strut/shock compression question

[rusty_sojah]

so i live in japan and just brought my 04 3.0i (+sport) z4 to a japanese mechanic (who later told me he had never worked on a bmw before) who i had asked to change out my springs with the H&R lowering springs. the shop calls me to come look at the first shock that looks like its in really good condition to me but once he compressed them to take off he was saying that it wouldn't decompress and that to him this meant it was broken.

basically he tells me i need to replace the shock ASAP and i'm all paranoid of driving home now but i tell him to put the factory spring back on the car and i drive off. well the car feels the same as normal, really tight very accurate sporty suspension feeling. is the bmw shock supposed to behave like this?



thank you,

[seank]

Originally Posted by rusty_sojah

so i live in japan and just brought my 04 3.0i (+sport) z4 to a japanese mechanic (who later told me he had never worked on a bmw before) who i had asked to change out my springs with the H&R lowering springs. the shop calls me to come look at the first shock that looks like its in really good condition to me but once he compressed them to take off he was saying that it wouldn't decompress and that to him this meant it was broken.

basically he tells me i need to replace the shock ASAP and i'm all paranoid of driving home now but i tell him to put the factory spring back on the car and i drive off. well the car feels the same as normal, really tight very accurate sporty suspension feeling. is the bmw shock supposed to behave like this?



thank you,

There's too many "do not knows."

-the rebound could be bad.
-he could be wrong, depending on his vehicle knowledge. It being his first time with a bmw would not affect this.
-most bmw's with a bad shock perform better than most cars in top shape. That being said, I'm not sure that you know what a blown shock feels like or you wouldn't have posted this.

Most competent shops can tell if the shock is blown just driving it for 5 min. Have someone else look at it if you don't trust him. And don't take your car to someone you don't trust.

[Racer20]

Originally Posted by seank

There's too many "do not knows."

-the rebound could be bad.
-he could be wrong, depending on his vehicle knowledge. It being his first time with a bmw would not affect this.
-most bmw's with a bad shock perform better than most cars in top shape. That being said, I'm not sure that you know what a blown shock feels like or you wouldn't have posted this.

Most competent shops can tell if the shock is blown just driving it for 5 min. Have someone else look at it if you don't trust him. And don't take your car to someone you don't trust.

It can be very hard to tell if a shock is bad or not just by driving the car. However, if you compress the shock by hand and it doesn't extend on its own, it has failed.

Modern shocks are filled with Nitrogen to keep the oil under pressure to make sure no air bubbles get into the working chamber. This gas pressure is what makes the shock extend on its own. If it doesn't, that means the gas has leaked out, and the shock won't produce the damping that it was designed to in certain circumstances. IF there is no evidence of an oil leak AND IF there's still damping resistance for the entire length of the stroke when you compress it by hand AND if you pull it up by hand, it's probably not a catastrophic failure, and you'll be ok to drive on it, but it won't ride and handle the way it should.

Source: I'm a suspension engineer specializing in dampers.