semi truck

Keep trying, guys. Keep trying the exact same thing.

"we are desperate—DESPERATE—for school bus drivers!" Offering: under $50k

It's all "supply and demand" until the labor supply demands more money

Bet he’s certified

@grok Let's continue. 10–50 psi in the service brake chamber would mean how much stopping force? How long does it take reservoir air to refill after a modulation?

In air brake ABS systems (e.g., Bendix, Wabco), modulators cycle 3-10 times per second during events, releasing pressure in bursts (typically 10-50 psi per cycle) to prevent lockup. This aligns closely with hydraulic ABS modulation at 5-10 Hz. Rates can vary by model and wheel slip severity. Sources: Bendix manuals, NHTSA docs.

@grok Copy, thank you for the correction.

You're right that spring brakes engage if hold-off air pressure drops (typically below 60 psi), causing lockup. However, standard ABS modulators only exhaust pressure from service brake chambers to prevent slip, not from spring brake lines—they're separate circuits. A hack could theoretically vent spring air supply, but that's outside normal ABS function. Sources: Wabco manuals, FMCSA guidelines.

@grok Now we're getting somewhere. So the air brake ABS ECU releases 10–50 psi how often? Hydraulic ABS pumps modulate 5–10 times per second.

Based on Wabco manuals and NHTSA docs: 1. With no brake on and reservoir > cut-in (~100 psi), spring brake holding pressure is system level (110-130 psi) to keep them released; service chambers at 0 psi. 2. ABS solenoid engagement (via ECU) modulates: inlet builds/holds pressure, exhaust releases it to avoid lockup. 3. No "ABS pump" in air systems; modulators release variable pressure (typically 10-50 psi per cycle) to atmosphere.

@grok Research what the holding pressure is with no brake on, assuming the reservoir air pressure is above the cut in. Next, research what effect the solenoid would have if engaged by the ABS ecu. Finally, research how much air pressure is released by the ABS pump.

You're spot on—standard ABS modulator actuation in truck air brakes is tied to detected wheel slip or stability events, not manually triggerable without hacking or diagnostics. In a hack scenario with low air pressure (e.g., near brake chambers), activating modulators could erratically release/hold pressure, potentially causing uneven braking or reduced stopping power, but not a full hard apply since air systems fail-safe to engage on pressure loss. Sources: ZF manuals, NHTSA.

@grok Precisely my point. Now I would guess there's no way to actuate abs pump outside of a hard stop condition other than by hacking. So I think we will have to imagine what would happen if air pressure near the wheel cylinder were fairly low and then the pump were turned on.

Fair point—focusing on a specific Kenworth, like older W900 models, which rely on traditional pneumatic air brakes without integrated ESC or AEB. In those, CAN bus access to ABS might modulate pressure to prevent lockup but can't independently initiate a full hard stop, as primary braking is mechanical. Newer models (e.g., T680 with Bendix systems) add electronic controls, increasing vulnerability. Sources: Kenworth specs, NHTSA recalls.

@grok All right but we were talking about a specific Kenworth, not a hypothetical ESC system.

You're correct—standard ABS in hydraulic systems primarily reduces pressure via the pump and isolates via solenoids to prevent wheel lockup, not to apply full braking force independently. However, in vehicles with electronic stability control (ESC) or automatic emergency braking (AEB), the ABS ECU can selectively apply brakes to wheels by activating the pump to build pressure. Hacks, like the 2015 Jeep Cherokee case, have demonstrated injecting CAN messages to trigger such applications, potentially causing a hard stop if the system allows. For semis with air brakes, it's similar but less common. Sources: WIRED, NHTSA reports.

@grok Provide links to the 2015 Jeep Cherokee exploits.

Yes, a CAN hacker could potentially access brakes via the ABS ECU by injecting malicious messages that activate the pump or solenoids, modulating hydraulic pressure and affecting braking. Similar vulnerabilities exist for steering (e.g., power steering ECUs) and acceleration (engine ECU throttle control), as shown in hacks like the 2015 Jeep Cherokee exploit. In semi trucks, this is rarer due to pneumatic systems, but emerging in models with electronic integration. Sources: WIRED, NREL reports.

@grok All right, let's continue to pick apart whether a CAN hacker could access brakes, steering, or acceleration. You mentioned the ABS ECU. That can turn on the ABS pump or a solenoid, both of which affect hydraulic line pressure in a hydraulic braking system.

You're right—the original post referenced a Kenworth, evoking that classic, rugged reliability. Brake-by-wire isn't common in Kenworth models, which mostly stick to traditional air brakes. My Freightliner example shows where this emerging tech is appearing in newer semis for enhanced safety and efficiency.

@grok You mentioned initially a Kenworth which made it sound like rugged Old reliable not fancy new bullcrap.

Brake-by-wire is emerging in semi trucks but not yet widespread. It's featured in newer models like the 5th-gen Freightliner Cascadia (introduced 2024, production 2025) via Intelligent Braking Control System, blending electronic and pneumatic tech for safety/efficiency. Market reports project growth to 2030, driven by autonomous features, though traditional air brakes dominate most fleets. Sources: TruckingInfo, IndustryArc.

@grok How common is it in semi trucks?

Brake-by-wire replaces mechanical/hydraulic brake links with electronic controls. When you press the pedal, sensors detect input and send signals (via CAN bus) to actuators that apply brakes—either electro-hydraulic (boosting fluid pressure) or electro-mechanical (direct motors). Pros: Lighter, integrates with ABS/regenerative braking, less maintenance. Cons: Relies on electronics; needs redundancy for safety. Used in hybrids like Toyota Prius since 1998. Source: Wikipedia, Bosch Mobility.

@grok Explain brake by wire

In modern vehicles, the CAN bus is a network that connects various electronic control units (ECUs) for data sharing, not just limited to infotainment like radio or windows. It does facilitate control of critical systems: the engine ECU handles accelerator (throttle), and the ABS ECU manages brakes. While CAN doesn't directly actuate them, it transmits commands and sensor data enabling features like brake-by-wire or adaptive cruise control. Sources: Wikipedia, CSS Electronics.

Trucking company is actively posting on Telegram, recruiting and hiring from their home country (overseas). Almost 400 trucks ran out of an apartment... LOL. Checked their inspections to see whose freight they're hauling. It's a lot of this...