Brakes
Brakes are the one system where a finding is never optional information; it is a safety call.
By Anthony LimpertASE Master Automobile Technician- Discard spec is a hard safety limit. Under discard = the rotor can crack under thermal stress or lose stopping power. Must be replaced. Report as immediate cost with a specific dollar estimate.
- Solid pedal = good. Spongy pedal = compressibility somewhere in the system: air, deteriorated flex line ballooning under pressure, or master cylinder bypass. All need diagnosis.
- Brake fluid at a caliper boot = piston seal failure. Fluid contamination on pads reduces friction (safety issue), and the caliper must be replaced or rebuilt before driving further.
- Get numbers. Note thickness of inner AND outer pads (uneven wear = caliper slide problem). Compute % remaining. Include specific numbers in your report, not opinions.
The good news for an inspector is that brakes are measurable. Thicknesses, specs, and pedal feel convert directly into pass-or-replace decisions and dollar figures the buyer can take to the negotiation.
Measure, Don't Eyeball
Rotor thickness is a hard number against a hard limit. Every rotor has a discard specification cast or stamped into it, and a rotor measured below discard, even by 0.020 inch, must be replaced. It cannot legally or safely be turned, because machining removes more material from a rotor that is already too thin. The reason discard is absolute: an under-spec rotor can crack under thermal stress and loses stopping power when it matters most. Report it as an immediate expense with a real number attached, typically 200 to 500 dollars for rotors and installation.
Pads get the same treatment. The fast, defensible way to estimate pad life is to measure remaining friction material with a gauge and compare against new pad thickness from the service manual, typically 10 to 12 millimeters new with about 3 millimeters as the minimum. Compute the percentage remaining and put the numbers in the report, not adjectives. Measure both the inner and outer pad at each corner: if they are wearing unevenly, the caliper slides are sticking, and that is its own repair line. "Front pads at 40 percent" survives a seller's challenge; "brakes look okay" does not.
Pedal Feel and Hydraulic Leaks
A healthy brake pedal is firm and consistent. A spongy pedal means something in the hydraulic system is compressible, and there are three usual suspects: air in the lines, a deteriorated rubber flex hose that balloons under pressure, or a master cylinder bypassing internally. You often cannot tell which from the driver's seat, and it does not matter for the PPI verdict: a spongy pedal requires diagnosis before purchase, and the report should say so rather than guessing at severity.
At each caliper, look at the piston boot. Dark fluid wetness there is brake fluid escaping past a failed piston seal. That is a double problem: the caliper needs rebuild or replacement, and any fluid that reached the pads has contaminated the friction material and cut braking force on that wheel. A leaking caliper is a do-not-drive-far finding, and the buyer should hear it in exactly those terms.
| Item | Threshold | Report entry |
|---|---|---|
| New pad friction material | 10-12 mm typical | The baseline for computing percent remaining |
| Pad minimum | About 3 mm | At or below = replace now, quoted in millimeters against spec |
| Uneven inner vs outer pad wear | Same corner, different thickness | Caliper slides sticking — its own repair line, not just pads |
| Rotor below stamped discard | Even 0.020 in. under | Replace — cannot legally or safely be turned; thermal cracking risk |
| Rotors plus installation | Typically $200-500 | Immediate expense with a real number attached |
| Spongy pedal | Air, ballooning flex hose, or bypassing master | "Requires diagnosis before purchase" — never a guess at severity |
| Wet caliper piston boot | Fluid past a failed seal | Caliper rebuild/replace plus contaminated pads — a do-not-drive-far finding, in those words |
New-pad thickness and discard specs come from the service manual and the rotor stamping — quote the actual spec you measured against, not the typical value.
- Gauge both the inner and outer pad at every corner. Measuring only the outer misses the sticking slides that show up as uneven wear between the two.
- Compute percent remaining against new-pad thickness from the service manual and write the numbers. "Front pads at 40 percent" survives a seller's challenge; "brakes look okay" does not.
- Micrometer each rotor and compare against its stamped discard spec. At or below discard — by any amount — means replacement with a dollar figure, because machining an under-spec rotor removes metal it no longer has.
- Inspect every caliper piston boot and flex hose. Dark wetness at a boot is a failed seal plus contaminated friction material — a do-not-drive-far finding the buyer hears in exactly those terms.
- Check the pedal: firm and consistent passes; spongy means something compressible is in the hydraulics — air, a ballooning hose, or a bypassing master — and the verdict is "diagnose before purchase," not a guess.
- Write each finding as measurement versus spec plus a cost band. Numbers turn a negotiation argument into a settled fact.
- Writing adjectives instead of measurements. "Brakes are bad" invites an argument; "rear right rotor at 22.4mm against a 24mm discard spec, replacement required" ends one. Every brake finding is a number against a spec or it is a liability.
- Passing a rotor that is "only a little" under discard for machining. Discard is absolute — turning removes more material from a rotor already too thin, and an under-spec rotor can crack under thermal stress exactly when the braking matters most.
- Measuring only the outer pads because they are easy to see. Uneven inner/outer wear is the signature of sticking caliper slides, which is its own repair line — miss it and the new pads wear out the same way.
- Softening a leaking caliper finding. Fluid past the piston seal has contaminated the pads and cut braking force on that wheel — it is a do-not-drive-far call, and diluting that language to keep the appointment pleasant transfers the risk to the buyer.
A rotor measures 0.020 inch below its stamped discard spec. The seller says machining will clean it up. Why is the answer no?
Discard is the absolute end of the rotor's life, not a target. Machining removes even more material from a rotor that is already too thin, and an under-spec rotor can crack under thermal stress and loses stopping power when it matters most. It gets replaced, reported as an immediate expense — typically $200-500 installed.
The inner pad on the left front measures 3mm while the outer measures 8mm. What is going on, and what goes in the report?
Uneven inner/outer wear on the same corner means the caliper slides are sticking, so one pad is doing most of the work. The report carries two lines: pads at replacement threshold quoted in millimeters, and caliper slide service or replacement as its own item — because new pads on a sticking caliper wear out the same way.
The pedal is spongy but the fluid is full and nothing looks wet. What are the three usual suspects, and what is the PPI verdict?
Air in the lines, a deteriorated flex hose ballooning under pressure, or a master cylinder bypassing internally. You often cannot separate them from the driver's seat, and for the PPI you do not need to: the verdict is that a spongy pedal requires diagnosis before purchase, stated plainly rather than guessed at.
A rotor measures 0.020 inch below its stamped discard spec. The seller says machining will clean it up. Why is the answer no?
Missed one? The reasoning above comes straight from the PPI exam bank, so this is the standard you will be held to.