Brazing vs Welding

[Randy Webb]

How worried would you be if you found out the front suspension pan repair on your car had been brazed not welded? And why?

My understanding is that brazing is usually not as strong as welding.....

[jpnovak]

There will be no problems if done properly. I would not be worried.

I personally would think that a well brazed pan would be stronger than your average resistace spot welder.

[Zeke]

I believe Colin Chapman used a brazing technique on his race cars when they were tube frames to lessen the metal stress. And, you get less warpage.

I have done a lot of brazing on my cars when doing metal work. I find that I can fill better when I get to places that want to burn holes. Once you start wiht the brass, you can't go back and weld over. It's done.

[juanbenae]

correct me if im wrong here, brazing hold the parts together by the solder medium melting and working like glue on the parts. welding actually melts the solder medium and tthe desired parts together?

if thats the case then the good braze would leave the adjacent metal in a stronger condition from not being heat so thouroughly?

am i on the right track here?

[unclebilly]

no.

The strength of the metal in the heat affected zone (HAZ) depends on many factors:

What alloy? How it was welded? How it was cooled? What filler metal was used...

Brazing the pan in is OK. Most of the skin frame race cars are brazed together.

BTW brazing doesn't necessarliy imply brass filler rod, we vaccum braze parts together here at work with a nickel - chrome braze powder with 3 - 5% boron in it so that the braze needs a much higher temperature t reflow.

[Zeke]

Thanks for the clarification on the brass. I was guessing on that.

[unclebilly]

I guess many of the more recent skin frame cars are aluminum, but the older steel (or chrome moly) ones were all brazed (or silver soldered).

[Randy Webb]

Thanks folks!

[911pcars]

Just wanted to add:

Welding melts the base metal.
Brazing doesn't

Sherwood

[no substitute]

If you wish to know more, The Welder's Handbook (I think that's it) by Finch addresses the remarkable strength of a properly executed brazed joint.

[911nut]

Technically, brazing uses a second, lower melting point alloy to join the base metal together. There is a small intermetallic layer at the interface between the braze alloy and the base metal where alloying occurs (unlike soldering which is done below 1000 degrees F and is the equivalent of using hot glue). Since lower melting point alloys aren't as strong as higher melting point alloys the joint strength is dependant on a secondary stress field which is only obtained by the proper joint gap. Lots of aircraft engine parts are brazed as unclebilly pointed out but under optimal conditions. Brazing in a floor pan does not fit the definition of optimal conditions for joint gap or atomic cleanliness (no oxides or other contaminates present).
Welding uses filler metal that is very similar to the base metal and complete fusion is achieved as a result. The strength of the weld usually exceeds the base metal. A heat affected zone is present (an area of the base metal where grain growth occurs;large grains are weaker than small grains) but in the low carbon steels used to make car bodies there won't be any possibility of fracturing as a result of service stress/hardened microstructure. Proper welding technique (stitch welding the seams) will keep distortion to a minimum.
Conclusion: when at all possible weld instead of braze.

[Early_S_Man]

Nickel-Silver brazing was a quite popular method for tubular frame light aircraft construction [using chrome-moly tubing] for years, and that is where Colin Chapman picked up the technique ... it introduced less distortion of the finished parts and required a less-complicated jig during fabrication. Of course, he was known for making suspension and 'wing' support struts a bit too light ... and some of the FIA's rule changes regarding 'moveable aerodynamic devices' were directly the result of some Lotus post-accident investigations, especially Jim Clark's 1968 accident at Hockenheim!

[kach22i]

Interesting topic, seems to be resolved now. However if I could side bar for a moment; what about body work?

I have a rust hole in each of my door openings. The driver's side is a little larger. It's in that famous spot where you open the door and see the curved area between the rocker panel/threshold and the vertical side of the door opening.

The size of the holes? Driver's side similar to; taking a dollar bill and fold it in half, fold it in half a second time.

The passenger side hole; fold the same bill again but into a little square (between a quarter and 50 cent piece size).

I think if these holes were any larger it could become a structural issue. Taking the seats out and carpeting to fix it seems unavoidable.

[Oldporsche]

I have seen a lot of brazing used in assembling sheet metal. The problem that I have seen as a result is that body filler material sometimes has a problem holding over the brazed/brazing material. It is not a optimum method as has been pointed out however I haven't seen any structural problems in a porsche develop as a result of using this method. This method was often used by body shops that didn't have gas shielded wire welders that could be used as spot welders.

