drewgold
04-27-2016, 10:00 PM
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?
http://uploads.tapatalk-cdn.com/20160428/1ee67fc9efd2a88c77c13b6f76c705e6.jpg
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.
http://uploads.tapatalk-cdn.com/20160428/cf8c988f9ecbef517cb7feb47152f258.jpg
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.
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?
http://uploads.tapatalk-cdn.com/20160428/1ee67fc9efd2a88c77c13b6f76c705e6.jpg
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.
http://uploads.tapatalk-cdn.com/20160428/cf8c988f9ecbef517cb7feb47152f258.jpg
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.