Rear anti-roll bar upside down?

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Re: Rear anti-roll bar upside down?

Post by Old and Slow » Thu Oct 20, 2016 1:58 pm

IMO there are significant "bending" forces on the links, because of the distance from the arb bushes (pivot points) to the axle (from the third MB picture above). When a wheel lifts the arb moves in an arc and I think this causes the bend in the drop-link in the direction queried by Simmit. After that I guess it is "metal fatigue" vs "work hardening"!
Hope this helps.


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Re: Rear anti-roll bar upside down?

Post by simmit » Thu Oct 20, 2016 5:35 pm

Old and Slow wrote:IMO there are significant "bending" forces on the links, because of the distance from the arb bushes (pivot points) to the axle (from the third MB picture above). When a wheel lifts the arb moves in an arc and I think this causes the bend in the drop-link in the direction queried by Simmit. After that I guess it is "metal fatigue" vs "work hardening"!
Hope this helps.
I've been thinking along same lines. Bushes at the axle bracket possibly too close to the axle (and in particular the large washer atop) thus not allowing much angular movement, merely vertical compression. Thus lower end of the bolt (at ARB) and bushes thereon take most of the angular movement stress. If we are correct this is a design fault and will eventually affect all MB's.

One remedy might be to use smaller diameter bushes and washer at the axle bracket end. I wonder if the poly bushes mentioned by Peter are in fact of smaller dia.
Another remedy might be to use different design of drop link and I'm looking into that possibility.



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Re: Rear anti-roll bar upside down?

Post by peter freeman » Thu Oct 20, 2016 5:50 pm

I bought two different types to try - one off a Ford and the other a Vauxhall ( IIRC ) but because the poly ones are still ok I have not tried them yet - still in their boxes waiting for the day.



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Re: Rear anti-roll bar upside down?

Post by Old and Slow » Thu Oct 20, 2016 6:03 pm

One alternative possibly worth exploring is altering the height of the pivot bushes where the arb is fastened to the chassis, as this might then mean the arc at the end of the arb wouldn't push against the drop link as much. Needs the geometry drawing out on paper etc to see what could be done.
Alternatively, put fitting new ones in the service schedule along with brake fluid change every couple of years?


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Re: Rear anti-roll bar upside down?

Post by Roger Pennington » Fri Oct 21, 2016 12:09 am

I was at our noggin tonight, and one of the attendees is a Middlebridge owner. So I thought I'd ask him if he had any problems with his rear anti-roll bar links?
"Oh yes" he said, "the rubber bushes are shot to pieces in next to no time, and the through-bolts keep on bending!" As far as he was concerned, it seemed to be quite a well-known problem, and something he'd been battling for years. I told him about Peter's experience with polybushes, so perhaps he'll be giving that a try too?


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Re: Rear anti-roll bar upside down?

Post by AJL Electronics » Fri Oct 21, 2016 9:12 am

If so, then the geometry must be totally wrong. I have a Middlebridge here, next time it is up on the lift I will have a good look.


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Re: Rear anti-roll bar upside down?

Post by simmit » Fri Oct 21, 2016 9:21 am

Roger Pennington wrote:I was at our noggin tonight, and one of the attendees is a Middlebridge owner. So I thought I'd ask him if he had any problems with his rear anti-roll bar links?
"Oh yes" he said, "the rubber bushes are shot to pieces in next to no time, and the through-bolts keep on bending!" As far as he was concerned, it seemed to be quite a well-known problem, and something he'd been battling for years. I told him about Peter's experience with polybushes, so perhaps he'll be giving that a try too?
Hi Roger.

So, all indications so far say this is a design fault, at least I now know my car is no different to others.

Thanks to all who contributed. Poly bush seems quick fix but if I settle on an alternative arrangement I'll post it on the forum for general information.



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Re: Rear anti-roll bar upside down?

