Today’s switch can be a bit of a head scratcher. It is labelled TAG DUMP. On our coach it has three options: AUTO, DISABLE, MANUAL.
Most Newmar owners leave this switch in the AUTO position because, like me, they find this switch confusing. To make it even more confusing, the way the switch is described in the Freightliner Chassis Manual is not consistent with the way the switch is labelled in the coach.
Here is the Freightliner rendering of the TAG DUMP switch:
This is what the switch looks like in our coach:
Two different switches. Freightliner describes the operation of the switch this way:
The tag-axle suspension dump switch is operated by a three-position, dash-mounted rocker switch. See Fig. 3.11. The manual TAG DUMP mode is activated by pressing the top of the rocker switch. The AUTO DUMP mode is activated automatically during reverse gear applications when the rocker switch is placed in the middle (level) position. When you depress the bottom of the rocker switch, the tag-axle suspension dump switch is placed in the OFF (down) position, and the TAG DUMP mode is inactive.
Unfortunately, that description does not match the switch that Newmar installed in the coach. When using the Newmar switch the middle position should disable the tag-axle suspension dump and depressing the bottom of the rocker switch should place the tag-axle suspension dump into manual mode.
What is this tag-axle suspension dump in the first place? On our coach we have three axles: steer, drive and tag. The additional axle, the tag axle, provides an increase in the gross vehicle weight rating. The TAG DUMP switch allows an operator to exhaust the air bags on the tag axle which, under certain conditions, may improve manueverability.
In AUTO mode, the tag axle air bags will automatically deflate when in reverse and when the speed of the vehicle is less than 8 mph. There may be certain situations where you might want to manually deflate the tag axle air bags. I have yet to run into such a situation. I always leave ours in AUTO.
There are numerous threads about the TAG DUMP switch on iRV2. This comment from one of the threads probably sums it up best:
This is an issue that has been discussed in this forum before because the description in the Freightliner manual does not agree with the way Newmar has installed it. The Newmar switch does not agree with the Freightliner description as the Newmar switch has 3 positions and the Freightliner only has 2 positions. In my experience none of the above descriptions are correct. The tag will always dump in reverse no matter what position the switch is in. The “off” position does nothing as this is not supported by Freightliner. “Manual” is a toggle switch. Press it once and the tag will always dump when your forward speed drops below 8mph. Press it again and it does not dump going forward.
A group of us had a long discussion with the instructor at Camp Freightliner about this issue and he was baffled that Newmar coaches had a different switch to what Freightliner had supplied. Just play with it and see how yours functions.