Measuring chassis deflection

[High Plains Mopars]

How have you guys done this in your shops/garage? There is always the trusty old floor jack and a tape measure, but what else have you used? Where and what points of reference are most important to look at and why? Checking torsional stiffness would be one, but what else can be readily checked by the average enthusiast without any specialized chassis equipment?

[David Pozzi]

Have you read this? https://www.pro-touring.com/forum/showthread.php?t=23278
http://www.xvmotorsports.com/engineering/sus_proc_rigidity.cfm

[High Plains Mopars]

Yes, I've read through that topic and even spent time on SN65's web site.

What I'm after is what have some of the average members on here done to check and measure changes without access to a four post rig or a surface plate. Since I have a complete and road worthy car that I want to base line before I change it, I really don't want to strip it to a shell to clamp it on a jig.

[David Pozzi]

I've done it by putting a piece of 2X3 square tube across the front antiroll bar mounts, chain it up to the frame on the near (long) end, you can put a block of wood or rag on the opposite end that pushes up.

Try to get about 8 feet from chassis center line. Support the rear frame on jack stands, i do it just in front of the front leaf eyes, support the front frame crossmember by a single floor jack under the exact centerline of the car. A small piece of steel or 2x4 running front to rear can help it act like a pivot point.

I used a digital angle finder with .00 decimal place resolution. A dial indicator and some calculations can also be used to arrive at degrees of deflection, but you support the opposite frame rail for that method and measure under the near frame rail with the dial indicator.

When standing on the tube, expect .2 or .3 degrees deflection. That's why you need a high resolution angle finder.

If you don't need to know foot pounds per degree, then just measure deflection with a dial indicator. You can measure at various places front to rear to find the area with most flex. but usually it's between the firewall and front A arm mounts.
David