Wasn't quite sure which forum this belonged in, but I figured this one seemed closest. Frame sag, more specifically the engine crossmember itself sagging, is a common problem in our Buick A-bodys, and the other cars in the A-body family. With age and stress on the front crossmember, it will eventually sag in the center, causing the two front frame horns to lean closer to eachother. In some cases it can go unnoticed, but in others people have had problems with headers clearing, steering & suspension issues, etc. Some of the factory welds in this area can also end up cracking under stress, and your frames integrity can suffer. Vintageracer from the pro-touring.com forum has a pretty good description of the most common problem area in the frame- "Go put any 64-72 GM A body car on a lift and look at the vertical weld on the front frame crossmemeber on the passenger above the right/passenger lower control arm. If the car has ever had any type of engine with any power and/or the car has been subject to hard driving, this weld will be probably be cracked/broken. You can only see this with the car on a lift/jack with the suspension/frame unloaded. This will allow the frame to sag and crack will open and be visiable. When the car is sitting on the ground the frame is in compression and you will not see the weld crack. This broken weld and crack are caused by the frame twisting under hard power/acceleration." The easiest way to find out if your frame is sagging, is to do a few easy measurements. Below is a diagram I removed from a 1970 edition frame manual, I forget what company put it out. It shows all the frame reference points on our Buick A-bodys, and what the measurements should be. When measuring make sure the car is on a perfectly level surface Hope this helps some of you guys. I didnt find a whole lot of info on this here, so figured someone should at least post some correct measurements.
