W123 racing setup - serious questions within

[Secondaries]

Hi all. I'm in the planning stages of building a $300 '85 300D into what I hope will be a competitive car in its SCCA Auto-X class. I am looking to stay within a budget, most of that money spent on wheels, tires and suspension upgrades, with perhaps a small turbo upgrade if modest pump mods will allow it.

My questions are primarily suspension related.

1) Can anyone tell me which car had the stiffest front / rear springs, regardless of length? My initial research leads me to believe 560sel front and 420sel rear springs are in my future. Plan is to find the stiffest and then cut them to ride height.

1a) Anyone have the above springs for sale?

2) Since the rear end alignment is non-adjustable, rear ride height will be dictated by what camber I end up with. Anyone know how low I can go to keep negative camber in the -1.5 to -2.0 degree range?

2a) With the above question in mind, what can I expect my rear toe to look like?

Thanks in advance for any help I get. I will post photos of my progress!

[Stretch]

The rear end - when stock - isn't adjustable, however, fastlane used to sell eccentric trailing arm bushings. I don't know if pelican still have them...

...you'll have to look...

If you want to see the springs fitted to W123s in a nice long list then look through chapter 32-250 in the FSM (don't just restrict yourself to the W123 FSM - the same chapter number is used on other models - however you probably won't be getting anything other than W114/115 W116 W123 or W126 springs to fit)

If you want to calculate spring stiffness / rate then have a look here More than you are likely to ever want to know about OM61X piston vacuum pumps (sure I'm droning on about vacuum pumps in this thread but there's coil spring calculations buried in there too)

If you need help making calculations just say.

I don't know exactly what you are trying to achieve however but there was a guy in England doing something similar - I can't remember his user name but he did post here as well as on BW asking similar questions

[Secondaries]

Originally Posted by Stretch

The rear end - when stock - isn't adjustable, however, fastlane used to sell eccentric trailing arm bushings. don't know if pelican still have them...

...you'll have to look...

If you want to see the springs fitted to W123s in a nice long list then look through chapter 32-250 in the FSM (don't just restrict yourself to the W123 FSM - the same chapter number is used on other models - however you probably won't be getting anything other than W114/115 W116 W123 or W126 springs to fit)

If you want to calculate spring stiffness / rate then have a look here More than you are likely to ever want to know about OM61X piston vacuum pumps (sure I'm droning on about vacuum pumps in this thread but there's coil spring calculations buried in there too)

If you need help making calculations just say.

I don't know exactly what you are trying to achieve however but there was a guy in England doing something similar - I can't remember his user name but he did post here as well as on BW asking similar questions

Thanks for the FSM chapter info - very useful info there. There is a 420SEL in a local junkyard that I intend to pilfer front and rear springs, as well as spindles/brakes for vented rotor upgrade.

I understand the fact that the reader suspension alignment is nonadjustable. My question was concerning lowering vs. camber gain. I do not want to lower so much that I overshoot my -2° maximum camber. I ask simply to avoid some or all of the guess-and-check method (read camber, lower, read again, lower ad nauseum). KMAC camber kits are out of my budget.

I guess a better thing to ask for is, if you have lowered your car, to post what camber you ended up with. More info the merrier.

[Stretch]

Originally Posted by Secondaries

...
I understand the fact that the reader suspension alignment is nonadjustable...

I can't answer by how much the camber will change by lowering but if you were to remove the rear springs and simulate different ride heights (change the ride height with a trolley jack) you could measure directly.

If you want lower but the camber isn't suitable you can then change the camber with those eccentric bushings I mentioned.

[97 SL320]

I've done this kind of thing before on various cars ranging from gutted regular cars to Formula Ford with a bunch of things in between ( Non MB so far but a 91 SL300 R129 is in the works )

Read the rules carefully if you intend on making a class competitive car. Some of the cars I've built ignore the rules going for low cost mods that are effective but put the car in a high end class.

