#2643: Breaking-in the Brakes
About this episode
A listener’s “girl car” question kicks things off, then the show dives into real brake know-how. The hosts explain that “modern brakes do require a break-in period,” and that new pads need time to seat into machined rotors so braking effectiveness improves quickly. They also discuss a mechanic’s advice for the first 500 miles—varying speed and limiting who can drive—using a 1998 Chevy Lumina example. The segment stays practical, with quick, test-drive timing rather than long mileage rules.
See pcm.adswizz.com for information about our collection and use of personal data for sponsorship and to manage your podcast sponsorship preferences.
NPR Privacy Policy
Toyota Camry
"...my son buy his first car, a beautiful 1991 Toyota Camry. Lately it seems I can't go anywhere without seei..."
The Toyota Camry is a regular passenger car (a sedan) meant for everyday driving. A 1991 Camry is an older version, but it’s still the same basic idea: comfortable transportation for commuting and errands. It often gets mentioned because many people find them straightforward to own.
The Toyota Camry is a mid-size sedan known for being practical and easy to live with, which is why it often comes up when someone is shopping for a first car. A 1991 Camry in particular is significant because it represents an older, simpler generation that many owners keep running for years. It’s the kind of car people discuss in the context of reliability and everyday usability.
Volkswagen Passat
"...y was looking at cars, and I recommended to him a Passat. But he said, oh, chick car."
The Volkswagen Passat is a sedan, meaning it’s a car designed mainly for carrying people comfortably on everyday trips. It’s meant to be practical, like a commuter car, rather than a special-purpose vehicle. The discussion in the podcast is about whether it’s a good choice despite how some people label it.
The Volkswagen Passat is a mid-size sedan that’s typically discussed as a comfortable, more “grown-up” alternative when someone wants a practical daily driver. In the podcast context, it comes up because the speaker recommended one to a buyer who dismissed it as a “chick car,” highlighting how the Passat is often judged by perception rather than its purpose. That makes it a common topic when talking about what makes a car a good first choice.
94 Mazda B3000 pickup
"So what's going on? Well, I have a 94 Mazda B3000 pickup. Yeah. That we just replaced all the clutch mechanism, too."
This is a Mazda pickup truck from the early 1990s. The caller says their clutch system was replaced, but it still wouldn’t let them shift correctly.
The Mazda B3000 pickup is a mid-size truck from Mazda’s lineup in the 1990s. In this call, it’s relevant because the host is discussing a clutch hydraulics failure that prevents the driver from shifting.
pressure plate
"The clutch, the throw out bearing, and the pressure plate, because I couldn't shift. Okay. So I drove it for a couple of weeks, and all of a sudden I couldn't shift again."
The pressure plate is the main clutch clamp. When you press the clutch pedal, it helps loosen the clutch so you can change gears.
The pressure plate is the clutch component that clamps the clutch disc to the flywheel. When the clutch is released, the pressure plate’s clamping force is reduced so the transmission can shift smoothly.
throw out bearing
"That we just replaced all the clutch mechanism, too. The clutch, the throw out bearing, and the pressure plate, because I couldn't shift."
The throw out bearing is a clutch part that helps the clutch engage and disengage when you press the pedal. If it fails, the car can be hard or impossible to shift.
The throw out bearing (also called the release bearing) is part of the clutch system on many manual-transmission cars. When you press the clutch pedal, it helps engage/disengage the clutch by moving the pressure plate mechanism.
hydraulic clutch fluid cylinder
"about it. It's the hydraulic clutch fluid cylinder, the reservoir, okay? Yes. And it was dry."
This is the clutch’s hydraulic part that uses fluid pressure to move the clutch. If it’s low on fluid because of a leak, the clutch won’t work right and you may not be able to shift.
A hydraulic clutch fluid cylinder is part of the clutch’s hydraulic actuation system, which uses fluid pressure to move the clutch mechanism. If it runs low (or is dry) due to a leak, the clutch may not fully disengage, making shifting difficult or impossible.
reservoir
"It's the hydraulic clutch fluid cylinder, the reservoir, okay? Yes. And it was dry. So I put the brake fluid in, that's what you used, that three, and pumped it up, and now it's driving okay, but it still is leaking out."
The reservoir is where the clutch fluid is stored. If it runs out, the clutch hydraulics can’t work properly.
