Tow hook discovery

[Bertram65]

My trucks did not come with tow hooks so I was planning on buying a set. I looked on eBay and found several sets of new hooks only, one set without any bolts was buy it now for $65, I was going to buy it but I figured with the shipping and then having to find the grade 8 bolts I might as well buy them from the dealer for $115. I also called the on-line places but they were not any cheaper when you added in shipping because they are so heavy. So I got the tow hook kit from the dealer, when I picked it up I asked if the mounting hardware was with it, the counter guy said he thought so as it was a "kit". Yesterday I decided to install them, turns out there are 4 brackets that come with the hooks that tie them back into the frame, the install was kind of a pain because you have to unbolt the intercooler and lift it up slightly, the point of all this is if I had bought the hooks off of eBay they would not have come with the 4 brackets although they would bolt right on without them, I would not have known there were additional brackets, probably the 1st time I would have used them they would have tore the front brackets and the hooks right off the truck, so if you are going to buy the hooks be sure you get the brackets as well. The kit also came with all the bolts.

 

[lschultz]

Thanks for the info. Mine came with them on.

 

[Steve St.Laurent]

FYI - you would not want to use grade 8 bolts on an application like tow hooks. Grade 8 bolts are strong in tension but brittle in shear. In an application where you are depending on the shear strength of the bolt you want to use grade 5.

 

[Tony T.]

Tow Hooks

I have also thought about getting the tow hooks also, but still undecided at this time. Thinking maybe a front hidden receiver hitch if they have one yet for the 3G's. Also if I'm not mistaken I seen where I believe one of the TDR members were chrome plating the hooks and doing a trade for yours an some cash.





Tony

 

[mrsnow]

That IS good info as I was thinking about getting them off of eBay.

 

[JHardwick]

FYI - you would not want to use grade 8 bolts on an application like tow hooks. Grade 8 bolts are strong in tension but brittle in shear. In an application where you are depending on the shear strength of the bolt you want to use grade 5.

I don't want to :-{} , but this is not accurate

 

[Steve St.Laurent]

This is what I've always understood and what was passed down to me. After further research I see that you are correct in that my explanation is not correct in that a grade 8 does in fact have a higher shear and tensile strength - however it is still more brittle. The advantage of using a grade 5 in an application like a tow hook is that the bolt will stretch before it fails allowing you to detect failure as it's stressed whereas a grade 8 will be more likely to break. Here's what I found on the net on it:

Todd Gorski wrote:



> For installations requiring shear strength, force is perpendicular to

> the bolt, grade 5 is normally better.

> For tensile strength, force is parallel to the bolt, grade 8 is better.

> This is because a grade 8 is more brittle and is more likely to snap if

> its is overloaded whereas a grade 5 is more likely to deform rather than

> break.



To which Chase Gregory added:



>I agree totally! Just about all winch hardware is grade 5 as is most

>bumper and tow hook hardware. Some go to grade 8 thinking it's an

>upgrade, but may in fact be worse depening on application.



I remember when this whole GR5 vs. GR8 thread started on the list a year or

so back, alarm bells started going off in my head. I've never liked this

different grades for shear vs. tension theory that's developed, but I never

had the time to look up some info I wanted to include in my argument. Well,

I can't take it anymore. I have to speak out. I'd appreciate it if anyone

who's a practicing civil/mech/mmat engineer could comment on my diatribe.

Keep in mind it's been years since I've taken a materials science course so

my memory may be off. If it is, I want to know!



Actually, before I get rolling, I should say that Todd's explanation is the

most accurate I've seen to date. I only agree with his last sentance though.



Here we go:



GR8 have a higher ultimate strength than GR5. FACT. It doesn't

matter--shear/tension/torsion. A GR8 bolt will resist more force/torque

than a similarly sized/threaded GR5 bolt. The difference is that the GR8 is

MORE brittle. The GR8 bolt will give LESS warning as it approaches its

failure point.



Before I break out the charts, I should say that there is actually no such

thing as a failure in tension. If you try to pull something apart in pure

tension, it actually fails in shear on planes 45 degrees to the direction of

loading. The x-sectional failure planes look something like this:



/\

/F \

||

____

| |

| |

| |

| /\ |

|/ \|



/\

/ \

| |

| |

| |

|____|



||

\ F/

\/





So for loading in shear or tension, the material properties remain the same.



Here's a stress (force/unit area) strain (change in length/length) curve

(ascii-ified) for a brittle vs. a ductile material that kind of illustrates

what's happening. Note that the GR8 bolt won't behave in quite as brittle a

form as the curves indicate, but you should get the general idea.



