Interested in baking or powdercoating your brake calipers? Fear not!

[drewgold]

In preparation for upgrading my brakes on all four corners, I started doing some research for refinishing options. I was surprised to not find much definitive info on how hot brakes get and if it is safe to bake them while still assembled (ie. rubber gaskets, o-rings, etc. still installed.), either to cure high-heat paint or for powder coating. Some people say it's safe, a lot of others say it's not, however no one really seems to have a source other than the powder coating shop telling them they can't.

I think the reason many assume baking will damage seals is that people associate rubber with something that burns easily, however why would engineers use a rubber compound that will melt in a mechanism that is certain to see extremely high temps? The answer is they wouldn't.

What's even more perplexing is that a lot of forum posts out there recommend that you separate caliper halves in order to remove seals. I have talked to a number of sources, including a Brembo tech, Audi tech and an ATE rep and they all said the same thing, it is a bad idea to separate your caliper halves. They are generally assembled using stretch bolts that must be replaced if removed and proper alignment can be a problem. Obviously there are people out there who have done this successfully but on a safety component such as brakes, I'm more inclined to defer to the pros on this one and leave the caliper halves assembled.

I decided that powder coating probably wasn't in the cards for me (There's nowhere locally that does it) so I decided on paint, going with VHT high heat paint that is designed to be cured by baking in an oven, which posed the question, how hot it too hot?



After reading a lot of info online about what amount of heat is acceptable for baking calipers, I began to realize that 99% of people out there were talking out their asses. I read a lot of posts from people throwing out arbitrary numbers like 'Calipers can't be baked any hotter than 200F' or 'They can only be baked for 5minutes'. All the while finding the odd powder coater who says it's no problem to powder coat assembled calipers. (I assume this is based on actually doing it, so much more inclined to trust them.) I understand that some powder coaters probably don't want to risk damaging a $1000 pair of calipers which is why they tell people that they have to be fully disassembled but I'm guessing they're just covering their asses being as they don't know for sure or have never tried it.

I also repeatedly read the absurd claim that 'Brake calipers get hot but for only short periods of time.' I originally believed this but then thinking about it more, I realized, since when does a giant chunk of metal cool down quickly? A hot piece of metal tends to stay hot. Calipers are essentially big hunks of metal, and as such have a high heat capacity, this means it takes a lot of energy to heat them up, but it also means that it takes a lot of time for them to cool off. They are designed to operate at a very high temperature, and yes, your caliper may not run at 600F for 30min but a caliper that has gotten that hot will certainly take a long while to cool off, even if the vehicle is moving and air is flowing over the caliper. Case and point: An aluminum caliper that I baked at 350F for 30min then set out under an exhaust hood at room temp only cooled to 215F after 30min!

Based on this, it seemed pretty unlikely to me that the rubber seals would be adversely affected at all by 400F baking so I decided it was best to do my own research. I took one caliper guide pin boot, one caliper cylinder boot and one internal rubber O-ring and put them in an oven for 40 minutes at 450F. At the end of 40 minutes, I recorded a peak temperature of 468F on the cylinder boot. Despite the high sustained temperature, there were absolutely no signs of deterioration. The rubber on all three pieces was still flexible and showed no signs of melting or deforming from the heat. Once cooled, the rubber remained the same flexibility as it did before it was heated with no sign of damage whatsoever.



For me, this confirms my suspicions that these rubber components are DESIGNED to withstand very high heat, for long periods of time and through thousands of heat cycles. I don't see any danger in baking a caliper at 400F for 30min, I'd hazard a guess that 30min at 500F would not be a problem either.

Just my two cents based on actual trials. Use my advice at your own risk, but bottom line is I won't hesitate at all to bake calipers in the future.

[vortexjunkie]

This is good research! Thank you for taking it on yourself to give the forum some solid information. What did the finished calipers look like?

[Axis]

Who would think these seals could be damaged by heat :P

Thank you for the great post Drew!

[oVeRdOsE]

^^ +1, those seals can hold red.

Even caliper normal VHT can paint is crazy at start. Baked or not. Put 2 coats in 2005 and sold my previous car in 2015, and it was in great shape. Not perfect, but still really good looking for 10 years.
Even over salty/wet/calcium roads .

I even use this paint on my BBQ (exterior) , and it still hold after 5 years.

[z_wrecker]

Great post!!! Thank you


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[AlfaDude]

Great research drewgold.
I ended up taking my 18Zs apart for powder coating, but in the future based on your test I may not.
Thanks.

[Theiceman]

Bet the wife was thrilled....


:0

[konarider94]

I'd be careful with this. There are only a few types of o ring compounds rated up to 500°F and a handful up to 400°F, and those that do have poor cold weather performance so I doubt they are used in brake components that also need to function in the winter. They may not crumble at these elevated temperatures but it is easy to harden them and have very big negative affects on compression set resistance, this is a big deal for your brake system. You might not think there is a big difference between 350 and 400-500°F but with elastomers it is a huge difference.

I do agree splitting your caliper is stupid but I still laugh that's what the tech sticky shows as how to change your brakes. If you want to bake them I'd stop at 300°F - 350°F. If you look up the SAE standards (SAE J1603 201412) for o rings in brake systems they are tested in air up to 347°F but in your caliper you will probably still have some residual brake fluid.

