ML wheel carrier, do i need new springs

[SATURDAY KIDS]

Hello Chaps, I have just bought a wheel carrier for my 2000 320 ML, i have noticed in a post on here that i will need uprated springs on the back, i had no idea, would it be okay without upgrading or is it essential, if so how much am i looking at.
Any help much appreciated

 

[Cole@MBS]

Whats the difference with putting a Engine bock in the back or a spare wheel! these things are built to stand off road crap,

Im sure it can stand up to a spare wheel on its arse!!

 

[SATURDAY KIDS]

Fair point, i would not have thought about it if i had not read the thread on here, so just thought i'd ask.

 

[Cole@MBS]

I fitted a set a few weeks ago, there a heavy set of springs! i dont think you need to worry!

 

[psmart]

The springs are poorly designed and stress fracture as the ends arent turned up/machined. Ive had a set replaced and another has gone on an 89K ML. Just for interest, the springs and shox are contained in one and are expensive.

Ive carried a lot of weight ovr the years in the back, so this could relate to me having to replace them, but in answer to the original poster, your already carrying a spare wheel under the rear end, so removing this and adding the bracket + full spare wheel isnt going to add much more weight.

 

[Xtractorfan]

You're not getting confused with heavier springs being needed when boot spoilers etc are added ..the springs in question being the actual boot lid or tailgate springs...

 

[SATURDAY KIDS]

Thanks very much, ive just been reading a US MB forum and some swear by the upgrade others shrug it off, i just want to be sure as an upgrade is going to be out of my price range by the sound of it.
Thanks for the advice.

 

[SATURDAY KIDS]

No definately heavy duty suspension spring upgrades, i must admit it did surprise me that ML's with factory fitted wheel carriers have an automatic upgrade, 'apparently'

 

[psmart]

That would be an admission by Merc, fitting uprated springs when carrying an external wheel = they know the Hydroponic units are of poor workmanship! I used to tow a caravan and I forget the towball limit, but it was high, more than a wheel.

One thing though, not sure how air mass travels over and around the ML, but perhaps a constant pressure applied on the wheel/carrier by wind warping round the vehicle could be cause for concern?

 

[oigle]

Jeez, PSMART, what planet are you on?? ML's don't travel at warp speed
Seriously though, I tow a caravan with a 210kg towbar ball weight (way over the reccommended 80kg) and I use weight distribution bars to redistribute the weight evenly front to rear on the ML. Even with this weight plus a boot full of gear, I have never had an issue with the rear suspension other than for poor rebound shocker control. This I cured with the use of Bilstein dampers - they are great.
To even consider that a spare wheel and carrier on the back would affect the vehicle suspension is quite ludicrous - as someone said, the smaller spare is already under the back and is just being relocated, plus a bit of extra weight.

 

[JEZ.S320L]

We drove from the UK and down to Spain with a VERY heavy load in the back - I guess it was a bit heavier than a spare wheel. Oh, I DID have a spare wheel in the boot..! Guess what? The suspension didn't brake - and all with standard springs

 

[SATURDAY KIDS]

Okay thanks chaps, i think that really answers my concerns.

 

[psmart]

Jeez, PSMART, what planet are you on?? ML's don't travel at warp speed

It does sound like a joke but I was actually being serious! Consider a sports car with a spoiler, the spoiler is there to use the air-flow over the car, as it speeds up, to apply pressure on the rear end of the car to keep the back in-line. The Spare wheel carrier, although a little lower, but thick and bulky, may exhibit the same properties.

One journey isnt going to break the camels back, but continuous pressure may!

I keep asking myself, why, having had the car from new for the last 8 years, why so many things have gone/needed replacing. I dont thrash the car, its driven with respect, other than it does do high speeds (> 100mph) regularly and it does go off road (soft-offroading to the hard-core offroaders). It also has the largest Thule ski box on its roof 4-5 months of the year (again, read down force due to air-flow), it does regularly carry a fair weight, it lives at sub-zero temperatures (coldest being -38 for a week) in the Alps etc. I've had to replace all shox (rear Hydroponic units twice), ball joints etc, all in 89K, so the question is why? This would then answer Saturday Kids as to wether upgraded Hydroponic units are needed!

Best advise, put the wheel carrier on and enjoy, you may not use the car in a manner needing upgraded Hydroponic units.

 

[oigle]

It does sound like a joke but I was actually being serious! Consider a sports car with a spoiler, the spoiler is there to use the air-flow over the car, as it speeds up, to apply pressure on the rear end of the car to keep the back in-line. The Spare wheel carrier, although a little lower, but thick and bulky, may exhibit the same properties.

