Flex in tow bracket

[Rob Cowell]

Not sure where best to put this, but I'll try here.

So I've bought a Pendle bike rack to get a couple of bikes to France. Seems a decent thing.

Having put it on I had a look underneath. I look underneath a lot. And it looks like the tow bracket is moving on the chassis. This is not good. The underside is pretty rusty so fearing the worse I took the bumper off to get a better look at the cross member.

Mud.

More mud.

But it once jet washed the cross member looks in decent condition. Albeit full of mud!

So if I lean across the rack, which is acting like a lever, and I'm not little I can feel flex here.

Thats the tow bracket where it's folded and sits under the crossmember and bolts on. I tried to video it but you can't see the movement with the whole chassis moving. You can see it by eye though.

This is the construction from the side.



The tow bar is two bits of 6mm plate. One at the back that turns 90 degrees and bolts under the chassis. You can't quite see the bend here, there's a thin plate obscuring it. The plate infront has the ball mounted on it. It bolts to the back plate.

All the bolts are tight. It can only be the bracket itself flexing. Does this sound normal / OK? I've never looked in detail at the bracket with something swinging off it. I tow 2.8 tons quite a lot. It could have been doing this since day 1. Or someone might tell me they notice theirs doing this the day before their cattle trailer overtook them on the M4.

 

[Sag]

Hi Rob,when you look at the last photo it looks like it's slightly bent backwards,may be its been reversed into something with the tow ball and bent it slightly back and weekend it at the top,is there any signs of splitting at the top of the plate will need a dam good clean off with wire brush I'd of thought to see.

 

[Rob Cowell]

Thanks Sag. It is square. Just the angle of the camera.

 

[Shayne]

Hook seems to protrude a very long way from the bumper , or is that just and extension included in the bike carrier ?

 

[StarCruiser]

I thought that Shayne. Is it possible that it is fairly rigid but is flexing the whole cross member tortionally?

 

[Rob Cowell]

Hook seems to protrude a very long way from the bumper , or is that just and extension included in the bike carrier ?

The tow ball does poke out a bit, but it's a standard Witter unit. The bike carrier has extended arms for a car with a spare wheel on the door, but I have the bikes mounted as close to the wheel as I can. I'll sling a ratchet strap round the bikes onto the tyre so they're not going to bounce around. If I only have one bike I just strap it to the tyre in any case, it's just fiddly holding it in place while strapping on. The rack was to make my life easier!

I'm hoping the brackets flex a little rather than any twisting force getting to the cross member. It would be easy to stop the flex by welding a length of angle iron to the bracket, but I don't want to go adapting it away from what someone who knows about tow bars has designed.

 

[Rob Cowell]

I thought that Shayne. Is it possible that it is fairly ridged but is flexing the whole cross member tortionally?

The cross member is definitely not flexing. Its the bracket. The cross member also has stengthening brackets onto the chassis legs which is part of the tow bar kit.

 

[Rob Cowell]

Right. Done my best engineering drawing. Blue blobby lines are where the bracket bolts to the cross member. Red bits are the bracket. When I swing on the tow ball, using the bike rack as a lever the back of the bracket flexes very slightly inward, and the tiny gap between the curved corner of the bracket closes onto the cross member, at the point marked with the arrow. Make sense? Is this bad?

 

[StarCruiser]

Right. Done my best engineering drawing. Blue blobby lines are where the bracket bolts to the cross member. Red bits are the bracket. When I swing on the tow ball, using the bike rack as a lever the back of the bracket flexes very slightly inward, and the tiny gap between the curved corner of the bracket closes onto the cross member, at the point marked with the arrow. Make sense? Is this bad?
View attachment 103727

I would guess that the thick red part shown in your drawing has become bowed or otherwise bent with your 2.8 tonne towing so that there is some movement available between limits. I would expect there to be some bowing or bending in the cross member where the bracket attaches as well.

 

[Shayne]

So its the Witter bit that flexes yeah ? which is likely made from Lloyds marine grade steel which will flex rather than snap .

 

[Rob Cowell]

So its the Witter bit that flexes yeah ? which is likely made from Lloyds marine grade steel which will flex rather than snap .

Yes, the Witter bracket. I can see it flex because the cross member is not flexing.

 

[Shayne]

If steel doesn't flex the first sign of failure is catastrophic and complete . I wouldn't worry about it .

 

[StarCruiser]

Ok Rob, is it flexing, or rocking?

 

[Rob Cowell]

Ok Rob, is it flexing, or rocking?

I would say flex. I can't feel any knocking that I think I would if the plate was rocking. This was the point of having the bumper off, other than suspecting a rusty cross member, to check all the bolts were tight, which they were. We're probably not talking about more than 2-3mm movement at the bottom of the bracket, and a fraction of a mm where the arrow is. But it's definitely deforming relative to the cross member.

 

[Rob Cowell]

If steel doesn't flex the first sign of failure is catastrophic and complete . I wouldn't worry about it .

Thanks Shane. I've convinced myself it'll be OK for a couple of bikes, and I'll strap them to the spare wheel to take load off the bracket. Last thing I towed was 50 sheep over the Bwlch and the Rhigos. Might try something smaller for a first go when I get back.

 

[Sag]

Where you say the flex is against the cross member,if its rusty between them and the tow bar fastened against the rust it could be that what's flexing as if that's the case it could be that it just needs removing the rust cleaning off and refitting if you know what I mean.

 

[frank rabbets]

I'm amazed we don't see bikes all over the roads the way some people put them on. Not the OP!

I carry 2 bikes on my 80. I climb on the carrier with the bikes and jump up and down. If they don't come off I assume it's OK.

I don't think there is much extra load in addition to the bikes just through driving, especially on tarmac.

If they do come off just drive faster and hopefully they will be sucked on to the back of the car like all the dust. .