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Powder coating brake drums ?

Started by Philippe M. Ruel, October 30, 2013, 03:01:14 AM

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Philippe M. Ruel

I found this post by Ray on a many-year-old thread I don't want to unearth :

Quote from: Ray on January 31, 2006, 02:22:07 PMPowder coating is definately better.  It resists rust better than ANY paint, and keeps its color generally better as well.
/.../
If you have heat exposure though, such as on brake drums or rotors, they will fare worse. High heat breaks down the powder coating.

The process of powder coating uses temperatures of about 200°C (400°F), can the surface of a brake drum get higher upon road use (i.e. hard braking) ?
Plus, I wonder if the ovening process can put a cast iron drum out of round.

Any experience on powder coating brake drums ?
1952 60 Special in France.

The Tassie Devil(le)

G'day Philippe,

I would strenuously not advocating Power Coating any Brake Drum, for the simple reason that the coating process will retard the heat dissipation performance of the Drum.

Might look good, but too dangerous.   On a show car that spends its' time travelling down the roads in a trailer it might work.

Bruce. >:D
'72 Eldorado Convertible (LHD)
'70 Ranchero Squire (RHD)
'74 Chris Craft Gull Wing (SH)
'02 VX Series II Holden Commodore SS Sedan
(Past President Modified Chapter)

Past Cars of significance - to me
1935 Ford 3 Window Coupe
1936 Ford 5 Window Coupe
1937 Chevrolet Sports Coupe
1955 Chevrolet Convertible
1959 Ford Fairlane Ranch Wagon
1960 Cadillac CDV
1972 Cadillac Eldorado Coupe

gary griffin



I agree with Bruce,  A layer of anything is insulation which will slow the rejection of heat  to some degree, and the most important function is to use friction to slow the vehicle and disperse the heat into the atmosphere. Any insulation would be undesirable. It may be a small amount but when you are going down a long steep hill do you want to wonder if your brakes are overheating??
Gary Griffin

1940 LaSalle 5029 4 door convertible sedan
1942 Cadillac 6719 restoration almost complete?
1957 Cadillac 60-special (Needs a little TLC)
2013 Cadillac XTS daily driver

joeceretti

I think I remember seeing some coatings that where intended to aid in heat dissipation?

Philippe M. Ruel

#4
What makes powder coating different from the original "ordinary" paint coat, as long as heat dissipation is concerned ?
1952 60 Special in France.

joeceretti

#5
Drum brakes become less effective as they heat up due to the expansion of the drum as opposed to disc brakes that actually become tighter as they heat. How much this effects the brakes and how much a coating will intensify that effect depends on a lot of factors. Size of drum, size of contact area with the shoes, the speed of the vehicle and long braking periods down steep hills or at high speeds. Condition of your braking system also is a factor as well as thickness of the coating. I imagine some coatings would have a higher heat transfer rate between the air and the coating. Others would act as an insulator and slow the energy transfer.

I think, for my car, the small amount of driving I do, coating the drums would not make any appreciable difference. My city is geographically located dead center on an escarpment and there are many access roads up and down. I haven't experienced any fade in my Cadillac during any runs down.

The owners manual for the 38 Sixty Special mentions that it is important to use your gearing as an assist when slowing from high speeds.

I will be coating mine to look like they are from the factory. Brake fade be damned.

Jim Stamper


     I can't say I have seen an actual new brake drum from a pre-war car, I wasn't quite born yet, but I have seen many others, and I can't say I have ever seen one painted any color. I only recall clean cast iron, ready for a slight coat of rust, like many other running gear parts. I am sure some cars had more paint under there than others, but can anyone actually say for sure the original pre-war brake drum was painted? Just curious.

     In my hot rodding days in the 60s I knew all about brake fade from over heated drums and linings too I suppose. None of us are going to get our old cars up to 100 plus MPH, but on mountain roads it might be a factor. Gearing down is definitely part of driving the old cars and spreading the slow down responsibility around between systems.

                              Jim Stamper CLC#13470

joeceretti

I actually don't know if mine should be painted or not! I will figure that out though.

I did have my car up to 75mph though. 100? no chance.

tozerco

Noting all the above comments about heat dissipation through any coating and the fact that my '36 and '37's have all had "gunk covered rust" as their coating from day one that I have owned them, I was always told that painting/coating brake drums was a no-no and that, when manufactured, they were given the lightest possible spray of un-primed black paint to stop them rusting just long enough before they left the showroom because buyers wouldn't like rusty anything on a new car. The fact that the paint burnt off after a couple of hundred miles didn't matter because, by then, the car was theirs!

Raises some interesting questions about authenticity, eh?

John Tozer
#7946

'37 7513
'37 7533

The Tassie Devil(le)

I can relate to the brakes fading on a winding mountain road where the brake application is in constant as heat builds up, and the next corner comes up before there has been a chance to cool down.   We have a lot of roads here in Tasmania where one has to slow down to 10 Mph hairpins, and you can't get up to much more than 30 Mph before slowing down for the next one, and that is going uphill.    Downhill is far worse.

