The problem lies in the geometry of the design and it’s the same with the current range of triples that Ransomes make.
If you look at the two front cutting units they are held by the brackets at the top and are being pushed from behind which makes them try to rotate forwards and downwards. With the skid at the back of the cutting unit being the only contact it has with the ground, this has the effect of cutting the grass shorter as they are pushed forward.
In contrast, the middle cutting unit is being pulled forwards from the top which gives a more consistent height of cut on the finished grass.
When I used to train operators to use these machines I always used to tell them to set the front units at least one graduation higher than the middle one to counteract this tendency; this was with new machinery as well, but once they’ve hit one or two trees then anything goes!
I hope that puts your mind at rest; at least you know that there isn’t anything fundamentally wrong with your machine.
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