Rear uniframe patch

BrennWagon

He’s just this guy, you know?
When I replaced my rear shocks in December, I noticed a little bit of what looked like batting inside the frame rail. I poked my finger in and found plenty of rust. Yesterday I decided to start taking care of the issue and broke off the rust and pulled out what was obviously an old rodent nest. The damaged area is directly under my shock mount but almost all along the horizontal plane with good steel about an inch from the bottom.

I’m planning on cutting out a 2” tall by 14” section and welding a piece of 16 gauge steel in place.
Is this heavy enough? Should I do a series of spot welds or a solid bead? There doesn’t seem to be any significant loss of structural integrity and no other frame rust to speak of. I’m certain that the van’s solid and nowhere near ready for the scrap heap. Thanks in advance for your advice.
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220629

Well-known member
If you are sistering a piece on to some basically intact structure then I wouldn't think continuous weld would be necessary. A continuous bead could set up a stress line. I will readily bow to others with more experience though.

:2cents: vic
 

BrennWagon

He’s just this guy, you know?
Just crawled under for pics of the area in question
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220629

Well-known member
The bottom looks pretty bad. Are the vertical walls as bad as the bottom? If yes, I would consider some sort of additional tie in to the flooring structure or other reinforcement. Especially to that plate involved with the shock mount.

It's tough to tell from pictures.

vic
 

BrennWagon

He’s just this guy, you know?
The rust was/is mostly confined to the bottom. The 2”x14” U shaped patch I bent up (by hand. I really need to get a proper brake but that’s another story) is larger than the rusted area, and I have yet to cut out the rust (maybe tomorrow) but the dimensions of the patch should give me plenty of good steel to work with. I suppose the cutting will be the most revealing thing, but it currently seems that the vertical walls don’t seem to have rust higher than the bottom edge of the shock mount plate
 

koenb

Active member
My gut tells me if 16gauge is good, thicker would be better. Especially in an already weakend area, it would be best to restore or improve upon the structural makeup of that area.
As to welding solid beads vs spots I think it really depends on the base metal makeup. If the steel used in the sprinter frame rail as a heat treatment welding solid beads will get the metal very hot and could affect the strength of the base metal. I'm not an engineer or a welder, so i'm not certain how much or little this matters, I'm just basing it on my experience working mostly with various heat treated aluminum alloys. Also have no clue as to what the steel composition of the frame rail is.

If available, I would also suggest putting the rear end up on jack stands to unload the shock mount, don't want things shifting while structural metal is being removed.
 

trc.rhubarb

Well-known member
I'd think you would stitch weld it and make several passes to get it all done up. Depending on your skills with the welder, it may get too hot for using adhesives and you want it to have as much structural support as possible. I'd try to match metals and thickness to original. I once "fixed" a truck that cracked it's framerails at the front shock mounts. (4x4 that had too much air time and big tires over the years). We decided to "do it right" and used 1/4" plate on either side of the frame rails, bolted and welded. Yeah, no flex at all, perfect! Until the frame cracked at either end of the plates.

Flex is designed in, to a point, and i'd try to maintain that same level.
 

Nautamaran

2004 140” HRC 2500 (Crewed)
Agreed: “hard points” are bad, as are crevices, so I’d fit the new metal into your cut then butt weld it together using a continuous back-stitch to minimize distortion. Perhaps use a step bit to bore holes at the corners of your planned cut so you have a radius in your weld.
I recall the interior wax coating making a good stink when I was TIG welding the my bench mounts into my van, even with an argon purge... certainly have someone on fire watch.
It appears you’re damage is 30% of the sidewalls + the flange, so the repair will likely be under compression at the bottom, but shearing along the length of the side welds. Size your beads accordingly, aiming to keep them as flat as possible. And of course be sure to rust-coat the interior of the box when you’re through.
Have fun!

-dave
 

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