Are Grade 8 bolts overkill for the front bumper?

UKTJ

UKTJ

TJ Addict
Joined
Dec 30, 2020
Messages
1,233
Location
Hampshire, UK
In another thread there was discussion about the difficulty of sourcing longer bolts for attaching the front bumper to the frame if you are adding tow hooks and are based outside the US. Basically it is really hard to find anything that is grade 8 and the correct size / thread. On another recent bolt question somebody helpfully pointed me at www.jeephardware.com. They had the other bolts I needed, but have a flat rate shipping cost that doubled the cost, so I looked to see if they did the longer bolts I needed for the bumper to spread the shipping cost over more items. I found these...

https://jeephardware.com/product/1-ea-1997-to-2006-jeep-wrangler-tj-front-bumper-torx-bolt/
What surprises me is that in the description it says they are grade 5, I had expected grade 8. My question therefore is whether grade 8 is overkill, or are the bolts in the link not up to the job? Any thoughts welcome.
 
Grade 8 is not necessary, Grade 5 is what they should be. I don't think a Grade 8 bolt would hurt, but it certainly isn't needed.
 
  • Like
Reactions: UKTJ
Chris said:
Grade 8 is not necessary, Grade 5 is what they should be. I don't think a Grade 8 bolt would hurt, but it certainly isn't needed.
Click to expand...
Thanks Chris. I was thinking that just to hold the bumper on grade 5 would be fine, but that for attaching the tow hook the stress would be greater and thus the need for grade 8. Finding grade 5 in the size needed is much easier over here than findjng grade 8, so that is good news.
 
I have no experience other than reading the internet, so take this with a mountain of salt.

But I think how grade 5 vs grade 8 bolts fail is different. Like grade 5 will yield more before breaking, but grade 8 will have higher strength. So it might depend on what you want to break first: do you want the bolts to yield and go, or do you want to twist something else?
 
  • Like
Reactions: UKTJ
Jerry Bransford said:
For just holding the bumpers on Grade 5 is fine. If you are installing aftermarket recovery hooks on top of the front bumper I'd go Grade 8 for the longer bolts that pass through them .
Click to expand...
That was my thinking too Jerry, but the bolts I linked to are specifcally sold as being longer and for holding recovery hooks?

IIRC in the US the TJ came as standard with recovery hooks, in the UK it had a loop recovery thingy on one side only. So do you know if the OEM bolts are grade 5 or grade 8? I can't see any markings on the ones on my TJ to say one way or the other.
 
Whatever you decide I find boltdepot.com is a good source. I've also had good luck with the clearance and sale prices at Grainger although I probably wouldn't pay their normal prices. You don't need 8 or 10.9 because you are running hooks, it doesn't change the math in a significant way. Washers don't change the strength of a fastener and neither do hooks since they don't really compress.
 
  • Like
Reactions: UKTJ
UKTJ said:
That was my thinking too Jerry, but the bolts I linked to are specifcally sold as being longer and for holding recovery hooks?

IIRC in the US the TJ came as standard with recovery hooks, in the UK it had a loop recovery thingy on one side only. So do you know if the OEM bolts are grade 5 or grade 8? I can't see any markings on the ones on my TJ to say one way or the other.
Click to expand...
The OE bumper bolts are Grade 5. Grade 8 gets recommended when installing aftermarket recovery hooks that add an inch of bolt length. It was found that longer bolt can bend in some recoveries when it's a Grade 5 which is why Grade 8 is commonly recommended.
 
  • Like
Reactions: MillenniumFalcon, Modoc Guy and UKTJ
pagrey said:
Whatever you decide I find boltdepot.com is a good source. I've also had good luck with the clearance and sale prices at Grainger although I probably wouldn't pay their normal prices. You don't need 8 or 10.9 because you are running hooks, it doesn't change the math in a significant way. Washers don't change the strength of a fastener and neither do hooks since they don't really compress.
Click to expand...
I'm not an engineer, so maybe I am thinking about it in the wrong way. But the logic to me was that the bolt with just a bumper is under little stress, the job of the bumper is to deal with impact and in that situation the forces will be pushing on the bumper and the frame, so the bolt would not be dealing with much. If a tow hook is in place and being used the forces are pulling on the hook and therefore the bolt holding the hook in place. Intuitively that felt like it would be putting the bolt under more stress, but like I say I am not an engineer.
 
