PeachParts Mercedes-Benz Forum - 300TD torsion bar in a 300D, are both needed?

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300TD torsion bar in a 300D, are both needed?

I recently just scored a 25mm 1985 300TD front torsion bar at my local pick your part and im rather excited to put this wagen bar in my 300D sedan. I had a question though about the pairing, Ive been told there is two torsion "sway bars." One in the front, which I have, and one in the back, which I can still pull from the salvage yard. I wanted to put just the big bar in my sedan but I need to know if that will cause problems if I dont have the wagen's rear bar placed in the rear of my sedan. Does anybody know if its okay to just have the front one "upgraded?" Would it ride better with both upgraded instead? I really want the low speed corner stability this bar will give me, but before I put it in, it is essential I know what difference itll make between axles. If I must pull the rear bar out of the stationwagen, could someone enlighten me onto how? Thank you!

Not talking about the rear "sway bar links" for clarification.

There is a balance between the front and rear bars affecting what IIRC is called "roll coupling".

The best ride will be with no swaybars (anti-swaybars, aka: torsion bars actually). The swaybar reduces body roll.

If you increase the stiffness of the front swaybar and leave the rear the same, you will increase "understeer" or make the car "loose", which means that the front end will have a tendency to slide more easily vs the rear. This is usually how FWD cars behave, and most cars today, it is safer for the novice driver to have the front end slide than the rear come around.

If you increase the stiffness of the rear swaybar and leave the front the same, you will increase "oversteer" or make the car "tight", which means that the rear wheels will break free more easily in a corner/curve and come around on you, which is more dangerous (especially to a novice or when unexpected) and you have the potential of losing control completely and going backwards into the trees like lifting the throttle on an early 911.

Badly worn shocks will have a similar effect: worn out front shocks and good rear dampers will allow the front wheels to bite on a quick double-lane-change type swerve as they will follow the road, and the stiff rear will lift a wheel enough to slide, ... vice-versa if the front shocks are new and rears worn.

This is not icy-road stuff, your car doesn't really have enough weight transfer on really slippery roads for the swaybars to have any effect. Mostly this is when you're at speed on dry pavement, and to some degree wet pavement.

In racing shocks are adjustable, swaybars are adjustable, and tire pressures adjusted as changing track conditions and geometry will require different suspension tuning to compensate. In a car such as yours, the balance that Mercedes has dialed in is a compromise between comfort and safety, handling and predictability.

So in short, stiffer bars on both ends should lead to better handling, but somewhat stiffer ride. Stiffer front will increase the tendency for the front end to slide in a curve, stiffer rear will increase the tendency for the rear end to slide. The same correlation with stiffer shocks front vs rear for quick maneuvers.

I do not know on the 123 cars whether the rear swaybar transfers from wagon to sedan, I don't believe that it does on the 124s.

There were two rear sway bars for the W123. Think stock is 13mm and the heavier duty
one as used in the police, ambulance and other heavy duty vehicles was a 15mm which I believe is NLA.

Been a while since I read up on them.

WINMUT installed the front TD in his 300D. There is and was pictures of the install
over on STD.

Yeah!!! found the thread. :D
Big front sway bar

I installed the TD front bar on my 85 300D, just haven`t got the car up and running.....yet.
I had the engine out when I installed it, and was a PITA to get it in. SOB isn`t going in :( ...and then
after the right combinations of words, she goes in. :)

Be sure you order the bushings for the TD and not the Sedan where it bolt to the Firewall.

Charlie

Quote:

Originally Posted by babymog (Post 3595276)

There is a balance between the front and rear bars affecting what IIRC is called "roll coupling".

The best ride will be with no swaybars (anti-swaybars, aka: torsion bars actually). The swaybar reduces body roll.

If you increase the stiffness of the front swaybar and leave the rear the same, you will increase "understeer" or make the car "loose", which means that the front end will have a tendency to slide more easily vs the rear. This is usually how FWD cars behave, and most cars today, it is safer for the novice driver to have the front end slide than the rear come around.

If you increase the stiffness of the rear swaybar and leave the front the same, you will increase "oversteer" or make the car "tight", which means that the rear wheels will break free more easily in a corner/curve and come around on you, which is more dangerous (especially to a novice or when unexpected) and you have the potential of losing control completely and going backwards into the trees like lifting the throttle on an early 911.

Badly worn shocks will have a similar effect: worn out front shocks and good rear dam;)pers will allow the front wheels to bite on a quick double-lane-change type swerve as they will follow the road, and the stiff rear will lift a wheel enough to slide, ... vice-versa if the front shocks are new and rears worn.

This is not icy-road stuff, your car doesn't really have enough weight transfer on really slippery roads for the swaybars to have any effect. Mostly this is when you're at speed on dry pavement, and to some degree wet pavement.

In racing shocks are adjustable, swaybars are adjustable, and tire pressures adjusted as changing track conditions and geometry will require different suspension tuning to compensate. In a car such as yours, the balance that Mercedes has dialed in is a compromise between comfort and safety, handling and predictability.

So in short, stiffer bars on both ends should lead to better handling, but somewhat stiffer ride. Stiffer front will increase the tendency for the front end to slide in a curve, stiffer rear will increase the tendency for the rear end to slide. The same correlation with stiffer shocks front vs rear for quick maneuvers.

I do not know on the 123 cars whether the rear swaybar transfers from wagon to sedan, I don't believe that it does on the 124s.

You've mixed up tight and loose. Oversteer is loose and understeer is tight. Putting on a bigger front bar will make the car understeer more.

I'd recommend putting on the rear bar from the wagon too as it will be a good match for the front bar.

The rear bar should be pretty easy to change....the front...not so much!;)

And if you run with no rear bar the rear of the car will feel a bit loosey-goosey..

Yeah, I always knew understeer and oversteer, saw the "tight and loose" more as a NASCAR thing, ... and always get them backward.

I've put larger diameter (stiffer) sway bars on both ends of my W124. The front is easy, the rear not so much--a lot more stuff to unbolt and get out of the way. Sounds like the W123 is different. I never played with the suspension when I had one.

Because the stiffness of a torsion bar is proportional to the fourth power of the diameter, a little difference can have a large effect. It's certainly wise to keep the two "balanced," that is, put wagon bars front and rear rather than just one.

Jeremy

Are the stock rear torsion bars on the sedan 13mm? I was looking and I heard the stock rear torsion bars on the wagen are 13mm too, and there is a special 15mm bar made for special purpose vehicles. As for the front I know to get wagen bushings, I took both the bushing bracket brace things from the salvage car as well.

Quote:

Originally Posted by Jeremy5848 (Post 3595425)

Yea it's the opposite on the W123. I haven't pulled them from a W123 but looked at trying to and the front requires a bunch of work while the rear shouldn't be bad. As for the W124, being the same set up as a W201, I've done both a couple of times, the front is easy but the rear requires dropping the subframe.

Great link charmalu, now lemme think what color to paint it!

Here is a good thread on the front bar and part#`s for the Bushings...with pictures.

Part numbers are as follows.

123 323 12 85 for the wagon version with a 25mm sway bar.

123 323 05 85 for the sedan and coupe version with the 24mm sway bar.

http://www.peachparts.com/shopforum/diesel-discussion/345909-w123-td-anti-sway-bar-bushings-n-la.html

Charlie