Hi all,
I posted yesterday that I ave gone a broken wishbone (in two places) and it will prevent me getting on the track at Combe on Monday. I thought I would share this with you all because I don't think I am alone in seeing this failure. On my car it uses the newer Westfield in-board anti-roll bar. It is a very stiff tube relying on long levers to transfer the roll forces from one side to the other. Putting it inboard requires a rocker to invert the motion. I think this has an intrinsic fault because the full force of a cross-body roll (or a pothole that looks like it) is directed directly at the front wishbone bracket but offset to one side. A pothole is a sudden huge force that has to be turned into a movement in the opposite direction so the poor wishbone bracket takes the full force of that - maybe five times the mass of the car with the peak forces. Something has to break doesn't it? What do you guys think? I am reluctant to rebuilt it the same way and see the same happen again. This is a near new car not a high mileage vehicle.
It should look like this:
(http://s18.postimg.org/xfpzr6m1h/Working_assy_from_front_RHS_Annotated.jpg) (http://postimg.org/image/xfpzr6m1h/)
(http://s14.postimg.org/w6jddzy7h/Working_assy_from_inside_RHS_annotated.jpg) (http://postimg.org/image/w6jddzy7h/)
Here is the damage on the failed LHS:
(http://s2.postimg.org/twuzu9lol/Mount_break_from_front_1.jpg) (http://postimg.org/image/twuzu9lol/)
Here are some other views:
(http://s21.postimg.org/4onim1en7/Mount_break_from_front_underside_1.jpg) (http://postimg.org/image/4onim1en7/)
(http://s13.postimg.org/wmbf0eusj/Mount_and_arm_break_from_front1.jpg) (http://postimg.org/image/wmbf0eusj/)
(http://s3.postimg.org/owmz90jzz/Reynolds_tube_break_close_up_1_Annotated.jpg) (http://postimg.org/image/owmz90jzz/)
(http://s10.postimg.org/wtxw88t6t/Mount_break_from_side_4_Annotated.jpg) (http://postimg.org/image/wtxw88t6t/)
My theory is that I did this as a result of a pothole . The ARB tried to compensate but all of the force acted on the wishbone front bracket and ripped it apart and as it did so the already fatigued Reynolds tube broke too. Oddly after this happened there was very little sensation trough the steering. It was raining cats and dogs but I got a little veer to the right on braking and as I crossed the white lines it tended to pick them up. I was one wishbone away from a disaster. When I tried to park on my drive, the steering was very heavy and that caused me to investigate. You can imagine I was pretty horrified to find what I had been driving on.
Any opinions very welcome. But my guess is that I need to change the whole set-up to something more conventional.
It's interesting that the limbs of your bracket failed the same as mine did. Colin's bracket has a small fillet between the two limbs, and the bracket has been pulled clean out of the chassis. It is obviously a weak area in the design for them both to have gone on relatively new cars, and must be down to the increased loads imposed by the ARB, as normally the lower wishbone takes most of the punishment.
Here is the repair I did last year, with small pieces of angle top and bottom which not only increased the bracket strength it spread the load on the welds.
(http://s18.postimg.org/nz9tvexw5/004.jpg) (http://postimg.org/image/nz9tvexw5/)
It certainly looks like a design problem to me. The top wishbone shouldn't really be doing all that much other than keeping the upright, well, upright! As such I guess the top bracket design will have been based on just those minimal forces, unless there was a substantial re-design of the top bracket when they introduced the ARB set up.
As you say, the forces created by the ARB are going to be directing some big forces into that bracket and even to a non-engineer it doesn't look all that strong. I'd say its a failure waiting to happen.
Are there any other instances of this on Westfield specific forums?
I note Ed's pic but it looks like the issue on that one was more to do with the top mounting of the coil-over rather than the upper wishbone.
Hard to tell from the pic of Colin's but is it the same thing? Does he have the same ARB set up?
From the moment I first saw the inboard ARB I thought the design ingenious.
I haven't had a car here long enough to draw and analyse the stiffness and weight transfer but I did note that it gives a rising rate performance.
ie the more the wheels displace IN ROLL the higher the value of weight transfer. Personally I doubted whether Westfield realized this because the size of little link prevents it being adjusted to optimize the potential.
As Ian notes suspension rockers are very highly loaded indeed.
My concern was that the rocker was in SINGLE SHEER so causing the loads to place the bolt, bracket and upper arm mount into a bending moment in normal operation.
Wow Ian yours is far worse than mine. It is the same set up ARB as yours. My bracket stayed intact it just ripped the chassis side away from itself. That part of the chassis definitely seem to be too thin a gauge steel tubing.
I have noticed when we put it back together that when the ARB is under load there is a slight twist to the mechanism to which I will show you tomorrow.
I'm steel in contact with Jamie who also had this problem which broke out on track so if you want us all to combine forces to speak to Westfield mate then I will be happy to give him a call. :)
Guys, I know we have a laugh sometimes in the forum but this is real what its about. I wonder how many others have had this problem outside of BKCC??
Best of luck with Westfield and I hope you get it sorted.
Bit of tough luck there Ian, shame about the track day :(
I'm sure I have heard of this happening many times so come on Mr Camber Dave - Time to build some strong redesigned replacements, I bet you could sell a few.
As it looks like the main forces are trying to pull the bracket off the chassis it might be as simple as having a bracket that wraps around the inner side of the chassis rail doubling up with the one welded to the outside. That would just need a u shaped bracket with longer arms and a slightly wider back. Maybe a bit more metal on the inside of the square section to spread the load out a bit. That would also mean there would be double the metal either side of the wishbone bush. Simples!
Yep,
It also looks like that rocker needs support on its outside edge because it puts its axle bolt in shear being outside of the bracket- if it bends due to a pothole - it is locked-up and the suspension is locked too. Oops!
Ian
Where there's blame there's a claim.
Sue Westfield. I went to school with her, nice girl but her rockers and brackets were a bit dodgey too :o ;D
I have not been aware of that happening before. People have had chassis break, and wishbones break but usually after full investigation there is a reason for it, not usually a manufacturing defect.
The 2004 chassis did seem to be one that had some quality questions, but from memory some were found to be aftermarket shockers actually bottoming out and the full load transferred to the chassis.
What I would certainly do is make contact with Julian Turner or Mark at Westfield to express your concerns especially if there is evidence of others failing in identical manners. They will investigate
I haven't ruled that out about contacting Westfield but there after service has gone considerably down hill over the years.