Why so sensitive to road crown? - PeachParts Mercedes-Benz Forum

Junkman · #1 11-22-2014, 05:28 PM

My SD seems more sensitive than it should be to road crown. It doesn't pull even at speed on a flat road but does with even a relatively slight crown. Lesser cars that I've driven recently don't do it and I doubt that the affluent original purchasers of these cars would have put up with it.

The front suspension doesn't appear to have slop in it and alignment doesn't appear to have an effect. I'm thinking the rubber in the suspension may be compressing even though it isn't obviously compromised.

Comments?

t walgamuth · #2 11-22-2014, 06:00 PM

Mercedes have a lot of caster in their alignment. It keeps them going straight in the wind but causes more pull on crown. They're designed to run true when being driven flat out on the autobahn. Most cars are built to steer easy around town.

PARSHOOT1 · #3 11-22-2014, 06:35 PM

He's a member with posts about the very same problem...and if I recall correctly, the very same car.

Junkman · #4 11-22-2014, 06:36 PM

Quote:

Originally Posted by t walgamuth

Mercedes have a lot of caster in their alignment. It keeps them going straight in the wind but causes more pull on crown. They're designed to run true when being driven flat out on the autobahn. Most cars are built to steer easy around town.

Perhaps. But I don't believe that the original owners would have liked it AND caster itself doesn't make for more sensitivity to road crown. Tracking straight is tracking straight.

pelon · #5 11-22-2014, 08:19 PM

Worn tires can be the problem.

leathermang · #6 11-22-2014, 10:53 PM

If you do not have the specs for vehicle height confirmed as being within limits... then an alignment is pretty much wishful thinking...there are two thick chassis manuals issued for most of our cars... which give all the specs for everything.... you know how those Germans are about this kind of stuff.....The combination of needing new springs and the rubber they rest in.... and any play in the steering components make a close approximation for toe in all you can really hope for on these old cars... this can easily cause the reaction to road crown you are describing....
ps... I worked at a spring and brake alignment shop at one time...first as mechanic then service writer...

Junkman · #7 11-23-2014, 05:27 PM

Sounds like a Summer project when I'm sure another car will be running.

SD Blue · #8 11-23-2014, 05:28 PM

Tire pressure and wheel bearing tolerances. The biggest one is overpressure of the front tires. If they are set to the pressures recommended inside the fuel filler door, they will wear evenly and cuts down on the "wander" considerably.

JamesDean · #9 11-24-2014, 08:56 AM

Quote:

Originally Posted by leathermang

If you do not have the specs for vehicle height confirmed as being within limits... then an alignment is pretty much wishful thinking...there are two thick chassis manuals issued for most of our cars... which give all the specs for everything.... you know how those Germans are about this kind of stuff.....The combination of needing new springs and the rubber they rest in.... and any play in the steering components make a close approximation for toe in all you can really hope for on these old cars... this can easily cause the reaction to road crown you are describing....
ps... I worked at a spring and brake alignment shop at one time...first as mechanic then service writer...

This is what I've come to understand as well. I just replaced my front coil spring and spring pads as per MB EPC. The rest of my steering components are all up to snuff too.

I just had it aligned on Saturday and it still needs some work. Somehow they managed to not get the wheel straight.

But the alignment is better though, mostly. I will have to scan/post the before/after spec sheets and get forum thoughts.

What pisses me off most is on two occasions I had great alignments. The car drove perfectly in the lane. No road crown BS. No pulling. I could let go of the wheel for a reasonable amount of time and the car would just drive straight. Still chasing after that...

I finally got my hands on the MB WIS from 2006. It appears to have lots of details about alignments and whatnot. More reading to do!

eatont9999 · #10 11-24-2014, 01:47 PM

After refreshing the front end on my first 300SD, I had it aligned at the MB dealership. It tracks as well as I could ask for. If the road has a lot of crown, the car will have a tendency to track towards the outside of the crown but every car I have driven does that. On a flat road at highway speeds, I can let go of the wheel for quite a while and the car tracks straight.

iamtheosprey · #11 11-24-2014, 10:42 PM

Quote:

Originally Posted by SD Blue

Tire pressure and wheel bearing tolerances. The biggest one is overpressure of the front tires. If they are set to the pressures recommended inside the fuel filler door, they will wear evenly and cuts down on the "wander" considerably.

Isn't that the truth...I was trying my hand at hypermiling by boosting air pressure only to find out that the car was eating tires.

I also noticed that the tops of the front tires looked like they were an inch further outward than the bottoms.

I set the pressure to factory spec and everything about the car improved.

It was smoother and handled much better.

What lesson did I learn?

TRUST MERCEDES ENGINEERS.

JamesDean · #12 11-24-2014, 10:53 PM

So how much would bearings have in the game? I noticed while changing my brakes a weeks ago or so that the passenger side hub spun much easier than the driver's. I also noticed some scraping sounds as the hub (passenger) side went around.

I did order new front bushings. FAG bearings. The listing said FAG but also said Ruville. I believe its FAG bearings with Ruville hardware (bolts, cap, etc). I also bought genuine MB caps too because I've not had an aftermarket one fit yet!

JamesDean · #13 11-24-2014, 11:58 PM

Might as well ask here:

In 40-0323 it talks about locking the steering with this contraption that attaches to the steering wheel. Then it lists out what else to do and says to adjust toe-in and then remove tools... Makes sense.

Then below that it shows the locking bolts for the steering gears...but makes no mention of them in the above instructions? Does that make sense?

I've never heard of that 129 589 01 21 00 tool before. Spreader bar and locking bolt/nut sure...

http://w124-zone.com/downloads/MB%20CD/W124/w124CD2/Program/Chassis/40-0323.pdf

Anyone have any thoughts?

fahrvergnugen · #14 11-25-2014, 12:24 AM

Alignment shops will have a tool to lock the steering wheel in place, MB might have a special tool for designed for Their cars but it isn't the Only one available.

JamesDean · #15 11-25-2014, 10:34 AM

I am thinking that my 300D's caster needs to be cranked up a bit higher than what it is currently at...I dont have the spec sheet on me right now so I am not sure.

Its going back to the dealership Friday because, somehow, they managed to not get the wheel straight. Going down a straight road puts the wheel around 11 o'clock.

When they correct this I'll ask about increasing caster. I just want it to drive straight down the road with me having to correct so frequently.