Welding Unibody Seams?

[Dwight Southerland]

Tom -
I appreciate your in-depth knowledge and analysis concerning this topic. While your rationale is inviting and attractive, real world experience will prove that welding the seams in a unibody car will make the car more rigid and reduce flex. You can increase strength significantly with a well -designed cage so that the unibody factor is reduced, but under current Stock Eliminator restrictions for cage construction, the stitched up seams will be a benefit. I agree with your comment about tig welding as a preferred method.

[Sean Marconette]

I do not know if this aplies to the Chevy II. On my fox body, thru the floor subframe connectors made a world of difference.

Sean

[Tom Goldman]

Dwight, I do weld some seams on the cars I build but I stich weld them .
The key is not overpenetrating the seam and burning thru or undercutting.
I agree on a car like a Nova that is inherently weak in some areas it will help to weld a seam here and there on the front end ,especially since many of them are already pulling apart from years of use [and abuse] , but I feel the roll cage for a car like this is still the best solution.
I have done several cars with weak front end mountings for Stock Eliminator ,early Mustangs ,Dusters ,AMX's and Novas and have welded plates to the driver compartment side of the firewall at the point of attachment for the front end and run a tube to the forward leg of the cage to tie it in.
This is legal for Stock and has been accepted on all the cars it was done on.

[Wade Mahaffey]

A problem with continuious weld is that the metal will shrink when cooling and thus be under tension untill it is relieved. Sheet metal does not like or perform well under extensive tension, and it has no strength under compression (it just bends). Without structure (frame work) it will crack at the weld edge and fail. Sheet metal is designed to go along for the ride, just as fiberglass panels do. Unibody construction is for light weight and not severe duty. If your not running in Stock eliminator I would run cage components thru the firewall and attach suspension points and foward frame point to the main cage. It should'nt be long before NHRA and IHRA allow (thru the firewall cage structure) in Stock eliminator anyway. You can design/fabricate the cage in preperation for thru the fire wall addition at a later date. If you just want to add a little insurance to a spot weld seam. I would tack weld a small spot (on the edge of the overlap panel in between each factory spot weld) to provide a zig-zag appearance without stressing the entire panel. I would not use the silicon-bronze filler rod for this, S-B rod is for light duty applications only.

Wade Mahaffey

[Tom Goldman]

Originally Posted by Wade Mahaffey

. I would not use the silicon-bronze filler rod for this, S-B rod is for light duty applications only.

Wade Mahaffey

I disagree, SIB has excellent strength for sheetmetal welding of this type.
Bickel ,Haas and other Pro builders use SIB to attach sheetmetal floor panels to tube chassis.
An how about the aircraft frames that are welded using SIB.
Low strength compared to ew70s2 or other alloy wires yes, but a good choice for this type of work

[Wade Mahaffey]

Tom, the floor panels, firewall, dash, as well as other panels thruout the car built by pro builders is a light duty area. It is just a panel covering some frame/chassis structure. This practice has been done for a very long time, but the panels are not there for chassis design and/or strength. The silicon-bronze is used because of it's low melting point to keep high heat off of the 4130 moly tubing. Now SlB is fine for that, But not for reinforcing unibody construction in my opinion. As far as aircraft, years of knowledge, skill, proper equitment, testing and evaluation, quaility raw materials are things the average back yard builder does not have, so I would not reccomend that direction IMO. I started welding with Silicon-bronze 40+ years ago and I have experience and my opinion in what it can and can't do.

Wade Mahaffey

[Tom Goldman]

Well Wade we'll have to agree to disagree.
My experience as a welder fabricator /builder also spans over 40 years.
And having worked on Pro built cars as well as having fabricated many full tube chassis and S/SS type cars, I,m very familier with why certain panels are welded with SiB.
By the way, My "backyard clientel " consists of several World Champions, National event winners, National record holders, and several National and Div. best engineered cars.
My work speaks for itself , as does yours.

[Wade Mahaffey]

I agree Tom, we both have built some nice cars in our time.

Wade Mahaffey

[RIGGATONY66]

Thank you everyone for the info and comments. Hope to be able to help answer a question sometime. Best wishes.

[BlueOval Ralph]

Just a piece of history, Ford used this practice starting in 1967 when the Tran-Am cars were built from Bodies in white they had no sound deadner or sealants. If you can find a copy of the Boss 302 Chassis Book there is pictures of where to weld that body!