Is wheel base an issue???

Heres a pic of my 97 3500. Short traction bars were the cause:doh: Lesson learned as I know have them about twice as long mounted to the box part of the frame.
 

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Heres a pic of my 97 3500. Short traction bars were the cause Lesson learned as I know have them about twice as long mounted to the box part of the frame.
Click to expand...
How do those STTs do for pulling?
 
teddybear said:
Heres a pic of my 97 3500. Short traction bars were the cause:doh: Lesson learned as I know have them about twice as long mounted to the box part of the frame.
Click to expand...

I have seen that pic around quite a bit. Sorry for your luck. I still would like to see a video or something of those other trucks breaking in half.
 
zstroken said:
I am wandering if there was a steel change.
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Dan, go back to your e-mech book again....

The type of steel has almost nothing to do with rigidity. Rigidity or resistance to flex is a function of the section moment of inertia, i.e., the design - "c" channel vs. boxed, etc. The most significant factor is the height (a cubed function), thickness to a lesser extent, and then width (linear) and material modulus of elasticity (linear).

For a rectangular solid, the section moment = base * (height cubed) / 12. For a rectangular tube you do the outside one and subtract the "hole".

The material modulus of elasticity (intrinsic stiffness) varies a lot between materials. Steel is a hair more than 2X as stiff as aluminum for example. What you do have to remember is that modulus, for the most part, is microstructurally insensitive. You can heat treat it hard as nails or anneal it dead soft, and the modulus may only change a few %.

For example, on a leaf spring, the rate would not change whether it was heat treated or not. The reason they heat treat it is to resist plastic (permanent) deformation when you flex it far enough to exceed the yield stress of the steel. If you are below yield, then again it does not matter if the steel is dead soft or full hard.

Now if the frames are staying bent, then the yield is being exceeded (obviously) and the strength of the material is relevant. But make the same frame out of hardened material, it flexes just as much, but it will return to its former shape after the load is removed because it stayed within its elastic range. If you were starting from scratch, it would be a ton easier and more economical to make the frame deeper and/or go up a gauge in material thickness. Heat treating a formed frame would be a PITA and expensive, but not impossible. Semi truck frames are heat treated but they're generally straight and simple and made up from simple structural elements.

Make sense?

If someone ever tells you to heat treat something to make it flex less, they're full of crap. Many people confuse this very critical point.

Corrosion could have a lot to do with why one would move more than another of identical construction.
 
nwpadmax said:
Dan, go back to your e-mech book again....

The type of steel has almost nothing to do with rigidity. Rigidity or resistance to flex is a function of the section moment of inertia, i.e., the design - "c" channel vs. boxed, etc. The most significant factor is the height (a cubed function), thickness to a lesser extent, and then width (linear) and material modulus of elasticity (linear).

For a rectangular solid, the section moment = base * (height cubed) / 12. For a rectangular tube you do the outside one and subtract the "hole".

The material modulus of elasticity (intrinsic stiffness) varies a lot between materials. Steel is a hair more than 2X as stiff as aluminum for example. What you do have to remember is that modulus, for the most part, is microstructurally insensitive. You can heat treat it hard as nails or anneal it dead soft, and the modulus may only change a few %.

For example, on a leaf spring, the rate would not change whether it was heat treated or not. The reason they heat treat it is to resist plastic (permanent) deformation when you flex it far enough to exceed the yield stress of the steel. If you are below yield, then again it does not matter if the steel is dead soft or full hard.

Now if the frames are staying bent, then the yield is being exceeded (obviously) and the strength of the material is relevant. But make the same frame out of hardened material, it flexes just as much, but it will return to its former shape after the load is removed because it stayed within its elastic range. If you were starting from scratch, it would be a ton easier and more economical to make the frame deeper and/or go up a gauge in material thickness. Heat treating a formed frame would be a PITA and expensive, but not impossible. Semi truck frames are heat treated but they're generally straight and simple and made up from simple structural elements.

Make sense?