Those with Drum Brakes have to be constantly aware of this Brake Fading phenomenon.

Out on the plains, not a problem as the brakes are virtually never used.

As far as I know, Brake Drums were never painted from the factory, or if they were, it was just a dusting, as John said, to protect prior to delivery.   The first Road Test would get rid of it, knowing how mechanics road test.

Bruce. >:D
'72 Eldorado Convertible (LHD)
'70 Ranchero Squire (RHD)
'74 Chris Craft Gull Wing (SH)
'02 VX Series II Holden Commodore SS Sedan
(Past President Modified Chapter)

Past Cars of significance - to me
1935 Ford 3 Window Coupe
1936 Ford 5 Window Coupe
1937 Chevrolet Sports Coupe
1955 Chevrolet Convertible
1959 Ford Fairlane Ranch Wagon
1960 Cadillac CDV
1972 Cadillac Eldorado Coupe

Roger Zimmermann

If somebody is restoring also the frame and floor of his car, I suppose he will not left the drums covered with rust. So, the drums will get a good coat of paint! Fading brakes on a car more than 50 years old? Those old vehicles are usualy driven in a way they cannot suffer from that, even in the mountains. After all, an automatic transmissioncan also be shifted down to avoid excessive brake's use.
To come back to the original question: why not? I painted my own drums with primer and then a 2-stage black paint; after 30 years the drums are still good looking and no, I have no fade problem.
1956 Sedan de Ville (sold)
1956 Eldorado Biarritz
1957 Eldorado Brougham (sold)
1972 Coupe de Ville
2011 DTS
CLCMRC benefactor #101

The Tassie Devil(le)

I can only go from experience.   Cruising, actually, really enjoying myself fanging it down one of our many hilly roads, in my '60 CDV, and using the gears to slow down, there is nothing worse than having to have both feet on the brake pedal, and just pulling up behind a car fitted with disc brakes near the bottom.

Now I know why Cadillac made those brake pedals so wide.   The two feet fit just nicely.

Bruce. >:D

PS.  The car was fitted with dual circuit Master Cylinder, and a good sized Booster.
'72 Eldorado Convertible (LHD)
'70 Ranchero Squire (RHD)
'74 Chris Craft Gull Wing (SH)
'02 VX Series II Holden Commodore SS Sedan
(Past President Modified Chapter)

Past Cars of significance - to me
1935 Ford 3 Window Coupe
1936 Ford 5 Window Coupe
1937 Chevrolet Sports Coupe
1955 Chevrolet Convertible
1959 Ford Fairlane Ranch Wagon
1960 Cadillac CDV
1972 Cadillac Eldorado Coupe

bcroe

My problem is with vented discs.  They never begin to wear out for me.  But the venting
rusts from the inside out, and eventually they give way.  I have lost a few this way over
the decades; there ought to be some treatment to stop this.  Bruce Roe CLC # 14630

Jim Stamper


     I suppose one has to decide what their intentions are.  For strict authenticity, if the drums should be bare, bead blast and maybe give a high temp clear coat to preserve that finish.

     I personally bead blast my drums and give them a light flat black engine paint coat. I always shift down for slowing and they don't get rusty.

     After posting last night about shifting down I remembered I actually know Cadillac club members who have never driven a stick shift car. An additional advantage of downshifting is that it keeps drag on the back end of the car and going straight, especially helpful in wet, snow or muddy conditions. And yes, downshifting an automatic provides that same result , for a rear wheel drive car.

                  Jim Stamper CLC#13470

Philippe M. Ruel

Brake fading is not due to drum expansion (which is minute, and well compensated by hydraulics), but to brake fluid boiling inside cylinder - or caliper for disc brakes. I experienced it riding down a steep hill (Mont Faron near Toulon, France) with my full-loaded (5 passengers plus luggage) old Mustang at a very reasonable speed. I could finally stop it, and proposed my passengers to step out and take a look at the landscape for a few moments - none was aware of what had been happening or could have happened  :o . It was probably the presence of water in brake fluid that made this happen.

Plus, excessive heat may boil bearing grease, destroy bearings and spray grease vapors inside drum and on brake shoes. This is what usually happens when bearing lack of grease and produce heat, I don't know if brake-originated heat may produce it.

I hardly admit that a light coat of paint drastically slows down heat dissipation. On the opposite, didn't they paint brass radiators black from the 1910s to help dissipate heat ? And a brass radiator is not prone to rust, so why would Scrooge Henry Ford, among all others, spend 2 cents more in painting late Model T radiators ?
Does powder coat have different properties ? And - initial question ;) - how does powder coat behave when submitted to brake heat ?
1952 60 Special in France.

joeceretti

I always have more to learn, and enjoy doing so. This is an abstract from Wikpedia:

Causes of Brake Fade [http://en.wikipedia.org/w/index.php?title=Brake_fade&action=edit&section=1]

