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How To Make A Bomb-proof Snatch Tow Point


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Another Phoenix rises from the ashes .... :lol:

Edited out some of the "padding" BTW

Sadly I now have a Td5 chassis which is made of Bacofoil and far harder to do a proper job on :(

----

scl

A while ago, in response to a question, I said I would post some pictures up on what I consider to be the way to make a virtually indestructible rear towing point suitable for snatch recovery etc.

Note that this post only applies to pre 99MY Defender and 90/110 vehicles, later models (Td5 age onwards) have an entirely different rear crossmember, far weaker in its design, and need a different approach to make suitable for snatch recovery. You must also be absolutely certain that the rear crossmember of your vehicle is 100% sound.

To start with you need the following heap of bits:

22142899lg.jpg

1 x NATO 4.07 tonne military spec towing pintle (shown here in bits, not all the bolts are shown in the picture)

2 x bits of good quality steel plate approx 190x110mm and at least 8mm thick

4 x M12 high tensile bolts, 8.8 grade or higher, nuts and washers to match

1 x Defender (obviously )

The above size of metal plate is as big as can be fitted in to the inside of the crossmember, which is what you need, as big as possible to spread the load. My bits were pre-drilled to suit a NATO hitch. I used 8mm steel plate and 8.8 grade bolts; to make it even stronger you could use 10.9 or 12.9 grade bolts, and thicker plate (although this is only really worthwhile for the inner bit) - you'll need longer bolts as well of course. It goes without saying that the nuts need to be the same grade as the bolts.

Fit the blue plate inside the rear crossmember. Why is it blue you ask? Because I had some Stratos Blue paint left over from my old 90 which I thought I might as well use.

Put the bolts through the NATO hitch, then through the outer plate (the black one in my photos) then through the crossmember, then through the inner (blue) plate, then some washers and finally nuts. I used Nyloc nuts but you can also use doubled up ordinary nuts locked together. Do everything up just tight at first to get it all seated in place, then wind the nuts up about as tight as you can get them with an ordinary combination spanner. You won't distort that bit of 8mm plate, and you really don't want them to come loose!

After this is all done, it is best to give the whole lot a good coat of paint. This will prevent moisture getting in - there was a lot of surface rust on my crossmember under the NATO hitch when I took it off, although nothing serious. I used some matt black brush on paint, which gives a finish I like for the crossmember and hitch.

The finished product from the inside:

22142896lg.jpg

and from the outside:

22142897lg.jpg

The function of the outer plate, for anybody who might be wondering "what is the point", is to spread any sideways forces generated on anything other than a straight pull back, and stop the crossmember distorting. Otherwise you can bend the crossmember slightly, then the bolts are loose and that's when large lumps of metal can start flying round rather too quickly to be healthy!

Now go and pull something ... but be wary of others because yours is probably now stronger than theirs which means if theirs isn't up to scratch, it'll be you getting the bumper round the back of the head

Always use snatch recovery with caution and preferably only if you know what you are doing, and know the other vehicles towing points are as good as this.

But if you manage to rip this setup out of the back end, you're either using a chain or trying far too hard! I know from experience that I can take off absolutely flat out in 3rd low difflock on the end of 10-12m of nylon rope and this won't even blink.

I hope somebody finds this useful!

Hybrid_from_Hell

Steve,

Absolutely spot on !....nice bit of work and info for many.

There is still the risk of the crossmember distorting, for even more bomproofness there are 3 holes under the bottom face of the Crossmember near the hitch....

(these are often used to mount drop tow units)...

If you drill and bolt onto this a large )5mm / 6mm thick) angle, then at the ends fabricate a mount, this can then be bolted to the mounting lugs on the actual chassis rails each side about 14 inch inbord of the back of the 90...

This way you in effect end up with a Triangluted frame between the Hitch and the chassis legs...

Depends just how bullet proof you wnat to go, but if you have those quiet moments !...........

Nige

scl

Nige,

Yes, there's a few ways of making it even stronger -- using a bit of U-section behind the crossmember instead of plate, doing what you suggest, or even going the whole hog and welding a huge bit across the whole back end between the chassis legs, and welding another bit onto the outside of the crossmember. Might need some heavier rear springs then though...

However, making it as I did it above, I know will comfortably stand any sort of pull that I will feel happy doing, bearing in mind the likely strength of most recovery points on most vehicles and my desire to prolong my existence.

Venturing into the sort of brutality that would twist a whole back crossmember with only a tow rope is definitely too close to the "death" side of "life or death" for me!

mark90

Stephen, you say M12 bolts for the NATO hitch, I've heard a few people say this. Are there different sized holes on some NATO's? I always used to think they where M14, when I fitted mine a few months ago M14 bolts fitted, and it is the stadard LR sized NATO hitch not the big truck version. The cross sectional area of an M14 is about 30% bigger than an M12 and hence should be about 30% stronger, so worth using M14 if they fit.

scl

I think they are normally fitted with either M12 or 0.5 inch, I don't know if I would have got M14s through the holes in mine, certainly the ex-military backing plates are drilled for M12s but I shall investigate - anything that makes it stronger has to be a good thing as you say, as the bolts are probably the weak (least strong!) point. Not sure where I might find an M14 bolt at the mo' but I'll have a scratch around.

