check frame for straightness

S

stillwater

Senior Member
What is a good way to check a bare "A" frame for straightness?

I'm pretty sure my dad is right that the frame on my pickup is bent, and I do have an extra one tucked away. My shop floor is not level (holds water puddles if it has a chance).
 
It could be fairly straight with a twist in it. But what I'd do is start with a tape measure and cross measure it for squareness. A few diagonal measurements should tell you the story. So with one end of the tape to the right rear and the other to the left front. Record this measurement and do the other side and compare the two. You could even break it down to different quadrants on the frame. The easiest is measuring to like holes from side to side. Hopefully this makes sense to you.
 
Take your truck to a good frame shop and they can test it and straighten it as a whole vehicle like wagga A'er states.

As for the spare frame, take a string along each rail and the string should touch the whole way.
Next measure from corner to corner to be sure the measurement the measurements match like Fordcrager said.
 
The normal sag area is by the rear motor mounts. My friends frame had enough sag to cause the brake cross shaft to hit the torque tube when the brake pedal was pushed. The body was still off the frame, so it was an easy fix on the frame rack.
 
Diagonal in each direction checks for out of square.
String line along each side rail checks for sag.
Body off to do it right.
 
90 percent have frame sag at the rear motor mount. Most of the time the driver side is the worst. If it is not fixed doors hood and ever thing else will not fit.
 
Any easy first-check for frame sag at rear motor mounts is to stand back from the vehicle about five feet, and look at the vertical meeting of the rear edge of the hood and the raised bead on the cowl: if it meets nicely at the beltline, but the gap increases as you go down towards the splash-aprons, that's a pretty good indication of frame sag.

If the hood>cowl joint looks good and even all the way up & down, check the front front body mount from under the vehicle, for extra blocks / shims between the body-mount and body sill... there should be: Frame rail + frame welt + splash apron + body sill, with one body block at mount location. If there is more than a 1/4" gap between the top of the frame rail and the body sill, that suggests the front of the body has been shimmed-up, to compensate for frame-sag.
 
I pull strings in an x pattern, and one from front to rear crossmembers from the holes for the spring bolts. I hold them proud of the frame rails with 4 equal size drill bits and use a fifth bit as a go-to go. I also use string and a marker to check measurements. I work alone and find it easier than trying to measure.
 
If it is bent, I'll check my spare. If need be, I'll take the frame to my friend's body shop and have him tie down the frame to the floor (pulling pots) and heat the frame while using a jack underneath it.
 
Don't heat the frame to straighten, do it cold and hammer and dolly it with tension on it. Then check it again and repeat as necessary.
 
stillwater said:
If it is bent, I'll check my spare. If need be, I'll take the frame to my friend's body shop and have him tie down the frame to the floor (pulling pots) and heat the frame while using a jack underneath it.
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fordcragar said:
Don't heat the frame to straighten, do it cold and hammer and dolly it with tension on it. Then check it again and repeat as necessary.
Click to expand...

If it is not straight the metal has stretched. The only way to truly take out stretch in to shrink and yes heat will shrink it. I don't mean red hot heating but enough to cause steam when a wet cloth is applied. How many actually use heat on the frame, most likely very few.
 
Mike V. Florida said:
If it is not straight the metal has stretched...........
Click to expand...
Not necessarily, there might be a buckle; which would mean that you have compression on that portion. You'll need to stretch that section to relieve the strain and help it back to straight. If you don't do it right, you can create a lot of problems.

It's possible that if for example, the horns are one way or the other, that the flanges could be stretched, but the web wouldn't be. So when you moved the horns back, you could see the bulging of the flanges (excess metal or stretch), top and bottom; which could then be shrunk with heat.

Not seeing the frame, it's hard to say what to do. But whatever you decide to do to it, have someone that knows what they are doing make the corrections or you could end up with a useless frame.
 
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