[Ridin]

I'm a bit confused.. or maybe I'm picturing the use of the anti crush tubes wrong.. But, What difference will anti crush tubes make here? Aren't they only intended to stop the bolts over tightening and crushing the chassis rail? The bolts will still be trying to shear through the chassis rail all the same, I don't see how it will strengthen the connection?

[zukenutter]

Every time you do a recovery without them the load on the hook will pull the top plate down against the top of the chassis, the only resistance (strength) is in that part of the fitment. Using crush tubes will spread the load between top and bottom plates and chassis surfaces virtually doubling the strength of the mounting method.

[Jim_Aus]

i just bolted mine to the bottom of the rail.....

until i figure out a proper way to mount it....

maybe fab up a sleeve that bolts over the chassis rail... idk yet.

im sure theres some one on here whos an expert..

[pete_79]

Wow, I go away camping for a few days and this conversation takes off.


This whole concept was to have something that was safe and simple to do for people with no fabrication or welding skills.
After reading a lot of the discussions on this subject and seeing some terrible ideas I thought I'd try something myself.

My thoughts on crush tubes was that they had to be welded in place to be effective. For me as a boilermaker with nearly 20 years of fabrication experience, I would hope that welding a couple of crush tubes is not a big concern.
But I wanted to do something using off the shelf items designed for the job that was really easy to do and others could copy.

I thought the 3mm top plate would be enough to protect the chassis from deforming when using this hook as it was intended. But if the design can be improved and make it even safer, then I'm happy to take on board the constructive ideas that have been offered up now.

jdk81 wrote:

You managed to drill holes already, so whats the challenge?
Find some tube suitable size and cut to length, then run a drill through the chassis from the bottom, and bolt it all up.
About the only challenge would be holding things in place while bolting it together.

This sounds like the best solution so I had to draw it to make sure I understand correctly.
Is this what you mean with the top of crush tube on the chassis and the bottom of the tube on the hook?

[zukenutter]

^ that's what I was picturing except I like the addition of the plate top and bottom as you already had

[Jim_Aus]

looks good to me.....

[Ridin]

Because the bottom of crush tubes are bearing down on the hook and not the chassis, if the hook pulls downwards and deforms the top of the chassis, the crush tubes are doing nothing to resist the pull down on the nuts at the top because they will move with the hook.

I think the most likely part to fail would be the bolts shearing through (or elongating) the two holes in the bottom part of the chassis, I would want to strengthen that part somehow.

[jdk81]

That's about what I was thinking, but I still don't like it (without welding)

I would use the 3mm plates you already have, make the tubes a little under sized (it may be tricky to get correct due to chassis profile), and keep the tolerances between bolt-crush tube-chassis as tight as possible.

If it was me, I would probably cut the front bar mount off, insert the crush tubes, then reattach front bar mount.
It would probably be easier to work out how to make that bar mount bolt on, so its easy to remove and install crush tubes, and replace.

[Jim_Aus]

i just cut the bottom tab off... can fold it up and down now....

would it really matter what crush tube you used. i got a heap of aluminium pool fencing laying around....

[Zook_Fan]

The point of a crush tube is to provide enough strength so the bolt can be adequately tensioned. The inside diameter should be a very close fit for the diameter of the bolt. Considering this is for a recovery I would want the bolt to be tensioned correctly, I don't think that aluminium pool fencing that is laying around will be strong enough to withstand the compression of the bolt. So yes it matters. I'd be using steel with a 2mm wall at the absolute minimum.

[jdk81]

Jim_Aus wrote:

i just cut the bottom tab off... can fold it up and down now....

That's exactly what I was thinking. I would either weld it, or possibly screw/bolt a bit of angle to support it once bent back into place

[Jim_Aus]

i just left it.... how much tension are you putting on these bolts ??? if your deforming the chassis surely thats to tight.....

[atari4x4]

Gwagensteve wrote:

Torque for a dry m12 8.8 bolt is 88Nm. That's a lot of crush force on the chassis. If the chassis deforms at all then clamping force is reduced, putting the load on the bolts into shear.

[Steven B]

Well i thought id come back and show what ive done considering i got the idea from auszookers, though its 20 months later !!!!
My excuse is that ive only just got a laptop so can manage my photos properly now (been using a phone and a tablet for too long).

I copied Pete's design but fastened the hook to the side rather than the bottom because i didnt want to (or have an angle grinder at the time) alter the tab on the chassis end plate. Also i feel using the narrower section of chassis is gonna be stronger, less chance of twisting compared to long bolts and long crush tubes.
Im considering doing an identical one on the drivers side chassis, that way i can snatch from both sides at once if needed so they will be sharing the load.

Wire brushed up, primed, painted black.


The bolt + crush tube.


Rated bolts (The highest we had at work)


The drilled holes (and primed to stop rust)


Other side


Used long nosed pliers to get the crush tubes in place, i needed 3 hands to do this without getting angry.
Also used a piece of steel as a spacer plate because the recovery point didnt quite sit flush against the chassis end plate, spacing it out 1.5mm was perfect.
I also used a spacer plate on the inside cavity of the chassis to allow me to have the crush tubes 1.5mm shorter than needed to allow easier movement inside the chassis while turning/twisting into place (This was where i needed 3 hands,lining it all up and pushing the bolt through).






Might put a reinforcing plate here rather than just 2 washers ???


I guestimated the hole in the bumper, made a few pilot holes with a 12mm drill and joined them up with a file, and neatened it up.
I made the hole a bit bigger than Pete's (The OP) so if i snatched sideways slightly the snatchstrap wont interfere with the bumper.