frame shortening

[flatbed51]

I am in the process of shortening my frame on my 51 . Would appreciate some help with frame measurements on a short wheelbase. For example rear axle centerline to rear cab shackle mounts, and from rear of frame to axle centerline. Any other input regarding shortening my frame would really be welcome.

[dicer]

IMOP, there is no reason to remove the spring mount points. The frame would be cut some distance ahead of them.

[OrrieG]

It should be shortened between the rear cab mounts and front rear spring shackles. Less things to keep track of or mess up.

[OrrieG]

It should be shortened between the rear cab mounts and front rear spring shackles. Less things to keep track of or mess up. There have been a few threads on this. If I remember right there is some adjustment to better center the rear tire in the wheel well.

[mr48chev]

Originally Posted by OrrieG

It should be shortened between the rear cab mounts and front rear spring shackles. Less things to keep track of or mess up. There have been a few threads on this. If I remember right there is some adjustment to better center the rear tire in the wheel well.

That is the way I would do it on that frame. To stay with standard short bed measurements you need to end up with a 116 inch wheelbase.

That means cutting 9.25 inches out of the frame if it is a standard longbed frame.

As Orrie said, some guys adjust the length of the piece that they cut out so that the spring bolt ends up being right at the 116" wheelbase spot so they don't have to offset the hole in the spring pad on the new axle.

I'm not positive what the difference is but it is the difference between the stock spring pad on the stock axle and the centerline of the axle. Something like 1-3/4 inch but it may be less.

You will have to trim a few inches off the back end of the frame rails anyhow so that slight adjustment in frame length isn't a big deal but makes things a lot easier for you in the long run.

One of our board members drew up this diagram a while back and shared it on a similar thread on shortening a 67/72 frame. The measurements WILL NOT WORK in this case as they should be 9.25 or your adjusted measurements.



This makes for a stronger shortened frame than just cutting straight down and butt welding the frame back together.

[flatbed51]

Originally Posted by mr48chev

That is the way I would do it on that frame. To stay with standard short bed measurements you need to end up with a 116 inch wheelbase.

That means cutting 9.25 inches out of the frame if it is a standard longbed frame.

As Orrie said, some guys adjust the length of the piece that they cut out so that the spring bolt ends up being right at the 116" wheelbase spot so they don't have to offset the hole in the spring pad on the new axle.

I'm not positive what the difference is but it is the difference between the stock spring pad on the stock axle and the centerline of the axle. Something like 1-3/4 inch but it may be less.

You will have to trim a few inches off the back end of the frame rails anyhow so that slight adjustment in frame length isn't a big deal but makes things a lot easier for you in the long run.

One of our board members drew up this diagram a while back and shared it on a similar thread on shortening a 67/72 frame. The measurements WILL NOT WORK in this case as they should be 9.25 or your adjusted measurements.



This makes for a stronger shortened frame than just cutting straight down and butt welding the frame back together.

Thanks guys that is exactly what I had envisioned doing. I had even drawn it out on the frame that way. It is great to be able to get confirmation that I am doing it the right way. Don

[mr48chev]

One of my running buddies has done several later model trucks that way and has even stretched a couple of 1 tons using the same method.

I'm going the other way and swapping a GMC half ton long wheel base frame under my 48 so I can stretch the cab 9-1/4 inches and keep the stock short bed. With everything around here breaking down and needing repairs the going is pretty slow on getting the frame for the 48 up and ready though.

[rgunlock]

Anybody have pictures of properly done "fish plates" they've done to add to this thread?