The bigger NATO hitch (7 tonne?) has a different bolt spacing and AFAIK won't fit onto the standard holes in a LR chassis, so I think there is only one type that will fit easily.

MOG, sorry I missed yours first time around, happy for that but some other way of hosting the photos will be needed as the Photoisland links will expire in 3 months and at the moment I don't have anywhere to put them ... without the photos it would be of limited use.

western

The bigger NATO hitch (7 tonne?) has a different bolt spacing and AFAIK won't fit onto the standard holes in a LR chassis, so I think there is only one type.

have a look here-- Dixon Bate Pintles

absolutly right, the next size up of NATO pintle is for fitting to trucks i.e. Bedford\LeylandDAF 4 tonners it's rated at 10 tonne, far to big to fit a LR's rear crossmember

Ralph,M3WRM, '89,110CSW-200Tdi\R380.

scl

it's rated at 10 tonne, far to big to fit a LR's rear crossmember

Oh I don't know, if one was feeling ambitious!

On the M12 vs M14 question, I see the Dixon-Bate site says M12 fixing bolts. I can't find a loose NATO around to measure the hole dia, but the holes in the back crossmember of one of the 110s at work (1996 model 300Tdi) are only 13.5mm according to my calipers, and an M14 bolt is exactly 14mm. So I guess you could fit M14s, but you'd need to run a drill through the holes. Mark, I suspect your hitch may have been drilled out to accept the bigger bolts at some point? When I find a hitch that isn't attached to a vehicle I'll see if an M14 will go through. It's certainly possible and not a bad idea at all but it looks like it would need some extra work.

Also, on a Td5 age onwards, if you fit a NATO to the rear crossmember with the Land Rover "reinforcing" kit (not my idea of reinforcement but there you go!) you have to use M12s because the threaded holes in the chassis are that size. However new Defender chassis are not suitable for heavy use without further modification the back end is far too thin and easily bend even with the LR kit fitted.

Also on the Dixon-Bate site I see the tensile strength of the 4.07 tonne NATO is 22 tonnes. I think that should be sufficient! No wonder I have never seen one break...

... and no wonder they cost an arm and a leg to buy new!

mark90

M14 vs M12......

I don't think my NATO hitch had been drilled out to take bigger bolts, unless it was a very neat job, looked totally original and unmolsted.

Don't know about chassis holes as mine is not bolted direct to the chassis as it didn't have the NATO hitch holes, and being a galv chassis I wasn't too keen to drill it. So my NATO hitch is bolted to a 10mm plate which had 14.5mm holes drilled in for the hitch bolts, as I'd already checked M14 bolts will go through the hitch ok. There is then another 10mm plate behind this which acts as a spacer for the bolt heads (the bolts face backwards and are double nutted on the outside). Both these plates are then bolted to the crossmember using the existing holes, with backinbg plates behind. Looks like this.....

alf-hitch.jpg

scl

Ah, didn't realise you were talking about a Series, now I see what you mean.

It appears that the M14s won't fit to a 90/110/Defender chassis then, without minor modifications. I'll probably stick with the M12s in mine as I haven't lost one yet.

Does anyone know the tensile strength of an M12 8.8 bolt? Just wondering how much is needed to break four off...

Silvio

The first digit indicates the traction resistance, in 100N/mm2: so an 8.8 has a traction resistance break limit of 800 N per square millimeter. The square section of a M12 bolt is about 84 sq.mm, so do your calculation. More significant is the second digit, which indicates the factor by which you find the limit beyond which the bolt is irreversibly stretched and begins yielding: in the case of a .8 bolt, this factor is 0.8, so take the 800 N/sqmm and multiply it by 0.8, you'll get the safe extension limit, that is 640 N/mm2.

In a 12.9 bolt, the break limit is 1200 N/mm2, the extension limit is 1200 x 0.9, that is 1080 N/mm2.

Everything clear?

scl

Hmmm.... ok but I make the cross section of a 12mm bolt about 113mm2 - IIRC from skool, area is pi.r2 ie 3.142x6x6=113?

So it would be 113x800x0.8=72320 which I think should be 7232kg? So four of them should be about 29 tonnes which I think ought to be strong enough

Thanks

Silvio

No Steve, you cannot calculate the section out of 12 mm, and so 6x6x3,14 (radiusxradiusx3,14): you must consider the depth of the threads, which are cut into the bolt and reduce its useful section: and in fact the actual section depends on the thread used, and varies slightly, for M 12 with 1,75 thread is 84,3 sq.mm, with 1,5 thread is 88,1 sq.mm.

Everything clear?

scl

aaargh! Too complicated!

But, that will still add up to around 21.35 tonnes tensile strength across all four bolts, which should still keep it in place as the tow rope ought to break at about 12 (24mm nylon), and I haven't snapped one of them yet...

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