if the mid shaft assembly does not hold oil then the cork seals are gone, there is some leather seals that will work and that's a good thing when that mid shaft is to be in oil.( 1 pound of it) all the oil you put in the mid shaft is draining into the rear end, there's another cork seal in the tube itself too. Like Mr.Don Stocker asked did you remove the ring and pinion from the housing? what it does sound like is your backlash is wrong and it will make a lot of noise. when you push in the clutch and the noise stops . if the vibration stops then its got to be in the rear end, if it was still vibrating when you push in the clutch it would be a bent shaft like Mr. Don Stocker said, but if it goes away it sounds to me the lash on the rear, they do need to be set with preload and backlash (.008-012)

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1936 1.5 wrecker,1937 gmc coe,1939 Chevrolet coe,1942 4x4 coe, 1942 coe,1946 dump,1947 2 ton dump,another 1947 2 ton dump,1950 coe,1967 c30,1937 cat 22,1936 Chevrolet 5 window foremans coupe, 1914 ford speedster.