The 1947 - Present Chevrolet & GMC Truck Message Board Network - View Single Post - Just bought a 1979 1/2 ton 4X4 short bed...

Bowed · 07-15-2014, 01:57 AM

350's are internally balanced and 400's are externally balanced . For the 400 you can look for weights on the engine side of the flex-plate and a balanced / harmonic balancer , which is usually done in the form of a cut or notch on the backside of the balancer . 400 casting #'s are 330817, 3951509 and 3951511 . If it has 3 freeze plugs each side it is 4 bolt and 2 freeze plugs each side are 2 bolt on the 400 .

07-15-2014, 01:57 AM	#3
Bowed Registered User Join Date: Oct 2002 Location: where it's hot Posts: 1,059	Re: Just bought a 1979 1/2 ton 4X4 short bed... 350's are internally balanced and 400's are externally balanced . For the 400 you can look for weights on the engine side of the flex-plate and a balanced / harmonic balancer , which is usually done in the form of a cut or notch on the backside of the balancer . 400 casting #'s are 330817, 3951509 and 3951511 . If it has 3 freeze plugs each side it is 4 bolt and 2 freeze plugs each side are 2 bolt on the 400 . Last edited by Bowed; 07-15-2014 at 02:03 AM.