55 f100
When I measure diagonally from a point just behind the cab on the LH frame rail, over to the rear of the RH rail, It measures 1/4" longer than when I measure from that same point on the RH rail to the LH rear.

Is this acceptable?

 

That would mean over the length of the frame, the rails are out of square, or "diamond" about a half an inch. That's enough to create dog tracking, potentially ill handling and misfitting of body panels. How does the front bumper look in relation to the front valance? Is one end closer to the fenders than the other?

 

What are you using for datums? Particularly just behind the cab?

 

If Your cross measurement is off by 1/4'' than that part of frame is only off by 1/8''. It is going to be very hard to get a good cross measurement on the whole frame with the body on.

 

Are you measuring factory bolt hole to factory bolt hole? The end of the frame rails themselves may differ slightly from side to side.

 

from the frt rivet that holds the crossmember behind the cab, to the rear hole where the very rear ceossmember goes.

 

I will be taking the cab off soon so I will measure the whole frame then.
It has a GM frt clip

 

Yes, factory bolt/rivet holes

 

Measure using the front cab mounts once the cab is off. Personally, I kinda doubt there is a problem.

 

Anyone else have this same issue and did you have the frame straightened or did you just run it like it is.

 

Mine was off about that much from my front to back cross measurements but it seems I read somewhere that 1/4" was within factory spec. I did go as far to speak to a shop that straightens frames and they said they wouldn't worry with it being that close.

I'm learning as I go so maybe some the more experienced members can chime in on what is acceptable.

 

If you've got a GM clip welded in the front, I'm guessing you're done. It's so important to measure and fix these things before one starts cutting them in half or even boxing and installing and IFS crossmember.

 

The clip was installed back in the late 70's by a shop that had done quite a few of these. I drove the truck in and they did the clip and I drove it back out. So it was never down to the bare frame until now.

Now that it is apart I noticed the lh rear frame horn is a little twisted, so it must have been hit there at one time.

I drove the truck for quite a few years and never felt any weird handling traits but I don't know if it dog tracked or not.

I guess I will call a couple of frame shops and get their opionions