Ok to heat and bend a pitman arm?

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DRoCk

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Pretty self explanitory question from the title, but since I am new I'll tell a little about the car. Its a 73 swinger with a 383. I'm in the process of adding headers, Hooker Comps and I don't think anyone else has put these in successfully. So far I've done it with no dents to the headers, but the pitman/idler arms both hit the primary tubes a little...3/8 of an inch or less. I don't want to smack the tubes, so can I heat and bend the idler/pitman arms to clear? I don't mind denting header tubes, but I would like to spread out the mods in that area so I'm not killing primary tubes.
 
I've done some reading on it, and it sounds like you run into trouble with strength of the part being compromised when you quench the metal, letting it cool naturally is much better for the part. Also, I should mention, this car will see less than 500 miles on it in any given year, and no track time. Its an in town car mostly...4.30 gears...never goes over 70mph. I mostly want to get it back on the road...obviously its not a permanent solution.
 
Try it cold and bend only what you absolutely have to. Try grinding a little off the end of the pitman arm swivel if that`s where it`s hitting. As you`ve read ,if you must heat it ,just let it cool without any speeding of the process. When everything is clearanced take the car to a competent front end specialist and tell him what you did before he aligns the front end.
 
No Dont Do It. Heat And Bent The Header But Dont Bent The Pitman Arm! Your Suspension Takes More Of A Horrible Beating Than You Realize! Heating Could Cause The Metal To Become Weak And Bending It Could Cause Small Stress Cracks...so Then If It Breaks On The Interstate And 70 Mph Your Car Will Star In A Big Beautiful Interstate Ballet.....lol ...
 
Sounds like a really bad idea to me, considering the tradeoff being what, a little dent in the header?
 
Tell you what guys, I have decided not to mess with the pitman arm... Actually, I'm thinking about selling the whole thing, its becoming to big of a pain.
 
i am going to have to agree with the majority, don't do anything to it. grind off a bit on the pitman/idler MAYBE, and then ding the tube a bit too. or just ding the header tube. a 3/8" inch or less ding will not sacrifice that much performance.
 
If you must raise or lower the tie-rod end of the pitman arm, do what the factory service manual tells you to do and add/subtract body shims between the steering gearbox and the K-member. Bear in mind, whatever you do to the pitman arm, you must also do to the idler arm. If you raise both, this will leave you with longer and steeper outer tie-rod segments. This WILL cause the wheels to toe out when you hit bumps, causing bump steer. Generally not a desirable handling trait. However, there is something that may save your bacon a little. If you set the front ride height lower than factory specs, the outer tie rod will be higher relative to the inner the inner at your static ride height, and possibly closer to the factory relationship (lowering and headers usually don't work too well together though). You can also add shims between the motor mounts and the K-member if you need to tweak the final engine position, but this might be going in the opposite direction from what you need. Oh and as long as you use a piece of iron pipe to make a nice radiused dimple, I wouldn't worry about denting the tubes too much. If they run under the steering linkage, you will dent them pretty good with the street.
 
Anytime you heat metal you're altering the carbon bonds in the metal that keeps it strong. If you don't know the actual temperatures used to heat it up, how to quench the metal (in oil, water, open air quench, etc), and get the proper temper/hardness then you are in for big trouble down the road. Either too soft or too hard spells disaster. Dent the header tubes as everyone else has said. How are the engine mounts? Is the engine properly mounted/aligned? Maybe you could move the engine over 3/8". A possibility I guess.
 
It`s funny how if you talk to the Hot Rod crowd they`ll say "bend away", the resto crowd will say never bend a suspension part.
 
Longgone said:
It`s funny how if you talk to the Hot Rod crowd they`ll say "bend away", the resto crowd will say never bend a suspension part.
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You are exactly right I have heated and bent lots of suspension and steering components when building street rods and it doesn't faze me/us in the least, but you need to let them cool naturally, quencing them will crystalize the metal. Also spreading the heat out is better than just concentrating in one area. I don't think you can heat an a-body pitman arm & idler arm without the heat ruining the ball joint in it.

DRoCk, like C130 Chief says the Mopar Chassis manual mentions using shims one way or the other to move the steering box to gain clearance for the pitman arm. For moving the idler arm the same amount it shows in the same manual slotting one hole of the idler arm bracket so it can be moved.


Chuck
 
340mopar said:
You are exactly right I have heated and bent lots of suspension and steering components when building street rods and it doesn't faze me/us in the least, but you need to let them cool naturally, quencing them will crystalize the metal.
Chuck
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I'm sure you got away with it Chuck, but that is probably only because you haven't yet found the failure point in a case-hardened steel suspension part that has been annealed in this way. I wouldn't trust it in a steet or competition-driven vehicle.

Funny how you were cautioning me me about towing advice a couple months ago and now the shoe is on the other foot! :lol:
 
Ace said:
I'm sure you got away with it Chuck, but that is probably only because you haven't yet found the failure point in a case-hardened steel suspension part that has been annealed in this way. I wouldn't trust it in a steet or competition-driven vehicle.

