Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
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HOMESERVICE MANUALSCHEVROLET1987HI-CUBE 6.2 J, 400/M40REPAIR AND DIAGNOSIS (SINGLE PAGE)TRANSMISSIONAUTOMATIC TRANSOVERHAUL - THM 400TESTINGVACUUM MODULATOR CHECKBELLOWS COMPARISON CHECK
1987 Chevrolet Hi-Cube 6.2 J, 400/M40
Bellows Comparison Check
1987 Chevrolet Hi-Cube 6.2 J, 400/M40SECTION Bellows Comparison Check
- Using Comparison Gauge (J-24466), compare load of vacuum modulator with known good modulator of same type. Part number is stamped on modulator dome. Install good modulator on either end of gauge.
- Install modulator in question on opposite end of gauge. Holding modulators in horizontal position, bring them slowly together under pressure. If modulator in question is bad, gauge line will remain Blue. If modulator in question is good, gauge line will be White.
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.