If someone ever tells you to heat treat something to make it flex less, they're full of crap. Many people confuse this very critical point.

Corrosion could have a lot to do with why one would move more than another of identical construction.
Click to expand...

Huh?

Yea kinda, that is why I ask you when it comes to mechanical questions.

I guess I was wandering if they did change the frame. I remember reading in the TSB's about having to do something different on the frame around the 97 and up time frame.

Thanks for the info Matt.
 
I guess being a GM guy I would have just assumed that they used different frames for the 1/2tons to the 1-tons.

I know with the 88-98 GM's every frame is different. Taller, thicker and wider channel. My frame on my Crew-Cab was from a 6.5 Diesel truck and the frame rails (Steel thickness) are 1/8" thicker than the same crew-cab frame that came with a gasser.

Where are these frames actually bending/breaking...right at the joint where the two frames meat and the rivets are? Again...used to the GM's...the joint is right below the center of the front doors and fully boxed, welded and beefed up. I have yet to see one crack in that area.

Ryan
 
Well OK maybe I can make it simpler. Think of wood joists like in your house.

A 2x8 beam section moment of inertia is:
2 * (8*8*8) / 12 = 85 in^4 (inches to the 4th power)
don't get hung up on units here, let's call it 85.

A 2x10 beam moment of inertia is:
2 * (10*10*10) / 12 = 167.....almost double! for only 2" additional height.

Or you could double-up the 2x8s beside each other and have the same stiffness as one 2x10. The height is by far the dominant factor.

Look at a single 2x12:
2 * (12*12*12) / 12 = 288! more than tripled 2x8s.

So not to beat a dead horse, but the taller frames can be WAY more resistant to flex than the shorty c-shaped jobbies.

This is how, by the way, that engineers come up with span tables for house building...all based off some pretty simple and basic equations that anyone can use.
 
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Matt, I followed it the first time. It is nice to be able to put some bite behind the bark, we have touched on this before, in the discussion of pulling hitches. I think the back portion of the dodges on the 2nd gen is weak, so moving the hitch forward on the frame, or boxing it in has more effect, than just moving the hitch point.
 
most one ton and under truck frames are heat treated or hardened if you will for exactly that, memory elasticity, with a thinner material and section, for reduced weight, in order to get better mileage.

Have been for years - thats why your not suppposed to weld on em.

I can still remeber in the early 80's the F150 and 250 frames with all of the holes in them for lightening and the resulting failures under load.

MTO here would take your truck off the road unless the weld/repair was done by an approved shop and the repair area re - treated if they even allowed it at all exactly because welding removes the elasticity of the treated steel, and can be cause for future catastrophic failure.

Although you may not readily see any differences i nthe frames from oen model to the next - I would be willing to bet there is considerable difference in the treatment/hardness of the frames, exactly so a 3500 series can carry more laod without deformation
 
seeker1056 said:
most one ton and under truck frames are heat treated or hardened if you will for exactly that, memory elasticity, with a thinner material and section, for reduced weight, in order to get better mileage.

Have been for years - thats why your not suppposed to weld on em.

I can still remeber in the early 80's the F150 and 250 frames with all of the holes in them for lightening and the resulting failures under load.

MTO here would take your truck off the road unless the weld/repair was done by an approved shop and the repair area re - treated if they even allowed it at all exactly because welding removes the elasticity of the treated steel, and can be cause for future catastrophic failure.

Although you may not readily see any differences i nthe frames from oen model to the next - I would be willing to bet there is considerable difference in the treatment/hardness of the frames, exactly so a 3500 series can carry more laod without deformation
Click to expand...


If you can plow right through your frame with standard drill bits, then they're not hardened much, if at all.

I've never drilled on a Dodge frame, but the GM frames are soft. There is quite a difference between the 1500s and the 2500/3500s in terms of section depth.

So I'll take your bet. Get me some samples and I can prove it to you...I'm a metallurgist by day.

Or maybe some night I'll go out and be the Phantom Phrame Driller :D
 
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