cabrio anti roll bar mount

[Mike]

Re: cabrio anti roll bar mount

So would fitting compression struts not similarly load the mounting plates more than the original ARB set up? Just a thought. Peter.

Without a doubt, particularly if there are no compliance bushes.

With the standard Sierra compliance bushes fitted it was easy to see the front wheels move under braking - this is eliminated by compression joints fitted with rose joints, but the penalty is it must transfer significantly more impact forces into the chassis.

That said, I think there was a significant flaw in the Marlin "design" - (some would call it butchery!).
- by cutting up a standard ARB and welding on large penny washers the resulting fixing must have generated a rotational load on the chassis fixing which is not induced through a well designed compression strut bracket loaded through its centre via a rose joint.

Although I like the steering on my Cabrio having fitted Compbrake compression struts, I do have concerns about the complete lack of any compliance in the set up, having solid fixings at both ends (as do the Burton Power ones I have seen).

I like the idea of being able to swap the rose jointed connector at the chassis end for a Powerflex type bush that would at least allow some compliance, whilst still improving the overall tightness of the suspension: its on my list of improvements to investigate.

[djj_engineer]

Re: cabrio anti roll bar mount

I understand Mike's comments.

I replaced the outer bushes and the chassis mounting with 'Polybushes' but found it hard and noisy.
I changed the chassis bushes back to the standard type and the noise and harshness in the front suspension was reduced.

I have recently changed both lower arms but have yet to drive FMB on the road

[cameronfurnival]

Re: cabrio anti roll bar mount

I thought it was the center part of the bar that dealt with the 'anti roll' properties through torsion? So how does cutting the big bit out work? Are you now relying on the stiffness of the remaining parts? I'm not being funny here, just would like to know (not being an engineer!).

[chris_cussen]

Re: cabrio anti roll bar mount

I seem to remember that Mark at Marlin said that an ARB was not really necessary as the CoG was low and the suspension stiff enough to stop any roll. As a result the cut ARB just locates the lower radius arm.

[andyf]

Re: cabrio anti roll bar mount

IMHO using a proper compression strut would be better

[Mike]

Re: cabrio anti roll bar mount

I thought it was the center part of the bar that dealt with the 'anti roll' properties through torsion? So how does cutting the big bit out work? Are you now relying on the stiffness of the remaining parts? I'm not being funny here, just would like to know (not being an engineer!).

Cameron, you are quite right - that was my reaction when I received my two butchered Anti Roll Bar pieces back from Marlin - see photo below: How does that work?!

When Marlin tried to fit a BMW engine into the Cabrio and found that the standard Sierra ARB fouled on the 3 series engine sumps Mark Matthews began to suggest that a road going Cabrio does not require an anti roll bar.

I don't have a problem with this - having driven my Cabrio with a standard Sierra roll bar, and then the lightest duty version - (there are at least 3 different torsional variants ), and finally without a roll bar at all, using compression struts, I found the ride improved each time. So, doing away with the Anti Roll Bar function, in itself, is not an issue. Separate struts are fine.

My issue is with the butchered ARB Marlin provided as the solution. The removal of the centre section, creating two L-shaped struts, introduces rotational forces around the rear chassis mounts. These are likely to be part of the cause of failure seen on Alan Hogg's Cabrio.

I have fitted race/rally designed compression struts which eliminate these rotational forces, and improve the tightness of the steering significantly. However, these also are a serious compromise for a road going car: having steel to steel connections at both ends means there is no compliance to rearward axle forces.

As Derek has suggested, I think the ultimate compromise, for a road car, may be to reintroduce poly bushes in place of the rose joints on the ends of the compression struts - has anyone seen any advertised?

[andyf]

Re: cabrio anti roll bar mount

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Form what I've read above the guys at Marlin felt that the car didn't need a anti-roll bar which is why the centre part was removed. The remaining parts only act a compression struts which hold the wheel I place fore/aft.

[djj_engineer]

Re: cabrio anti roll bar mount

I think I bought them from Demon Tweeks ( I will check)

[dogoncrazy]

Re: cabrio anti roll bar mount

Mike and I discussed this at some length a few years back, mainly from the general 'look' of Marlin's solution. I think we both agreed that while it was certainly not an elegant solution it served it's purpose in that it controlled the for and aft movement of the TCA.
I personally agree with Mike in that the ideal answer would be to introduce a compression strut that still had some degree of compliance built in rather than the solid set-up I believe is more suited to track use , not road.
Only time will tell whether the additional strengthening I have had built in will solve the problem I initially experienced, I just have to live with the fact ' it ain't pretty' !!