In a hydraulic clutch system, the reservoir is the fluid container that supplies the clutch hydraulics. If the reservoir is dry, the system can’t build pressure, which can lead to shifting problems.
brake fluid
"So I put the brake fluid in, that's what you used, that three, and pumped it up, and now it's driving okay, but it still is leaking out."
Brake fluid is the hydraulic fluid that helps pressure move through the system. Some cars use the same type of fluid for the clutch, so using the right one is important.
Brake fluid is a hydraulic fluid used in many cars’ brake systems, and in some vehicles it’s also specified for the clutch hydraulic system. Using the correct fluid type matters because the clutch hydraulics rely on proper fluid properties to generate pressure and avoid damage.
pumped it up
"So I put the brake fluid in, that's what you used, that three, and pumped it up, and now it's driving okay, but it still is leaking out."
When someone “pumps it up” after adding fluid, they’re trying to get the clutch system working again by restoring pressure. If it still leaks or feels wrong, the system may need bleeding.
“Pumping it up” in a hydraulic clutch context usually refers to building hydraulic pressure after adding fluid, often to restore clutch operation. It may also be a sign the system needs proper bleeding if air entered the hydraulic lines.
slave cylinder
"No, there's a slave cylinder and a master cylinder. [312.3s] We don't like that terminology, but that's what it is."
A slave cylinder is a small hydraulic part that helps move the clutch. If it leaks, the clutch hydraulics can run low, and the clutch may start acting weird or stop working right.
In a hydraulic clutch system, the slave cylinder is the part that receives hydraulic pressure and converts it into mechanical movement to actuate the clutch. When a slave cylinder leaks, the system can lose fluid pressure and the clutch may start behaving inconsistently or fail to fully disengage.
master cylinder
"No, there's a slave cylinder and a master cylinder. [312.3s] We don't like that terminology, but that's what it is."
A master cylinder is the main hydraulic part that creates pressure when you press the clutch pedal. If it leaks, the clutch may not work properly because there isn’t enough pressure in the system.
In a hydraulic clutch system, the master cylinder is the part connected to the pedal that pressurizes brake-fluid-like hydraulic fluid. If the master cylinder leaks, the system can’t build or hold pressure, which can lead to poor clutch operation and eventual loss of clutch function.
leaking
"So one of those is leaking. [322.5s] I think the bottom one is leaking."
When a clutch hydraulic part is leaking, it means fluid is getting out of the system. As fluid level drops, the clutch can start working poorly and eventually may stop working.
A hydraulic leak in the clutch system means fluid is escaping faster than the system can maintain pressure. That can cause progressive loss of clutch performance—starting with inconsistent operation and potentially ending in a situation where the clutch won’t work at all.
Ford Explorer
"So what's up? Well, I'm calling because I have a 1994 Explorer, Ford Explorer that is doing some pretty crazy"
A 1994 Ford Explorer is an older Ford SUV. The caller brings it up because something is going wrong with the brakes.
The 1994 Ford Explorer is an early-generation midsize SUV from Ford, known for being a common family hauler and a frequent subject of DIY maintenance. In this segment, the caller mentions it because the brakes (the episode’s theme) are behaving unusually.
transmission fluid
"I've been putting transmission fluid in it because it seemed like it was slipping a little bit."
Transmission fluid is the special fluid that helps your car’s gearbox work smoothly. It belongs in the transmission, not in the engine oil area.
Transmission fluid is the lubricant and hydraulic fluid used by an automatic transmission (and some manual/transfer cases). It’s meant to live in the transmission system, not the engine’s crankcase, because the two fluids are not interchangeable.
oil was getting higher and higher
"But the strange thing is that I noticed that my oil was getting higher and higher and higher. And I know it sounds totally crazy, but when I changed my oil, it completely overflowed."
If your engine oil level suddenly keeps going up, it can mean something got mixed into the oil. In this case, it sounds like transmission fluid may have ended up in the engine oil.
When engine oil level rises unexpectedly, it can indicate contamination—often from adding the wrong fluid into the crankcase. In this segment, the host connects the rising oil level to the earlier transmission-fluid mix-up.
crankcase
"No, I put the tranny where the tranny fluid goes, you know, in the oil in the crankcase."
The crankcase is where the engine oil sits inside the engine. Putting transmission fluid in there by mistake can mess up the oil the engine needs.
