The introduction of single leaf trailer springs in circa 1970 was quite an innovation which wasn’t universally welcomed by “the old guard” but I thought and believed it was a vast improvement on the 7 and 8 leaf springs that up to that time were the acceptable “norm” ! from the second new trailer on that I bought at Bewick Transport I specc’d single leaf springs on both York and CF chassis and they gave faultless service for many years. The only extremely rare problem encountered was that the locating pip on the base of the spring sheared but that was on less then the fingers of one hand !
Any second-hand trailers I bought in the 70’s with multi leaf springs were converted to single leaf with bought in kits from CF and although we did continue to operate multi leaf suspensions we were able to use the springs we had removed from the conversions to replace the multi leaf springs that failed ! Happy Days ! Cheers Bewick.
Mono leaf springs were certainly easier to change than multi leaf Dennis, especially at the side of the road, and as you say were more robust despite looking as if they wouldn’t be up to the job and some took some convincing that they would be fine. Franky.
I remember my Dad changing the front springs on his ERF B series from multi leaf to parabolic and the slip of plastic on a trailer spring was a Delrin liner iirc ?
Punchy Dan:
I remember my Dad changing the front springs on his ERF B series from multi leaf to parabolic and the slip of plastic on a trailer spring was a Delrin liner iirc ?
Yer getting technical now Dan’l and I had clean forgotten about that sliver of “plastic” ( well that’s what I call it 
) and again I had omitted to mention those three leaf? parabolic springs which appeared on trailer suspension but I didn’t reckon them too many leaves eh ! Cheers Bewick.
Bewick:
Punchy Dan:
I remember my Dad changing the front springs on his ERF B series from multi leaf to parabolic and the slip of plastic on a trailer spring was a Delrin liner iirc ?Yer getting technical now Dan’l and I had clean forgotten about that sliver of “plastic” ( well that’s what I call it
In later yrs those 3 leaf trailer springs were considered road friendly so the trailer could be operated at 44 tonnes gtw without air suspension.
I suppose air suspension stormed in during the late 80’s with the additional price tag which IIRC was about £ 1000 extra and no way would I wear it but IIRC in when things were slowing down a bit economically in the early 80’s I was offered three stock C/F chassis on “air” at Bo alloy for the same price as the single leaf Task chassis we currently had in build ! So I went for it and from then on I bought both “air” and “steel single leaf” chassis ! for a few years with Air eventually coming out on top in later years 100% ! Cheers Bewick
Some of the regular 40-ft trailers in the Middle East used to have leaf springs stacked to increase weight. The driver of the Syrian truck I chatted to on Tangiers docks one afternoon about 22 yrs ago, told me he ran at 60 tonnes gross. When I looked under his fridge trailer at the suspension I could see why!
If you’re wondering what the black flags are all about; it was because Assad (the Current Assad’s father) had just rattled his clack 
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Not a trailer but we had a new Foden S83 tipper (TWB37S) and I had the task of removing all eight of the multiplate springs and fitting taperlite ones front and rear. That became ‘the norm’ on Fodens until the rubber rear suspension appeared. Rear taperlite’s tended to break easily in service but the fronts lasted longer.
Pete.
Sed Ack 401 twin steer front axle sat on monoleaf springs, which was fine until braking (not particularly hard) for a red traffic light when one of them snapped clean.
That wouldn’t have happened requiring immediate replacement on the previous 400 because multileaf so could have driven back to base workshop to get fixed, i don’t know if the spring had a fault or if this was a known issue, but drove it gently to the nearest main dealer who had me going again in short order, other than that the 401 was a big improvement over the old model.
Juddian:
Sed Ack 401 twin steer front axle sat on monoleaf springs, which was fine until braking (not particularly hard) for a red traffic light when one of them snapped clean.That wouldn’t have happened requiring immediate replacement on the previous 400 because multileaf so could have driven back to base workshop to get fixed, i don’t know if the spring had a fault or if this was a known issue, but drove it gently to the nearest main dealer who had me going again in short order, other than that the 401 was a big improvement over the old model.
Our Sed Ak 400’s broke the multiplate springs for fun! They usually broke through the eye so that stopped the job, I snapped two 2nd axle ones pulling off of our weighbridge and had another rear one break going through the tunnel on the A38 through Brum but managed to get to the delivery point. We changed at least one a week, at least everything came undone easily! 
Pete.