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Rush SR Service Manual

    Triage trees

    Symptom → system decision trees. Each leaf ends with: the static test to run, the manual page(s) to fetch, and applicable bulletins. Ask ONE narrowing question at a time to move down a tree — pick the question that best splits the remaining branches.

    Trees encode the path; specs and procedures come from live fetches of the cited pages.

    Tree 1: Rear noise (worked example of the character × correlation matrix)

    Section titled “Tree 1: Rear noise (worked example of the character × correlation matrix)”

    Q1 — Character: whine/grind, knock/clunk, rattle/buzz, or click/tick? Q2 — Correlation: engine RPM, wheel speed, bumps, load transitions, or turning?

    Knock/clunk, both turn directions, low-speed/paddock-only

    Section titled “Knock/clunk, both turn directions, low-speed/paddock-only”

    → Plate-LSD behavior. Clutch-type LSD; chatter at parking-lot speeds is often normal or oil/wear-related, not a broken part.

    Clunk on load transitions (on/off throttle), straight line

    Section titled “Clunk on load transitions (on/off throttle), straight line”

    → Chain slack, cush/sprocket interface, diff backlash, halfshaft CV lash.

    Click/tick correlated with wheel speed, worse under turning + load

    Section titled “Click/tick correlated with wheel speed, worse under turning + load”

    → Outboard CV joints under articulation, or side-loaded wheel bearing.

    Whine/grind correlated with wheel speed

    Section titled “Whine/grind correlated with wheel speed”

    → Frequency-discriminate: once-per-wheel-rev (hub/bearing/tire), once-per-chain-rev (stiff link, damaged roller), multiple-per-rev (sprocket teeth).

    Whine/grind correlated with engine RPM (any gear, incl. neutral revs)

    Section titled “Whine/grind correlated with engine RPM (any gear, incl. neutral revs)”

    → Engine/gearbox/primary side, not final drive.

    Rattle/buzz over bumps

    Section titled “Rattle/buzz over bumps”

    → Suspension/chassis hardware, bodywork, heat shields, exhaust hardware.

    • Static tests: weekend nut/bolt inspection pass; push down on each corner and listen.
    • Fetch: maintenance/each-weekend/inspecting-nuts-and-bolts.md.
    • Bulletins: 2025-11-03 Control-Arm Retaining Compound, 2025-11-04 Upgraded Spherical Bearing, 2026-01-16 Misalignment Spacer.

    Tree 2: Shift faults

    Section titled “Tree 2: Shift faults”

    Start at the manual’s own symptom index — fetch maintenance/electronics-and-wiring/gcu-debugging.md and use its “Where to Start” routing. Summary of the branches (fetch the page for the procedures):

    Q1: Do BOTH paddles work sometimes? Does the compressor run? What does the AiM show for tank pressure?

    SymptomBranch (on gcu-debugging page)
    Both paddles dead AND compressor won’t runNothing Works (signal fuse → heartbeat LED → power-supply cap → pressure sensor fail-safe → Mega 2560)
    One paddle direction deadOne Paddle Direction (wire swap → ground pin → filter cap bypass → wheel swap)
    Both directions miss intermittently (false neutrals, missed shifts)Missed/Incomplete Shifts: tank pressure first, then countershift setting, then mechanical
    One direction weaker / sounds differentAsymmetric Shifts (valve block, Amphenol connector pins)
    Missed up- OR down- but not both, incomplete engagementShift Linkage Mechanical (arm clearance, rod length/cylinder alignment)
    Can’t find neutral engine-runningClutch disengagement + technique (hold neutral, then pull direction paddle)
    Erratic, no clear patternGCU water intrusion (daily water check!)
    Compressor runs continuously / never / short-cyclesCompressor Issues (leaks → relay → MOSFET; drain-tank test separates sensor vs board vs compressor)
    Limp mode / no blip / no cut (Gen2 DBW)Speed Emulator → Clutch Switch → Gearshift Sensor Mimic, in that order
    No blip (Gen1 cable)Blip cylinder air supply + throttle cable
    • Key bisecting static test: Manual Pneumatic Shift Test (bypasses GCU; splits electrical vs pneumatic/mechanical in one test) — procedure on the gcu-debugging page.
    • Second bisector: serial console at 115200 baud — paddle-press lines vs shift-completed lines tell you which half of the chain is lying.
    • Fetch as needed: maintenance/electronics-and-wiring/shift-harness.md (pin-level), maintenance/electronics-and-wiring/gcu-firmware.md (console access, versions).
    • Bulletins: 2025-09-12 Compressor TSB — check before condemning any compressor.
    • Interval note: shift valve and compressor are four-event service items; overdue service masquerades as faults.

    Tree 3: Electrical / voltage issues

    Section titled “Tree 3: Electrical / voltage issues”

    Q1: Constant or load-dependent? Which loads (fans, fuel pump, compressor)? What does the dash voltage read engine-off vs idle vs 5000 RPM?

    Voltage sags under load (e.g. fans on), recovers when load drops

    Section titled “Voltage sags under load (e.g. fans on), recovers when load drops”

    → Charging system: regulator/rectifier output, battery health, main power distribution connections.

    Dead circuit / single subsystem dark

    Section titled “Dead circuit / single subsystem dark”

    → Fuse → connector → harness segment, in that order.

    Dash alarm showing (oil pressure, water temp, oil health, clutch)

    Section titled “Dash alarm showing (oil pressure, water temp, oil health, clutch)”

    → Treat the alarm as instrumentation first, mechanical second — but never dismiss oil pressure without proof.

    Intermittent everything / erratic behavior

    Section titled “Intermittent everything / erratic behavior”

    → Grounds, water intrusion (GCU and connectors), chafed harness.

    Tree 4: Overheating

    Section titled “Tree 4: Overheating”

    Q1: Overheats everywhere, or only in sessions/traffic? Gradual creep or sudden spike? Losing coolant?

    Sudden spike

    Section titled “Sudden spike”

    → Airlock, failed hose/clamp, water pump. Stop running it; inspect for loss first.

    Gradual creep over a season

    Section titled “Gradual creep over a season”

    → Radiator fouling (open-wheel cars eat rubber and debris), coolant age.

    Only in traffic / low speed

    Section titled “Only in traffic / low speed”

    → Fan operation (also cross-check Tree 3 if fans drag voltage down), airflow.

    After maintenance / new engine

    Section titled “After maintenance / new engine”

    → Airlock from an incomplete bleed; verify before anything else.

    Tree 5: Handling deviation from baseline

    Section titled “Tree 5: Handling deviation from baseline”

    Q1: Deviation since when — after a change (setup, crash, curb strike), or gradual?

    After a setup change

    Section titled “After a setup change”

    → Compare every touched parameter against the factory baseline before diagnosing hardware.

    After contact / curb strike

    Section titled “After contact / curb strike”

    → Alignment check first; then inspect suspension hardware, rod ends, control arms.

    Gradual deviation, no changes made

    Section titled “Gradual deviation, no changes made”

    → Wear items: shock gas pressure, tire heat cycles, plate LSD seating, bushings/sphericals.

    One-corner misbehavior (pulls, uneven wear)

    Section titled “One-corner misbehavior (pulls, uneven wear)”

    → That corner’s alignment, shock, bearing, or a bent component.