I learnt an important lesson yesterday. Sharing it here as it may help others.
I was towing a car trailer with the wagon, bringing the FB home from panel repairs. Have towed this way a few times with the wagon, and it is within the legal weight limits for NSW and within the acceptable load ratings marked on the trailer. I suspect the rental trailer was of different axle location to what I normally hire, and put more vertical load on the towball. It was loaded as per the rental company's instruction, FB facing forward and all the way to the front of the trailer.
The wagon rear suspension was loaded, and I could hear it working. Not happy with the noise, I found a place to pull over. As I came off the tarmac edge onto the dirt the drawbar gave way. Trailer, drawbar, safety chains and all remained connected to each other, but disconnected from the wagon. Trailer nose dropped into the dirt, skidded about 30cm and stopped. No damage to the trailer or load. I am thankful this was walking speed, and not on the road. Thanked the man upstairs, changed undies. NRMA recovered the trailer home for me, wagon was driveable.
Thinking through, there are some big differences in the types of towbar out there. They all bolt through the rear bumper bolts. Some (probably most) have the end plates directly welded onto the drawbar, like the images below:
- Towbar direct weld.jpg (51.52 KiB) Viewed 2711 times
The towbar on the FB was of this type, and did A LOT of towing. The towbar on the wagon though has stepped rear end plates, like the image below:
- Towbar indirect weld.jpg (33.6 KiB) Viewed 2711 times
The part that bolts to the Holden subframe is a small run of angle, welded on to the main end plate. The weld is oriented as per the red line on the diagram, and is what gave way. Looking at the failed weld, it has some rust in parts which says it has failed over time rather than abruptly. Looking at the design with an experienced chassis fabricator yesterday the verdict is that the design is not well executed, and puts substantial load on the fillet weld. The fillet weld was a lot less substantial than the welds used to hold the main bar to the end plates.
The other difference between towbars are that some of them have auxilliary mounting tabs, circled in green above. The tabs take some of the load off the endplate welds. The towbar on the wagon did not have these tabs. From memory the towbar on the FB had those tabs.
The lesson for me: if you really want to tow with an FB/EK, then aim for a towbar without the stepped rear end plates, and one with the auxilliary mounting plates.
Cheers,
Harv
327 Chev EK wagon, original EK ute for Number 1 Daughter, an FB sedan meth monster project and a BB/MD grey motored FED.
The towbar in my sedan has a "dimension A" of 41.25". When I put the two plates either side of it, I get a width of 42.5". This is the distance between the two rear subframe rails on the sedan.
Does your sedan towbar have (A + W + W = 37 + 3 + 3 = 43") across the subframe rails, or have I counted two thickness of 1/4" plate twice (ie it's really 42.5")?
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