menschie

Normally I'd say you're right, but this actually was one of those perfect storms. Can't remember on the brakes. I got ceramic pads, not OEM. My rear OEM's are starting to squeak and they're pretty new. Grrrr.

Kyle C

​​​​​​@KrustyKustom For first time setting up the WDH, does it have the same procedure, maybe a write up on a hot to step by step set up?

lkchris

After reading the following, it seems a “weight distribution hitch” is unnecessary with the GL.

https://www.etrailer.com/faq-weightdistribution.aspx

Assuming your trailer ball is at the correct height and your trailer weight is within specification, Airmatic will prevent trailer weight from lowering the height of the rear of your vehicle. And, automatic traction control will prevent trailer sway. It’s really not necessary to apply ‘merikun covered wagon technology to a Mercedes.

As a side note, German regulations are very strict as regards headlight aim, and Mercedes uses Airmatic to maintain correct aim when weight is added to rear of vehicle ... including trailer weight.

six weeds

We have a 2012 GL350 and are buying a 25' 2017 Airstream. It's GVWR is 7,300 lbs. From everything I've read above, there is no need of a weight distribution hitch. Is that correct? The Airmatic will raise the rear height until it is level? Our GL had a hitch on it, but no wiring harness. I'll have to look at it tomorrow to see if it is a factory, or an aftermarket installed to carry a bicycle rack (no lights needed for that). Assuming it is not a factory installed MB hitch, and that the hitch is rated for 7,500 towing and 750lbs tongue weight, does anyone foresee any issues? I did install a 4 blade/pin wiring harness to tow our little cargo trailer. I haven't checked the Airstream (buying it out of state), but assume it is like my Nomad travel trailer with 5 or 7 pin round connector. So I'll most likely have to find a 4 pin to 5 or 7 pin adapter, or wire up a bigger harness to fit the Airstream. Also, the Bluetooth brake controller seems like the way to go and if it doesn't pair from the GL, I can pair it with my Toyota Tundra, then just move it over to the MB.

Any feedback y'all have concerning towing an 25' or longer Airstream with a GL350, weight distribution hitches, anti-sway bars/brakes, hitch capacity, towing capacity, wiring harness, brake controllers, and finally, miles per gallon when towing with a GL350 would all be greatly appreciated. I did just have all four airbags on the GL replaced.

Thanks!

N_Jay

The issue is the weight on the back will lighten the front even if the air levs the car you still have less traction when turning.
You will also have more bounce in the back which will wear the back tires.

six weeds

N Jay,

What is the solution for this "lightening of the front" end?

Thanks,

N_Jay

That is what a WDH does. It levers the back up and the front down.

The caution is you don't want to overload the front suspension as you can't tell load by height as with springs.

From axles do not have as much reserve margin as rear.

DennisG01

As noted above, the purpose of a Weight Distributing Hitch is to, well, distribute some of the tongue weight further forward, thereby lessening the amount that the rear axle sees. This will give a smoother, more secure ride.

rapidoxidation

How much is the GL rated to tow and what is the rated tongue weight? I'd offer that the vehicle tow rating is of way more importance than the hitch rating.
Asking as a 2013 ML350 Bluetec airmatic owner (7200# tow, something less than 500# tongue) that uses a weight distribution hitch on my 18' 1987 Kit Road Ranger (2800#).

Max Blast

7500 lbs with 600 lb tongue limit.
it’s really tricky to get all of those 7500 pounds behind you and staying within the 600 pound tongue limit.

Add that you have self-leveling suspension that is going to make a WDH set up very challenging unless you pull the air matic relay during bar setup.

N_Jay

Generally, if the car is off, and the doors are not opened, the AIrmatic will not try to adjust.

Also, set just a little lighter than you would with steel springs.

lkchris

Airmatic is a weight distribution system.

if your weights are within Mercedes specs, the headlights and the vehicle will be automatically and correctly leveled.

You do NOT need two leveling systems … meaning weight distributing hitch is irrelevant to GL.