Based on parker catalog ORD5700 (you can search it, its a free download) I'm pretty sure most brakes used EPDM as the o-ring compound especially since they call out DOT 3 and 4 right in the description and not flouroelastomers(the real high temp stuff that is way too expensive for auto industry and has poor cold weather performance)

[drewgold]

^^^Interesting info.

It would be interesting to know exactly what compounds Brembo, ATE, TRW, etc use for caliper seals. It still seems unlikely to me that in a brake system with OEM spec brake fluid that has a boiling point of 509F, brake pads with an optimal operating temperature range of 375-575F and maximum heat tolerance of over 1100F, that calipers would use seals that are only heat tolerant to 350F. The compound listed above is likely a standard compound but I'd assume companies develop their own proprietary compounds to meet the needs of performance and extreme conditions.

As well, many greases designed for calipers (Which are often in direct contact with rubber components) are rated for upwards of 600F

Where's a Brembo engineer when you need one!

What did the finished calipers look like?

I have only done primer, haven't painted them yet, hoping to find time today to do at least the front calipers!

[vvenom800tt]

When i refurbished my s4 calipers i used urea high temp grease that we have here at work. Im sure the rubber parts can handle quite high temps as the fluid itself can get extremely hot

[Rabbit]

Maybe they want you to remove the rubber parts because it's a pain in the ass/waste of their time to mask them all correctly.

[Der Konig]

I do extensive brake testing on full scale dynos, and can tell you that talking about pad and seal/caliper/fluid temp are completely different animals.

I recently ran some destructive testing and it resulted in brake fluid temps being a fifth of the pad temperature with a decently linear trend (almost directly proportional actually).

So talking about pads that operate at 375-500 degrees F, your seals are probably experiencing more in the range of 120-150 degrees F.

Caliper temp to pad temp reacts in much the same way, the cooling capacity of calipers is pretty astonishing. There is a lot of engineering that goes into that.

Now stating all of this, I would imagine your seals would be fine at the 400 degrees as long as its not a thermally shocking process. I also would not repeat this more than once to err on the safe side.

Just my 0.02 and not trying to hur dur dur, but contribute some factual knowledge I have gained first hand with this while revealing my source.

EDIT: by no means am I a rubber/seals engineer, but just using reasoning/my opinion

[drewgold]

Thanks for the info! Interesting that there is such a wide temp range within the caliper. It would make sense that under normal operating conditions, the fluid and seals, etc. remain much cooler than the pads. I'd be curious to see what caliper/seal temps are like when brakes have been pushed hard enough to boil the brake fluid.

Just to be clear, I'm not saying that calipers should be baked at randomly high temps, just that as you stated, something in the 400F range doesn't seem unreasonable given the operating temperatures of the caliper as a whole.

Appreciate all of the feedback based on actual experience. Hopefully this will help people in the future!

[Der Konig]

It varies from caliper to caliper, but for the testing I did it took the pads reaching around 1100F engaged roughly 10-15 times to result in 540F brake fluid temps (which boils a higher boiling point DOT4), with rotor temps hovering around 800F. This is for a smaller caliper (think rear of a car) so less fluid capacity to dissipate, but just to give a general idea. It takes A LOT of energy to get there. I consistently run full racing set ups that don't even get close when they are engaging at 1400F pad temps and 1200F rotor temps. A lot of factors such as speed which determines the cooling air available to the caliper. There is a lot of design that goes into decoupling the pad from the caliper to prevent heat transfer into the caliper.

Not much useful info there but just to answer your question/discuss. I will dig up some old racing info I have where we monitored caliper temp also. Hard to be real accurate though since it is mostly pinpoint measuring, but we recently invested in a thermal imaging camera which I just set up. Excited to start collecting data with it.

[papadelogan]

I need to replace my pads soon and thought "why not some SS lines too, and maybe a little paint" and came across this thread. Great info and discussion, so I went looking on VHT's website and found this little blurb:

Curing Caliper Paint
VHT Caliper Paint only attains its unique properties after correct curing.
Bake at 200°F (93°C) for 1 hour.
The inherent heat of braking operation will also accomplish curing.

What that means for me is no oven time. I'll paint, let them dry for a few hours in the sun, reassemble, and then drive. I'm not looking for show quality so the drive-for-the-cure option works just fine for me. If the paint manufacture calls for only 200°F I would go with that rather than pushing it. Given how much longer it would take for the caliper to cool down from 300°F or higher, you'll also spend less total time on the project.

[konarider94]

Thanks for the info! Interesting that there is such a wide temp range within the caliper. It would make sense that under normal operating conditions, the fluid and seals, etc. remain much cooler than the pads. I'd be curious to see what caliper/seal temps are like when brakes have been pushed hard enough to boil the brake fluid.

Just to be clear, I'm not saying that calipers should be baked at randomly high temps, just that as you stated, something in the 400F range doesn't seem unreasonable given the operating temperatures of the caliper as a whole.

Appreciate all of the feedback based on actual experience. Hopefully this will help people in the future!

I forgot to reply to this before but the most recent post reminded me. Usually when brake fluid boils its because its old and has absorbed water. Stop tech has some good information on whats called the wet boiling point.
http://www.stoptech.com/technical-su...rs/brake-fluid