Btw, in one of the official films produced in the '70's by Porsche, they show an assembly technician securing the tunnel/floor pan area using braze.

There are some benefits in using braze. It can hold as well as needed without raising the temperature of the material that you are brazing to the point of burning.

I did see onetime, while visiting a hot-rod shop, a technician (mechanic) using silver solder on some stainless steel tubing. He was making an expansion chamber for the motor in a dragster. I suspect that this method could be used for building a muffler system out of stainless without heli-arcing. The stainless steel doesn't have to get hot enough to burn the nickle out of the stainless steel. When the nickel goes, the stainless/no rust properties leave also. Silver solder, methods are used to secure carbide bits to lathe tools. These methods are also used in the eyeglass/jewelry repair business. It has great holding power.

Good luck,
David Duffield

[911nut]

David, silver solder is actualy slang for silver brazing filler metal. The difference between soldering and brazing is soldering is performed below 1000 degrees F according to the American Welding Society. Many people braze stainless since it requires less skill than TIG welding. My previous statement about the strength of brazed joints vs. fusion welded joints still applies here.

S_man, grade 4130 Cr-Mo tubing is brazed because fusion welding it requires post weld heat traetment. 4130 won't require this heat treatment if it is brazed so it's a more attractive process for large structures like aircraft and race car frames.

By the way NASCAR long ago outlawed the use of 4130 rollbar structures because of brittle failures caused by improper welding technique, ie., no post weld heat treatment.

[Randy Webb]

911nut - shold I be concerned about the brazed suspension pan?

And, is there any way to check on its safety?

[Oldporsche]

Most of my repairs are done with hardware store options. Mostly to the pain of my Porsche friends.

I really just wanted to point out that there are a couple of options open to the guy that has to "get it fixed" that don't involve inert gas shielded environments.

Yes, its all braze. I wanted (and didn't get the job done) to show that the brass/bronze techniques could be used with a gas (acetylene) welding technique. This results in a very good repair in most instances.

Utilization of a "silver solder" method could be used for other repairs. You can unite things like stainless steel and copper with this materal. Also you could do repairs on outside oil cooling lines which are brass on our cars or patch them with copper lines, etc. Actually you could use probably you lead solder for these type of repairs. I know of alternator repair shops locally that use "silver solder" methods on electrical connections in their products for the racing community.

I wanted to show that a repair done with the brass/bronze brazing method is not necessarly bad. It was even used by the factory on our cars.

As always, good luck to you guys with your projects.

Today, my wife promised to help me with the headliner in the hardtop. (She used to work in a car interior shop)

David Duffield

[Tim K]

How did you find that your pan was brazed? Can you see that it has been brazed all the way around (w/o large unsupported spans)? If done properly, I wouldn't worry about it. Do you have pics? I had considered brazing as an alternative to seam welding for a racecar tub, but because of the work involved, I was convinced otherwise .
In response to kach22i, patches for rust repair are often brazed in because it will also stick to rusty surfaces. While this isn't a permanent fix, it certainly is a quick fix. Although I wouldn't assume that the area was rusty because it was brazed.
I believe that rust isn't worth "fixing" unless you give the repair a fighting chance. That is one of the reasons I bought my TIG. I've only had it a little while, but I love it! It might seem like overkill for a home garage, but I'd buy it again in a heartbeat. Here is one of the repairs from this week.


Hours of fitting before hammer welding and metal finishing. The repair should only need an aplication of highbuild primer.

[Randy Webb]

no pics. also no rust. yes, you can see that it was brazed (or people that know about this stuff tell me that they can see it was brazed). It looks pretty even all the way around.

[chrisp]

I was awaiting a response from JPAchard on this subject. I'll add what I can but I am not a welder but I seen it done many, many times.

Brazing "sweats" the filler material under a overlapping joint. It was (and still is) used in bicycle construction becuase, as mentioned, it doesn't distort the base material. It also provides a larger contact area than welding. If the overlap joint (a tube inside a lug) is 1/4" you'll have 1/4" of bonding. If you have 1/2 of overlap and sweat in enough material then you'll have a solid 1/2" overlap.

Welding melts the two joining parts and mixes a filler material in. A good weld fails beyond where the base material will fail.

I would guess that you want to have your pan overlapping with the chassis area around it and you want to spot weld it all in place. To make it really strong, then seam weld after that.

I do not know whether brazing in that area is good or bad I just had some info to add about the differences between the two.