So I have had a mechanical slope meter on two different production class graders. The one on my 730 A was close to being deadly accurate. I used to park her on the scales, set it to zero, drive off, turn around, drive back on and it would still read zero. Out in the field I would get the tec to shoot the tops of the center of each chain case, and figure out the crossfall and he would get the same result. My 940 Volvo is always off by about a half a percent when you swing around. They bought one for my Maulden maintainer. Now the maintainers are a four wheel rigid frame, and a lot shorter than their big cousins. I realize that these meters read your back wheels, and not your blade, and are really only good if you stop for a second. I have tried all of the above, and there is no way in hell that I can set that damn thing in this grader. Zero on the scales is fine, but if you do a 2% cross fall, mark your hind wheels, turn around and park your rear wheels on the same mark it will read 9%. Thoughts.... I've always gotten along without them, but they want me to have it. I'm thinking black tape cover the numbers that slope meter you wanted me to use????? Sure.....works great....
The three things I would check: 1. Tire pressures on both sides. 2. Make sure the glass vial is not loose in the housing. 3. Check if the cab is shifting on its mounts. You could also try the SlopeMeter from the 730 in the Maulden. If it does the same thing, the issue is in the mount relative to the axles.
These are a mongrel of a thing and given me a lot of grief. I have marked the wheels and turned the machine around like you have for zero and the result is aways different! I argued the toss with the foreman about it rather than run string boys and got run off for my trouble! Tyre pressure, type, varied brand names, location of blade side shift, circle side shift all add up to various weight combinations over each side of the machine and you will do your head trying to figure it out. Even the batterybox on one side alone will make a difference. The machine I was on was John Deere 772G brandnew, indentical tyres all round. Centre shift and blade side shift un altered except for turning the circle for your return cut and where I think the main problem is and beginning of the headache. Got one now just thinking about it! Good luck with that cuttin edge man!
We no longer have the 730, but that's where the slope meter came from. We have 2 mauldens, and I guess the other one does the same thing. I'm guessing it has to do with it being a 4 wheel grader, or just cab movement.
I still like to grade with my ass, but the white hats always want to know what my slope is