Spring Color Codes

[Longtooth]

I need to get front end aligned, replace rubber, new shocks (perhaps)etc. and want to use the correct? rubber shims. Looking at the Big Blue Book (Service Manual) there are 2 versions of springs for the 250SL....

  Standard (PN 113 321 04 04)
  Harder (PN 113 321 08 04)

My front springs are color coded with 4 yellow spots, but my Service Manual (Modifications thru Oct '67) doesn't have "yellow" color codes for the springs -- just white, red, & blue.

1. Does anybody know what the 4 yellow spots on my front springs designate in terms of PN's or stiffness?... or where I can find the associated information?

2. According to the tables in my Manual, the Rubber shims come in 3 thickness's for cars with Air Conditioning (mine) + one other adder (Power Steering in my case)... which depend on the spring's color code... white color coded springs use 32.5mm, red 30mm, and blue 27.5mm... so of course, my springs having yellow markings on them doesn't tell me which shim thickness to use.

I want the harder springs

'67 250SL, 4 spd manual with air conditioning.


Longtooth
67 250SL US #113-043-10-002163
'02 SL500 Sport

[jameshoward]

The comment made by Jeff at as first response to my query was accurate.

http://index.php?topic=6576

I found the 4 yellow spots, then found the very faded colour coding.

JH

[hauser]

This was discussed briefly here before.  "Dotology"

http://index.php?topic=2746

1969 280sl 5 spd
Gainesville, Fl.

[Bob G ✝︎]

This is one of my projects I hope to get done when the weather clears. I took the stock springs out which gave a height of 25/1/4 to 26 inches rear left side and put in John Olson's progressive rate springs.We both did not have any idea of which pads for the front and rear would work. John Olson's springs are shorter.
 
I choose 25 MM front took out 32.5 I have AC. The front end is too low. I put 24 MM in the back end and took out 18MM. Now I have too much positive camber.

I meet a father and son Mercedes-Benz service in Long Beach and liked what the son had to say. I am going to give them a try and see if they can straighten out the mess I created. The only accomplishment is that some important bushings front and rear were replaced so it should be a taut ride with the new Bilsteins when I get it back.
Bob Geco

[Longtooth]

Bob, Spring length in unloaded state, especially when/if shifting types (standard, harder, progressives, etc) is not a valid measure of what size rubber shim you need to get a specific curb wt. height.  Reason is that the spring material properties (specifically, Young's modulus), diameter of spring rod material, and total length of the rod determines how much it will compress under a given load.

The spring height (as wound) in its free state (unloaded state) depends on the diamater of the rod and the total coil pitch (distance between adjacent coils, summed over all coils).  If rod diameter's are the same for one spring to the next, & Young's modulus is the same, then the difference in the sum of the coil pitch for one spring vs the other can be used to determine the correct rubber spacer thickness by for the new spring by adding the difference in sum of coil pitch to the old rubber spacer thickness ---- that will give you the same height of the car at curb wt as the old springs did.... assuming old springs weren't deformed.

Longtooth
67 250SL US #113-043-10-002163
'02 SL500 Sport

[Raymond]

Longtooth,
How is someone other than an engineer with the right tools supposed to calculate all that?  If you can do it, bless your heart.  The rest of us kind of use Kentucky windage.

Bob, For the rear, you have two choices.  Get the 18mm pads again, (cha-ching$) or cut a linear inch off of the spring rod.  A little shortening of the coil will go a long way so don't get carried away.  If you have progressive springs be sure to do that from the end of the spring with the wider coil spacing.

For the front, you can get some flange gaskets from McMaster-Carr that are the diameter of the spring pads.  They come in a pack of 6 for 4.95.  They are about 2 & 1/2 mm thick each.  You put them between the upper spring rubber and the seat.  Except for the having to remove the darn spring, it's an easy and inexpensive way to adjust the thickness of the rubber to adjust ride height.

Ray
'68 280SL 4-spd Coupe

[Longtooth]

Bob & Ray,
Sorry ... I'm an engineer.  Ray, you gave Bob the following as a possible solution to his camber problem:

Bob, For the rear, you have two choices. Get the 18mm pads again, (cha-ching$) or cut a linear inch off of the spring rod. A little shortening of the coil will go a long way so don't get carried away. If you have progressive springs be sure to do that from the end of the spring with the wider coil spacing.

When you cut the overall length of the spring you increase it's stiffness AND consequently for the loads being carried (dynamic loads) this increases the stress on the metal rod, therefore brings the spring material closer to it's yield limit & fatigue life.

At Curb wt, the spring will compress slightly less than before it was cut, so the net difference in curb height will be not be by how much the spring ht was cut, but will be that much LESS the reduction in compressed ht at curb wt.  For an approx. example, if you're cutting enough off the spring's ht (unloaded spring) to reduce the total windings by 1/2 of a turn (say 1/2 inch off spring height), the deflection at curb wt will be reduced by about 1/8th inch.... therefore the NET reduction will be 3/8ths inch rather than 1/2 inch.  This is a very approx. example just to illustrate the problem, since the actual values will depend on precisely what material the spring's made of, how many total turns it has before cutting it, & the rod diameter (and the curb wt, which I assumed for this example was 500 lbs on each spring at curb wt.)

Point is that there are some significant caveats to cutting the springs.. not the least of which is the increase in stress on the spring, a reduction in load to yield (permanent deformation), not to mention a reduction in fatigue life (the latter may not be an issue if the car's not driven a lot anyway, especially on rougher roads or on lot's of curves).  

Kentucky windage, huh?  When I was in Army we had some boys who used Kentucky Windage at the shooting range the 1st couple of sessions... sorry to say they couldn't score a passing mark until they started using the rules (distance to target with x clicks on the sight, not to mention some other things).  That was with some modified M1's in those days during Basic Training.  It wasn't that they couldn't hit the mark... it was that they had to take at least 5 shots before they homed in on it... in that time the "enemy" target would have either ducked for cover or shot back.  I will add, however, that the Kentucky Windage guys were better than everybody else in our company the 1st 2 sessions... after that though, the guys who'ed never had a carbine in their hands before actually scored the best in the end.

Being an engineer, I'm a tad bit biased though.

Longtooth
67 250SL US #113-043-10-002163
'02 SL500 Sport

[Raymond]

Okay.  Cutting a half a turn off the spring would be about seven or eight linear inches.  I don't have the spring in front of me but, from memory, the circumfrence is about 16 or 17 inches.  I can only tell you from my one experience that one inch made a more significant difference in ride height than your calculations suggest.  I had several conversations with Jim Villers before doing anything.  He has done several suspension improvements on 190s and Pagodas and I found all of his advice to be spot on.

My intended ride result may be different than yours.  I found my 39 year old stock suspension to be mushy.  I wanted something tighter, stiffer, and more predictable in a decreasing radius turn, (like an interstate clover leaf).  I got just what I wanted with the sport springs up front.  The progressive rate springs on the rear suspension have been a bit of a disappointment for me but might be just what the doctor ordered for someone else. I enjoy the experimentation.  

Perhaps instead of "Kentucky windage", I should have said, "An estimate of expected result derived from collected experiential knowledge and executed within the parameters of available means."  :mrgreen:

Ray
'68 280SL 4-spd Coupe