Futureal

I am sorry to break this to you but this was it for me, I have 240,000 miles on this car and I know it very well. Every OEM size tire I tried on it caused this rear wheel drift on bumps especially when tire got low on tread.

I put non OEM size , problem gone, GL drives like GL should be. Period.

eric_in_sd

The tire is an undamped spring. You can see this in monster trucks; they don't really have suspensions, except for the tire sidewalls, which are about as tall as the truck chassis. They bounce around like it's a game.

I bet the springiness of the stock size tires interacted with the springiness of the rear end, especially if the shock absorbers were not adequately damping. Futereal probably needs to replace the rear shocks. It can be very difficult to tell from ride feel if the rear shocks need to be replaced; it is something you only notice improvement on after replacement.

When a shock absorber is worn out, tire cupping often results. This can be masked if you rotate your tires front to rear, which evens out the wear. The exact mechanism is unclear to me, but has something to do with the tire wiggling freely in small displacements.

Futureal

I replaced my shocks when I noticed extra bouncy rear end over bumps about 150,000 miles after the tire / rear end shifting issue that was resolved by going to a wider tire. Not sure if shocks were contributing to rear end shifting because they had only 30,000 miles on them, early for them to go at that mileage and cause rear end shifting like I had and OP had ?

Max Blast

I’ve also had the “suv head shuffle” when going over a speed bump or railroad crossing at even the slightest angle in every GL I’ve had. This is a feature inherent in a unibody construction; tire sizes and compound can mitigate some of it, but it’ll still be there - and to your point, it seems worse with worn tires and especially with low cost tires.

eric_in_sd

Strange, I have never noticed it. Can't imagine what the unibody would have to do with it, except perhaps because it implies not a solid rear axle?

Most automakers design, or at least used to design, the rear suspension to toe in upon deflection. This makes the vehicle understeer - that is, steer to the outside of the turn - when the body leans. Very possibly this is what the GL is doing.

Recall also I figured out how to eliminate, or at least reduce, the rear negative camber. Tires develop what is called "camber thrust", in which the tire pushes in the direction it is leaning. So possibly our friend noticed a difference because he went to different tires because the different tires had a different (lesser) inclination to camber thrust.

It is a puzzle that MB specs allow for negative camber at ride height. Maybe that is to prevent excessive positive camber when the suspension is raised. But at ride height you really want all four tires to be perpendicular to the road and parallel to the direction of travel, possibly with some toe-in to offset flex in the suspension allowing toe-out deflection on the front wheels, especially when braking.

Max Blast

I thinks this thread may be beginning to pull together two similar sensations - one, being swayed side to side (particularly in the back seats) when taking a bump or unevenness at an angle, and the other being sideways roll from excessive camber due to worn shocks.

OP had worn shocks, presenting as roll over bumps. Later contributors are, I’m feeling; commenting more towards the inherent “suv head shuffle” you get when crossing uneven surfaces at an angle - more a sway motion.

Eric, try to take a speed bump or short speed strip at an angle with rear seat passengers. They might probably feel this sideways sway sensation more pronounced that you, the driver.

This sensation is completely absent in my 3/4 ton Chevy, for other reasons such as high sidewall and body on frame.

BlownV8

My old GL450 had the bad swaying action at slow speeds over side to side bumps. When I switched to a wider offset and 305/40/22's the side to side motion was mostly eliminated. My GL63 doesn't do it but my GLS450 does. The wheel width/offset/wheel/tire ratio has a big affect on the swaying.

Wicksy

Hey Everyone,
I have a 2014 GL550. Same issues, rear suspension hits too hard over bumps, vehicle will jump to the side hitting bumps at high speed, it's eating up rear tires in about 4 months and is not good in the snow. My wife refuses to even drive it in bad weather anymore.
I've replaced tires, new shocks, new struts and had an alignment and the problem still persists. Our mechanic can't figure it out either. They say all readings for ride height etc are correct, bushings etc look good. I don't know how much more money I can throw at this thing, we love the vehicle, but live in Minnesota and we can't have something dangerous for my wife to haul around the kids in.
Any ideas before I lose my mind for the millionth time?!

Miguk_Saram

Sounds like either your SWAY BAR, or SWAY BAR BUSHINGS are the issue (not the LINKS, the BAR itself).

Wicksy

One main reason the rear tires are being eaten up so fast is the suspension seems to hit hard on the recoil of a bump. Could this be the stabilizer links as they seem to connect up and down rather than side to side? There is definitely a rattling in the rear when we hit bumps.
Or is this a bigger issue such as subframe bushings? Would these allow the suspension to drop too fast making the tires hit harder after a bump?
As sorry, just want to get it dialed in before I spend more money on this mystery.

Miguk_Saram

Stabilizer bar = sway bar. Stabilizer links = sway bar links. Different terms for same component(s).

Yes, the links may also need replacement, however, the sway (loss of stability) is typically a symptom of the sway bar bushings needing replacement. When the LINKS go bad, you would typically hear a clunking noise going over bumps (as opposed to a rattle).