Post by simmit » Fri Oct 21, 2016 9:24 am

peter freeman wrote:I bought two different types to try - one off a Ford and the other a Vauxhall ( IIRC ) but because the poly ones are still ok I have not tried them yet - still in their boxes waiting for the day.
Hi Peter.

Photo's please, if not too much trouble.



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Re: Rear anti-roll bar upside down?

Post by simmit » Fri Oct 21, 2016 9:30 am

AJL Electronics wrote:If so, then the geometry must be totally wrong. I have a Middlebridge here, next time it is up on the lift I will have a good look.
There will be many cars that have had bushes/ bolts replaced in the past but now do low mileage and show no distress at present, but that doesn't mean the problem has gone away. I suggest corrective action is still needed.



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Re: Rear anti-roll bar upside down?

Post by Roger Pennington » Fri Oct 21, 2016 11:36 am

AJL Electronics wrote:If so, then the geometry must be totally wrong. I have a Middlebridge here, next time it is up on the lift I will have a good look.
Yes, I suspect that's the underlying problem. The end of the ARB is probably going to travel in more of an arc than the axle, which will be more up-and-down. So the ARB needs to have the right relationship to the axle, and needs the right type of link, in the right location, to minimise the impact of that discrepancy, which is probably where the design falls down.


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Re: Rear anti-roll bar upside down?

Post by peter freeman » Fri Oct 21, 2016 1:44 pm

These are the two types of links I bought but have not yet tried - one ford and the other vauxhall - I think.
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Re: Rear anti-roll bar upside down?

Post by simmit » Fri Oct 21, 2016 5:45 pm

peter freeman wrote:These are the two types of links I bought but have not yet tried - one ford and the other vauxhall - I think.
Thanks Peter.
I'm considering drop link type that has cushion type pads one end and round silentbloc type bush at the other. It would mean some fabrication work to incorporate but the link could be set more or less in a neutral position before tightening the silentbloc through bolt, I think. Alternatively similar drop link to that used on Scimitar front ARB (again with some metal bashing).



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Re: Rear anti-roll bar upside down?

Post by Will Anderson » Sat Oct 22, 2016 4:07 pm

As promised, photos of MB14 and MB46 drop links.
MB14
Image
MB46
Image
Spot the difference.
I don't know which, if either, is the original design as I have never replaced them but the longer link definitely alters the geometery.
Last edited by Will Anderson on Mon Jul 03, 2017 10:16 pm, edited 1 time in total.


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Re: Rear anti-roll bar upside down?

Post by Corky » Sat Oct 22, 2016 4:27 pm

The longer link looks like the SS1/Chevette/GM one. Used on lots of cars and available from around £12 a pair. They're easy to shorten if need be.


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Re: Rear anti-roll bar upside down?

Post by simmit » Sun Oct 23, 2016 2:22 pm

Will Anderson wrote:As promised, photos of MB14 and MB46 drop links.
MB14
Image
MB46
Image
Spot the difference.
I don't know which, if either, is the original design as I have never replaced them but the longer link definitely alters the geometery.

Thanks Will for the photo's, enlightening!

Photo of MB46 (similar drop link length to my MB50) is bent and like MB50 in need of replacement whereas the longer drop link of earlier MB14 is good and straight. Clearly, the longer drop link brings the working faces of axle bracket and ARB more into parallel alignment and thus presents less stress to the link. So, provide both MB46 and MB14 can be sensibly compared (similar mileage) then perhaps all we need do is adopt the longer drop link design, perhaps throw in poly bushes for good measure, and problem solved.

It would be interesting to know if all earlier MB's had the long drop link and if there was a factory change to shorter ones at some time. If more people give feedback on the drop links fitted to their cars we might be able to establish if this is so.

Photo MB46 shows the ARB to be other way up to my MB50 (can't see which way up for MB14), nonetheless the bad news effect at the drop link is same.

Finally, Will, for absolute clarity can you say if ARB's on both MB46 an MB14 are the same?



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