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Tow bar designs
https://www.ausmini.com/forums/viewtopic.php?f=2&t=64576		 Page 1 of 2
Author:  Kennomini [ Thu Jul 22, 2010 9:54 pm ]
Post subject:  Tow bar designs
I'll be building a tow bar on the weekend hopefully and was wondering what designs people have come up with.
I know about the "t" design that bolts to the rear of the subframe, the boot floor and the base of the rear seat, what others are their?.
I was wanting to mount mine to the subframe only.
I was thinking, have a plate running along the bottom of each side of the frame and joining across the back of the rear bar on the subframe and also bolted to this bar. So long as I have clearance from the beaver panel and the exhaust pipe it should be strong enough.
Any ideas or thoughts?
Author:  KLAS [ Thu Jul 22, 2010 10:37 pm ]
Post subject: 
sounds like the towbar made by Westfalia over here.
Westfalia AHK Typ 323 005 / Westfalia Towbar Type 323 005 very hard to find now

only found the documents at ebay, but no pics
http://cgi.ebay.de/Papiere-fnr-Westfali ... 0452818105

but the drawing may help
Author:  Harley [ Thu Jul 22, 2010 10:40 pm ]
Post subject: 
I'm working on a custom tow bar myself at the moment as I don't like the factory ones.
I'm going to start with a 3D model of the rear subframe and get a finite element analysis of it to determine how strong the original bars are and how I can improve on it.

Like you I'm trying to eliminate the mount to the body and keep it purely on the subframe.

WOn't happen for months ofcourse, so anything you find along the way will still be of use to me. :D
Author:  superSeven [ Thu Jul 22, 2010 10:41 pm ]
Post subject: 
there's some photos in here from recent thread

http://www.ausmini.com/forums/viewtopic ... ht=tow+bar

tim.
Author:  Lockie91 [ Fri Jul 23, 2010 9:05 pm ]
Post subject: 
Take a look at this thread,

http://www.ausmini.com/forums/viewtopic ... 487#751487

I have just posted up my pics of my van one, (been meaning to do for a while) which sits inside the subframe, and also bolts to the floor for extra reinforcement.
Author:  simon k [ Fri Jul 23, 2010 9:52 pm ]
Post subject: 
I found one of the pictures of my towbar with it out of the car, there is showing all of the parts but I can't find it... but I went out and took some pictures of it in the car

the parts are as follows, going from the tongue back to where it mounts to the rear of the subframe, all of these bits are bolted together, and to the subframe

tongue
rear subframe rail mount
2 x rear mount load spreaders
2 x rear mount captive nut plates
forward subframe mount
2 x side forward mount plates

here's the picture out of the car, this is looking at the bottom of it, from the rear of the car, so imagine the car is on a hoist, and you're standing behind it

Image

here's the tongue, I was given one of those nasty towbars that bolt through the boot floor, so I modified it and drilled holes in it.

Image

here's the view from the rear, the red circled bolts go right through from the subframe, through the load spreaders and out the other side of the rear subframe rail mount. The purple circled bolts go into plates inside the subframe channel with nuts welded to them.

Image

here's the view from the other side, nice thick angle, and any load on the rear rail of the subframe is taken by the spreaders behind those bolts circled in red. However, there isn't a lot of load on the rear of the subframe, the rear part is for side/side and up/down stability. You can see that I had to compromise a bit to fit around the hydrolastic, I would have liked to make the angle go all the way out to the side, but just couldn't without taking the subframe out of the car

Image

this is where the forward part and the rear part join together, also circled in purple is the notch in the rear part to clear the hydro channels. I didn't originally have it there, and the hydro pipes cleared OK, but when I had it out I thought I'd notch it

Image

here's the notch again

Image

This is the drivers side forward mount plate. The bolt right at the front is through the strongest point of the subframe, where there are 3 pieces of metal together.

