Slant Six Forum :: Drums VS Discs

Too bad the '55 Chrysler type disc brakes were judged too expensive to carry on making. Those were full-contact disc brakes, kind of like a clutch plate at each wheel.

Joshie225.

Just cause its new, don't make it better

Yeah...the self-energising feature is what I was getting at. I don't know if the '55 setup used vented discs, but I suspect it did not. You're right there'd be less heat rejection than the spot-contact systems that have become industry standard. I also don't know if the '55 system was double-sided (friction material applied to both sides of the disc) or single-sided. I suspect it would be possible to build such a system so as to have good heat rejection, but it would surely be costly.

I really don't see the trouble with drilling a couple of holes in your drums to help with cooling and off gassing. Assuming the drums are in good or new condition, as is the rest of your set up.

After all, disks are made more effecient and less prone to fade by drilling or slotting. It is that micro thin layer of gas created by the extreme heating of the friction material that causes much of the brake fade.

The holes give the gas somewhere to go and braking is improved.

All this being said, I am still going to put factory disks on the 68 Valiant

I really don't see the trouble with drilling a couple of holes in your drums to help with cooling and off gassing.

After all, disks are made more effecient and less prone to fade by drilling or slotting.

Quote:

I really don't see the trouble with drilling a couple of holes in your drums to help with cooling and off gassing.

Then...you should re-read this whole thread. The problems have been described in great detail.

Quote:

After all, disks are made more effecient and less prone to fade by drilling or slotting.

Not necessarily, no. See here and here.

Yeah...the self-energising

Author:	slantzilla [ Wed Sep 05, 2007 8:02 pm ]
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I understand what he's trying to do, but there is no way in hell it is better than a set of disc brakes.

Author:	emsvitil [ Wed Sep 05, 2007 8:22 pm ]
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A drum system can be lighter than a disk system (don't forget the weight of the caliper) What I think would work is a finned drum with the old fashioned riveted shoes (giving you holes)..........

Author:	SlantSixDan [ Wed Sep 05, 2007 9:10 pm ]
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Calipers can be made out of aluminum or magnesium. Really, there's no inherent theoretical weight advantage either way, but the evolution of both systems has meant that for any given level of stopping power and fade resistance, the drum system is generally going to be considerably heavier because of the massive drums. All kinds of techniques were tried when the US auto industry was dragging their feet and resisting what they perceived as the dumb, silly, nonsensical European idea of disc brakes. They tried composite drums made out of steel bands encased in aluminum. They tried all kinds of fins. They tried segmented shoes. Some of these worked better than others, but the writing was on the wall by the mid '60s, solidly in favour of the disc brake, and nobody's come up with anything better in the interim. As for riveted vs. bonded...well, the claim made for the bonded linings when they were new was that you got increased friction area because there weren't any holes in the lining surface contacting the drum surface. And that's true. But perhaps there's less cooling from the loss of those holes (even though the generally don't go all the way through, since solid rivets are used). Without knowing for sure, I'm guessing it's six of one, half a dozen of another. Too bad the '55 Chrysler type disc brakes were judged too expensive to carry on making. Those were full-contact disc brakes, kind of like a clutch plate at each wheel.

Author:	emsvitil [ Thu Sep 06, 2007 12:41 am ]
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What about some slotted drums....

Author:	Joshie225 [ Thu Sep 06, 2007 8:44 am ]
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Quote: Too bad the '55 Chrysler type disc brakes were judged too expensive to carry on making. Those were full-contact disc brakes, kind of like a clutch plate at each wheel. They were also self energizing. I'm not convinced they would be better than open disc brakes when it comes to heat rejection. Conventional vented disk brakes expose the outer friction surface to cooling air which the enclosed Chrysler discs do not.

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Author:	SlantSixDan [ Thu Sep 06, 2007 9:25 am ]
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Yeah...the self-energising feature is what I was getting at. I don't know if the '55 setup used vented discs, but I suspect it did not. You're right there'd be less heat rejection than the spot-contact systems that have become industry standard. I also don't know if the '55 system was double-sided (friction material applied to both sides of the disc) or single-sided. I suspect it would be possible to build such a system so as to have good heat rejection, but it would surely be costly.

Author:	440_Magnum [ Thu Sep 06, 2007 10:40 am ]
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Quote: Joshie225. Just cause its new, don't make it better That is certainly true, as far as it goes. But disks are better than drums in almost every measurable way. Don't get me wrong- its dumb to spend thousands on FOUR wheel disks with fancy-ass drilled/slotted rotors and 4-piston calipers, when a junkyard conversion to factory front disks with existing rear drums will work just as well for far less money. But drums in front, no matter how well maintained and tweaked, will simply not resist fade as well as factory-issue vented disks. Its simple thermodynamics- drums don't have as much heat rejection capacity as vented disks.

