Welding Unibody Seams?
 

Happy New Years everyone. I have been reading the forum for sometime now and found it very helpful, Thanks. I have a 66 Chevy II Sport Coupe that I'm building for bracket racing. I plan on installing sub frame connectors and a 6pt roll bar. Will welding the uni-body seams help strengthen the body and keep the car from flexing? Would this be a waist of time? The car has a small block, 4 speed and 4:88 gears using M/T ET STREETS. Thanks for the help.

Re: Welding Unibody Seams?
 

Welcome to the forum,,,theres a bunch of Chevy II guys on here that will jump in I'm sure. I had a '66 Nova SS in the '70s, a stick car, and one problem I remember we had was with firewall flexing. You could stand there and watch while a buddy pushed the clutch in and see the master cylinder move back and forth with the pedal movement. I'm not sure what they do nowadays but back then we made a brace from the shock tower to the mastercylinder mount. I had a 6 point roll bar also which really stiffened things up, but I know I should've had frame connectors. We didn't bother with welding the body seams. Good luck with your car,,,keep us updated with your progress, especially with pictures.
Danny Durham

Re: Welding Unibody Seams?
 

Make it an 8 point with short bars behind the seats going from the sides of the main hoop at the cross-bar down into the frame connectors. Triangulation is the key. Welding the uni-body seams can only help if you want to go through the trouble.

Re: Welding Unibody Seams?
 

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.

Re: Welding Unibody Seams?
 

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.

Re: Welding Unibody Seams?
 

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.

Re: Welding Unibody Seams?
 

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.:eek: I agree adding a full cage would be time well spent.Good luck with your project.

Re: Welding Unibody Seams?
 

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.

Re: Welding Unibody Seams?
 

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

Re: Welding Unibody Seams?
 

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.

Re: Welding Unibody Seams?
 

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.

Re: Welding Unibody Seams?
 

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

Re: Welding Unibody Seams?
 

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.

Re: Welding Unibody Seams?
 

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

Re: Welding Unibody Seams?
 

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

Re: Welding Unibody Seams?
 

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

Re: Welding Unibody Seams?
 

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.

Re: Welding Unibody Seams?
 

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

Wade Mahaffey

Re: Welding Unibody Seams?
 

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

Re: Welding Unibody Seams?
 

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!

Re: Welding Unibody Seams?
 

GM issued "unofficial" bulletins back in the day with similar instructions for the Camaro bodies being used in TransAm to the racers, too. That's the reason I zipped up the seams of my '67 in 1982.

Re: Welding Unibody Seams?
 

Ford needed it more than Cheby as the front susp. was part of body spring towers and cross members engine mounts Camaro had sub frame that bolted on, weren't the seams on them rewelded up?

Re: Welding Unibody Seams?
 

The welding on the subframes from the factory was atrocious - incomplete, overburned, etc. The racers were instructed to reinforce and reweld the subframes. There were some skunkworks subframes in '69 that were hand crafted in the R&D department with subtle changes in shape and material. The factory instructions concentrated on the firewall/front footwell area and the area from the front of the rear spring eyes back past the "crossmember" where the shocks were mounted.

Re: Welding Unibody Seams?
 

And mounting points for susp