While using stock springs sounds like a low cost way to go, it requires much research and a spring rating tester. You then get to juggle spring height and rating to get the ride height you want.

A much better route is to use universal racing springs and adjusters, these can be had in 2" or 2 1/2" ID with flattened and ground ends , 5" ( Ford ) and 5 1/2" ID ( GM ) with one end open pigtail and one flattened and ground end. The are also available in a multitude of pounds per inch of compression ratings and are all over the used market due to racers constantly changing their setups.

These are not difficult to adapt to a regular car but it does require some welding.

Have a look at oval track parts sellers, AFCO is a big name. You will be looking for " Weight jacks" these are threaded shafts and a spring plate. Also look for "hidden adjusters".

You will want to take most of the roll stiffness in at the front unless you have a limited slip rear.

Does the motor have a turbo now? Don't get lured into a large turbo, your RPM will be lower than you think so stick to a small one.

Do you have any pics of the rear suspension system? Is this a swing axle type or the multi link found on a W124 / R129 / W210? A couple of heim joints and a sleeves can make adjustable camber at low cost.

The amount of rear toe is dictated by the amount of motor in the front. More power requires more rear toe in. However, in an autocross situation you can get more aggressive with less and less toe in as you want the tail to step out a bit.

You will want some toe out in the front to give the car good turn in.

[Secondaries]

Originally Posted by 97 SL320

I've done this kind of thing before on various cars ranging from gutted regular cars to Formula Ford with a bunch of things in between ( Non MB so far but a 91 SL300 R129 is in the works )

Read the rules carefully if you intend on making a class competitive car. Some of the cars I've built ignore the rules going for low cost mods that are effective but put the car in a high end class.

I don't intend this car to be class competitive. I intend it to beat a friend of mine (friendly rivalry).

While using stock springs sounds like a low cost way to go, it requires much research and a spring rating tester. You then get to juggle spring height and rating to get the ride height you want.

A much better route is to use universal racing springs and adjusters, these can be had in 2" or 2 1/2" ID with flattened and ground ends , 5" ( Ford ) and 5 1/2" ID ( GM ) with one end open pigtail and one flattened and ground end. The are also available in a multitude of pounds per inch of compression ratings and are all over the used market due to racers constantly changing their setups.

These are not difficult to adapt to a regular car but it does require some welding.

Have a look at oval track parts sellers, AFCO is a big name. You will be looking for " Weight jacks" these are threaded shafts and a spring plate. Also look for "hidden adjusters".

Preaching to the choir buddy! I would love to use coil sleeves but it seems very difficult to adapt them to use with W123 suspension, front or rear. I also can't use stiffer sway bars to utilize 800+ lb/in springs!

You will want to take most of the roll stiffness in at the front unless you have a limited slip rear.

Does the motor have a turbo now? Don't get lured into a large turbo, your RPM will be lower than you think so stick to a small one.

Yes turbo. No turbo swap. If anything I intend to use a larger trim compressor wheel for better high boost efficiency. Stock compressor goes downhill fast after 12psi and I'm imagining at least 16psi.

Do you have any pics of the rear suspension system? Is this a swing axle type or the multi link found on a W124 / R129 / W210? A couple of heim joints and a sleeves can make adjustable camber at low cost.

The amount of rear toe is dictated by the amount of motor in the front. More power requires more rear toe in. However, in an autocross situation you can get more aggressive with less and less toe in as you want the tail to step out a bit.

You will want some toe out in the front to give the car good turn in.

I doubt I will overpower this chassis. The rear toes in dramatically with lowering, and there is no way around it. I autocrossed my 300td and quite frankly, the thing holding me back most was corner exit power, body roll be damned!

Thanks for the good insight, but I think I need some more 123 specific info (like that exists).

