My 1980 Fiat Pinninfarina Spider has a bolt-in crossmember that has been welded in place. Dose this make it too rigid? Could it cause stress fractures or any other problems?
Thank You,
Eric
If whoever welded in the crossmember knew what they were doing, it won’t be a problem.
Tester
Frankly it’s probably an improvement in the original design. That is, until you need to remove it for some underside maintenance. Could be any minute now.
Basically, the welding was done long enough ago that there is a good build up of grime. Recently I had new tires and an alignment done. Shortly after one of the lower control arms ripped through the crossmember, and cracked the crossmember on the other side. The claims department sent my car to a shop they suggested and that guy does not want to do the work due to liability issue. Stating that those cracks may have already been there(which they are shinny) and that the crossmember is supposed to be bolted but he won’t be able to due to damage… replacing the whole front-end is the only solution. Welding will make it too rigid, which will cause this again. In short, the alignment guys didn’t tighten down the nuts properly.
I could see stress fractures developing because it was welded. A bolt-on would at least dampen some of that transmission and driveline vibration.
It seems to me that it would not be that difficult to redo the crossmember and make it a bolt-on.
It also seems to me that if the cracks are shiny this means it was recently cracked; maybe due to this control arm problem.
Therer is no way to make a 1980 Fiat too rigid.
It depends on how it was welded in. Most likely, it is not flexing in the same manner that it did when bolted in. Understand, the frame and related components are designed to flex. Too rigid can be bad if the suspension is not designed to match. I once worked with a guy who did frame design and fabrication. One lesson I learned well was that modifying something without understanding how it affects the overall performance is a mistake. He had countless stories of well intentioned racers continuous welding their frame seams or boxing in things thinking more rigid is better and getting the opposite result.
The notion that the front end has to be replaced is ludicrous. No part of that frame or crossmember cannot be ground out and new plate or end pieces welded onto it to make it like it was before the modification and stress failure. I’ve patched back together many frames and relocated cross members in numerous cars. It’s only a matter of desire and welding skill. He either can’t do it or doesn’t want to do it.
TwinTurbos posted an excellent explanation. I’d like to add to it.
In addition to the things TT discussed, there’s also the issue of the welding “zone’s” affect on the metal. Around the weld is an area called a “heat affected zone” where the material’s structure has been changed by the welding heat as well as by the material added. These areas can be more prone to rusting and to cracking (more brittle) than the original parts. Since this is a very old weld on a very old car, it’s entirely possible that this is a factor in the problems you describe.
It may well be that the only really safe solution at this point is to replace the members themselves. Your shop may be correct. The car is, after all, 30 years old.
Thank you everyone for your input. The cracks were on the lower side of the crossmember, so it was not heat affected. I thought a plate could be welded in, with appropriate holes drilled, so that I may use it like before; but these “machanics” were blowing smoke. I may try that, I may just sell my pile of parts. Can you believe I acctually drove with the control arm chained up? (I kept it low speeds…saved some tow bills)
Just to cite an example of how vibration can do funny things consider what happened with SAAB 900s quite a few years back. They changed to a different A/C compressor and bracket and it went like this.
Two hard to access bolts were shaking loose. TSB issued on how to keep these bolts in place.
Bolts stayed in place and the 1 piece bracket started cracking in half.
TSB issued for new and improved 2 piece bracket.
Soon several other bolts were shaking loose but the bracket remained intact.
Repair to keep those bolts tight and the new and improved 2 piece bracket started breaking.
TSB issued about new and improved 3 piece bracket.
By this time they were planning to chuck the entire arrangement and redo the entire shooting match. 
All I can say about those pics is Good Lord.
Thank you for the photo, and you should be commended for your honesty and forthrightness.
With respect, this has to be the single most unsafe jury-rig I’ve ever seen in my life. I urge you to please never try anything even remotely like this ever again. You saved some tow bills, but you risked lives to do it. If this had let go…and if you had kept going it definitely would have… you could easily have ended up in someone elses front grill, or even off the side of a cliff or in a river.
Please, I beg you, don’t ever do this again.
No worries. I am a VERY safety concious person. By low speeds, I meant at a speed that would allow me to stop in four feet or less. Generaly five, maybe seven miles per hour with a trailing car and plenty of flashing lights. Choose routes that would allow people to pass so no one could get upset at this little Italian car going so damn slow. That is two different chains that should be able to handle about three times the wieght of the car. And, I even re-aligned that wheel so it wouldn’t pull out from the car.