One journey isnt going to break the camels back, but continuous pressure may!

I keep asking myself, why, having had the car from new for the last 8 years, why so many things have gone/needed replacing. I dont thrash the car, its driven with respect, other than it does do high speeds (> 100mph) regularly and it does go off road (soft-offroading to the hard-core offroaders). It also has the largest Thule ski box on its roof 4-5 months of the year (again, read down force due to air-flow), it does regularly carry a fair weight, it lives at sub-zero temperatures (coldest being -38 for a week) in the Alps etc. I've had to replace all shox (rear Hydroponic units twice), ball joints etc, all in 89K, so the question is why? This would then answer Saturday Kids as to wether upgraded Hydroponic units are needed!

Best advise, put the wheel carrier on and enjoy, you may not use the car in a manner needing upgraded Hydroponic units.

Understand your concerns re airflow but doubt seriously that a wheel, mounted on the rear, out of the main airflow and living in a low pressure area, would affect the downforce at all. Way different from a spoiler which is situated deliberately in a high airflow area and shaped specifically for downforce.
Your issues with your car seem to be excessively bad, considering its age and mileage. I'd be inclined to think low temps could be blamed for much of it. Metal can become quite brittle at very low temps and I imagine shockers would almost seize up.
Your rear suspension units must be different from the ones fitted to the Oz spec vehicles. Made in the USA, perhaps the springs are local (USA)manufacture and don't have the design deficiencies evident in yours. I have really abused mine at times - a fully loaded camping trailer with 230kg ball weight all the way to central Oz and back (10000km) with no weight distribution gear (ML was sitting about 4 inches lower than normal at rear) and no broken springs. Plenty of rock damage underneath though due to lack of clearance:sad:
The USA spec shocks (KYB) are woeful. Bilsteins have proved much better.
Unless Saturday Kids is intending to heavily load his ML and use it very roughly, I would be very surprised if any upgrade to springs would be necessary.

 

[psmart]

Understand your concerns re airflow but doubt seriously that a wheel, mounted on the rear, out of the main airflow and living in a low pressure area, would affect the downforce at all. Way different from a spoiler which is situated deliberately in a high airflow area and shaped specifically for downforce.

Just floating ideas really as to potential reasons why Mercedes (may) upgrade the rear units (I was thinking more on the lines of Eddies and Vortices, but have no proof and could find nothing to substantiate this on the web). I spent quite some time looking at Detali to see if there were different part numbers, but my Russian is not very good, and then it struck me what the problem might be. Basically the unit is Hydroponic (combined spring and shock absorber) and the 'upgraded' unit probably has stiffer damping to cater for the wheel. Besides ride comfort, this would be important as the rear ESP would be working more to cater for the effects of having a weight pivoting on the rear of the vehicle bouncing up and down on every road undulation.

Your issues with your car seem to be excessively bad, considering its age and mileage. I'd be inclined to think low temps could be blamed for much of it. Metal can become quite brittle at very low temps and I imagine shockers would almost seize up.

I did consider this, but the motorhome and the Seicento both lived in these conditions and neither batted an eyelid (metaphorically speaking)! The motorhome was excessivey loaded (as they are, ie > 5 tons) to boot and no issues occurred. No other ideas really. As mentioned before, the Hydroponic units are of poor design (not my comments, but that of a Chief University Engineer after he examined the old and the new) and have a stress raser on them, which perhaps the cold excarcerbates!

 

[oigle]

Besides ride comfort, this would be important as the rear ESP would be working more to cater for the effects of having a weight pivoting on the rear of the vehicle bouncing up and down on every road undulation.

You are right about the ESP, but doubt the little bit of extra weight involved in moving the spare would have much if any effect, particularly if the rear shocks are of a good variety and not the KYB's fitted to the Alabama manufactured versions. When I use the ML to tow the van, particularly with the old KYB shocks, the bouncing motion caused the ESP to apply the rear brakes intermittently to attempt to control it. This resulted in the rear brakes wearing out in 43000km, and again at 85000km, versus the fronts still original at 86000km. I say this as something of an assumption as I can see no other reason for it and my MB dealer tells me the issue with excessive rear brake wear has only appeared since ESP was introduced...... I'm hoping the Bilsteins, which are much firmer, will resolve the issue.

With your rear suspension, have you investigated the possible use of another type of spring - either non-genuine or maybe Alabama manufacture - along with Bilstein shockers? I am rapt in the setup I have now.:grin: