I was talking to another H-T member tonite and it seemed like a good idea to post the subject matter.

If you have an adjustable body length damper, how do you determine the correct length to set the body?

Using the front as an example, like this:

Thread the lower mounting boss onto the threaded body with at least an inch of purchase. Don't run less than an inch. There are rules of thumb regarding purchase vs threaded diameter - I don't have it handy.

Install the damper assembly - without spring or bumper.

Use a jack to push the suspension to full bump (till something prevents further travel). Take note of what that is. If it is the damper body hitting the top of the rod/retainer, screw the body further into the boss (increasing purchase).

On a G3 with a Skunk upper a-arm the limit of travel is the arm hitting the top of the inner fender / tower. At that point you want to set the shock body length so that there is about 1/4 inch of shaft travel left. The point of this is to leave just enough room to prevent the bumper from being destroyed if you bottom hard. Remember that shock mount bushing deflection will push wheel travel ahead of shaft travel.

If you are using stock arms in the low caster postion you can get more bump travel from a given ride height. If you use a BFH to increase clearance between the Skunk arms and the inner fender / tower you can get more bump travel. In either case you will thread the body further into the boss. Again, at mechanical interference bottom, you want about 1/4 inch of free shaft travel.

Modern bumpers are exponential rate bottoming springs and, depending on the rate and how far you are into them, they can change the dynamic balance of the car. You want them to do their job when you need them, but you don't want them interfering with entry phase cornering. You don't want to be regularly operating the car deep into the bumper curve.

So there's the damper length. There's really nothing more to it.

Adjust your ride height with spring perch position. You may or may not need alot of preload depending on your rates and desired ride height. Your rate selection effectively makes your ride height selection for you. You can figure this out from data published on H-T, or you can set the car up without bumpers and put o-rings on the shafts and do it the old fashioned way - uh, start high and bring it down slowly.

The softer the spring and the shorter the shock body (the shorter the droop travel) the more preload you'll likely need. Don't fear preload in general, but excessive preload can make edge of envelope transients too quick, and is probably an indication that you've got a combination that doesn't make sense.

The first step in any chassis tuning regime is to work out the very basics.

Scott, who's benefited from slightly higher ride heights lately.....because increased speed and load led to some problems.....

 

Thanks Scott!

Warren

 

just one quick question. if u adjust the height by the spring seat(after u have meassured all the stuff), when u drop the car down from the jack, the piston of the shock will sit lower than the stock setup, right?(meaning with the zero spring preload). will the damper rate change? for a mono tube, gas/oil separate shock, will the damper rate is same wherever position of the piston is? to my understanding, when u set the piston/rod lower, the gas room is compressed, right? so u are saying adding preload of the damper?

P.S. if the reason of what u are doing is to aviod the a-arm hitting the tower, will adding more preload of the spring be easier?

 

Thanks for the info