Author:	dakight [ Thu Sep 06, 2007 11:31 am ]
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In addition to that, as I've noted in the past, when drums heat up they expand away from the shoes. That phenomenon is the major cause of drum brake fade. A rotor also expands radially but since the friction surface is at right angles to the primary axis of expansion and because the friction surface is always in light contact anyway, pedal travel is virtually unaffected.

Author:	ValiantOne [ Thu Sep 06, 2007 12:05 pm ]
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I really don't see the trouble with drilling a couple of holes in your drums to help with cooling and off gassing. Assuming the drums are in good or new condition, as is the rest of your set up. After all, disks are made more effecient and less prone to fade by drilling or slotting. It is that micro thin layer of gas created by the extreme heating of the friction material that causes much of the brake fade. The holes give the gas somewhere to go and braking is improved. All this being said, I am still going to put factory disks on the 68 Valiant

Author:	Joshie225 [ Thu Sep 06, 2007 12:48 pm ]
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Quote: Yeah...the self-energising feature is what I was getting at. I don't know if the '55 setup used vented discs, but I suspect it did not. You're right there'd be less heat rejection than the spot-contact systems that have become industry standard. I also don't know if the '55 system was double-sided (friction material applied to both sides of the disc) or single-sided. I suspect it would be possible to build such a system so as to have good heat rejection, but it would surely be costly. I'm pretty sure there were two friction plates. I recall the plates rode up on ramps as they were pushed in the direction of forward wheel rotation by the wheel cylinder and the plates departed from each other to contact the enclosed rotor. The outside of the rotor was quite well finned, but appeared to be sealed or nearly so keeping air from circulating within the housing.

Author:	Joshie225 [ Thu Sep 06, 2007 1:11 pm ]
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Quote: I really don't see the trouble with drilling a couple of holes in your drums to help with cooling and off gassing. Assuming the drums are in good or new condition, as is the rest of your set up. After all, disks are made more effecient and less prone to fade by drilling or slotting. It is that micro thin layer of gas created by the extreme heating of the friction material that causes much of the brake fade. The holes give the gas somewhere to go and braking is improved. All this being said, I am still going to put factory disks on the 68 Valiant Most modern brake materials do not out-gas like old materials and therefore benefit very little from slotting or drilling. That said slotting with a radius cutter (no square corners!) is much safer than drilling. The vehicles that come with drilled rotors from the factory have very large rotors and suffer less from the loss of rotor mass than they gain from the extra cooling. Even so there is a decrease in brake rotor life from wear and also from cracking. The cars you see factory equipped with drilled rotors can be classified as high maintenance. Don't get me started on Chinese rotors! If you can't verify the country of origin of any rotor, let alone slotted or drilled ones, don't buy it! My Dakota has US made rotors. My Valiant has Canadian made rotors. I know of at least one RX-7 owner that replaced his Japanese rotors with Raybestos rotors made in North America to cure a rotor warping problem. I know of a Mustang racer that had Chinese rotors with voids in the hub. He broke the hub and lost the wheel during practice. You will never see Swiss Cheese rotors on my car unless I hit the lottery (which I don't play) and you see me rolling in a Porsche GT3.

Author:	SlantSixDan [ Thu Sep 06, 2007 1:53 pm ]
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Quote: I really don't see the trouble with drilling a couple of holes in your drums to help with cooling and off gassing. Then...you should re-read this whole thread. The problems have been described in great detail. Quote: After all, disks are made more effecient and less prone to fade by drilling or slotting. Not necessarily, no. See here and here.

Author:	Rick Covalt [ Thu Sep 06, 2007 2:02 pm ]
Post subject:	Wet conditions
Aren't the discs at a significant advantage under very wet (Or standing water conditions) It seems I remember as a teenager having to slow way down and ride my drum brakes through the water or they were not able to grip. I don't think discs are nearly as affected by this. Rick

Author:	ValiantOne [ Thu Sep 06, 2007 2:09 pm ]
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Quote: Quote: I really don't see the trouble with drilling a couple of holes in your drums to help with cooling and off gassing. Then...you should re-read this whole thread. The problems have been described in great detail. Quote: After all, disks are made more effecient and less prone to fade by drilling or slotting. Not necessarily, no. See here and here. Well Dan, I'll agree to disagree with you

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Author:	440_Magnum [ Thu Sep 06, 2007 2:25 pm ]
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Quote: Yeah...the self-energising I'm more and more convinced that self-energizing brakes were at best a necessary evil from the get-go. Its a non-linear function with hysteresis introduced smack in the middle of the braking control system, and it makes it harder to get a nice predictable, linear pedal feel. And as for weight, during the conversion on my '66 Polara I had the stock drum system right next to the replacement disk system (factory issue from a '73 Newport) on the garage floor. The disk setup was several pounds lighter, even with the big iron Kelsey-Hayes caliper. Of course my car had the optinal bigger C-body drums that came with the 383 engine, and was getting the "big" disks (15" wheels required) so the same might not be true going from wimpy little 9" A-body drums to the "small" disk setup from, say, a 74 Dart.