Rear shocks in question...

[ARad]

Hi,

Rear shocks in question: NEED to know HOW MUCH gas pressure when pushing down the rear shocks (Green Bilstein shocks) for instance, they should be STIFF and VERY HARD to push down and retracts steadily fast meaning as "GOOD" gas pressure??

The rear green bilstein shocks I got from a guy says or so claims they were removed from his "30K miles" 87 911 and when I got them and they were so easily pushed down even at a very slight pressure with one hand and it goes down pretty fast and very slowly retracts - so that means no pressure or worn out - BAD??

I have no idea of how much pressure (good or bad gas pressure) of the rear green Bilstein shocks SHOULD BE ??
Honestly I wish I could know exactly what the "pressure" it should be like as it should be either HARD to press down with both hands and knowing they are good or another instance - hardly any pressure when pressing down with ONE hand like as I would say very light hand pressure that it goes down very easily - meaning no life left/bad ? (So soft pressure that is so easily pushed down with your pinky finger - NO KIDDING!)

Perhaps from your own experience on used shocks and what kind of gas pressure as they should be??
Will be hearing of your answers before I return them to a seller. Any tips or help will be much appreciated! Thanks!

[Rawknees'Turbo]

When uninstalled (no spring pressure working against them), car-sized dampers are fairly easy to compress by hand. For example, if one end is against the ground, you can put one hand on the other end and collapse it fairly easily, but there is definitely resistance there - takes effort, but not too much - definitely more than a pinky, though (unless you are Popeye ). You can also "hear" the gas and oil moving inside it as you compress the damper.

I have good, Bilstien yellows here from another, non-911 vehicle, but the principle is the same. Maybe someone with greens on hand will chime in, though.

Also, the slow, re-extend (I think that is what you are calling "retracts"), relative to compression, is totally normal; there is more rebound damping than there is compression damping.

[wally509]

You might want to search the tech forum if you haven't already.

I think there is a way to test if used gas shocks are "in the ballpark" using a bathroom scale. When I was dealing with Mustang SVOs guys were constantly buying and selling the SVO specific Konis. IIRC (and this is 20 year old memory) if they would make ~40 pounds on the scale as you compressed them, they would be considered good, bad ones would only do like 15-20.

Obviously no substitute for a shock dyno and don't know what the numbers should be for your Billies.

[ARad]

Did test on bathroom scale for strength of gas pressure when compressed - both billies ( rear green bilstein shocks) are in the range 30's lbs. of gas pressure. Good or bad??

[Driven97]

There's no set answer. Depends on the shock.

Shocks are filled with oil, which is a fluid, and fluids are incompressible. A shock shaft as it enters the shock body has volume, which has to be taken up somehow.

On a monotube like a Bilstein there is a floating dividing piston between the area where the oil is, and a pocket of nitrogen. As you compress the shock, you're also compressing that nitrogen. It's pushing back at (whatever psi is in there x cross section area of the shaft.) A healthy monotube should extend back fully when compressed.

No idea how much pressure is in an OTS 911 rear shock, but Bilstein rebuild guides suggest ~200psi of charge. Sounds like a lot, but it only gets to act on the pretty small shaft cross section. Other brands or even models may use different gas pressures.

Sounds to me like for your shocks in question, at least some of the nitrogen has left the building. Mileage definitely speeds things up, but you can also lose charge just over the march of time.

A twin tube shock has a base valve and a reservoir, and is typically under very low pressure so you won't get the strong push back. I don't think Bilstein makes any twin tubes.

EDIT: Bilstein does indeed make twin tubes. Ha, learn something new every day.