REAR RECOVERY HOOK

[holden]

Hi All,

Thought I would share this with you guys.

This is the rear view of the recovery monut. Can allso see my 3" body lift and tank lift.


I drilled out the the old holes that were not storng enough and welded crush tubes in there.


Top view I put a 10mm think plate along the back of the chasses so that it has to brake somthing really bad to get it off. Not that I want somthing to brake.


The 2 bolts on each end are there to help hold the 10mm plate on.






Kane

[sprey]

looks good as.
gonna get the hooks done on my vehicross soon shame it isnt as easy to mod as the mu.

tho ill prob go with a rear hitch and slide in hook.

[supamu]

Looks good. Here's ours, still some finishing to do.

[holden]

Thats one big bumper. you might need a new tow hook. But looking good. Its a great way to mount a tow hook.

[Demonic]

I got my design from seeing daisys hook, Seems we are all doing the same though. Like to show you mine before I mount it up to the Mu.

The mounting plate (backing plate, hook mount and gussets) is 12mm steel that was welded at MetalWorks in wellington then takin to work and hardened by one of the heavy steel welders at work, I Fab'd it all except for the welding as our welders were not powerful enough to get enough penatration into 12mm plate, hench why i never got my welding tickets


Below is the Full kit, it has crush tubes and 12.9HT Cap bolts, the backing plate is 200mm x 90mm x 6mm plate, and 5mm square washers on the back of that, The round washers are 5mm thick aswell, but due to the amount of weld on the mounting plate they required a small amount of modification


They dont call me Mr Over-engineering for nothing you know.

[geeves]

Supamu. Your hook looks like a cast truck hook. Several years ago one of the clubs I belong to did a lot of testing. The truck hooks break instead of bending although it was at a force beyond what should ever be used. The only hooks that bent were the hooks with a 10000 pound rateing and sold as recovery hooks. There are hooks sold as recovery hooks by a certain large retailer with a 4500kg rateing These broke.

[Demonic]

Do you think that Supamus mounting bracket would be substancial(?) enough for a revovery?

@Supamu, not intending to be nasty, just wondering about it due to the "forces" its would be put under for recovery.

[geeves]

Im no engineer. Its lighter than Daisys and yours but stlill looks to be 8mm for the main tongue and 5 for the gussets. In the flesh its probably ok as long as the welds are as good as they look to be but the advice of the local 4wd club safety officer will confirm. Also cant see how its attached so cant comment.
If I wanted this style of attachment I would go the heavy way even if only for piece of mind

[Demonic]

Fair enough. I know CCVC has quite strick guidelines and the way Supamu has made it was going to be the same way i was gonna go, but it seemed to thin to be accepted in a club situation.

[supamu]

It's all done with 12mm steel, except for the plate on the front is 8mm and the plate behind the chasis is 8mm. bolted through with 4 12mm bolts and a 14mm bolt directly behind the hook. All high tensile bolts. The hook is a cast hook off a large truck, unsure of hook rating.

[geeves]

Should be ok for the bracket. CCVC did some testing on hooks and the cast truck hooks broke at 13 tonne. You should never be useing that force unless you are doing something very wrong but the issue is it broke instead of straightening which is what you really want to happen if it goes pear shaped. Ive seen a hook straighten Its not pretty but at least theres no hunks of metal flying around

[mulover]

Demonic, I wouldn't be using that higher tensile bolt, they are alot more brittle than 8.8 and hence can't handle shock loading. everyone I know don't use anything over a grade 8.8.
Also just wondering why you got your mount hardened??

[Yarno]

Demonic, I wouldn't be using that higher tensile bolt, they are alot more brittle than 8.8 and hence can't handle shock loading. everyone I know don't use anything over a grade 8.8.
Also just wondering why you got your mount hardened??

Wrong, the higher the tensile strength the more the bolt can take before it breaks.

http://www.sciencedaily.com/articles/t/tensile_strength.htm

http://en.wikipedia.org/wiki/Tensile_strength

[Demonic]

Yeah, i asked an engineer about the bolt, he suggested Cap bolts @12.9, but i know what you saying. Also the only reason I got it hardened was .. well because the guy asked me if i wanted to.. lol... seemed a good idea at the time

[mulover]

Yarno, Sorry to say but you are not right. the harder the bolt, yes the more tensile force the bolt can take but only in when it is being stretched. Tensile strength is a measure of how much "stretch" an item can take before it is permanitly deformed. ie you can tighten a higher tensile bolt more than an ordinary bolt before it stretches/breaks. This is why I use high tensile cap head bolts to hold my front hubs on as they don't stretch.

How ever, the harder an item, the more brittle it is, hence anything higher than a grade 10.8 cannot hande shock loads as it is so hard it has no "give" in it and will break. This is why they don't make cutting edges for bulldozers or graders any harder as they would be so hard they would shatter.

Demonic, Getting the mount hardened won't hurt, but again, having a bit of give in the metal is better as alot of the time if it is over loaded, it will bend so you can see its damaged. If its harder then it may just break giving you no warning.

[jezza]

Caterpillar use grade 14.9 bolts for the tracks and I would like to think that they know what they are doing. When I redo my rear hook I'm planning on using 12.9 Cat cap bolts, only reason grade 14.9 bolts is because Cat don't have a listing for anything under 16mm.

[mulover]

Caterpillar may well use that harder bolt, I'm guessing your talking about holding on the track plates?
As hard to believe as it may be, these plates aren't subjected to as much shock loading as the bolts holding on your hooks.

[supamu]

Agree, the harder it is, the more brittle it is. An example of that would be no. 8 wire compared to the high tensile fencing wire we use now days. no8 wire is easier to bend, high tensile wire harder to bend and can be snapped off, yet a stronger tensile strength. So all depend on the type of forces we are putting on the bolts that hold the hooks on. We've used 8.8, but I'm no expert on these things.

[jezza]

Just to stir it up more. Yes lower graded bolts have a greater sheer strength than high grade bolts but the bolts are there to provide clamp load, all the shear forces are taken by friction where the two parts meet. So there isn't a large amount of shear load, if they are torqued up correctly.

[mulover]

LOL, I do agree with you to an extent there jezza, but as not all loads are applied in a direct line with the bolts, usually from all angles in a recovery situation, the bolts are subjected to multipul stresses and shock loading which they can't handle as well as a lower tensile bolt.
It comes down to the fact that 10.8 or higher bolts can't handle shock loadings that are applied in a recovery situation.