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Help Soldering Brass Chassis - Rusting Issues

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  • Help Soldering Brass Chassis - Rusting Issues

    Hi guys,
    Im going to have a go at scratch building my own chassis. Ive made up a few chassis many years ago. Im not the best solderer but good enough to get a car moving around the track. Not all but some chassis ended up with rusting issues around the soldering. One chassis I soldered the motor to the bracket & the whole motor rusted & also the axle to the oillites. The whole thing was locked up tight! I couldn't free it up at all, tried everything. The whole chassis was painted as well. What am I doing wrong as I don't see others having issues like this. I just want to make sure that I don't have the same issues again.

    The solder Im using is 60% Tin, 40% Lead. The flux is unknown. I purchased it from a local at the time slot car shop. It is clear red liquid in a small dropper bottle. Unknown brand, no label. Im thinking it might be the flux is the issues Im having. I once even got the local slot car shop to solder something for me & that rusted up as well.

    Any help would be great as I obviously don't want this to happen again. Do you need to use any special cleaner on the chassis after its built?
    Many thanks Greg

  • #2

    You are probably using an acid flux -- highly effective but also corrosive.

    The cure is to thoroughly clean off any flux that remains on an assembly after soldering. There are many different ways to do that. What works best is whatever can get into the least accessible areas of the assembly. Wire brushing and/or spray cleaners are a good start. I have used a vibratory "brass polisher" -- sold for cleaning ammunition brass cartridges -- for cleaning a lot of assemblies at once. I use pulverized walnut shells as the abrasive medium.

    I use acid fluxes exclusively. I have had such poor luck using less aggressive fluxes that I have given up on them. So I cope with the corrosion issues of acid flux by careful and thorough cleaning. Like any other strong chemical, acid flux needs to be treated with respect. As acids go flux is not very dangerous, but respect it anyway. Wear eye protection when soldering with acid flux because it will boil and there will be some spraying droplets.

    Ed Bianchi
    Ed Bianchi
    York Pennsylvania USA


    • #3
      Do like Ed said on cleaning after soldering. You can run as much water over a motor or even into a motor as you want, it won't hurt it. I had guys running cold water over their motors between heats to cool them down, didn't hurt them.

      But I was told by a guy who rebuilds motors to never use acid flux on a motor, either to solder it in or solder on lead wires, use paste flux. The secret to good solder joints is clean parts, plenty of flux and plenty of heat.
      Butch Dunaway
      Oxford, Ohio


      • #4
        Try adding some bicarbonate of soda to the water to neutralize the acid. Use rosin core solder for electrical work.


        • #5
          After a chassis is complete, I take it to the sink. Hot water and dish-soap with toothbrush, and clean it thoroughly. Have yet to see any rusting on any of the chassis or solder joints.
          Scott.....War Eagle River......Tampa, Florida, USA



          • #6
            Yep, clean em up after you're done soldering.
            I have tossed em in lacquer thinner, but less trouble and completely effective is rubbing alcohol in an old tupperware, let it sit for a few minutes and brush the areas, it melts away, shoot brake cleaner through the bushings if you want, (at times melted flux travels in the sintered bushings and can lock up after time sitting),
            and then whole show in the sink with dawn then let it dry, like Scott said.



            • #7
              I’ve had good luck with the brake cleaner spray and I’m also in the process of building a tumbler to try some polishing right now
              Peterborough Ont


              • #8
                Since the mid 60's ,the most often used, and preferred method of cleaning up after chassis soldering with acid flux has been an old toothbrush with some Ajax/Comet cleanser......all the best. and most prolific chassis builders used/use this method.

                Chris Walker


                • #9
                  Baking soda neutralizes the acid. Use a toothbrush and some baking soda.
                  Matt B
                  So. In


                  • #10
                    Thankyou guys. All makes sense. So in Harry’s latest you tube video about soldering oillites in, he uses Stay Clean flux. A flux like that do you need to do similar cleaning? Or is it good measure to clean your chassis after soldering no matter what you use?

                    Lastly, I’ll need some new flux soon. I tried to find the Stay Clean flux in Australia. No luck. Can anyone recommend a good flux & I’ll see if it’s available here. Preferably one that is not so aggressive?

                    Thanks for your help


                    • #11
                      Stay Clean is an acid and must be neutralized. It is the best I have ever used. You can find a life time supply online for $7-$8. It is really the best and makes soldering so much easier.
                      Matt B
                      So. In


                      • mopargreg
                        mopargreg commented
                        Editing a comment
                        Thanks. I’ve tried to find Stay Clean here in Australia & don’t seem to have it here. I only had a quick look though. Looking for other suggestions?

                    • #12
                      As Rich & Matt said, use baking soda. Whenever I've built, I also prepare a small dish of water & baking soda to use as I work. When I'm done for the day, I soak a paper towel in the mixture & scrub all soldered joints that have steel in it. When a chassis is complete, it goes to the sink for a good scrubbing using whatever abrasive powder my wife has & an old toothbrush. The final step is to wipe/blow everything dry, then wipe it down with an oily rag. I built my first brass/wire chassis in 1968 & I've never had a rust problem when I cleaned the chassis first. Many of today's spray cans of tool cleaners & rust-preventers/removers ought to work too. I've used some on cast iron, but not a chassis.


                      • #13
                        rusting makes it look real
                        Merrimack, NH


                        • #14
                          Great thread here...pretty much everything mentioned here I do and once you dry it all off I take a hairdryer to make sure I get ALL the water or residue left in all the nooks and crannies...especially in the axle tube if you mounted one!!! Great info here and good luck!!
                          TOM...HOME RACING GOO GOO!!!
                          Warren, Ohio