The 1947 - Present Chevrolet & GMC Truck Message Board Network - View Single Post - 47-55.1 Pressure bleeding

dsraven · 10-17-2021, 10:19 PM

curious, did you burnish or bed in the new brakes? burnishing does 3 things. it converts the materials/resins in the pads and rotors/drums to work better under the heat conditions they will see. it smooths the surfaces of the pads and rotors/drums by depositing a thin layer of the friction material onto the metal surfaces of the rotors/drums and it heat cycles the parts. I am sure you could find details on google. basically things heat up and theoretically changes the material. some of the friction material bonds/transfers to the surface of the rotors/drums and smooths the surfaces and makes for better friction. that's what brakes are all about, good friction.
when I burnish brakes I find a stretch of road that is going to let me do 60 mph for awhile. no lights, minimal traffic, high speed limit. the theory is to make several time spaced stops from 30-45 mph, this will allow the parts to heat up slowly and not thermally shock but also not overheat. then I make a few fairly aggressive stops. not enough to worry about skidding a wheel but enough to make smoke sometimes and also make me want to find a stretch of road where I won't get rear ended when doing this and also allow any vehicles behind me to pass safely. I don't want to make any full stops once I start the burnish process because I don't want the friction material to heat soak in a single position on a rotor/drum so I pick a section of highway etc with no stop lights for miles. I may notice the pedal seems to get spongy like brake fade. time to just do some driving now without having to use the brakes. this is to allow the parts to cool down evenly and also allow the resins n the friction materials to cool and cure. if I make a stop now the friction material will heat soak and thermally bond pad/shoe material to the rotors/drums in that contact spot and that makes for an uneven surface causing pulsating brakes later. the metal surfaces can also get like heat treated hard spots which will wear at a different rate than the rest of the surface, again causing pulsations. keep driving for long enough to allow a good cool down, this can be weather dependant. understand that the next brake application may seem like the brakes are on steroids. that is because some of the pad material has transferred onto the rotors/drums and that makes things kinda sticky. better friction.
a lot of friction materials (pads or shoe sets) will have instructions on how to break in, bed in or burnish.
here are a few

bendix
https://www.brakeandfrontend.com/tec...pads-or-shoes/

raybestos
https://www.motor.com/magazine-summa...eaking-brakes/

https://www.brakepartsinc.com/dam/jc...Burnishing.pdf

wagner
https://www.wagnerbrake.com/technica.../break-in.html

powerstop
https://www.powerstop.com/brake-pad-break-in-procedure/

they kinda all say the same thing. I am wondering if you have had a chance to do this step. if not done or not done correctly sometimes the parts will glaze and require excessive pedal pressure in order to stop the vehicle and/or the brakes can apply unevenly causing the vehicle to pull one way or the other.

10-17-2021, 10:19 PM	#16
dsraven Registered User Join Date: Nov 2010 Location: calgary alberta Posts: 7,825	Re: Pressure bleeding curious, did you burnish or bed in the new brakes? burnishing does 3 things. it converts the materials/resins in the pads and rotors/drums to work better under the heat conditions they will see. it smooths the surfaces of the pads and rotors/drums by depositing a thin layer of the friction material onto the metal surfaces of the rotors/drums and it heat cycles the parts. I am sure you could find details on google. basically things heat up and theoretically changes the material. some of the friction material bonds/transfers to the surface of the rotors/drums and smooths the surfaces and makes for better friction. that's what brakes are all about, good friction. when I burnish brakes I find a stretch of road that is going to let me do 60 mph for awhile. no lights, minimal traffic, high speed limit. the theory is to make several time spaced stops from 30-45 mph, this will allow the parts to heat up slowly and not thermally shock but also not overheat. then I make a few fairly aggressive stops. not enough to worry about skidding a wheel but enough to make smoke sometimes and also make me want to find a stretch of road where I won't get rear ended when doing this and also allow any vehicles behind me to pass safely. I don't want to make any full stops once I start the burnish process because I don't want the friction material to heat soak in a single position on a rotor/drum so I pick a section of highway etc with no stop lights for miles. I may notice the pedal seems to get spongy like brake fade. time to just do some driving now without having to use the brakes. this is to allow the parts to cool down evenly and also allow the resins n the friction materials to cool and cure. if I make a stop now the friction material will heat soak and thermally bond pad/shoe material to the rotors/drums in that contact spot and that makes for an uneven surface causing pulsating brakes later. the metal surfaces can also get like heat treated hard spots which will wear at a different rate than the rest of the surface, again causing pulsations. keep driving for long enough to allow a good cool down, this can be weather dependant. understand that the next brake application may seem like the brakes are on steroids. that is because some of the pad material has transferred onto the rotors/drums and that makes things kinda sticky. better friction. a lot of friction materials (pads or shoe sets) will have instructions on how to break in, bed in or burnish. here are a few bendix https://www.brakeandfrontend.com/tec...pads-or-shoes/ raybestos https://www.motor.com/magazine-summa...eaking-brakes/ https://www.brakepartsinc.com/dam/jc...Burnishing.pdf wagner https://www.wagnerbrake.com/technica.../break-in.html powerstop https://www.powerstop.com/brake-pad-break-in-procedure/ they kinda all say the same thing. I am wondering if you have had a chance to do this step. if not done or not done correctly sometimes the parts will glaze and require excessive pedal pressure in order to stop the vehicle and/or the brakes can apply unevenly causing the vehicle to pull one way or the other.