Welding Unibody Seams?

[Myron Piatek]

Originally Posted by Tom Goldman

Spend the time you would spend on welding the seams, not recomended, and use it to put in a complete roll cage rather than a roll bar.
A 4 speed car will thank you for the extra stiffness the cage will provide.
I would add a bar from the cage to the firewall to stiffen the front clip mount area.
You can also add a brace from the cage bars to the area Danny mentioned to stiffen the clutch/brake mounting.

Tom, I understand a full cage will help, but why would welding the seams not be recommended? It's an awful lot of work, of course, but I can't see how it would hurt.

[RIGGATONY66]

Thanks for the replies, I'm making notes. Never know about the firewall flex. That's information that is great to hear about. I can plan some welding to support up that area. I'll get some pictures up shortly.

[Mark Ugrich]

With clutch pressures in the 200-300lb range I doubt firewall flex will be a problem.On my own car, once I put an updated clutch in it, the overcenter spring would hold the clutch pedal to the floor. I agree adding a full cage would be time well spent.Good luck with your project.

[Run to Rund]

The factory pinch welds are very strong. I doubt you would gain any strength, and otoh you will burn off all the paint and rust resistant coating inside. As others recommended, install a good roll bar or cage for stiffness.

[Lew Silverman]

If memory serves correctly, the front suspension on the early Chevy ll/Nova bolted on to the firewall, so anything you can do to stiffen up the uni-body would be beneficial. There are a number of companies that offer after-market (tubular) front suspension kits for the Chevy ll, with upgraded springs, shocks,steering and BRAKES! That and a well designed roll cage should do wonders for your performance.

Good luck with your project!

Lew

[Tom Goldman]

Originally Posted by Myron Piatek

Tom, I understand a full cage will help, but why would welding the seams not be recommended? It's an awful lot of work, of course, but I can't see how it would hurt.

The problem with welding seams ,especially on an old body with possible rust and remanants of seam sealer, is undercutting the sheetmetal next to the seam and actually weakening the structure rather than making it stronger.
If the body has been chemical stripped or blasted, tig welding the seams with silicon bronze is a good way to do it ,but not mig welding.
The best thing is to make the cage an integral part of the body structure so it does the work ,not the body.

[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