1970 GTO Version 2.0

[TomT]

Andrew, You're right in that it seems the discussion always centers around pinion angle rather than lateral alignment. I'm assuming that you're rear end is mounted 90 degrees to the chassis center line even if it is offset a little (otherwise it would "crab"). If I'm thinking about this right then you would want the center line of your engine/transmission to also be parrallel with the centerline of your chassis in that same plane. I expect that's a little harder to measure than pinion angle at least with the body on. I guess you could use plumb bobs on the center of the balancer and tailshaft and mark it out on the garage floor. It will be interesting to see how you solve this one.
Tom

[andrewb70]

Andrew, You're right in that it seems the discussion always centers around pinion angle rather than lateral alignment. I'm assuming that you're rear end is mounted 90 degrees to the chassis center line even if it is offset a little (otherwise it would "crab"). If I'm thinking about this right then you would want the center line of your engine/transmission to also be parrallel with the centerline of your chassis in that same plane. I expect that's a little harder to measure than pinion angle at least with the body on. I guess you could use plumb bobs on the center of the balancer and tailshaft and mark it out on the garage floor. It will be interesting to see how you solve this one.
Tom

Tom,

You are right in stating that the vast majority of pinion related questions discuss alignment as viewed from the side. The lateral alignment is rarely addressed. There are two issues when dealing with lateral alignment. One is simply the position of the pinion in relation to the transmission output shaft. The transmission output shaft and the pinion should be inline. The other aspect is parallelism. This is the same concept that is addressed by the adjustment of pinion angle from the side. The transmission output shaft and the pinion need to be parallel not only when viewed from the side, but also as viewed from the top (or bottom). The position of the engine and transmission cross member becomes critical. If the engine and trans are angled to one side that can cause the output shaft of the transmission to be out of parallel with the pinion. Also, if the rear end housing is cocked to one side, that can cause similar issues.

Ron S, please chime in. I talked to Ron and he told me how when he builds a chassis or backhalfs a car he has plumb bobs hanging everywhere. He told me how critical it is to make sure that the engine and rear end need to be plumb and square to avoid vibration problems. We drive old cars that have been through God knows what, and we often assume that frame stands, engine adapters, crossmembers, control arms, etc...locate the driveline components in their proper place. I think this is far from the case in many instances and people should pay special care to double check everything to assume a smooth running car.

Andrew