[Vwdiesel] a2 Jetta rear suspension

[James Hansen]

Taking part of a compression spring out of action increases the rate,
rate being pounds supported per inch of compression.  ie- 500 pound 
spring needs 500 pounds to comress the first inch, 1000# to get to the 
second inch of compression, 1500# for the third inch etc..
Factors you can change to increase spring rate are decreasing the number 
of coils, making them bigger, or using thicker wire in the coils.  Since 
the spring wire can't be changed, taking a coil out of action increases 
the rate, or load the spring supports per inch of travel.  When you 
change to a "heavier" spring, that's what you're doing, selecting a 
spring that has heavier wire, or less coils over the same distance. (or 
different steel, but that's not as big a factor in passenger car stuff)
Passenger cars also have variable rate springs, where one end has the 
coils closer together, so part of the spring is more easily compressed, 
part is stiffer, giving a better ride over small bumps.  It's pretty 
common to lose a chunk of two off the softer end, because they fatigue 
from doing more of the work.
In the racecar, we just change springs to effect a rate change, and save 
the spring rubbers for small adjustments at the track during race 
conditions.

If the car is bottoming out, you need springs of a higher rate, or to 
load lighter.  ANYTHING you do to increase rate will improve on that. 
For instance, if my stock car has too much travel on the right front, 
adding half a rubber to the 1175 pound per inch spring that is in there 
now will add about 60# to the rate and decrease travel by approx 3/4 
inch in the turn.

When you say fully bottomed out, the springs still shouldn't be in coil 
bind Brian, the bump stops on the shock should prevent that.  Putting a 
spring repeatedly into coil bind kills it dead, and is usually why a 
spring gets broken- the shock dies and the oil leak kills off the bump 
stop, which kills off the spring, increasing the $ to fix eventually.

Some math just for giggles:

spring rate= modulus of spring steel X Wire diameter4 / 8 X number of 
active coils X mean coil diameter3

where modulus of spring steel = 11,250,000 pounds/inch2

With this, if you want to raid the junkyard and make informed choices so 
you can choose, and modify existing springs from other applications to 
suit what you have.

Sorry this turned into an essay....

-james

brian gochnauer wrote:
> I agree it might work, but will it still work if the car is 'bottom'ed out
> with the springs "fully" compressed or maybe just the shock fully
> compressed?
> 
> If you try this idea out Mike, let us know .  :)
> 
> 
>>
>> On 11/10/08, James Hansen <jhsg at sasktel.net> wrote:
>>> for that kind of change, just increase the rear spring rate- that's what
>>> "stronger springs" mean anyway....
>>> You do this by rendering a portion of the spring ineffective- say by
>>> installing a spring rubber- one of those circular rubber spring rubbers
>>> you can get a canadian tire/flaps or the like that have an "H" shaped
>>> cross section.  should cost 12 bucks or so for one, which should be all
>>> you need, just cut one in half so you have 2.
>>> See; > http://www.springrubber.com/?section=1
>>> this just came up on google, but you'll get what I'm talking about.
>>> zip-tie the thing in as well, they fall out at the damndest times.
>>> if you have chunks of your springs missing, then you need to get springs
>>> in the future and the rubber is just a band-aid, but if they are intact,
>>> that's what I would do.
>>> -james
>>>
>>>
>>>
>>> mikel wrote:
>>>> Greetings fellow v-dubbers.
>>>>
>>>> My Jetta has been being good to me for the last 3 or 4 months now, I now
>>>> have time to work on something besides the power unit.  I carry probably
>>>> about 100 -150 pounds in the trunk usually and it looks like it's
>>>> slightly squatting in the rear. Is there some cheap, easy and quick way
>>>> (2 out of 3 would be ok) to raise the load capacity?  I hauled 5
>>>> 5-gallon buckets of gravel in the back seat the other day and it was
>>>> definitely maxed out.
>>>>
>>>> Any ideas as to stronger springs that would fit from any specific other
>>>> vehicle models?  The shocks are all in good shape still, all the way
>>>> around, but I don't know how old or what kind they are.
>>>>
>>>> Thanks for any pointers,
>>>>
>>>> Mike in NC
>>>>
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>>
>>
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