Can anyone help .on a twin steer that isn’t a midlift should the airbags on the 2nd axle deflate when you press the air dump switch that helps to increase traction .on mine I press the switch the ride height increases slightly but the airbags above the 2nd axle are staying inflated .not sure if its gone faulty or not am pulling a short trailer that sits back and leans back and its a pain when empty in the rain spinning tyres all the time.
MAN F2000 I assume. If it is not a midlift then the pressure only reduces. You will need to check the actual pressure in the 2nd axle bags to see if anything is amiss.IIRC there is a 90 second time limit to pressure reduction when operated. The ASR hasn’t been switched off by accident has it?
Shouldn’t there be a levelling type valve on top of the diff that controls the mid axle air ?is there a 3-2 valve sticking or grown bent on top ?
I have had a read of my tech course notes on this from some 16 years ago. Unfortunately I never got to do any work on the system because the vehicles were all new at the time and the dealership folded soon after. However, the second axle air bags maintain a residual pressure of .3 bar via a shuttle valve. This .3 bar pressure is controlled by a pressure reducing valve for the second axle only. There is a pressure switch in the line to the rear axle air bags. This switch is also electrically triggered by the air dump switch in the cab. This is set so that in theory when the rear axle is carrying 9 tonnes the 2nd axle air bags inflate to share the imposed load. This is achieved by the switch electrically activating a pneumatic solenoid.
Hopefully this will help with the fault finding.
Edit: It was more like 20 years ago. 