Grade 5 Bolts...what am I missing

[WM-300]

Today I had a Draw Tite Gooseneck hitch put on my 2003 Ram CTD. Its uses the Draw Tite Frame plates, rails and the Removable Ball. All hardware supplied is Grade 5. The manual even states its Grade 5. Is Grade 5 strong enough, I would have used Grade 8 had I installed it. The side plates on the frame rails use only (2) 1/2" bolts per side.



If it would be safer, I would rather take the time to replace the Grade 5 with Grade 8 but I may be missing some important engineering Draw Tite did. The Hitch is rated for 30,000#



Thanks

Paul

 

[Eric_77]

The Grade 8 bolt has more strength than grade 5 at breaking point but it is more brittle. so the grade 5 may be used for its flexiblity?

 

[SRadke]

Depending on how they designed the hitch and how much force in what direction is against the bolt grade 5 might be plenty sufficient. If they went out of their way to specify grade 5 I would stick with them just for the reason Eric mentioned.



-Scott

 

[Texas Diesel]

Then again they may be supplying the lowest cost parts that barely meet the needs

 

[KevinO]

The way things are now days with that type of application they are probably strong enough draw tite wouldn't want to be sued by everyone loosing their loads by weak bolts. just my . 02

 

[jarsong]

Originally posted by WM-300

Today I had a Draw Tite Gooseneck hitch put on my 2003 Ram CTD. Its uses the Draw Tite Frame plates, rails and the Removable Ball. All hardware supplied is Grade 5. The manual even states its Grade 5. Is Grade 5 strong enough, I would have used Grade 8 had I installed it. The side plates on the frame rails use only (2) 1/2" bolts per side.



If it would be safer, I would rather take the time to replace the Grade 5 with Grade 8 but I may be missing some important engineering Draw Tite did. The Hitch is rated for 30,000#



Thanks

Paul

I talked to my hitch installer about this. He said it had something to do about shear strenght and breaking instead of Bending. He then showed be a picture of a Burb and a large trailer that bit the dust laying on it side after getting thrashed and bent. Still hooked together. He said, see, you want it to bend not break. I said ok...

jarsong

 

[Joseph Donnelly]

Another example--

The Drawtite ultra frame hitch on my 97 uses four 9/16" diameter bolts on each frame rail. They are grade 5. They could have avoided the need to drill out the frame holes and used grade 8 bolts in 1/2" instead. They went with the bigger grade 5s for the bend vs. snap reason, I suspect. Similarly, when Lakewood bellhousings and block plates became popular in the 1960s and 1970s, grade 5 bolts were supplied and we were told not to "upgrade" to grade 8 because 5s would bend instead of snapping if the clutch exploded.

 

[RustyJC]

Although a Grade 8 bolt will have a higher ultimate tensile strength, it will have less ductility (% elongation before failure) than a "softer" Grade 5 bolt. That is, the Grade 8 bolt will tend to fracture rather than elongate. Depending on the application, ductility may be more important than ultimate tensile strength - in that case, the designer may go with more or larger Grade 5 bolts to get the required strength and have the advantage of greater ductility.



Rusty

 

[Mschevey]

Agree with above comments.

I spent weeks trying to explain this to a local farmer I did a lot of work with. He was always pushing his bailer to the max and breaking shear pins (1/4 bolt). He thought by using "strong" grade 8 bolts it would transfer more torque before shearing.



Well when I finally got him to go "generic" bolts for the shear pins, he would run much longer before one would break. Some times when you stopped you could see the bolt was bent significantly but it had not broke.



A lot of work is used in specifying fasteners. In general the stronger it is, the more likely it is to brake, not bend.



Mike Schevey

 

[SRadke]

If a shear pin is actaully shearing a grade 8 will be stronger. They have higher shear strength. If it bends and breaks, something softer may be better.



-Scott

 

[Casey Balvert]

Pullrite specifies grade 5 bolts as well. Works for me.

 

[wsurf]

RustyJC is correct. Stronger is a relative term (ultimate, shear, bending, etc). I would think that with the correct torque applied to grade 5, thus preloading the bolt and providing strength, that the bolt would still be allowed to "move" when in service. If they wanted things that strong they would weld everything together.

 

[Fireman]

Paul,



I think we all tend to think that way, especally on something that carries the weight and pushing and pulling forces that a hitch does. On the surface if gr5 is good then gr8 would be better or if 20. 5 is good then 25. 5 would be better . But if the manufacturer specifies gr5 and supplies gr5 trust him, I'll bet he put a little bit of engeneering into it. I think everybody pretty well "nailed it" on the strength vs ductility.



Just a 12th opinion, like you really needed it

Fireman

 

[RustyJC]

Have you seen photos of trucks pulling 5th wheel RV's that have been in a major accident? Many times, the hitch will be deformed but I've never seen one detach from the truck (I'm sure they have, I've just never seen it personally). The hitch designer wants the hitch to stay with the truck, come what may! Therefore, he would rather have a bolt that stretches and releases its preload but stays intact if overstressed (that is, a more ductile Grade 5 bolt) rather than a more brittle bolt that will likely fracture and release the hitch if overstressed (like a higher UTS but less ductile Grade 8 bolt).



Rusty

 

[BV]

Rusty and the others are right on track - Hitch manufactures design the attaching hardware to bend and twist long before they tear, snap or sheer off. I personally like the idea of a hitch staying with the rig during an emergency maneuver or accident.

 

[rrausch]

All the above arguments are mute IF the bolts in question are of Chinese origin.

I've had Chinese metallurgy fail inexplicably, usually by snapping under medium torque. It has gotten to the point that I made a decision to NEVER put my life at risk with a Chinese bolt. If I am working under a load, it will be an American Hardware that holds that load.

 

[wsurf]

RRausch, interesting, how do you tell it is a Chinese bolt. I'm sure they do not have to make them to any standards such as SAE (?)

 

[rrausch]

I try to look at the box they came in whenever possible. Then too, Chinese Hardware all has a certain "look" to it, and American Made, to my eye, has a huskier, different look to it. Hard to explain, but I can usually pick out U. S. A. hardware made over foreign, but it's easier if you can see the boxes.