Okay, so it looks like I was indeed mistaken. I measured a 240D rear spring, not front. Front spring are indeed 4 9/16" in diameter. Apologies, DV.

All is not lost, however. With a turned down front frame plate to fit the stock upper spring cup, and a shorter spring, along with a custom made lower spring perch, I think the weight jack setup will still work. I just have to keep the adjustable upper spring perch adjusted lower than the body sheet metal. Either that or cut W116 springs which would be ~500lb/in at 13.5" tall (cut down 5"!).

The rears should still work with 5" or 5.5" springs and adjusters.

What are you thinking for sway bars?
I have an idea for the rear by using a 90's Ford Thunderbird rear bar. I was at my local wrecking yard and shoved a Thunderbird rear bar under a w123 sedan. I think this may work with a little fabing. It is about an inch or so narrower than then the w123 bar, but it clears the wheel well. It is also short on the arms, but you can easily make and bolt on extensions to make up the length and perhaps the width by angling the extensions outward.

Here are some pics of the bar next to the stock bar. It's about 18-19mm thick compared to the stock 13mm.

http://www.peachparts.com/shopforum/...arswaybar4.jpg
http://www.peachparts.com/shopforum/...arswaybar1.jpg
http://www.peachparts.com/shopforum/...arswaybar2.jpg
http://www.peachparts.com/shopforum/...arswaybar3.jpg



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DV, I was actually thinking of not even attempting a sway bar upgrade. Anything OEM would be a very minor upgrade and anything non-OEM would be a bit too pioneering for me.

Does anyone know if lower control arms are the same for W123 and W126? If the arms are the same without spring perches, then the perches should interchange. If that is the case, I can use 5" standard springs, so long as the weight jack located the top of the spring below the upper spring cup.

The lower control arms (front) on the first generation W126 are the same as the W123.

The trailing arms are shared too (and with other models)

Don't go too stiff on the rear bar without a limited slip diff, you will be lifting the inside rear wheel allowing it to lift off the pavement. ( Remember, anti roll / sway bars just transfer weight from the outside to inside wheel.

With your front suspension, clamping a 2nd bar the original might be a better option. ( or adding a bar in a more facing forward conventional location. )

You can get straight bars with splines on each end and clamp on arms.

Speedway Engineering's Sway Bars

Sway Bars

In order to give people a general idea of the direction I'm taking this project, I wanted to outline the budget that I have laid out thus far:

So I'm up to over two grand and I haven't done any power upgrades or maintenance. My initial goal was to complete this car for under $2000 including the $400 purchase price. Now with a minimum of a front end rebuild and water methanol injection, it's looking like I need to increase that number to $3000.

I knew from the get-go that I'd probably lose my ass. But damn! :(

Personally I don't think going to 18-19mm in the rear sway bar will not be too drastic. Both R107 and w116 has about a 19mm rear sway bar and a 24mm front sway bar from the factory. The smaller r107 handles pretty good, but has a completely different front suspension setup - rear is the same as the w116, w123, and w126.
Since I bring up the w126 chassis, the offered swaybar setup is 24 mm up front and 13 mm out back with an optional 17 mm rear on some models.
Now the w116 has a similar front suspension setup and rear suspension as the w123 and w126, but I'll tell you, I'll take the factory w116 handling over the w126 any day. My experience, those factory w116 will out corner any factory w126.
In taking what Mercedes offered, I think an 18-19mm rear swaybar will help immensely on a w123. I don't even think oversteer would be an issue with this thicker bar.




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Well there were other routes you could of taken on the cheap, but it would seem so far you are going to have a fully adjustable suspension that you can fine tune rather than throw in the cheap parts and hope they will compete to your satisfaction.



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I know of people who have spent way way more than $3000 just getting a W123 road worthy.

Like the saying goes - there's no such thing as a cheap Benz.

I think you are doing really well - considering your initial budget you've got some treats in there for yourself.

It doesn't need much. I have to pull the front end apart anyway to install W126 spring cups, new springs and shocks. The driver front LCA ball joint is missing the boot, so if I have to replace one I'll do both, and probably the other front end rubber bits, at the same time. I'll be doing both this car and my wagon semi-simultaneously, so I can save on tool rental fees.

I haven't actually got all what I listed above. I have wheels and tires ready to go and that's about it. So if I need to abort I still can. Besides that, I have most of what the car needs to be road worthy - shifter bushings, air cleaner bracket/rubbers (which now I don't think I will use! :( ). It needs front brakes (plan: first gen W126 vented rotors and calipers). But all this stuff is relatively minor. I think I'm doing alright.

Ok, so this is the method I used to determine what spring I need I the front. I need a hand with double checking my math.

This is the information on the stock front springs that I got from Brian Carlton on this site.

And using the drawings from earlier I made the following rough estimates.

Using a tape measure through the spring hole, I measured the compressed spring length to bee right 12 in at stock ride height. Thus, to lower the front end 1.5 in from stock, I would need a total height (of the aftermarket spring plus weight jack) of 10.5 inches. Additionally, since an aftermarket 5 in spring is too large to fit the upper spring cup, it will have to reside completely below it. The cup is around 1.5 in tall, I'll call it 2 in to be safe. More rough math follows.

Therefore: I need some spring that, with a 912 lb weight, will be somewhere around 8.5 inches tall. Using a 600 lb/in spring (wheel rate = 390 lb/in) that has a free height of 10 in will end up being 7.66 in tall compressed. Adjusting my weight jack to 2.84 in tall will then bring me up to my requested 10.5 in "race spec" ride height.

Whoo! Anyone feel free to poke holes in that bilge. Ideally I want to run the tallest springs possible with the shortest weight jack. I can probably fit an 11 in spring, with a jack height of 1.83 in, but I have to more accurately measure how tall the upper spring cup is first.

Ummm - it is a bit difficult for me to follow exactly what you are up to but I think you might have missed the point that the stiffness or rate of a coil spring is proportional to the number of active coils.

An active coil is a coil that is not touching another.

Look back at the link I gave to that vacuum pump thread to see the equations you need - also please note different springs were fitted with different stiffnesses / rates for different chassis and engine weight combinations. You should ideally pick out a couple of springs that you think you might be able to find and then start from scratch with the measurements and length adjustments.

Stretch - aftermarket springs are available in known rates at varying lengths - 9.5, 10, 11 ,12, 13, 14 inches seem to be the most common. When I refer to using a 10" or 11" spring, I am not talking about cutting coils, I am talking about totally different pieces.

Behold! An 11" 600 lb/in spring.

Nice find on the spring. Can't comment on the Math, though I think it looks good.

Looking forward to seeing the progress...


BTW - looking at the picture of the spring I see it is flatten on the ends. This will work on the top, but if you plan to use it with the stock shape MB bottom perch/plate, you may have to cut a coil off to have it seated properly.


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No I get that - but - you need to know how many turns of the coil you have for each spring.

When you have a spring that has say 10 free coils that are not touching each other you've got a stiffness that is equal to say X N/mm

Compress the spring to fit it in the car and you might find that you've only got 8 free coils that don't touch each other. The stiffness will be INCREASED to say XX N/mm

If you then want to change the height again for a race situation then you may only have 6 free coils that don't touch each other so you've then got a stiffness of XXX N/mm

The over all length of the spring and the number of turns and the gauge of the wire and the mean diameter are all important considerations (assuming you know what stiffness you want from a stability calculation)

[Also if you want a height change on the front springs you'll end up with some pretty messed steering geometry / camber / castor on a standard W123 front suspension design]