Black magic of front to rear ride height adjustment

ulrichd · 10-24-2006, 04:31 PM

I have just re-indexed all four corners of my 78SC and my rears turned out about 3/8" to 1/2" too high which I can adjust with the spring plate nut. Fronts are perfect. This is as close as I've ever been.

Now how do I not screw this up? I know there is a cross connection between the opposite corners. Can I isolate the fronts somehow by putting them on jackstands while I adjust the rears on the ground?

How would you proceed? Thanks in advance.

Ulrich

PS. I had a guy in a Yukon yell "Are you a Pelican?" today. At least I know what it means now.

dfink · 10-24-2006, 06:05 PM

First let me say that anyone would need to know what the heights are are now and spring rates. Stock springs you don't want to go too low or will get tire rub.
Second search for corner balance and get a host of information. I say this second because I don't like being told to do a search first. :-)
Next let me say that without some sort of scales I think you are really just shooting in the wind. You can maybe get close but I found that corner heights don't really mean a balanced car. Many can attest that cars are as much as 3/4" off when finally balanced. As others have stated if it is primarily for the street close and "balanced looking" may be good enough. The harder you want to push it, the more accurate you should be.
I while saying this have recently been asking for corner balance advice so there you go. Ironic isn't it.

911pcars · 10-24-2006, 09:04 PM

Ulrich,
I think you're on the right track as you understand each corner ride height affects all others to some degree. If you raise the front end from the center of the suspension crossmember, the "true" rear rides heights will be revealed, isolated from any affect by the front corners.

Once you confirm the ride height at each rear corner, set the front end down, then procced to adjust each rear spring plate to arrive at the desired ride height. Without corner weight scales, repeat the tripod method to confirm your adjustments. It think this method should get you pretty close.

Will Ferch and Thom Fitzpatrick have collaborated on a calculation table that provides the correct spring plate angle for the ride height you desire.

http://rennlight.com/cgi-bin/spring.cgi

Hope this helps,
Sherwood

ulrichd · 10-25-2006, 05:28 AM

Thanks guys. Doing a search on corner weights instead of ride height revealed info about stabilizer preload and the triangulation method. This will be huge help.

Ulrich

Zeke · 10-25-2006, 06:31 AM

When you get where you want go with the rears, the rear toe will have changed. I recommend that you have an alignment done when you're done fiddling.

Wil Ferch · 10-25-2006, 07:10 AM

This can get long so let's just cut to the chase....

Whatever you do at one corner will also occur on the opposite diagonal. So...if you're lowering the right/rear, you will take some weight off there and a similar amount of weight off the LF. If you lower BOTH rears the same amount...then the corresponding diagonals ( both fronts...but as a diagonal pairing ) will be likewise affected...yielding..hopefully...no net change...just a lowering of the rear.

However, since you don't know *starting* corner weights....you won't know if the (same) ending corner weights are "good".

The pivotal thread...IMHO...was the revelation I got talking to Randy Blaylock on what a "proper" target would be. I had previously thought the "proper" target was "pure" corner balance ( each corner getting its apportioned weight). I realized late in that thread, that a more desirable compromise is to target equal weight for each of the two front wheels, and let the rears end up where they may be. This is not corner balance..it's purposeful "weight-jacking"...but a desirable compromise as it promotes equal front wheel loading when threshold braking ( equal tendency to lock)...at a "slight" compromise to left/right turning equality.....

- Wil