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Apr 26th, 2026 | | AD Chevy Trucks  Over 6,000 pictures Brad Allen has an awesome collection of Chevrolet factory pictures that he has set up from film strips. Check them out!
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| | | | Joined: Jan 2013 Posts: 1,518 'Bolter | | 'Bolter Joined: Jan 2013 Posts: 1,518 | When does it vibrate? which gears, idling in neutral, idling in gear with clutch in?
Check the first/reverse gear for rock on the main shaft (requires the mainshaft removal and disassembly), it should be no more than .015".
Also, check the shifting yokes for wear, the clearance between the shifting yoke/fork and sliders should be no more of a gap of .020, prefer .010.
I recently rebuilt a sm420 for a guy and it had a hell of a vibration in the shifter and on inspection I found both situations, the first gear was worn allowing a rock on the main spline of .040 and clearance on the 1st and 2nd shifter yoke on the first/reverse gear to be .035.
Last edited by sstock; 01/17/2019 3:12 PM.
1953 Chevrolet 3100261 cu inch, sm420, 3.55 rear, torque tube still,omaha orange, still 6 volt, RPO green glass, side carrier spare, all done In the DITY GalleryVideo of the 261 running1964 GMC 1000305 Big Block V6, sm420, the next cab off restoration
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