wierd shake


Junior Member
Corpus Christi
Hello all,
My '77 K-15 GMC(HP350ci, TH350, NP203{no conversion}, 10 bolt ft, 12 rear)
has a bad shake above 50mph when the throttle is feathered. When any gas is applied it smooths out, and when you take your foot off the pedal it smooths out. It does the same in 2nd at higher rpm, and occationally in nuteral going downhill, but always above 50mph worsening with speed, and only when pedal is feathered so no troque is applied to the drivetrain(engine matching speed) Tranny regulator and u-joints have been suggested but drive shafts are not loose at all, tranny performs flawlessly in downshifting and reverse but I dont know how to check for regulator. The TH350 has a B&M shift improver set to RV/towing. Could it be axel bearings or screwey tires?(they are pretty worn).
please advise.:confused:
thanks, sawbones.


Senior Member
Lafayette, LA
More than likely I'd say its your tires. Could be that one or the other isn't balanced, water in teh tire if they went flat and sat for awhile before reinflation. ALso many brands especially of mud grip tires are known for their shakeyness and vibration at higher speeds. Interco Super swampers and boggers especially. Interco made a special swamper for highway prone vehicles. Even on All terrains at a certain speed the lugnuts expand, but thats usually a shakiness limited to a small range of mph. Since its a 4wd you might also check to be sure that your leaf springs are snug...thats my 2cents

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