MONTE CARLO Ensuring Frame Alignment

[R.Hodges]

Hello, so I have a 79 Monte that I’m doing a full frame off restoration and has also been sitting for close to 25 years. Before I get too far into the build I want to check my frame measurements.

What is the best way to get the centerline marked in order to measure out from the centerline? I was looking online and found the diagram with all the measurements.

Also once I do find my centerline and let’s say the rear rails are out of whack. Are there any suggestions on how to correct the alignment?

I have all new suspension and rebuilt engine ready to go in. But holding off until I’m sure I won’t have any frame issues.

 

[ck80]

To be honest, variations in the ground not being perfectly level, or variations due to production differences in the jack stands you use can throw off measurements.

IMO aside from leveling all surfaces and all those variables, I can only think of one idea.

Go to the middle of the frame rail, where the middle of the door would be. Put a level on the top of it.

Shim that side at the jack points until the middle of the rail shows level.

Repeat on other side. Hopefully both center sections are easy to get level.

Then use diagonal strings with hanging levels like you use in building a deck adjusting for what those measurements say on the chart. So, to use round non-realworld numbers, if a front corner is supposed to sit +10" and a rear +11", use a clamp and filler material 1" thick on the bottom of the rear. Now that rear is supposed to be 10", and the front is supposed to be 10". If the frame was level, and is straight, the cross string will be level.

Only issue is, these things are FLIMSY. It's very easy to have them droop when bare and go closer to spec when everything is mounted which pulls em straight.

 

[R.Hodges]

To be honest, variations in the ground not being perfectly level, or variations due to production differences in the jack stands you use can throw off measurements.

IMO aside from leveling all surfaces and all those variables, I can only think of one idea.

Go to the middle of the frame rail, where the middle of the door would be. Put a level on the top of it.

Shim that side at the jack points until the middle of the rail shows level.

Repeat on other side. Hopefully both center sections are easy to get level.

Then use diagonal strings with hanging levels like you use in building a deck adjusting for what those measurements say on the chart. So, to use round non-realworld numbers, if a front corner is supposed to sit +10" and a rear +11", use a clamp and filler material 1" thick on the bottom of the rear. Now that rear is supposed to be 10", and the front is supposed to be 10". If the frame was level, and is straight, the cross string will be level.

Only issue is, these things are FLIMSY. It's very easy to have them droop when bare and go closer to spec when everything is mounted which pulls em straight.

Thanks for the detailed response. I’ve checked all my measurements from center line to outside and there all within a 1/8” .

I didn’t know if this was normal or not.

And I’m double checking for levelness later today which the frame was pretty close previously.

 

[ck80]

Thanks for the detailed response. I’ve checked all my measurements from center line to outside and there all within a 1/8” .

I didn’t know if this was normal or not.

And I’m double checking for levelness later today which the frame was pretty close previously.

The frame rails were assembled from a bunch of sticks of metal that were welded together by hand without the assistance of robots. Add to that the quality tolerance of the 70s and 80s at gm. I think it's close enough to normal with holes so big the body mounts can take up any slack in the tolerance.

 

[oldsofb]

I never measured mine once the whole time I had the frame off. I looked for signs of impact repairs on the body and frame. Nothing that looked like prior crash damage, slapped it back in and checked the alignment holes. Tight tolerances in the 80's were more of an after thought than a rule.

Hutch

 

[abbey castro]

the picture shows exactly from what edge of the measuring hole for the dimension. As to the CL that doesn't matter as dimensions are shown from hole to hole not to the CL. If the frame is out of dimensions, the measurement will not be right. Like a house builder they check from corner to corner and if he dimensions are the same it's square. (basic geometry) That is at least if you don't have a laser measuring device. The frame is so flexible that it will flex to the body when bolted down, that is why bracing of the frame like jounce bars, rear seat brace an rear LCA bracing, rear horns cross brace is so important so that the frame become more rigid (less flex)