I have always had very serious doubts about the use of Rose/Heim/spherical rod-end joints on road going cars ever since seeing the breakage of one during an Ebworth Trial. Had it sheared on the road then the consequences of the total suspension collapse are obvious.
Last night I found this interesting website :- http://www.infrastructure.gov.au/roads/vehicle_regulation/bulletin/pdf/Street_COP_sec_5.pdf
Full of very practical advice and safety measures for special builders - and unlike our SVA test it seems to avoid nonsense such as 'not using a steering wheel with holes in the spokes - in case you get your finger stuck'.
In Australia they have a total ban on Rose joints being fitted to road going specials :-
Heim joints are not to be used as a suspension or steering component - other than as a steering intermediate shaft guide bush.
Spec them correctly, protect them, inspect them and maintain them, just like you should with a conventional style bush, then I can't see a problem. I know what force I would expect the original links to fail at (or a pretty good idea anyway FE analysis is good!), so I found some spherical bearing rod ends of similar capacity - and then added my own factor of safety 'cos I don't want the bother of changing them too often. Seems to be working so far. Bri (BEng hons and just a few years of proper engineering since ;-) )
ReplyDeleteI agree with what mrbricol has said. I have used my Troll now for 12 years and never had a problem with all the Rose joints used. The important thing is on a trials car you must use the rubber covers to protect them from mud and grit. I then inject waterproof grease into the rubber cover, this keeps the joint lubricated and keeps the water out. But you must inspect the joint reasonably often. I have also found it false economy to buy cheap Rose joints, they do not last nor do the ones with a non steel lining. A bit of common sense is required, do NOT fit and forget. If you let them wear too much the inner ball will just drop out of the housing! Stuart Harrold
ReplyDeleteI think the clue lies mainly in mrbricol's first three words - "Spec them correctly" and also the proviso of designing the suspension properly. Whilst proper engineers clearly know what they are doing, the problem lies with amateurs who - in the words of Automotive Products Ltd when asked for basic advice on brake cylinder sizes said - "We don't give advice as we find that the level of enthusiasm outweighs the skills available". The Aussies must have had some sort of a disaster that caused such a total ban ? Apart from the Ebworth incident (which showed that 'fail dangerously' is as easily achieved as 'fail safe') I have seen other examples that reveal non-engineers producing lethal modifications. There was the special at a Malvern show that had had its steering arm cut and welded, turning it into a Z shape - with no strengthening gussets and splattery welding. The VW spring plate reduced to half its original depth with a notched cut. The Dellow modified to take an open propshaft 105E back axle with nothing but the shock-absorber eyes preventing the axle from rotating - no trailing links or A-frame! SVA, although imperfect in certain areas, at least should weed out some of these howlers. Stuart's practical advice is 100%
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