S |

T | UX

R | B WHERE:

E | B UUUU B is the brittle curve

S | B DDD DDD D is the ductile curve

S | B DD X X is the point of failure

| B D U is the ultimate strength

| B D

| B D

| B D

| B D

| B D

| BD

|BD

|D______________________________

STRAIN



The curve shows the brittle material material behaving linearly. The more

ductile material starts out behaving linearly, but as it approaches its

ultimate strength, it starts to "neck" which means that the cross-sectional

area is reduced. At that point, the material stretches considerably for

very little increase in stress. Finally, the stress the material can resist

drops as it until it finally pulls apart.



What does all this mean in terms of bolts? Well, GR5 bolts DO have one

advantage for things such as tow hooks. If you put too much force on the

hooks, the bolts will distort so you can see that something is wrong. The

GR8 bolts will appear normal until much CLOSER to the point of failure.

That failure loading WILL be higher than for the GR5 bolts though. Still,

it is advantageous to have a warning of impending failure when a bolt that's

being loaded in tension, is it not? There should be NO differentiation

between bolt grades based on loading in shear and tension.



I should say at this point that my background is in Civil Engineering so

things that move frighten me (so hard to determine loadings) I hope there's

an SAE type out there that can expand on/correct what I've written.



The way I see the breakdown betwen GR5 and GR8 working is something like this:



If you can't anticipate/calculate the potential loading of the bolt (for

something like a tow hook that's going to be subjected to impact loads etc)

go with GR5 so you'll get more warning before it fails.



If you can design in a big enough Factor of Safety (FoS), you'll be better

off with a Gr8 bolt.

 

[JHardwick]

This is what I've always understood and what was passed down to me. After further research I see that you are correct in that my explanation is not correct in that a grade 8 does in fact have a higher shear and tensile strength - however it is still more brittle. The advantage of using a grade 5 in an application like a tow hook is that the bolt will stretch before it fails allowing you to detect failure as it's stressed whereas a grade 8 will be more likely to break. Here's what I found on the net on it:

I'll agree with that, the grade 5 does have more elongation than the grade 8.



IMO, knowing that the grade 5 will be broke well before the grade 8 will begin to yeild, and with the introduction of nylon tow straps ... ... ... . i'll go with the grade 8.



Perhaps back in the day when log chains were the norm, I'd have gone with the grade 5 ... ... ..... those old chains would hit hard, and shorter the harder



I miss the fun, but the Sunday morning clean-up was a real pain ... ... . get out the rain suit and goggles :-laf

 

[jsimpson]

Grade 8's don't yield; they snap. It's a lot easier to replace a stretched bolt than a snapped bolt. And I sure wouldn't want a tow hook rebounding toward me after theb grade 8 bolts snapped.

-bj



IMO, knowing that the grade 5 will be broke well before the grade 8 will begin to yeild, and with the introduction of nylon tow straps ... ... ... . i'll go with the grade 8.

 

[DocDetonancour]

My truck also came w/o the hooks. I wanted the matching grille in the spot where the hooks go, so I made my own brackets that are under the air dam. Like um better as if I need to tow the cable won't get near any paint. Doc

 

[diesel DOG]

by the time you snap grade 8 a bunch of other things will have given way. What does it take to shear one bolt?

 

[XJSuperman]

What difference does it make if the GR-5 will bend before breaking(shearing)?? The GR-8 is stonger in EVERY way... including SHEARING strength. So why not go with the better of the two?



And as for GR-8 breaking before bending... UH-UH. I have bent GR-8 bolt quite a few times... from 1/4" dia bolts all the way to 5/8" dia bolts.



You have to figure if the force is strong enough to shear the bolt... it doesn;t matter if it bends or not... because if the force is enough to shear it it's gonna shear... end of story whether or not the bolt bent is irrelevant.



Besides... you gonna stand close enough to see a bolt with that much tension on it to see if it bends... ??? I sure as hell hope not... I've been hit with a stray tow hook and I can tell ya... if I;d have been close enough to 'ask' the bolts if they were bending or breaking... I'd be dead most likely.

 

[JHardwick]

Grade 8's don't yield; they snap. It's a lot easier to replace a stretched bolt than a snapped bolt. And I sure wouldn't want a tow hook rebounding toward me after theb grade 8 bolts snapped.

-bj

Grade 8 bolts do yield actually. I've been a machinist for 20 years, and a few of those were running a machine shop in a foundry equipped with a lab for testing. Above machining the ductile iron and steel castings, we also had to machine the test bars for the lab to break ... ... ..... I guess I'm saying that I know a little bit about this, but may not be exact.



The 21st edition of the Machinery's Handbook (machinists Bible) says... ...

