Brake fades if hot

[Flathead]

Originally Posted by J Franklin

I wonder how juice brakes will solve brake fade?

Yeah, I was wondering the same thing.

[Werner]

Originally Posted by ericr

man,

after reading Werner's comments, do you guys think what he is using for brake shoes on front or rear is an issue? I understand his analysis and don't wish to second-guess him but how often have we seen modern-style improvements to original designs complicate performance?

Erich,

what you write is not to be dismissed. But in this case, I let the pairing of the new pads made with match the material of the drums, namely cast iron.

The brakes grip well, that's why they get very hot. But they have a very strong fading.

I think, as also noted above writers, that is also normal for the large drums. It only happens when I make very steep descents, as is typical here in the Eifel and the Ardennes. I can't name a comparable terrain in USA because unknown.

[updraught]

"With brake fade, the pedal still feels normal, but the vehicle is not slowing down as you would expect. You’ll typically be able to smell the brake pads overheating, and though the brakes are applied, the vehicle isn’t stopping well. The friction created by the brake pads and rotors is used to slow the vehicle. This friction or effectiveness tends to increase as the braking temperature increases, but above certain temperatures the brake pads begin to break down. Gasses can be released as the brake pad material breaks down, these gasses form a microscopic layer between the pad and rotor reducing friction. This decrease in braking effectiveness is considered brake fade."
https://www.powerstop.com/brake-fade...ke-fluid-boil/

I guess you would smell this.

[bavArian]

Has anyone here tried cutting diagonal grooves into the brake pads? I'd suppose 1/32 inch width grooves with a pitch of 3/4 inch should help at least a bit?

[SAJ]

Updaught's post is why I always press and release the brakes on long downhill runs. This releases the gases that form from thermal decomposition of the phenolic bonding agent used in most moulded linings. The result is better braking each time the pedal is quickly released and re-applied, that you can easily feel.
Possibly the grooves bavARIAN mentions might help, but there will still be a trapped layer of constantly reforming gases in the contact areas between said grooves.
I have always felt moulded linings have more resin than woven, which need less adhesive to hold the friction media together due to the mechanical interlocking of the weave. And hence woven off-gas less than moulded on long downhill runs,.
Just my opinion.
SAJ in NZ

[Werner]

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Guten Tag.


I think that the main cause of brake fading does not depend on the gas layer, but that the friction coefficient between the friction lining and the drum decreases more and more with increasing the temperature.

Because that is the physics. The energy of the accelerated car mass must be decelerated by the friction brakes. The friction generates a lot of heat. The higher this temperature of the drums and the linings becomes, the more difficult and slower is the dissipation of the heat. As a result, the temperature continues to rise and the coefficient of friction decreases until at some point there is hardly any frictional force left.

Modern disc brakes are therefore additionally ventilated from the inside.

And this is why the old racing cars with drum-brakes used many cooling fins outside on the drums.

[Flathead]

Energy can neither be created nor destroyed, if I remember correctly from Physics class. Therefore the energy of motion is converted into heat by the brakes, the brakes need to transfer this heat into the air which is left behind as you speed down the hill. The more mass the brake drum has the more heat it can absorb, new cast iron drums are heavier than the thin steel originals that have likely been resurfaced even thinner over the years. Fins would help to get heat out of the drum faster by increasing the surface area exposed to the air. When the drum gets super hot it will expand into a slight bell shape that hinders good shoe contact, but at that point it probably doesn't matter much. The only way hydraulic brakes will improve a fade problem is if the conversion includes larger finned drums, and that is about drums not hydraulics.

[Werner]

That's exactly the thing, how you describe it. However, it takes longer for heavy material drums to cool down.

I'm surprised that no other A-drivers, that lives in the mountains, has written that they also has fading. Because I do not think that I'm the only one with this brake heat problem.

A good solution would be to enlarge the drum surface with a corrugated aluminum ring sitting tightly on the drum or to put cooling fins with MS-hard solder on the drums. Neither is easy.

I am also surprised that these accessories are not available for purchase to my knowledge.

[Vic in E-TN]

Werner is correct in that the coefficient of friction decreases with temperature. I looked at the German chart that he posted. Although I cannot read German I can look at the first small chart which shows Coefficient of friction (COF) vs. temperature and it shows a drop from 0.42 at 100 Deg C to 0.34 at 300 deg C (572 deg F). I am not a brake engineer but this material looks pretty good relative to fade. Randy Gross says that his material for the last 15 years is unclassified but is suitable for slower cars that do not travel more than several thousand miles a year. Don Snyder does not provide any information to Werner. In my opinion Randy Gross's lining material is superior to Snyder's brake linings for our cars. I would like to discuss this subject with Walt Bratton and Steve at Bert's. If I can get more information I would like to submit an article to one of our club magazines.
Vic

[Synchro909]

Originally Posted by Flathead

Yeah, I was wondering the same thing.

Hydraulic brakes will fade just like mechanical ones. I used to drive a 1967 Toyota. Brake fade was a part of the "character" of that car. I don't know how many times I had both feet on the pedal and my backside off the seat.
Another property of drum brakes is that as they heat, the drum expands and the pedal goes down. With external brakes, you adjust them so that they start working with the pedal near the floor. As the drum expands, the pedal rises. If they are adjusted like drum brakes, they would expand to the point where they are locked on and you must wait till they cool before being able to move again.

[Pete]

See if you can find "Velvet Touch" lining that can be adapted to the model A brake shoes. It is a sintered bronze metalic type lining. It IS still available somewhere.
The hotter it gets, the better it works. I have seen the drums red hot on race cars with it and still worked good.
I used it on my service truck for years. On the street it seemed like it lasted forever.