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Customs Sway Bar Tempering

Discussion in 'The Hokey Ass Message Board' started by Jobewan, Jun 10, 2021.

  1. Jobewan
    Joined: Jun 10, 2021
    Posts: 7

    Jobewan

    Hello Everyone!

    So it's been ages since I cut, turned, and tempered my very first center punch in shop class. Don't remember much about it if I'm honest.

    Fast forward: I chopped the mounting plates off of my rear sway bar; the new coilover mounts didn't clear the bar, so I moved the bar back an inch or so.

    The Question: test fitting seems to indicate the sway bar is not as aggressively controlling body tilt as it was before.

    I expect this is due in part to the change in geometry, but I wonder if I didn't take some of the temper out of the outboard legs in the welding process.

    Looking for informed opinions as to whether or not to attempt re-tempering and if so to what level. I have an induction heat gun that may or may not be up to the task of heating just the outboard legs to what I imagine would be a dull cherry red. Alternately, have a smallish Mapp / acetylene / oxy torch.

    Looking forward to your feedback!
     
    Last edited: Jun 10, 2021
  2. KevKo
    Joined: Jun 25, 2009
    Posts: 577

    KevKo
    Member
    from Motown

    Photos would help. I'll assume the bar is mounted to the rear axle and the arms are mounted to the frame. Shortening the arms, moving the frame mounts closer to the axle, would make the bar "work" more and could help. But I can't help with your heat question.
     
  3. Mike VV
    Joined: Sep 28, 2010
    Posts: 2,354

    Mike VV
    Member
    from SoCal

    Don't understand..."chopping the mounting plates off".
    These are not normally "part" of any anti-sway bar.

    In any case, yes, heating any part of an anti-sway bar WILL soften it. It will have little to no "spring" left in it. Just like heating coil springs, the car will...fall.

    Doing any heat treat at home will be a big crap shoot, in the best...of circumstances. Proper quenching will be a FUN task..!

    As for trying a home remedy...Google is your friend..! Just look up heat treating, and the material you have (?), and you should be able to get the temperatures and the quenching method.

    I'd just by another bar.

    Mike
     
  4. G-son
    Joined: Dec 19, 2012
    Posts: 775

    G-son
    Member
    from Sweden

    (Electrical) welding hardened steel tend to harden the weld so it's too hard & brittle, while the area around it gets heated to a lower temperature, annealing it and making the steel soft there. Neither is good for something that is supposed to work as a spring, but being soft may be preferable over being brittle, so one might want to anneal the welds.

    Welding on spring steel is rarely a good idea, and if you have to do it you want to redo the heat treatment process from scratch. Since most people can't, it's generally best to keep the welder off hardened steel.
     
    Crazy Steve likes this.

  5. Jobewan
    Joined: Jun 10, 2021
    Posts: 7

    Jobewan

    This sway bar began life from the manufacturer as a welded unit (spring steel bar welded to 3/8" inch thick mounting plates); I think the manufacturer welded it up and tempered it as a finished assembly. If I buy another one I'll end up with the same problem.

    Extending the mounting plates in order to change the mounting points would have still introduced heat into the equation, but perhaps not as much. The 'file test' indicates that just the 'legs' have softened and I don't want to over-harden or otherwise alter the unaffected main section of the bar, hence the idea to induction heat just the affected area; research indicates that some if not most manufacturers use induction heating to final temper their products.

    I have enough used motor oil to create an oil quench bath; seems that using water would basically turn the metal to a glass-like level of brittleness.

    That a final tempering step is required to regain a springy character is understood; researching that now.

    No biggie; I like fiddling with this stuff, and I have a concrete pad and plenty of fire extinguishers. (O;
     
    Last edited: Jun 10, 2021
  6. Rather than gamble on whether you can weld it or not, why not hit the wreckers with a tape measure ... there must be something already out there that can be fitted to your car without the need to adjust the bar.
    Keep in mind, I have absolutely no idea what your car is and what bar you are presently modifying.
    Or, go ahead with your modifications and welding and see if it works.
     