Image

so there you go.... I made it in a few afternoons before dragging my little trailer to Sydney for MDU in 2005. All mounted to the subframe, and despite a few compromises, I reckon it'd pass an FEA test with flying colours :D
Author:  Lockie91 [ Fri Jul 23, 2010 10:03 pm ]
Post subject: 
Image

yep thats exactly where mine bolts onto the subframe at the front of the car. The box tube I have that looks like and "I" is the one that bolts onto that subframe part. The strongest part, I agree too :) It was thicker than I thought when I drilled through it :)
Author:  Kennomini [ Thu Jul 29, 2010 7:37 pm ]
Post subject: 
This is what I came up with.
Image
The 2 lengths of rod will be removed soon, they were just bracing while I welded the whole lot together.
It has 1/4 inch plate that is 80mm wide running all the length of the subframe. The rear bar is 40mm (3m thick) box section which is butt welded to the side plates and has 2 pieces of shaped box section on each side welded in under the edge to strengthen the join.
Image
Image
The tongue and bolting plate are off an old Commodore and the bolting plate is welded onto the box section on each side (4 surfaces).
Image
It will have 4 bolts through the rear section into the subframe cross member (which in my car already has a length of box section welded into it and onto the sides of the frame). Their will also be another 16 bolts running down the length of the frame, through the 1/4" plate, through the subframe and through another "sandwich" plate on top of the lip on either side.
Author:  Lockie91 [ Thu Jul 29, 2010 8:10 pm ]
Post subject: 
good work mate,, only thing I don't like about it, is the weight of all the flat steel going down the length of the subframe, and all those bolts. (16 more bolts ontop of whats there :shock:, its only a little mini sedan, the 8 bolts that hold the subframe on are going to be the weak point ultimately that's what's taking everything... what are you going to be towing.... we can't exactly tow much with the minis..

i only put the amount of steel I did into mine, because it was the van, and I had to go much further back then the sedan does to reinforce it, but otherwise I would have opted for something much lighter.. so long as you don't mind weighing the car down more, it doesn't matter i guess :wink:
Author:  simon k [ Thu Jul 29, 2010 9:37 pm ]
Post subject: 
just my 2 cents on that Kenno....

the welds above the tongue here are coping with all of the load, and up/down movement every time the trailer goes over a bump

Image

to put it another way, would you jack up the back of the car from under the towball?
Author:  Kennomini [ Thu Jul 29, 2010 10:04 pm ]
Post subject: 
Lockie I did think about cutting the flat steel shorter but, near the rear of the red G clamps but that will only save 1-2 kg's at most, the whole thing only weighs around 17 kilos plus the extra length will help spread the load.
I'm a little unsure about the bolt plate too Simon that's why I left the 'tail' on it (I was very tempted to cut off the excess steel). If I find it flexes to much I'll probably extend and support it like yours onto the inside of the subframe, and if I do that then I might shorten the flat steel back 200 odd millimeters. Also depending on where the real beaver panel sits I will add a plate from the front edge of the bolt plate to the top of the 40mm box and a couple of gussets on either side of that.
This isn't the strongest thing I've built but hopefully it will do the job.
Author:  Kennomini [ Thu Jul 29, 2010 10:07 pm ]
Post subject: 
Out of curiosity how much do your frames weigh? including tongue and ball.
Author:  simon k [ Thu Jul 29, 2010 10:26 pm ]
Post subject: 
Kennomini wrote:
Out of curiosity how much do your frames weigh? including tongue and ball.


dunno, but it's not light.... I actually wanted it to be fairly heavy to make my hydro sit a bit lower at the back :D
Author:  gafmo [ Thu Jul 29, 2010 11:16 pm ]
Post subject: 
:lol: considering your from Wodonga. put a bag of cement in the boot like the Ute guys do
Author:  Bubbacluby [ Thu Jul 29, 2010 11:33 pm ]
Post subject: 
Worst thing about a tow bar is trying to undo your boot and let it rest without holding it up while you put something in it or take something out
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