Trying to resolve a 45-50 mph vibration in my '60 with an sm420.. Removed the driveshaft to rule it out, and the vibration occurs in exactly the same way: in 4th gear at 45-50 mph. Don't suspect motor or clutch since thi only occurs in 4th. Transmission is not original to the motor (283). Replaced a very tired 3spd.
Any suggestions would be appreciated. Headed towards either a full rebuild kit, or finding another trans, but hoping I can find out what is wrong and save some money.
49 GMC 1/2ton (Work in progress) 66 Chevy II (Better than New)
Ok, I have read this three times and cant figure out what you are saying here. You removed the driveshaft? How did you get it up to 45-50 mph then/
1953 Chevrolet 3100 261 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 Gallery Video of the 261 running
1964 GMC 1000 305 Big Block V6, sm420, the next cab off restoration
By and large the biggest rotational mass in this transmission is the giant first gear. It travels continually at the speed of the main shaft regardless of the speed of the truck or what gear it is in. That said, a vibration could be caused by excessive clearance between the first gear and the main shaft. There is a check on this that requires the disassembly of the main shaft. It is measuring the rock of the first gear to be no more than .015. Good time to inspect the friction ring and neoprene strip inside the diameter of the first gear for wear. Also, I have seen the second gear syncronizer ring retainer broken on a few transmissions that would cause the second gear synchronizer ring to flop around on the inside of the first gear, that could cause a nice noise and vibration too. Steve
Last edited by sstock; 02/17/20203:38 PM.
1953 Chevrolet 3100 261 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 Gallery Video of the 261 running
1964 GMC 1000 305 Big Block V6, sm420, the next cab off restoration
Offering parts for sale outside the Swap Meet Forum is not an approved activity. Please take it to PM or post in the Parts for Sale Forum. Thanks
Martin '62 Chevy C-10 Stepside Shortbed (Restomod in progress) '47 Chevy 3100 5 Window (long term project) ‘65 Chevy Biscayne (Emily) ‘39 Dodge Business Coupe (Clarence) “I fought the law and the law won" now I are a retired one! Support those brave men/women who stand the "Thin Blue Line"! Hug a cop! USAF 1965-1969 Weather Observation Tech (I got paid to look at the clouds)
