steering and suspension Lowering Rear End

[JohnH]

It doesnt matter whether you take it from top or bottom. Its is however very important that you file and round the cut end so that it doesnt bite into the rubber mount.

 

The thing about BMW springs of the era is that they are, a semi open end design. By cutting, you are making that end, fully open. In there standard state the first 3/4 of the coils at both ends is non working. My experience is that initially, for first six months or so, after cutting the spring remains open (and the spring rate doesnt change much) but it does eventually change shape and become more semi openish with an attendant increase in spring rate. I'm a big fan of cutting springs!!!

Edited February 21, 2016 by JohnH

[xferboy]

or, get the GC rear kit and some springs.  Goes in with out modifications to the car, and you can get many spring combinations providing infinite adjustments.

[BrentF]

TobyB wrote:

 

"Do keep in mind that the rear spring's at about a .68:1 ratio with the rear wheel.

So for every .68" you shorten the spring, the wheel will drop an inch.

That's why the spring pads make such a difference.  You wouldn't think they would..."

 

I'm trying to understand this? How can the ratio be anything other than 1:1? Please explain. Thanks!

Edited February 21, 2016 by BrentF

[Rozz]

 

 

I'm trying to understand this? How can the ratio be anything other than 1:1? Please explain. Thanks!

 

It depends on where the spring and rear hub are in relation to the trailing arm pivot point. Maybe this diagram will help.

[BrentF]

_{Excellent explanation. Thanks!}

[BrentF]

Now that the warm weather is here, I thought it would be a good time to lower my car's rear end.

I confirmed that my car has 3 dot spacers which measure 37mm in thickness.

I could replace them with 1 dot spacers that measure 28mm in thickness.

This difference of 9mm translates into a height reduction of 13.23 mm, based on the .68:1 ratio mentioned above by TobyB.

 

13.23 mm is a mere 1/2 of an inch.

 

Have I got this correct?

 

If so, swapping out the spacers won't achieve the rear height reduction I am seeking.

[TobyB]

Probably not, but it's pretty easy to do and entirely reversible.

 

You DO, if I remember right, have to undo the halfshaft and the shock to get enough

trailing arm drop to swap springs or pads.

 

Try swapping pads.  My number's not as exact as it seems, just because the darned system's a scissor,

not a vertical column.  It SHOULD be able to model the spring as a point load on the body

and trailing arm, but my experience with cut springs on the 2002 and E30 proved that it

doesn't 100% follow that model.  So rotating the (cut) spring inside the 'scissor'

changed both the ride height AND the spring rate enough to be noticable.

 

Personally, I've become a fan of small (2 1/2, 1 7/8, whatever) springs and collars or shims.

But we spend a lot of time on springs and rates compared to what you do on a street car.

 

hth

 

t

 

[BeMyWay]

On 2/18/2016 at 11:44 PM, mike said:

Easier way...check the rubber spacers atop each rear spring.  They came in three different thicknesses, denoted by one, two or 3 dimples in the rubber.  AFAIK they're all still available.  US spec cars had 3 dot spacers due to the spacers inserted in the front suspension to meet Federal bumper height requirements.  You can drop the rear nearly an inch by going to one dot spacers in the rear, and they're easy to swap out.  Check archives for how to do it.

 

cheers

mike

 

Alright now ...I had no idea there were different thickness rubber spacers.  I will have to look at mine and hope that I have a "1 Dot" because i want to raise the tail ever so slightly.

Thanks.

[TobyB]

You can always add a shim.  Even 1/4" plywood will work, under the pad, to see how much you need.

 

I set rear ride height on the E30 this way- that way I can run a slightly longer spring, and stay that much

farther away from coil bind, which is a problem with those cars at low ride heights. (the threaded sleeve arrangement

eats up just enough room to make a 5" spring too long at the rates we run)

 

t