robroy:
If he lifted the back of the trailer up would that not have put more down pressure on the legs?
Edit… Hang on, …I’ve read it again and he did lift the front of the trailer up first.
Just consider a trailer standing on its own legs. Take the tractor unit away (although the air supply will probably be needed). If you now raise the trailer suspension, the whole trailer acts like a giant seesaw with its pivot point located at the legs and the nose of the trailer dips accordingly. It doesn’t dip as far as the rear rises (due to unequal length of the “arms” of the seesaw) but it definitely will dip. Now try it again, this time with the unit under the trailer. The nose will still try to dip, but as the unit is supporting it, it will instead lift the legs (or at least, reduce the pressure on them).
robroy:
If he lifted the back of the trailer up would that not have put more down pressure on the legs?
Edit… Hang on, …I’ve read it again and he did lift the front of the trailer up first.
Just consider a trailer standing on its own legs. Take the tractor unit away (although the air supply will probably be needed). If you now raise the trailer suspension, the whole trailer acts like a giant seesaw with its pivot point located at the legs and the nose of the trailer dips accordingly. It doesn’t dip as far as the rear rises (due to unequal length of the “arms” of the seesaw) but it definitely will dip. Now try it again, this time with the unit under the trailer. The nose will still try to dip, but as the unit is supporting it, it will instead lift the legs (or at least, reduce the pressure on them).
Old John:
Raising the trailer suspension would not make the problem worse
Given that raising the unit to its max was insufficient to take any weight at all off the legs then yes it would, simple maths and physics. If you raise the rear of the trailer you lower the front as well as transfer weight onto the front because the legs would still be the pivot point.
There is no “transfer of weight to the front” involved when lifting the rear by only a few inches (unless it’s a tanker, and even then the effect is marginal) until you start bearing down heavily on the rubbing plate, at which point there is indeed a transfer - but onto the rubbing plate which now bears some of the load previously supported by the legs (so now it takes less effort on the handle to move them). The weight acting on the trailer axles stays relatively unchanged as the whole trailer pivots through only a couple of degrees.
dcgpx:
3 - if it doesn’t then I stop and call office saying trailer legs stuck what do they want to do
I’ve not come across a trailer yet that doesn’t raise / lower on low gear no matter how much weights loaded !
You’ve obviously never picked up (or tried to) a trailer that has come of the boat, where the legs are bent to ■■■■ then, by the Tug motors that have clattered them on the ramp edge on the way down.
Tbf most did wind up on low gear…eventually, but after me being totally knackered.
(And tbh even then I did not ring the office, I’d be too embarrassed to do so. )
trevHCS:
With regards the legs being too high - that’s a problem often when people shunt the trailer around by lifting the suspension and only partly wind the legs up, then forget to reset the suspension when they drop the trailer and wind the legs down. Leaves it hanging in midair.
The most common reason for a trailer being dropped too high (at our place at least) is when it was dropped by a Scania with the midlift up. There are even (allegedly) a few “fannies in a Scanny” that have reportedly then lifted the air on their units to intentionally drop the trailer too high for the other non Scania units to struggle to get under.
The depot I work at run 5 or 6 Scanias and we have in particular one Scanny driver who thinks it big and clever to do this. His problems start when I’m shunting as I watch him do it ('cos that’s what us shunters do ) , I then find out the trailer number he’s picking up the next morning, go find it, lift it with the tug and wind the legs as far down as they’ll go! Live by the sword etc…
.
There is a place north of Peterborough, a while ago had a night shunter who was a total (not nice person) would either drop our trailers high or low, no hand brake on, we no longer drop trailers there, and I think he left, The day shunters is a very nice men, a cheerful wave, a doofing of the cap.
dcgpx:
3 - if it doesn’t then I stop and call office saying trailer legs stuck what do they want to do
I’ve not come across a trailer yet that doesn’t raise / lower on low gear no matter how much weights loaded !
You’ve obviously never picked up (or tried to) a trailer that has come of the boat, where the legs are bent to [zb] then, by the Tug motors that have clattered them on the ramp edge on the way down.
Tbf most did wind up on low gear…eventually, but after me being totally knackered.
(And tbh even then I did not ring the office, I’d be too embarrassed to do so. )
Tbh no I’ve not but then again that environment is probably renowned for it!
I was thinking more about in land generally [emoji4]
The depot I work at run 5 or 6 Scanias and we have in particular one Scanny driver who thinks it big and clever to do this. His problems start when I’m shunting as I watch him do it ('cos that’s what us shunters do ) , I then find out the trailer number he’s picking up the next morning, go find it, lift it with the tug and wind the legs as far down as they’ll go! Live by the sword etc…
Superb, i’m definately going to buy you a pint if and when we meet, though if in working hours it’ll be a quality coffee
I used to work with a half wit like that back in the days of steel springs, he had a Marathon that was way higher than anything else in the yard, our few flat trailer only had the one gear on the legs, hence when said numpty dropped the thing as high as he could, it was search the yard for planks (the wooden sort) and blocks to build a ramp to try and take some of the weight so we could shift the bloody legs.
Juddian:
Superb, i’m definately going to buy you a pint if and when we meet, though if in working hours it’ll be a quality coffee
And I’ll gladly take you up on your kind offer my friend. Robroy bought me a pint the other week. The only problem was he was neither working nor driving whilst I was doing both! Consequently his pint had a nice frothy head whereas mine had bloody ice cubes and a straw! . He did look like he enjoyed it though
Topcat1522:
I tried lifting air in trailer as well
That would make it worse.
Assuming you tried lower gear setting on landing legs btw…or they could have been bent.
When I’ve picked up trailers off boats dropped far too high by Terbergs, with a low ride unit, I’ve even had to back on to blocks to gain height sometimes.
Old John:
Raising the trailer suspension would not make the problem worse
Given that raising the unit to its max was insufficient to take any weight at all off the legs then yes it would, simple maths and physics. If you raise the rear of the trailer you lower the front as well as transfer weight onto the front because the legs would still be the pivot point.
How do you know that raising the tractor suspension took none of the weight of the trailer?
You don’t.
For all you know the legs were within half an inch of being clear. It would still have been difficult if not impossible to turn the handle and raise the legs with high gear engaged. If the unit is taking any weight at all, then raising the rear of the trailer will cause the fulcrum to move from the legs to the hinges under the fifth wheel plate, and raising the rear of the trailer far enough would have had the desired effect. (I know it is unlikely that there would have been enough travel in the trailer suspension to achieve this, but the principle is correct)
In short , the driver used the head, did all the right things, and was maybe let down by his lack of experience regarding the two speed gearing on the landing legs. There is no shame whatsoever in that!
I bow down to Roymondo’s Physics O level, I failed mine twice, I’m more of a Classics man myself!!
. He did look like he enjoyed it though