The crankcase is the lower part of the engine that houses the crankshaft and contains the engine oil. Adding transmission fluid to the crankcase can dilute or contaminate the engine oil, which can cause serious running and lubrication problems.
dipstick
"You pulled out the dipstick for the tranny. Yep."
A dipstick is the tool you pull out to check how much fluid is in a car. Using the wrong one (or filling the wrong place) can cause the fluids to mix.
A dipstick is the removable stick used to check fluid levels in the engine or transmission. Pulling the wrong dipstick or filling the wrong reservoir can lead to overfilling and cross-contamination between engine oil and transmission fluid.
transmission cooler line
"[619.6s] You got two problems, man. [621.4s] The transmission cooler line is leaking into the... [626.6s] Oh, God, you..."
It’s a line that moves the transmission fluid to a cooler so the fluid doesn’t get too hot. If that line cracks or leaks, the fluid can spill into the engine’s cooling system.
A transmission cooler line is a hose/pipe that carries transmission fluid to and from a heat exchanger (often mounted in front of the radiator) to keep the transmission from overheating. If it leaks, transmission fluid can end up in the wrong place, like the cooling system.
radiator
"[629.0s] No, no, don't even go there. [630.3s] Don't even go there. [632.0s] It's leaking into the radiator. [634.3s] Yeah."
The radiator is part of the car’s cooling system that helps get heat out of the engine. If something leaks into it, it can mess up how well the engine stays cool.
The radiator is the primary engine cooling heat exchanger that uses airflow to remove heat from the engine’s coolant. If transmission cooler fluid leaks into the radiator area, it can contaminate the cooling system and cause overheating or other cooling problems.
cracked block
"[634.3s] Yeah. [634.7s] And he's got a cracked block."
A cracked block means the main engine housing has a crack. That can lead to dangerous leaks of coolant or oil, and it usually isn’t a quick fix.
A cracked block means the engine’s cast-metal block has a fracture. This can allow coolant and/or oil to leak internally or externally, and it’s often a serious failure that may require major engine repair or replacement.
rust
"It's coming in my radio and some mechanic said, no, no, that's rust. Well it could be rust."
Rust is corrosion—metal breaking down over time. If you see rust-colored coolant or fluid, it can mean the system is corroding inside and needs attention.
Rust is corrosion, often caused by water and oxygen reacting with metal surfaces. In a cooling system, rust-like discoloration can suggest internal corrosion or contamination, which can lead to blockages and overheating if ignored.
ethylene glycol
"But it could be that the orange ethylene glycol and the red transmission fluid have turned, the leaves have turned to brown."
Ethylene glycol is the antifreeze inside the engine’s cooling system. It keeps the coolant from freezing or boiling over, and if it looks weird, it can mean the coolant isn’t in good shape.
Ethylene glycol is the main antifreeze ingredient in many engine cooling systems. It helps prevent freezing in winter and raises the boiling point, but it can change color or look contaminated if it mixes with other fluids or degrades.
rotor caps
"And I'm wondering if it's the rotor because I'm going through rotor caps real quick. [1177.2s] You are? [1177.6s] What happens to them?"
They’re talking about parts in the ignition system that help deliver the spark to the engine. If those contacts turn black, the car may run badly or fail to start, especially when conditions change.
“Rotor caps” refers to the rotor/contact components inside a distributor-style ignition system. If the contacts get carbonized/blackened, the spark can become weak or intermittent, which can cause rough running and no-start conditions.
contacts get all black
"What happens to them? [1178.9s] The contacts get all black? [1180.9s] Yes."
Black buildup on ignition contacts usually means the spark is arcing in a dirty or inefficient way. That can make the ignition less reliable, so the engine may stall and then refuse to restart.
When ignition contacts “get all black,” it usually indicates carbon buildup from arcing and incomplete combustion of the spark event. That buildup increases electrical resistance and can make the ignition unreliable, leading to symptoms like stalling and failure to restart.
Weber Cabaret
"I thought it was the Weber's. [1208.6s] I thought it was the Cabaret's. [1209.9s] And for once you agreed with me, you suggested the temperature compensator in the Weber [1213.8s] Cabaret is, and we hammed it hard and we told him the problem is in the Weber Cabaret."
Weber is a company that makes carburetors. In this story, they think the problem is inside the Weber carburetor setup—specifically a part that’s supposed to help the engine run well at different temperatures.