Funny how you were cautioning me me about towing advice a couple months ago and now the shoe is on the other foot! :lol:
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You still carrying that burr in your saddle? you need to move on, I completely forgot about that.

Steering parts are just forged steel, there is nothing special about them. They are heated when they are formed. We weld our own spring hangers on our cars that attach our suspension parts and this is different how? It is not, it is the same thing. If done right there is of no issue. To remove king pins & bushings in semis it is common practice to use lots of heat and these trucks haul over 80,000lbs, no big deal.


Chuck
 
340mopar said:
Steering parts are just forged steel, there is nothing special about them. They are heated when they are formed. We weld our own spring hangers on our cars that attach our suspension parts and this is different how? It is not, it is the same thing. If done right there is of no issue. To remove king pins & bushings in semis it is common practice to use lots of heat and these trucks haul over 80,000lbs, no big deal.


Chuck
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When you forge form a piece of metal you realign the grain structure to follow the shape of the part. This is why a forged metal part is stronger than a cast part or one machined from a lump of metal.

When you heat a peice of steel up to it's red hot so you can bend it the grain structure will re-align it self into a more random pattern which reduces the strength of the part. Basically you have negated all the benifits of the forging process. Depending on the actual make up of the alloy if you do not cool it properly or peform the proper heat treatment after the heating you can cause carbon to parcipitate into the boundaries between the grain structure which makes the material very brittle and causes intergranual stress corrosion. You now have further reduced the parts ability to perform it's function. I have seen high strength alloy bolts have the heads just pop off sitting in the box because of improper heat treatment.

To say heating and bending a part like a pitman is no big deal without knowing all the details about the design and function is akin to saying playing Russion Roulette is no big deal without knowing if there are bullets in the gun.

My 30+ years as an engineer would look at a pitman arm and say it is a forged part because it's a convienent and cost effective way to make it more than the strength derived from forging. But I am not sure, and if the choice is between denting a header tube and potentially creating an unsafe part I would dent the tube.

Citing the heavy truck practice as justification is reckless. When a structural part is designed, a safety factor is built in. The heating on the big truck is likley reducing the overall strength but there may be a much larger safety factor that in the end your margin is still acceptable. Where as in car parts there is much more of a concern for reduced weight for performance & economy and the safety factor may not be as big. The heating could reduce the strength to a point of where no margin is left.

Before doing anything like this you need to understand what the potential consequences are and decide if you want to take the risk.
 
Suspension and steering parts are forged or cast out of malleable iron and will bend before they break. They are designed to do that. As some have correctly pointed out, if you cool the parts rapidly you will make the iron brittle (you are introducing a temper, and unless you have a heat treating oven and some experience best not to fool around with this). With the exception of the spindle, and parts of articulating joints, nothing is hardened, and those parts which are typically get induction hardened locally at the point of wear. Now, if you cold bend a part you WILL harden it and make it more brittle. This is called work-hardening, and is why it is preferred to replace suspension components damaged in accidents rather than straightening them.

However, the main reason I suggested shimming various components was to make the mod reversible or adjustable in the future. Your headers will change shape even if you never whang them onto the street. Your unibody will change shape if you try going fast with big blocks. A 440 moves the headers out and up some, if you ever swap.

One other thought before you get too carried away. You do have the car sitting level with the weight on the wheels right? If you have jackstands under the unibody, and a big block hanging up front, you have more than 3/8" of bend in the chassis that won't be there when you are driving. When you add subframe connectors, and I suggest you do, make sure the car is weight-on-wheels then as well. Wheel ramps up front and stands under the rear axle are the way to go.
 
Come on DroCK, don't let a little thing like a header hit get you down. Look down the road at the nice ride you'll have after getting it done. Mike
 
ValiantMike said:
Come on DroCK, don't let a little thing like a header hit get you down. Look down the road at the nice ride you'll have after getting it done. Mike
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Ditto, I`ve got a 440 in mine with 2" tubes, so I feel your pain, I`ve made dents in my $700.00 headers, however there`s a big payoff in the end .When these big blocks are tuned and ready in these little cars, there`s nothing like it! Don`t let clearance issues make you throw in the towel, remember Chrysler put HEMIS in these cars. :toothy7:

Longgone`s 68 Barracuda 440-6.jpg
 
My dad makes folding pocket knives and huntng knives as a hobby and he uses a kiln for tempering the blades. He can pretty much make the steel as hard or soft as he wants depending on what the blade is intended for. He's very well read in metalurgy. If I knew the compostition of the part I could ask him how he would bend the piece and retain the original strength. He uses a Rockwell hardness tester and other tools for this kind of work. Anyways, i'm sure Drock gets the point. Good discussion though.
 
Heated and bent pitman arm.
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So far, seven years of this kind of abuse has not produced a failure.
pumpkin_jump2_lowres.jpg


thaven_640.jpg


dana44_crossmem.jpg
 
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