rust insulates.

I agree with Marc, you'll never notice any difference with the different brands. It is just a hunk of cast iron going around.

If you have stock wheels that work with the hub centric part of the rotor, go for it. I find them easier to put the wheels on and find the lug holes. You can put the wheel on the centering ring, then grab the grease cap and turn the rotor until the bolt holes line up. The non-stock wheels I use have a smaller diameter for the hub, so my buddy machined off the lip from the rotors. In hindsight, I should have had him turn the diameter down to match my current wheels. Next time.

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Chris V
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Post by Chris V » Sun Mar 16, 2008 6:05 pm

Bruce2 wrote:...If you have stock wheels that work with the hub centric part of the rotor, go for it. I find them easier to put the wheels on and find the lug holes. You can put the wheel on the centering ring, then grab the grease cap and turn the rotor until the bolt holes line up. The non-stock wheels I use have a smaller diameter for the hub, so my buddy machined off the lip from the rotors. In hindsight, I should have had him turn the diameter down to match my current wheels. Next time.
FWIW...I bought some stock 15x5.5 Porsche steel wheels from another forum member and three were hubcentric and the fourth looked liked it was meant to be, but had missed the final operation on the press to flare the edge...We use them as spares w/125's mounted on them...to use that one you've got to be sure to have a spacer thick enough to clear the hub-ring.

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Post by Scott Novak » Sun Mar 16, 2008 11:28 pm

Does anyone know if the lip that the dust covers fit over on a hub centric rotor is smaller in outer diameter than the lip on a plain front rotor?

The dust caps that I use on my 1972 Super Beetle drums, 1974 Standard Beetle drums, and have also used on plain front rotors are about 0.020" too large in diameter for the hub centric rotors that I have. The dust caps just won't stay on.

Or do I have a pair of rotors are are out of spec?

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Marc
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Post by Marc » Mon Mar 17, 2008 2:22 am

Scott Novak wrote:...do I have a pair of rotors are are out of spec?...
Certainly sounds that way. They all use the same dustcaps (111 405 691 B for left, 111 405 692B for right). You could buy some new Brazilian ones for $3-4 each to see if they'd fit any tighter, but I'd be surprised.
I've encountered a few drums over the years that had this problem - I used a punch to disturb/raise the metal on the O.D. of the snout enough in 8-12 places so the dustcap would stay on, then put on a little RTV before final installation to make it watertight.
Others have simply squished the caps a little in a vise to make them oval - that and RTV will do on the right side, but I wouldn't expect it to last very long driving the speedo cable.

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Post by Scott Novak » Tue Mar 18, 2008 12:06 am

Marc,

I tried a dozen different dust caps and they were all loose on the rotor.

I punched around the dust cap in at least 40 spots and it tightened it up fairly well. I also ordered a set of new dust caps. I'll see if they work any better.

Thanks for the suggestions.

Scott Novak

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sideshow
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Post by sideshow » Tue Mar 18, 2008 8:30 am

The low tech fix is a wrap of tape on the dust cover. Budget allowing powder coating them adds slight o.d.
Yeah some may call it overkill, but you can't have too much overkill.

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