Finished install of a fresh '71 Buick 8.5 10 bolt under our '70 GS455 and as expected driveshaft is too long. When taking measurement with the car back on the ground and slip yoke bottomed out in transmission it's still 1/2" inch from a tight fit. My thought is have it shortened an inch and a half to allow it to bolt in and allow for suspension travel. I know a lot of you have done this swap so any shared experience is appreciated. 1970 GS455 with short TH400 and above mentioned rearend. Thanks to all-Scott
I would shorten or get a 71-72 shaft. I knew someone with opposite issue 68 3.23 posi in a 72. Scary with that shaft so far out but it never broke (low 13s 72 455)
I recall reading on George N's site a while ago going from 8.2 to 8.5 would require shortening 1" so I think that's the plan. Thanks BQUICK and Larry for your input!
Just looked at the TSB covering the different lengths from 1970 to 1971 models... Difference is 0.856" shorter for the 1971 models. Just under 7/8 inch... (closer to 55/64) 71 GS455 with TH400 should be 54.241" center to center on the U-joint; 71 GS455 with 4 speed should be 54.429" center to center. SOURCE: Technical Service Bulletin 71-I-5A (re-issued to correct Bulletin 71-I-5) : All 1971 43-44000 series propeller shafts are .86" shorter (approximately 7/8") than the 1970 propeller shafts. (etc, etc) (Chart on following page has exact dimensions)