Your vehicle will handle 600 pounds hitch weight without any effect on handling or steering. There is a gross vehicle weight rating specified, and you can put passengers and/or cargo and/or hitch weight in/on the vehicle up to that safely.

Again, within these published limits, you do not need a heavy duty radiator or transmission cooler. Mercedes builds your vehicle able to do what it says it can do.

when your hitch wiring harness is factory and properly connected to rear SAM, the vehicle will detect the trailer and vehicle will not lower at speed (like it does without trailer to promote better aerodynamics and fuel economy).

DennisG01

Chris, I'm not sure that is entirely correct. The air system and anti-sway control are extremely good. I've purposefully (aggressively) tested the anti-sway with a 6K boat/trailer and was quite amazed. However, while the air system LEVELS the car, it does not distribute any of the tongue weight further forward on the vehicle. Or, at least, I don't understand HOW it can do that, if it does!

Max Blast

To Chris’s point, I do have an experience on using WDH on a 6K trailer… It was scary. Might have been maladjusted, but I was left with the feeling that it shouldn’t be like this.

What I should’ve done was go without the WDH and do a trailer for Trailer comparison with how and if the airmatic levels and transfers load with and without WDH.

DennisG01

I can't speak to actually using a WDH with the Mercedes - or any air system, for that matter - as I have never done it. I've used WDH setups on spring axles and there's is NO DOUBT they make a noticeable improvement. I can't understand why (if setup correctly) it wouldn't work with air systems? But maybe I'm not thinking it through all the way.

N_Jay

It does not and can not transfer the load. All it does is level the car.

The GL has a fairly long rear overhang, so the trailer hitch has significant leverage on the rear axle (lifting weight off the front axle)

I have no idea how you adjusted (or misadjusted) the WDH, but would like to know what you felt when driving that seemed 'wrong'.

N_Jay

I use a WDH on my GL with a two wheel trailer and have moved the trailer without.
It is VERY valuable.

I also tow a 4 wheel trailer on a standard hitch, but although the tongue weight is higher it does not feel like it since the tongue gets lighter as it goes down. As opposed to the two wheel which has about the same weight all the way down.

Since the GL is IRS, any bounce in the back scrubs the tires in and out, and the non-WDH trailer wears rear tires much faster than the WDH trailer (since it has much less bounce.)

six weeds

Update on the 2012 GL350 towing: The Airstream 25' twin axle trailer has a GVWR of 7,300 lbs. The GL is rated for 7,500 gvwr and 600 lb tongue weight. My GL has a Curt hitch rated at 3,500/350 and only a 4 blade wiring harness. Lampert Hitch in Denver were very knowledgable, friendly, and professional. They simply told me that there are no aftermarket hitches that match the GL's ratings. Fortunately, I found a factory hitch with frame bracing and wiring harness from a dismantler for $350. Next week I'll pull the Curt hitch and replace with the stock hitch and wire in a 7 pin harness, add a Bluetooth wireless brake controller.

The Airstream came with a WDH. I'll follow the instructions posted above regarding hooking it up, adjusting it, then letting the Airmatic do its thing.

Thanks for all the great feedback and info. I'll keep you posted.

N_Jay

Make sure you have the factory 7 pin converter (tow module)
(It could be a function of the rear SAM, but if so you need programming.)

It adjusts the suspension and the transmission shift points when it detects a trailer.

With out it you will have a problem when at speed the Airmatic lowers and screws up the WDH alignment/adjustment.

six weeds

N Jay,

Thanks for the info. The factory hitch I found has the factory female connector and wiring harness. It should just plug in to a connector in the right or left LED brake light assembly. Do I still have to have the vehicle programmed, or is it plug and play?

Thanks!

N_Jay

I am pretty sure the factory wiring does not hook to the car tail lights.

The car even knows when a trailer bulb is out, separately from the regular tail lights.

Mine was factory, so I can't tell you how to retrofit.

six weeds

Thanks!

N_Jay

Is you mechanic VERY familiar with MBs?

Most will just hack in an aftermarket adapter.

six weeds

Yes, he's good.

N_Jay

Good can be really good at hacking things together which is a whole lot different than understanding the complexity of these vehicles.