Lengthening a frame?
 

Hi guys, need some insight.

We have a 2008 Volvo 670 that we are going to use as the base for our RV but we want to put a 20 foot box on the back so we need to add about 5 feet of frame rail ahead of the axles and about the same behind the axles. Now the most logical thing to do is add the extra length we need to the end of the frame, slide the front axle back to rear position and re-drill for the new rear axle placement. My question is....could one bolt the frame extension on[with gussets of course] or does it have to be welded? This added section of frame really will only have about 8 feet of the box on it and its not like it going to have a fifth wheel on it pulling 80000lbs.

What do you think? Can it be bolted on or because its between the axles it needs to be weld?

My suggestion:
* acquire a vehicle fitting your needs.

Factory engineers get 'the big bux' to fiddle with the potential liabilities of frame flex leading to failures.

'Yes', any frame can be stretched to any length.
Any heavy-truck shop can do this.
Ask around, you can probably locate a vehicle in a shop in the process of a stretch.

After you establish your Requirements Statement, you can choose to a) shrink your needs, or b) sink a bundle into a declining asset (aka 'liability').

My choice?
Quit them tuba lessons, take up harmonica.

Moving the axles back and then adding onto the rear is the best. Any joint you have before the axles is a place to crack and break. The back is just along for the ride and is not subject to torque twisting. It does need to be welded and plated by a competent welder. If you go to a truck shop that installs bodies they do it all the time. One of the best place to get frame rails is where they scrap school busses.

Thanks for the tip! Never thought of scrap yard for school buses.

Sadly they dont really make it, hence the adventure we are partaking.....i hear yah though.

Thank you Jo Diesel, I’ve been debating if I should just add to the end of my rig. I have the frame rails already and I really don’t want a long rig. Max 32ft. so adding to end will make the entire job easy!

A bit of engineering insight on frame stretching. Dry math talk until his conclusions at the end.

https://youtu.be/mtwDvFTfBn8?si=LczAoUPIvQVM17TL