2017 - grabby brakes when cold

So, this has been the case since new in 2017 (now @82k miles) but just never really bothered me. When cold, the brakes seem to grab with about double the intensity that I'd expect for the amount of pedal pressure that I'd normally apply. I just anticipate it happening at the first 2 stop signs after I leave the house, and then it's fine.

What I didn't expect, was how it affected my trailer brakes. I installed a redarc brake controller, and tow a 1600lb teardrop trailer, as of July 2023 - so it's all pretty new. When first driving the truck on a cold morning with the trailer in tow, the brakes do their normal extra grabby behavior, but it locks up the trailer brakes. So I have to basically turn off the trailer braking for about 10 minutes, and then it's fine.

Any ideas? Have all new rotors, drums, shoes and pads that I've replaced over the summer. The cold braking behavior is the same. Just not sure if there's anything I can do other than remember to turn off the trailer brakes first thing.

Thanks!

 

Just some thoughts, definitely not certain if this would be the case.

When it’s cold your brake fluid is more viscous. Since the brakes are electrically boosted in the OR maybe the system doesn’t compensate for that. If so there would be an increase in pressure applied at the caliper. If the system uses a pressure sensor to determine brake percentage applied to the trailer brakes it would also increase that effect.

Like I said, no idea if that’s actually the case but it sounds good in my head.

 

Yeah my OR is also the same way, brakes are super grabby for the first few stops, they even squeal a bit.
I thought maybe it was just the material the pad is made of, not sure what pads it has, as I got the truck used.

 

Fluid viscosity isn't really at play here. If it was more viscous there would be more pumping losses in the system and you'd see *less* pressure at the caliper. At least, as far as the effects I can think off. And when the pressure sensor is in the mix as a feedback signal the net pressure will be the same and thus the force at the caliper will be as well (this is how the rear brakes on the OR are operated via the EBD). Also, normal driving isn't going to drastically increase brake fluid temperatures in the first few minutes and brake fluid is fairly non-viscous at room temperatures anyway.

 

My guess is you're experiencing flash rush on rotors and drums as much as anything. Just overnight parking outside especially in humid areas creates a buildup on raw metal surfaces. Those first few braking events are grabbing and cleaning off that build up. This also affects the software control of the braking system because the expected mu is different from the actual mu. If it was just temperature related it would probably take more than a couple stops to get to normal and would happen again if the vehicle sat for just an hour or so.

 

I suppose that's possible. Central Oregon is quite dry, but we get dew in the mornings. I've had the same issue at the coast, where it's at least double the humidity, but wouldn't say it's worse. It's definitely worse on cooler mornings.

 

I thought the same about the pads, but new pads over the summer didn't change anything. Such an odd anomaly.

 

I'm pretty sure the brake controller uses the signal from the truck, and an accelerometer internally. So I'm not sure if the locking up of the trailer brakes is from the truck's brake signal, or because the controller senses the harder braking.

 

My 05 has done this forever, touchy as hell then normal. I’ve never had an issue, and when I replace things when needed, or check fluids it’s all good