Grade 8:

130,000 psi yield strength

150,000 psi tensile strength



Grade 5:

92,000 psi yield strength

120,000 psi tensile strenght



What this tells me is a grade 5 bolt will become plastic (begin to stretch) at 92,000 psi and break at 120,000 psi. The bolt will hold 30. 4% more load once it begins to stretch before it breaks.



Once the grade 5 bolt breaks, you can add another 10,000 psi (8. 3%) before the grade 8 bolt begins to yield. Once at 130,000 psi, you can only add another 15. 4% before the grade 8 breaks at 150,000 psi.



Another way to look at it is this ... ... .



A grade 8 has a 41. 3% higher yield strength than a grade 5, but only a 25% higher tensile strength.



They also tested for elongation (% of length increase), and reduction of area (% of diameter shrinkage), but we don't need to get into that here.



I guess it's all in what you'r looking for, I don't like the word brittle here, but the grade 8 does have less elasticity.



One thing to remember when designing or backyard engineering, you always want the weakest part to be the cheapest. The tow hook is cheaper than a frame horn repair. And, 4 bolts are cheaper than a tow hook.



As I said before, with the tow straps not applying the shock that logs chains used to, I'd go with the grade 8 ... ... ... ... but, that's only my opinion.

 

[mgonske]

Well, not that it matters in light of all the above, but the factory tow hook mounting bolts on a 3G are loaded in tension, not shear

 

[Tomeygun]

My trucks did not come with tow hooks so I was planning on buying a set. I looked on eBay and found several sets of new hooks only, one set without any bolts was buy it now for $65, I was going to buy it but I figured with the shipping and then having to find the grade 8 bolts I might as well buy them from the dealer for $115. I also called the on-line places but they were not any cheaper when you added in shipping because they are so heavy. So I got the tow hook kit from the dealer, when I picked it up I asked if the mounting hardware was with it, the counter guy said he thought so as it was a "kit". Yesterday I decided to install them, turns out there are 4 brackets that come with the hooks that tie them back into the frame, the install was kind of a pain because you have to unbolt the intercooler and lift it up slightly, the point of all this is if I had bought the hooks off of eBay they would not have come with the 4 brackets although they would bolt right on without them, I would not have known there were additional brackets, probably the 1st time I would have used them they would have tore the front brackets and the hooks right off the truck, so if you are going to buy the hooks be sure you get the brackets as well. The kit also came with all the bolts.

Thank you for pointing this out, I have not used my hooks for anything over 2500lbs, but I am a bit worried now...





Good news:



Found the part numbers for the brackets = 55077316AD, 55077316AD



Bad news: They are around $100 a piece!!...



SO now I will have to check and see if the kit (part# 82207917) comes with the brackets, if not, than we can use the mopar website to tell us the rating:

Tow Hooks are rated with a towing capacity up to 5,500 pounds or 1. 5 times the vehicles GVWR (depending on vehicle). These tow hooks securely mount to the frame and are fully tested for durability and load capacity. http://www.mopar.com/m_acc_home. jsp?page_name=dodge

 

[Joseph Donnelly]

I am a bit nervous about jerking on the Ram from a corner of the frame. I made a front receiver hitch so I can spot a trailer into a tight parking place, or attach a tow strap to the center of the truck. Anyone thinking about force that could break the four grade whatever mounting bolts on a stock tow hook is really pulling on that corner.

 

[XJSuperman]

I doubt seriously they'd mount tow hooks on a vehicle that couldn;t handle the vehicle's weight provided the hooks are used properly... WAY too much liability there. Sort of like putting tires on a truck that were'nt rated for the MAX capacity of the truck and then some.

 

[WhiteSheep]

Hidden Hitch for G3s

I have also thought about getting the tow hooks also, but still undecided at this time. Thinking maybe a front hidden receiver hitch if they have one yet for the 3G's. Also if I'm not mistaken I seen where I believe one of the TDR members were chrome plating the hooks and doing a trade for yours an some cash.





Hidden Hitch sells a front receiver hitch for our G3s. I installed one as a front skid plate and so I could move my trailer around my yard easier. I ended up having my 4x4 shop, Fly-N-Hi, modify the hitch by moving the receiver part from below the cross member to above the cross member. It now pokes through the air dam and looks good. Stock it is below the air dam and seriously reduces the approach angle. It is rated at 9,000 lbs. I have factory tow hooks too. It cost more to have the hitch modified than I paid for the thing, but it is a much better installation.

 

[Grunt]

Marc... welcome to the forum.

Do you have any pictures of the receiver before/after modification?

 

[Bertram65]

The Dodge part number for the kit which includes 2 hooks, 4 brackets and 8 bolts and nuts is 82207917.