New Sachs shocks, but no rebound. Which part of shock Absorber 101 am i missing?

[pontiff]

hi all,

I just bought a new set of Sachs shocks for the 6n1 polo as the old OEM ones have no rebound at all as in you push them in and they dont spring back out at all.

Well the new ones I just bought (pics enclosed) are exactly the same, you can push the piston in all the way quite easily, its a little harder to pull it back out again, but you can do it.

I normally buy bilstein shocks and the piston comes under pressure so you cannot really push it in at all which i what I would expect.

Given the box size I would assume that its the way they are suppose to be, but if that is the case, how do they actually work? Isn't the car just going to be riding on the springs like it is currently?

As I say... what I am I missing? I cant see how they would actually do anything? Especially when there is no rebound, you push the piston in and it sits there and does not come out unless pulled.

I have even read the instructions yet it doesnt mention anything about preloading or priming or anything that would suspect they are somehow 'set' different for shipping

Are they faulty? Could someone who knows please enlighten me?

[h100vw]

You've got it wrong mate. Most OE shocks are just oil damped. The size of the ports inside governs the speed of compression and rebound.

If you pull on the piston, with your thought in mind there would be no resistance.

However, the piston doesn't just pull out does it.

Move onto another style of shock which is gas pressurised. The gas helps to prevent the oil from frothing up when it's working hard, keeping the damping characteristics constant during all use.

Gavin

[kaanage]

What you are finding is that there is no compression damping - this is quite common for OE dampers.

Bilsteins are hard to compress, not only because they usually have compression damping but also because they are usually have monotube construction so they have a high pressure piston inside - this gives them a strong air spring effect (which also makes the overall spring rate stiffer)

Edit - beaten to it...

[pontiff]

hi guys,

Okay I think i understand it. Going off that then I dare say that every set that I have replaced about 4-5 or so now, that they were all probably okay, as when you push down on the front corners its pretty 'weak' and you can get quite the wobble up, so i would take out the shocks and remove the springs and compress the damper and go "yep.... they should rebound, they're stuffed" but going from what you're saying they were probably perfectly fine just working differently. Naively (I see now) i had only ever thought of a shock as like the Bilstein, a monotube with compression damping. The standard 6n1 polo damping must just be REALLY REALLY soft.

Thanks for clearing it up for me guys, muchly appreciated.

[kaanage]

I dare say that every set that I have replaced about 4-5 or so now, that they were all probably okay, as when you push down on the front corners its pretty 'weak' and you can get quite the wobble up, so i would take out the shocks and remove the springs and compress the damper and go "yep.... they should rebound, they're stuffed"

Just look at what you did as upgrading - you didn't waste money

[pontiff]

Just look at what you did as upgrading - you didn't waste money

hahah yes, thats the best way to look at it

[Tom87]

there would be compression control there, it is very likely to be progressively valved so the faster it is compressed the greater the resistance it has. The old "bounce" test isn't always that accurate.

Also, just because a gas pressurised shock wants to push open doesn't mean it isn't worn out. And on that, an oil slick on the body of the shock doesn't mean it is stuffed or about to be stuffed.

Now for something which will make it about as clear as mud....Bilsteins along with a number of other brands can be fitted with a special type of piston valving (bilstein calls it Digressive) which allows their shocks to control body roll (and provide a firm ride as a result) but still be able to be compliant on stiff roads as the valve "opens up" at a certain shaft velocity, allowing less resistive suspension travel...so you have a firmer car on smooth roads but potentially a better ride and more control on a bumpy road than you would with say the stock Sachs...

Fun stuff!

[pontiff]

there would be compression control there, it is very likely to be progressively valved so the faster it is compressed the greater the resistance it has. The old "bounce" test isn't always that accurate.

Also, just because a gas pressurised shock wants to push open doesn't mean it isn't worn out. And on that, an oil slick on the body of the shock doesn't mean it is stuffed or about to be stuffed.

Now for something which will make it about as clear as mud....Bilsteins along with a number of other brands can be fitted with a special type of piston valving (bilstein calls it Digressive) which allows their shocks to control body roll (and provide a firm ride as a result) but still be able to be compliant on stiff roads as the valve "opens up" at a certain shaft velocity, allowing less resistive suspension travel...so you have a firmer car on smooth roads but potentially a better ride and more control on a bumpy road than you would with say the stock Sachs...

Fun stuff!

Fun indeed... just shows how little I know , thanks for providing valuable details

[kaanage]

Now for something which will make it about as clear as mud....Bilsteins along with a number of other brands can be fitted with a special type of piston valving (bilstein calls it Digressive) which allows their shocks to control body roll (and provide a firm ride as a result) but still be able to be compliant on stiff roads as the valve "opens up" at a certain shaft velocity, allowing less resistive suspension travel

Actually, this is how all really good dampers work - the flow paths open up with higher speed so high speed compression damping is at a lower rate than for low speed which gives good body control in braking/corners (low speed suspension movement) and suppleness over bumps (high speed suspension movement).

Cheap dampers used in bottom end coilovers are even worse than OE as they have very simple valving that results in compression damping increasing with speed which is opposite to what is preferrable and which is why these coilovers give a teeth rattling ride.

[Tom87]

Internal bypass is becoming more common on large body dampers in the USA aftermarket. Perhaps this is a technology we might be going to see a bit more of in the future on passenger cars.

For now if I change my shocks it'll likely be for newer factory replacements. Although to be honest I've had 2 mkV GTIs now and both have suffered shock fade on some of the rougher country roads out near Toowoomba and the worst part about it is when they fade the suspension starts getting thumpy and bottoms out alot more regularly so I'd probably look towards a Bilstein with road orientated valving (past experience indicates they tend to have aggressive valving for euro applications) or a Koni yellow.

Infact, I don't think I'd really consider anything else. Factory springs would be more than likely to stay as well. I went through a few shocks on my last car and the Bilsteins were the stand out products particularly value for money.