Jerry Bransford said:
The OE bumper bolts are Grade 5. Grade 8 gets recommended when installing aftermarket recovery hooks that add an inch of bolt length. It was found that longer bolt can bend in some recoveries when it's a Grade 5 which is why Grade 8 is commonly recommended.
Click to expand...
OK, so if the additional length of bolt is less than an inch grade 5 would be fine?
 
  • Like
Reactions: Chris
Chris said:
Grade 8 is not necessary, Grade 5 is what they should be. I don't think a Grade 8 bolt would hurt, but it certainly isn't needed.
Click to expand...
Grade 5 is a bit "softer", and my winch specifically calls for grade 5 over 8.

Grade 8 has a greater shear strength (lateral hold) but can be more brittle.
 
  • Like
Reactions: Chris
Grade 5 hardware is appropriate to hold a winch, that's what Warn provides.

But for an aftermarket tow hook that has additional leverage over the longer bolt it requires, Grade 8 is my standard recommendation since Grade 5 bolts in that position can bend during recoveries.
 
  • Like
Reactions: Moon Eyes
Jerry Bransford said:
Grade 5 hardware is appropriate to hold a winch, that's what Warn provides.

But for an aftermarket tow hook that has additional leverage over the longer bolt it requires, Grade 8 is my standard recommendation since Grade 5 bolts in that position can bend during recoveries.
Click to expand...
I am a bit confused, if I understand the standard US issue TJ came with tow hooks held on with grade 5 bolts. If the after market hooks are no thicker than the OEM ones, would the same grade 5 bolts be OK?

On a UK issue TJ there is no hook on one side and a loop on the other that is less 'chunky' than the US standard issue hook. I am now wondering if Jeep would have bothered using a shorter bolt on UK models, or just used the same longer ones used on US models, so maybe they are long enough to go through an after market recovery hook if it is no thicker than the OEM ones. 🤔
 
UKTJ said:
I am a bit confused, if I understand the standard US issue TJ came with tow hooks held on with grade 5 bolts. If the after market hooks are no thicker than the OEM ones, would the same grade 5 bolts be OK?

On a UK issue TJ there is no hook on one side and a loop on the other that is less 'chunky' than the US standard issue hook. I am now wondering if Jeep would have bothered using a shorter bolt on UK models, or just used the same longer ones used on US models, so maybe they are long enough to go through an after market recovery hook if it is no thicker than the OEM ones. 🤔
Click to expand...
If your using the item within the parameters as designed... go with what manufacturer says to use.

Grade 8 will pretty much cover what your trying to do, and then some.... but just know that mechanical anchoring has a lot of variables and nuances.

Just cuz the hold strength is greater..
Doesnt mean it is best for that application.


Summary...
1. Use what manufactuer says to use.
2. Grade 8 is very likely appropriate to use, but not always.
 
Last edited:
UKTJ said:
I am a bit confused, if I understand the standard US issue TJ came with tow hooks held on with grade 5 bolts. If the after market hooks are no thicker than the OEM ones, would the same grade 5 bolts be OK?
Click to expand...
OEM tow hooks have a low profile and can use the factory length bolts. The aftermarket tow hooks I am used to installing have a significantly heavier base and require 1" longer bolts. A longer bolt has more leverage against what it is threaded into which is why, again, they can bend when in a difficult recovery.

Like this one...

Capture.JPG



If you're using a Mopar or similar hook a Grade 5 is fine. If you're using a heavier-duty recovery hook like the above use a Grade 8 bolt.
 
  • Like
Reactions: UKTJ
Top Bottom
Back