"The reduction of friction termed brake fade is caused when the temperature reaches the "kneepoint" on the temperature-friction curve and gas builds up between disc and pad. [All brake lining is cured under mechanical pressure following a heating & cooling curve backstroke, heating the friction material up to 450°F to "cure" (cross-link) the phenolic resin thermoset polymers: There is no melting of the binding resins, because phenolic resins are thermoset, not thermoplastic] In this form of fade, the brake pedal feels firm but there is reduced stopping ability. Fade can also be caused by the brake fluid boiling, with attendant release of compressible gases. In this type of fade, the brake pedal feels "spongy". This condition is worsened when there are contaminants in the fluid, such as water, which most types of brake fluids are prone to absorbing to varying degrees. For this reason brake fluid replacement is standard maintenance."

and also from Wikpedia:

Disadvantages (of Drum Brakes) [http://en.wikipedia.org/w/index.php?title=Drum_brake&action=edit&section=15]

"The other consequence of overheating is brake fade.[1] This is due to one of several processes or more usually an accumulation of all of them.

1.  When the drums are heated by hard braking, the diameter of the drum increases slightly due to thermal expansion, so the shoes must move farther and the driver must press the brake pedal farther.

2.  The properties of the friction material can change if heated, resulting in less friction. This can be a much larger problem with drum brakes than disc brakes, since the shoes are inside the drum and not exposed to cooling ambient air. The loss of friction is usually only temporary and the material regains its efficiency when cooled,[1] but if the surface overheats to the point where it becomes glazed the reduction in braking efficiency is more permanent. Surface glazing can be worn away with further use of the brakes, but that takes time.

3.  Excessive brake drum heating can cause the brake fluid to vaporize, which reduces the hydraulic pressure applied to the brake shoes.[1] Therefore, the brakes provide less deceleration for a given amount of pressure on the pedal. The effect is worsened by poor maintenance. Brake fluid that is old and has absorbed moisture has a lower boiling point, so brake fade occurs sooner.[1]"


As Philippe pointed out, none of this does answer the original question.

I did completely flush out my brakes lines a few days ago.




Scot Minesinger

I powder coated the rear brake drums on my 1970 Cadillac with a very light coat of high temp (intended for exhaust manifolds), being aware of possible negative heat dissipation characteristics.  Have driven the car several hundred miles since then and not noticed any change in brake performance.  They sure look nice. 

In general in today's driving people tailgate, break way to late and assume everyone else has amazing breaks.  Even with disk brakes in front on my 1970 Cadillac that is driven 5,000 miles per year in generally lite traffic, I have to assure a safe distance and be patient when other drivers use that space to cut in front of me.  Based on success of rear brakes so far, I probably would powder coat front drums too.

Keep in mind that I myself operate the powder coating, not anyone else, so I can be sure that the coating is not over applied.  If you hand your drums over to a powder coater they probably will media blast the inside where the shoes press against after you told them not to, and apply too much powder before baking.  Powder coaters do not have the brightest people always operating the equipment (including media blasting) and they often don't understand the function of the part either and how that may influence the work.  As posted many times before out of necessity I perform as much of the repair and other work myself as possible.

Enjoy your Cadillac!
Fairfax Station, VA  22039 (Washington DC Sub)
1970 Cadillac DeVille Convertible
1970 Cadillac Sedan DeVille
1970 four door Convertible w/Cadillac Warranty

The Tassie Devil(le)

One must remember that the rear brakes don't really do that much work, in the scheme of things.   They are there to provide sufficient retardation to stop the wheels from braking traction, and causing a total loss of control of the vehicle when braking hard.   

Too much braking at the rear, and the back of the vehicle will try to overtake the front.

The front brakes do 90 % of the stopping.

Bruce. >:D
'72 Eldorado Convertible (LHD)
'70 Ranchero Squire (RHD)
'74 Chris Craft Gull Wing (SH)
'02 VX Series II Holden Commodore SS Sedan
(Past President Modified Chapter)

Past Cars of significance - to me
1935 Ford 3 Window Coupe
1936 Ford 5 Window Coupe
1937 Chevrolet Sports Coupe
1955 Chevrolet Convertible
1959 Ford Fairlane Ranch Wagon
1960 Cadillac CDV
1972 Cadillac Eldorado Coupe

Philippe M. Ruel

Quote from: The Tassie Devil(le) on November 01, 2013, 07:10:06 PMThe front brakes do 90 % of the stopping.
Jim and Roger emphasized on the advantages of downshifting to slow down the car or to maintain a reasonable speed downhill.
Of course it won't be very helpful in emergency braking or bringing the car to a full stop -  upon which front brakes actually do most of the job.

As Jim noted, one can use a stick shift car almost without having to depress the brake pedal but in heavy traffic or parking. This way of driving needs some anticipation and a light foot on the gas pedal, too, but is therefore very efficient in improving mileage.
1952 60 Special in France.

Philippe M. Ruel

#19
Just got my drums and miscellaneous parts and hardware back from the shop.

Everything was sandblasted, zinc coated and powder coated in gloss black.
Places like threads and bearing locations were carefully masked.

It seems to me that they have been heavy-handed on coating - part# is hard to decipher on last picture.
1952 60 Special in France.