Shortening a 51 GMC LWB Frame to SWB

[JRBECK64]

I have seen the how to shorten the frame of a 67-72 but are the dimentions the same on a 1951 GMC Pickup? If they are not does anyone know where I could get that information?
Thanks,

[samcrf450]

This is off of the 1950 page but I checked the short bed on the 1951 page and the dim. are the same. It looks like the wheel base length has a difference of 9.25 inches and if ou look behind the cab and infront of the back wheel it looks like that is where the 9.25 inches is gained for the long bed.

[samcrf450]

the image is small so here is where you can go to look at it.
http://chevy.oldcarmanualproject.com...resto/5055.htm

[BIG CHEVY 3600]

Guys over at www.stovebolt.com that have done this say cut 9" out between the cab and hump. I may be wrong, go over there and ask. Mine is a long bed and I want to keep it that way.

[mr48chev]

You might have a slight offset in the rails due to the taper but that should be easy to deal with.

I've got a bare GMC frame out here that was headed for a extended cab project and If it isn't raining in the morning I'll try to take a couple of photos and take a few measurements.

[JRBECK64]

First I would like to thank everyone for the help your giving. I Think the direction we are heading is taking another SWB frame and scabbing it into the original frame. The only reason they are not wanting to start with a whole new frame is because this 51 they have has a High Dollar Welded in IFS system. I figure if they can take that SWB frame and cut it off at a certian place on the frame and then use the SWB frame from there back it should work as long as they keep the same dimentions from the SWB frame. It all sounds good until you start cutting. I have the feeling there are going to be some lessons learned in this process.

[Atomsplitter]

As long as both frames are straight and in good condition it would be easy to weld on the SWB frame at the straight section behind the cab. Remember to measure 10x and cut once (well, twice in your case). While your re-enforcing the joint you could also box it in to make it even stronger! The front section of the frame will be boxed in anyway for the IFS. Look into doing staggered joints to ensure the strongest connection possible.

[BIG CHEVY 3600]

Go for it! Life is one long lesson. We all pass!

[OrrieG]

Make sure you use temporary reinforcing and cross bracing to keep things from moving when you cut the frames loose. In the factory manual I think there are frame holes and dimensions called out that are used for frame straightening and repair. If not you need to find the same point on each rail for the front and rear sections to check the diagonal dimensions to make sure the rear is square with the front and perpendicular to the frame rail long axis. Because of frame taper the long axis may not be parallel with the frame rails, that is why you need the diagonal measurements. Like atomsplitter said measure 10x, tack, measure again and weld in increments alterating sides to make sure you don't pull the frame out of alignment. Good luck.

[JRBECK64]

Originally Posted by OrrieG

Make sure you use temporary reinforcing and cross bracing to keep things from moving when you cut the frames loose. In the factory manual I think there are frame holes and dimensions called out that are used for frame straightening and repair. If not you need to find the same point on each rail for the front and rear sections to check the diagonal dimensions to make sure the rear is square with the front and perpendicular to the frame rail long axis. Because of frame taper the long axis may not be parallel with the frame rails, that is why you need the diagonal measurements. Like atomsplitter said measure 10x, tack, measure again and weld in increments alterating sides to make sure you don't pull the frame out of alignment. Good luck.

OrrieG,
Thank for the info, I think after talking with my friend that is actually doing this, he is going to build a temporary gig to do this so we wont loose the dimentions because of twist or frame flex. Believe me knowing these guys they will measure 20x before welding these two peices together.

[mr48chev]

after thinking it over I would suggest cutting the frames under the cab and doing the graft there. That will give you a longer area for overlap, let you line up the rear running board brackets and cab mounts. It should also be a pretty easy place to do the measuring and cutting . And the frames should have the same dimensions in that area to match up nicely.

That also saves having to fight with the rivets in the extra cross member that the longbed frame has.