    G-son likes this.
  7. Doublepumper
    Joined: Jun 26, 2016
    Posts: 1,019

    Doublepumper
    Member

    I know a guy that took his home made anti-sway bar for his '37 Plymouth pickup to a spring shop, to have it heat treated. Might check with one of them for a fix.
     
    Budget36 likes this.
  8. G-son
    Joined: Dec 19, 2012
    Posts: 775

    G-son
    Member
    from Sweden

    Well... The heat treatment of steel is a multi step process.

    First you heat the steel about cherry red (a bit beyond the point when it is no longer magnetic).

    Then you rapidly cool it down, often in an oil bath but different steels require different methods.

    Then you reheat it to a much lower temperature for some time, perhaps 3-400C for a spring but this also depends on the steel, desired hardness and so on. This takes the steel from very hard and very brittle, to somewhat less hard but not brittle. Then you just let it cool down, and you're done.

    The thing is, you can't re-treat one area without softening the metal next to it, if you heat the ends enough to harden them, the metal near the hot ends will be completely annealed and lose all hardness. To have the entire piece hardened you need to do it all in one go, get the entire thing cherry red and toss it in (probably) an oil bath. Then you temper the entire thing at a relatively "low" heat, and it's ready to use.
     
    Truckedup likes this.
  9. Jobewan
    Joined: Jun 10, 2021
    Posts: 7

    Jobewan

    That sounds like a great idea; I'll look into it. Thanks!
     
  10. Jobewan
    Joined: Jun 10, 2021
    Posts: 7

    Jobewan

    See, that's what I was worried about - that bit next to the area I wanted to heat. I don't have the facility to safely handle the entire assembly.

    Doublepumper had the idea to see if I can get a speedshop to heat treat the finished assembly, which seems like a grand idea.
     
  11. drtrcrV-8
    Joined: Jan 6, 2013
    Posts: 1,432

    drtrcrV-8
    Member

    NOT a SPEEDSHOP!! a SPRING SHOP ! Two VERY different animals!!!
     
    Hnstray and Budget36 like this.
  12. HAMB Metallurgist here. Sway bars are usually heat treated. This allows it to flex more (higher yield strength) and return to original shape. Heat treating does not change the modulus of elasticity. Modulus of elasticity is basically the spring constant. Unheated treated has the same anti-roll resistance force, but can yield and permanently deform since lower yield strength.
    I need pictures to understand OPs case, but my gut feel is the modifications will be fine as is.
     
  13. Not sure where you are located.
    But up here I got a customer that all he does is heat treating.

    huge building with a few dozen large furnaces they do heat treating for all sorts of different companies and shops.

    they will do “ off the street “ work as well and cheap considering .

    might want to look around your area.
     
  14. Jobewan
    Joined: Jun 10, 2021
    Posts: 7

    Jobewan

    Yes; your right of course. I grew up next door to three (one after the other) part-time mechanics pulling heads, doing tuneups and brake jobs with their kids, went to a technical/industrial high school for computer-controlled machining and tool/die making, and worked as a forklift mechanic in my earlies. It was just a careless slip. I wouldn't imagine a speed shop would have the facilities and I wouldn't actually go to one when the time came. Thank you and good watching out.
     
  15. WZ JUNK
    Joined: Apr 20, 2001
    Posts: 1,720

    WZ JUNK
    Member
    from Neosho, MO

    I modified the ends of a sway bar a couple of years ago by heating and reshaping the ends. I did not temper the parts I heated when I finished. It is has been driven a lot of miles without problems.

    My theory is that the flexing that makes the bar work takes place in the center part of the bar and the ends act as levers. The ends would not need to be heat treated. Whatever is taking place, mine is not heat treated, and it works.
     
  16. Jobewan
    Joined: Jun 10, 2021
    Posts: 7

    Jobewan

    Thank you for the factual feedback. Reminds me of the metallurgy assignments in high school of which I have forgotten most of. :)
     
  17. Jobewan
    Joined: Jun 10, 2021
    Posts: 7

    Jobewan

    Thank you for the practical feedback. I already test-welded and re-installed the bar; it still works, just not as aggressively.

    I've gotten a good bit of factual as well as practical feedback to consider now; I welcome more but am already on the way to an outcome. Thanks All!
     

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