Weber is a well-known carburetor brand, and “Weber Cabaret” here refers to a specific Weber carburetor/kit configuration. The hosts argue that the temperature compensator inside that Weber setup is the likely cause of the intermittent no-start and rough running.
temperature compensator
"And for once you agreed with me, you suggested the temperature compensator in the Weber [1213.8s] Cabaret is, and we hammed it hard and we told him the problem is in the Weber Cabaret."
A temperature compensator is a part that helps the car adjust how much fuel it uses depending on temperature. If it’s not working right, the engine can start fine at one temperature but struggle at others.
A “temperature compensator” is a device used on some carburetion/mixture-control setups to adjust fueling or starting behavior based on engine or ambient temperature. The idea is to help the engine start and run correctly across temperature ranges, so a faulty compensator can cause hard-start or rough-running symptoms.
BMW 2002 Ti
"the irony of the whole situation is that her lawyer drives a 73 BMW 2002 Ti."
The BMW 2002 Ti is an older BMW from the 1970s that car fans love. It’s a small, fun-to-drive coupe, and the “Ti” version was the more performance-oriented trim.
The BMW 2002 Ti is a classic 1970s BMW “02 Series” coupe known for its lively, lightweight feel and enthusiast reputation. The “Ti” denotes the higher-performance trim, and it’s especially remembered for its carbureted setup and driver-focused character.
carburettors
"Now that you have the carburettors fixed, you may be able to win."
Carburettors are parts that mix fuel with air so the engine can burn it. If the carburettors are fixed, the engine should run better and respond more normally when you press the gas.
Carburettors are fuel-mixing devices that combine air and fuel before it enters the engine. When people say “carburettors fixed,” they usually mean tuning/repairing the carburetor components so the engine gets the right fuel mixture for smooth running and good throttle response.
wearing-in period
"And the brakes do require a wearing-in period because these new fangled metallic brakes do require that they seat into the disc rotors, especially if the rotors have been machined."
After you install new brake parts, they don’t always work perfectly right away. They need a little time to rub in and match the rotor, so braking gets better as you use them.
A wearing-in period is the short time after installing new brakes when the brake surfaces need to “settle” against each other. During this time, braking feel and effectiveness can be inconsistent until the friction material and rotor surfaces mate properly.
seat into the disc rotors
"And the brakes do require a wearing-in period because these new fangled metallic brakes do require that they seat into the disc rotors, especially if the rotors have been machined. They have to kind of find a home."
Seating means the new brake material is rubbing in to match the metal rotor surface. When that happens, braking becomes more predictable and effective.
“Seating” is the process where new brake pads (or similar friction material) conform to the rotor’s surface. Proper seating improves friction consistency and reduces early braking issues, especially after the rotors have been machined smooth.
machined
"And the brakes do require a wearing-in period because these new fangled metallic brakes do require that they seat into the disc rotors, especially if the rotors have been machined."
Machining means the rotor’s surface was cut or ground smooth again. New pads have to rub in against that fresh surface before braking feels normal.
When rotors are “machined,” their surface is cut or ground to restore flatness and remove wear or damage. That fresh surface can change how the new brake pads contact it, which is why seating can take extra effort after machining.
braking effectiveness
"And the braking effectiveness is improved as the brakes wear in. But this happens very fast."
Braking effectiveness is basically how well the brakes stop the car. With brand-new pads, it can start off weaker or inconsistent until everything rubs in properly.
Braking effectiveness is how strongly and consistently the brakes slow the vehicle, which depends on friction between pads and rotors. After new brake parts are installed, effectiveness often improves as the surfaces wear in and the pad material transfers and stabilizes.
breaking period
"And usually this breaking period is accomplished. Well, we take a car out by the time we've test driven it for 10 or 15 minutes. The brakes have sufficiently broken in."
They’re talking about the early “break-in” time right after new brakes go on. The point is that brakes should bed in quickly, not after a huge mileage number.
A “breaking period” here refers to the same idea as brake bedding-in: the early phase after new brakes are installed where performance improves quickly. The hosts argue that it shouldn’t require hundreds of miles for normal bedding to occur.
Request an Explanation
Heard something you'd like explained? We'll add it to this episode.
Sign in to request explanations for terms you heard.
Want to learn more?
Browse our glossary for plain-English explanations of automotive terms, jargon, and concepts.
Help improve this episode
See something that's not quite right? Our annotations are AI-generated and can sometimes miss the mark. Click the flag icon on any annotation to suggest a correction.