Front lowering using BMW coils and Koni shocks

[raygreenwood]

Wally....what you are not getting from my posts...is that if the spring and damper combination is properly set up.....there should be little or no spring compression...just from sitting still. It should govern ride height.

More precisely said...and this is the crux of my posts concerning this....and is also getting back to the original thread........if you lower the spring height by lowering the perch....you are allowing even greater rebound travel...that that 1" or so of compressed rod length.
It WILL rebound the entire length of that excessive compression.
Thats a very uncontrolled reaction....that the stock type 4 already has way too much of.

Saying it controls ride height... may very well be be a misnomer. But by assuming it shouldn't...and ignoring what simply lowering the perch will do without shortening the strut rod....you will find out the hard way...what it causes. If the spring used were actually going to be softer...but longer....to maintain preload even when the too long strut rod over-rebounds...there would be no risk of damage to spring at all....but the pitch up on rebound will be unsightly....and hard to control at speed.

Can you control this? yes....with a very tight rebound stroke. Problem is...wthout fully adjustable (bi-directionally) cartridges....you generally get too much stiffness in the compression stroke as well. This breaks things. This can only be done really well....with a gas strut cartridge.

I applaud all experimentation that keeps these cars on the road. don't get me wrong at all! What I think would be even better than doing potentially damaging spring grafting.....is swapping in whole struts with cartridges whose damping rates match the pre-set compression level of the springs matched to them.

As an aside...you will notice that most quality factory adjustable spring perch systems that are used for the street...(see Bilstein)...use twin coils with two perches. Thats because this is the only way to get the progressive-ness...and maintain ride height and preload and rod extension to control rebound. Full race...depending on track type...most commonly uses single coils.

By the way...as noted..I already found a cartridge with a high rate of rebound control....awesome compression control...and the ability to work with slightly overcompressed stock blue coils. But...and this tells the complexity of valving....it only works in the low pressure gas version...not the high pressure gas version. The high pressure version is way overdamped. It breaks things

I weigh 185 lbs. Last night I jumped up onto the front bumper of my 412. It compresses about 1/2 ". No kidding! The rebound ...with so little energy took about 2 seconds to return to level. That is good balance. A very stiff front end...that takes speed bumps at about forty without a hitch...and without pitching from rebound.
Because its lowered about 7/8" lower than stock....and also has 2* more caster...which lowers the apparent front rake by about 1/2"...and add to that about 1.2" lower profile tires...and I am pushing about 2.5-3" lower than stock. The 7/8"....just brought it level front to rear from that nose high appearnce....which is not actually as high as it looks. What also adds a huge volume of apparent lowering...is when the rear drops down just slightly from the lower profile tires.

Just be careful how you lower. there is not much room in the control arm area...to play. There are significant geometry issues. also...and I know this from experience (as I have had mine lower than it is when I played with other struts like the 5000 cartridge)....lowering too much further than I have it already....without even lower tires...and even then (as anything belwoe a 55 series means the strut valving will no longer be correct).....has little added benefit. Some lowering of the 411/412 has large benefit. Too much does nothing more for the car.

The chassis rides to high on the wheels..the drivers position is high...and the "bubble roof"...is too high. Since you cannot "sling" the car much further down between its wheels...without seriously re-designing the front control arms....lowering too much simply impars suspension travel. Ray

[Wally]

Ok, I have dismantled my original struts today. It still had the original VW modular shocks. As I have a rather low milage 412, this is not really surprising.
I did have to make a special tool for turning loose of the large screw holding the shock in place, but t was worth making it

Then I inserted the new Koni shocks, which have a stiffer rebound action than the inbound. All in all, they are already stiffer inbound than the old vw shocks were, very largely due to the rather thin oil that cam out of them.

The stock oil amount in the shocks was: 400 cc (quite exactly).

One shock had 10-20 cc less, so the largest amount must be close to the original volume.

Assembling the BMW spring was easy as they have less preload.
After mounting the top spring perch and bearing housing, I had a only a little preload, so I shortenend the spacer that came with the Koni shocks by 10mm. This is the extra thread I had on the top screw.
After that, the spring had more preload and enough for my taste.

Here are the original and Koni shock side by side and also the BMW and the original (blue) springs:



After assembling, the fender to ground distance is now 61,5 cm, so its lowered 5,5 cm, which is a little more than 2"

To say I am pleased with the resuls is an understatement

Regards,
Walter

[Wally]

Before:



After:

[raygreenwood]

Drop me a personal e-mail....and I will send you a digital picture (which you are welcome to post)of how far mine was lowered using the audi 4000 cartridge and the stock spring...and with 205/60-15 tires. Mine is very very similar. Nice work! Ray

[Wally]

Cool, we need more pictures instead of long posts

Ray, could you maybe send me an email or your email through PM?
For some reason (tho I know why ) I have no direct e-mail connection when I hit that button...

Tnx,
Walter

[raygreenwood]

No problem. Ray

[Bill K.]

Nice work Wally! How's it drive?

[Wally]

Nice work Wally! How's it drive?

Don't really know yet, as I haven't done any driving more than up and down the street yet.
But its a lot stiffer from a first impression which I like, as I found the original ride a bit too soft for my taste. Probably due to the Koni shock

I do wonder where the original rubber strut bump stop sets in, as I have not shortenend that one (should have probably).

Greets,
Walter

[vwbill]

Wow Great job!! She looks like she is sitting sweeeeeet!! Thanks for the great post! bill

[rupert]

right, so lowering my type 4s dead simple then,

[Wally]

right, so lowering my type 4s dead simple then,

Yes and no. Please read the above very carefully

[raygreenwood]

Wally...that is the perfect answer. Yes ...and no. Not much has to be done to...physically to lower the car. But a lot of little relationships must be examined....in order not to break things and for teh car to be able to drive usefully.
Even the term usefully has degrees. If all youwant to do is drive limited miles and be a show car...you can get away with a lot more. If its going to drive long miles and be reliable....you can get away with a lot less. Ray

[MattKab]

Great timing, I've just overhauled my 411 front end, I need springs before it goes out on the road. 'previous owner cut the springs. Mentioned was a couple of inches preload on the spring, with no load on the strut. Well my springs are short of the maximum extension by ~4"

Wally, did you keep the 5.5cm you removed so carefully, I need it:



Matt

[rupert]

you got a PM MattKab

[Wally]

Wally, did you keep the 5.5cm you removed so carefully, I need it:

Matt

Here's the lowered result with my porsche rims:

http://www.shoptalkforums.com/viewtopic.php?t=97099