Conquering GM's Auto Levelling System

[Pat Cassity]

I continue to struggle with the auto leveling system on my 2014 Yukon Denali. I have followed GM's recommendation to completely inflate the shocks before applying weight distribution. However, once the weight distribution bars (Blue Ox) are attached, the system will inflate again for 5 seconds or so. I am concerned that this additional inflation of the shocks is taking pressure off the WD bars. Has anyone developed a tried and true procedure using this system?


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[slowmover]

Have you re-weighed it? Three passes across the scale. Determine that there is first a problem.

[dcheshire]

I have a 2007 Tahoe. I back the truck into place, then shutnit off..

Then I hitch up and set the wd bars to relieve the TV.

Only then do impute key back in ignition. it usually won't inflate much then, so it is likely close

[dznf0g]

IMO and experience, dcheshire has it right. Pull the fuse, then set up the weight distribution and hitch correctly. When you put the fuse back in, it will run the compressor just a few seconds and not do much leveling. To dial in the WD, you can compensate for this little run time by "over WD application" a little bit. Once you have it dialed in, you won't have to go through this exercise again, unless your load changes significantly.

[Pat Cassity]

I really appreciate the help but the steps you describe is contrary to both GM's and Blue Ox's recommendation. They both say that the shocks should be allowed to inflate entirely before applying the WD bars. Pulling the fuse is the same as having the ignition off. Doing so will not allow the shocks to inflate. I'm certainly willing to try but I need to understand the rational.


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[guskmg]

I believe your leveling system is compensating for the aded weight the spring bars have added to the TV. Remember, the spring bars in a perfect world place one-third of the tongue weight on the TV front and rear axles each and another third on the TT wheels. The best method of setting up with auto leveling would be to turn off the system, adjust the spring bars, then turn on the leveling system. Always verify with scales if you are not satisfied with the results. I have been doing this for years and it works.

[dznf0g]

Pat,

The problem with just having the ignition off is that, in my setting up routine, I have to move the vehicle sometimes, or cycle the ignition, for whatever reason. Then the pump comes on and I have to start over.

You need the static height when the vehicle is empty then pull the fuse, then load the vehicle with normal gear, load the trailer, then hitch up and adjust WD....as if it were a vehicle without level control. After you get the WD right, then put the fuse back in and see how much the system adjusts the height. Done right, the loaded and hitched trailer and vehicle won't move much. Most likely it will rise, maybe 1/2"...unless you add just a bit more WD than normal.

Once you get this initial setting, you shouldn't have to do it again, unless you significantly change your AS or TV load....as long as you adjust WD to the same spot. Take a pic for a reminder.

If you just let them inflate with the load on and then apply WD, you will not apply enough WD to move weight off the rear axle...the system will "mask" proper WD adjustment. It'll "look" good and level, but the rear axle could be overloaded, if you have a larger AS and/or a lot loaded in the rear of the truck.

[phbarnhart]

I've always wondered why GM would include a procedure in their manuals that might allow for overloading the rear axel, especially given that the rest of the manual is almost neurotically cautious. I mean, if we really need to load the bars without triggering the load leveling, why not tell us to do that with the ignition off first?

[Pat Cassity]

Today I followed your advice and removed the fuse before hooking up and applying WD. I then took it to the local CAT scales for the result. Attached is the weights of the TV only. The other two tickets are from 2 different passes on the scales. The first with the WD at 8 links, the second at 9 links. At nine links I appear to be about 40 lbs away from restoring the front axel to its unloaded weight. Also, The wheel well height was about a 1/2" higher at 9 links than at its height unhitched.


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[ROBERT CROSS]

Pat,

You did it, now.........Go camping

Bob

[SSquared]

Hi Pat,

That looks like a pretty good set of scale tickets. After you get used to the feel of the rig with that WD setting, you might try one chain link tighter and see if you can tell any difference.

I have been offline for a week, so my next comment is somewhat late....

On my rig, it's easy to hear the air pump run, even though the car engine is also running. But when the system releases air, it is quieter, and hard to hear over the engine noise. I am not strong enough to tighten the chains when the TV/TT are hooked up level with the tongue jack raised. So I lift the tongue with the car attached, by a few inches. Then insert the bars and tighten them. I do this with the engine off (don't like breathing the exhaust). By the time I have both bars done, the car will have noticed the back end is too high, and will dump some air out of the shocks. (my car will never run the pump when the car is off, but it will dump air)

After I retract the jacks and start the car, it is normal for the air pump to run--it's restoring some of the air that I just tricked it into dumping.

You car is a newer model than mine, and it may be quieter when it dumps air, so you might not have the same sequence of events I have. But for me, it is normal to have the pump run an extra time at the end.

[dznf0g]

SSquared has it right. It has been my experience that once set up as I described above, the pump shouldn't run more than about 5 seconds after startup if you have set everything up right. If you take out the fuse to avoid pump running or exhausting.....DO PUT THE FUSE BACK IN after WD setup. It is important of any air "shock" system to have some air pressure in them, both for the health of the suspension.....and, in the case of factory systems, the stability control, trailer brake control, etc. systems are calibrated to the suspension tuning INCLUDING air in the system.

[Pat Cassity]

While testing my setup yesterday (during the 8 link test), after reinserting the fuse, the shocks inflated to the point that the rear end rose about an inch and a half. During the the 9 link test, there did not appear to be any additional inflation. Although, my weights appear to be good, I feel that I would experience better handling if I was able to go up to the 10th link (9 1/2 would be prefect!). However, it is extremely difficult to attach the bars on the 10th link.


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[dznf0g]

Don't ya know.....seems we always need half-links on the chain setups.

Pat, did you get any de-flation after moving to the 9th link? 1.5" seems like a lot....but the scale tickets don't lie. I assume the AS is level after all this?

[Pat Cassity]

No. No deflation after the 9th link. I set it on the 9th just off the scales. It was incredibly noisy so I'm not completely sure but I didn't hear the pump, as before.


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[Pat Cassity]

And yes, the airstream was completely level! I could probably get to the 10th link if I could jack the trailer up high enough. I wonder if there are issues with extending the jack to its highest point?


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[ROBERT CROSS]

Pat,

Jack away....but don't bump the stop, the fiber gears may strip if abused.

Bob