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Rear Main Seal Leak on a Diesel Truck: Confirm It First

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A rear main seal leak on a heavy diesel truck is confirmed when dyed engine oil, seen under a UV lamp through the lower flywheel housing opening, traces back to the crankshaft flange and nowhere higher, and the crankcase is not over-pressurized. Confirm all three points before anyone books the transmission split. Last updated: October 12, 2026 Key takeaways Oil at the weep hole proves oil reached the flywheel housing, not that the rear main seal let it in. Dye the engine oil and look through the lower opening with a UV lamp: no glow after a proper run, no engine leak. Check crankcase pressure before the split; a new seal will not survive a pressurized crankcase. With the transmission out, measure flywheel housing runout and inspect the clutch. "Rear main seal" is the US shop term; Detroit calls the part the rear crankshaft oil seal, and most sources outside North America say crankshaft rear oil seal. On a truck, replacing it means removing the transmission. Symp...
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CDL Air Brake Test Steps Explained, Part by Part

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The CDL air brake test is a sequence of seven checks made during the pre-trip inspection: low-air warning, automatic spring brake application, pressure build-up, leakage with brakes released and applied, governor cut-in and cut-out, a parking brake hold and a slow service brake stop. Each check isolates one part, so a failed reading points to a component. Last updated: October 12, 2026 Key takeaways Low-air warning on before 60 psi; spring brakes applied at 20-45 psi (New York CDL manual). Build-up from 85 to 100 psi within 45 seconds in a dual system; Ontario allows 2 minutes at idle. Leak limits: under 2 psi (single) or 3 psi (combination) per minute released; 3 or 4 psi with the pedal held. Each failed step names a suspect part, from the warning switch to the governor. What does the air brake test actually prove? Federal rules put the duty on the driver. Under 49 CFR 392.7 , a commercial vehicle may not be driven until the driver is satisfied that the service brake...
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