[Stretch]

I don't know if this guy can help

http://www.peachparts.com/shopforum/performance-paddock/320795-w123-track-car-i-need-stiffer-springs-info-needed-help.html

[97 SL320]

Originally Posted by Secondaries

Preaching to the choir buddy! I would love to use coil sleeves but it seems very difficult to adapt them to use with W123 suspension, front or rear. I also can't use stiffer sway bars to utilize 800+ lb/in springs!

I never said to use coil over shock mounts ( Though they are the way to go if a car has struts, in that case you will spend sub $ 75 per corner less springs ) . The springs will remain in the stock location just a bit shorter and with a threaded adjuster in the upper spring perch. Again , look up weight jacks in an oval track catalog. Adjustable spring spacers can even be made from a couple of pieces of pipe and large washers though the screw type are faster to adjust.

You might even be able to retain the stock springs and cut them,( though I'd just head straight for universal racing springs to reduce the hassle ) the rears on my R129 have flattened and ground ends on the car side, open end on the suspension side. The open side is where the cut will occur.

Remember, when you cut a spring the rate goes up. In general, if you have 800 Lb/in springs with 10 coils, each coil cut increases rate by 10 %. Only a rate checker will get you closer. Also be sure to use a properly formed lower spring seat otherwise the pig tail will be active altering the rate.

Someone please post a pic of W123 front and rear suspension showing the springs. Converting to adjustable perches isn't as difficult as you are making it out to be and well worth the effort.

In general, the stiffer the springs the softer the anti roll bar. Road cars usually soft springs for good ride and stiff ish bars for roll control. On a race car there are limits to how much bar you can run without lifting the inside wheel. My Porsche 914 has stiff springs all around, a front bar and no rear, when I ran a rear bar it would lift the inside wheel. Lacking a limited slip the car would then just spin the inside wheel.

Originally Posted by Secondaries

Thanks for the good insight, but I think I need some more 123 specific info (like that exists).

It's your choice to ignore what will work then struggle in the dark.

[Secondaries]

Front suspension.
click here for a large photo of the spring/shock arrangement.


Rear suspension (from a wagon, disregard the hydraulic stuff).

[97 SL320]

Use the Adjuster Weight Jack for the front, the disc on the left has a threaded hole. Remove the stock spring and rubber stuffer. Trim the disc to fit where the old spring was. Install with threaded nub up _ THROUGH THE HOLE THAT ALREADY EXISTS IN THE UPPER SPRING SEAT_. Use a couple of 5/16" dia grade 8 bolts through everything to keep it from falling out.

Install the threaded rod through the hole, the end of threaded rod then sits in the cup ( from the top as the pic shows ) . This cup should work for 5" or 5 1/2" ID springs, if you are using smaller dia spring, a proper cup will need to be made. This will be adjusted using a 1/2 drive ratchet from under the hood of the car.

For the rear, use a Adjuster Hidden, the gold one on the left would likely be more suited to your needs. These are usually installed loose but you could bolt it to the car. This will be adjusted by trial and error with the spring out of the car. If you measure ride height before a change, how much you rotated / how tall the spacer is you can generate a If / then chart.

in any event you will need to decide on what diameter spring you are using to be sure the adjuster will fit.

Simple no?

[97 SL320]

Another type of weight jack.

Also, if going with a universal racing spring, be sure to alter the non adjuster side spring seat so the spring does not escape. This consists of welding in a 2" ish tall tube that engages the ID of the spring.

[Secondaries]

This is honestly the first time I've seen that setup but it is interesting. Having trouble finding what it looks like installed. Any help?

[97 SL320]

I'll look around a bit. Also have a look at oval track race cars where this type of thing originates.

Also have a look at Ford Mustang " Fox Body " rear spring adjusters.

[97 SL320]

Here is another company that sells weight jacks. Weight Jack/Spring Cup

Half the battle in building a race car is finding out that parts exist and where to get them.

[97 SL320]

More. For your front suspension, the upper disc goes against the body, the lower cone against the spring. These light weight jacks are too light for your needs but HD ones ahve the same shape.

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