Two very different units, two very different failure modes at the valve body level. The 42RLE is a conventional hydraulic valve body you can work on at the bench. The 8HP75 mechatronic unit is a different animal entirely. 42RLE Valve Body: The primary failure point is the underdrive solenoid and its bore. The underdrive solenoid controls the underdrive clutch pack — the most heavily loaded element in the 42RLE. When the bore wears or the solenoid O-rings degrade, underdrive apply pressure drops and you get 1st and 2nd gear slip. The fix is a new solenoid with fresh O-rings and a bore inspection. Measure the bore with a small-hole gauge: spec clearance is 0.0005–0.0015 inches between spool and bore. Over 0.002 inches, the bore is worn and a sleeve kit is needed.
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42RLE Solenoid Set with O-Ring Kit
Replace all solenoid O-rings when the valve body is on the bench — the cost is negligible and it eliminates the most common source of 42RLE soft-shift comebacks.
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