Another Bilstein ride height question

[SCWDP911]

Had Bilstein HD's installed on all 4 corners as well as a bump steer kit on my 83 cabriolet this weekend. Work was done by a couple of buddies (one a Pelican). I have been swamped with work and a medical issue with my wife and I really needed to get this work done. Well, all went well, but they reported that I had what seems to be a standard - noticeable ride height increase after install (we replaced the original worn out Boges). I have read about this before and reread some info tonight. It seems that the general experience is to not readjust height until riding on the "new" struts/shocks (I bought a good used set thinking maybe I would not have this somewhat common problem).

Is this right, or should we go ahead and readjust a bit. Is there a best-practice ride height to use for Bilstein HD "break-in". Mine are used, but they have not been on a car for at least a few months.

I will try to post pics when I can. In the hospital with my wife right now. Maybe Scott will see this thread and post some.

[KNS]

When I put new Bilsteins in the rear they raised the car about a half inch and never really settled. You could give it a few hundred miles (although you said they were used) and then readjust if needed.

[gabenheimer]

Wait a for a few hundred miles. Mine took a while to settle in.

[Flieger]

If you have rubber bushings, wait for a while. If you have Polybronze, then the car has probably settled as much as it will ever.

[schoward]

Some settlement will likely occur but it may not be enough. Let it go several hundred miles and decide. Mine did noticably settle after being installed a month or so.

[JFairman]

There's something like 300psi of nitrogen gas in Bilstein shocks. The reason is to keep pressure on the oil that goes through check valves and orifices to dampen the springs or torsion bars on jounce or compression and mostly on rebound... the gas pressure is to keep the oil from being aerated or frothing inside the shock over repetitive bumps

If the nitrogen gas does not leak out then the shocks expansion leading to increased ride height does not change or break in.
If it did, Bilstein would be a lousy and inferior shock absorber.

[Flieger]

The breaking in is from rubber bushings.

[JFairman]

Suspension parts and links with bonded in rubber bushings should be tightened with the car settled on the ground. Easist to do with a pit between the wheels like mechanics had before lifts.

If they are tightened in place with the wheels in the air and then the car is put on the ground then the rubber bushing will be twisted and will add to the torsion bar spring rate.

New rubber bushings in the shock end mounts will have no effect on ride height if installed correctly.

[David Borden]

Originally Posted by JFairman

There's something like 300psi of nitrogen gas in Bilstein shocks...

Wow, really that high? Shocks like Penske recommend around ~100-150psi.

300 psi with the front motion ratio will add a substantial amount of wheel rate. I'd have to do the math using Bilsteins shaft and piston size but my guess is it would be fairly significant.

David

[JFairman]

I'm not sure of the exact gas pressure in Bilsteins, it may be less than 300psi but the nitrogen gas pressure is why they expand when relaxed and ride height is increased after installing them when everyday common single wall tube shocks like Boge or Koni were in there before or the previous Bilsteins are totally used up..
That said, Koni has made a low pressure gas shocks for over 20 years now.

Reindexing the torsion bar splines on 911 suspension around 2-3 splines in opposite directions at each end on both rear corners will lower it about the right amount to compensate without changing corner balance because there are 40 inner splines and 44 outer splines on the rear torsion bars.

I said 300psi before as a generalization because I have a Fox racing shock with the remote reservoir on a monoshock motorcycle which has the rebound adjustment and shrader valve for charging the shock with 300psi nitrogen on the reservoir.
The compression damping adjustment is on the bottom of the shock body below the threaded spring height collars.
Let out the gas pressure and those shocks have no rebound damping at all.

Nitrogen gas is used because it is an inert gas and has no oxidizer like oxygen or humidity moisture in it so the shock internals do not corrode or oxidize.

[SCWDP911]

here is a pic