71 BB Frame Flex or do I have a frame problem?

[John L.]

I was working this weekend on adding a few body shims to the rear trying to close up the gaps in the tops of the doors (the car is a coupe). I have the frame supported in the rear with jack stands forward of the trailing arms. I noticed it when jacking up the body and adding 2 shims on the left side and I would let the body back down on the frame the frame would move down 3/16" (measured at the sway bar mount location) when the weight would be on it. Also on the right side I added 4 shims and when I let the body down the frame settled 1/4". I measured this 2 times.
On the left side adding the 2 shims did help close up the gap in the door.
On the right side adding adding 4 shims helped very little.
The frame appears to be in good shape with a little surface rust all over it. Is this amount of movement acceptable?
Appreciate any responce to this.
John Liner

[John L.]

Re: 71 BB Frame Flex or do I have a frame problem?

I also noted that I could jack up the frame 1/4" to 3/8" at the right rear body mount before the frame would lift from the jack stand. In doing so the gap at the top of the door would close up at least 1/8" to 3/16".
All this to say/ask is this amount of flex acceptable or do you think I may have a rust-frame problem?
Thanks,

[Chuck S.]

Re: 71 BB Frame Flex or do I have a frame problem?

John, I'm thinking you have a frame problem...it's definitely needs further investigation.

Corrosion at the ends of the main frame rails is common on C2-C3 frames, and such corrosion can be entirely limited to the interior when road salt and water collects inside and is not allowed to drain out. Use a sharp punch or awl to see if you can punch through the frame at the end of the frame rail. If the metal is sound, you will do no harm (maybe a minor punch mark); if it's rotten, you may easily punch through.

[John L.]

Re: 71 BB Frame Flex or do I have a frame problem?

Thanks Chuck, I'll try that. Makes me sad to think I might have to pull the body and do frame repair on this car. It's such a tight car, numbers matching, just tired and old...kind of like me

[Dick W.]

Re: 71 BB Frame Flex or do I have a frame problem?

John, from my experience that is probably nothing to worry about. A slight amount of movement would be normal