Suspension Redo!

[Captain Obvious]

i usually equate a high amount of gas pressure with a high amount of legume consumption, and i don't know why you can legally do that...

 

I have found the same thing. And that high of a gas pressure damps the spirits of those around me. Shocking, huh?

[rossiz]

shocking, indeed - fortunately a few minutes with an open window and they rebound from the experience.

my wife usually gives me a bump to stop it...

 

 

(jack over, back to the thread at hand)

[marvelous240Z]

Patcon I'm not sure. When you say loaded I assume you mean assembled on the car and on the ground?

[Zup]

Loaded= all the weight of the car on the suspension and on the ground---then torque to spec

[Zedyone_kenobi]

Yeah, you have to torque the inner rear bushings with load on them if I recall.  You have the two large bolts, one each end of the inner control arm, then you have the 4 smaller bolts per side that hold up the arm.  I forget which order you have to install these.  I will probably have to loosen and redo all of these.

 

Captain obvious, I hear what your saying, but the ease at which the removed struts can compress and then slowly or not rise means that there is little to nothing left in the way of gas pressure left.  NO damping to be had in them. I hear what your saying about hard to press down is not an indication of damping, but to me it is an indication of a healthy strut.  The ones I took off are definitely NOT healthy. I equate health to damping more than an arbitrary 'hard to press down'.  I should have been more clear.

[Captain Obvious]

Zedyone, I'm not a suspension guy, so my explanations come from the point of view of a non-expert who hasn't known this stuff forever. I apologize in advance if I'm telling you stuff that you already know. That said...

 

Hard to press down is not necessarily an indication of damping. But neither is a slow or non-existent rise after being compressed. So when you say "there is little to nothing left in the way of gas pressure left. NO damping to be had in them", you're mixing somewhat unrelated functions together. The only thing that you can glean from a slow or non-existent rise after compression is that the gas has leaked out. You can't make any claims about the damping functions from that test.

 

The gas pressure inside the shock has nothing (directly) to do with the damping. The only reason the gas is in there at all is to increase the static pressure on the hydraulic fluid which reduces the tendency of the oil to foam as it passes rapidly through the damping valve orifices under strenuous use.

 

It's the oil that provides the damping, not the gas.

 

Under non-strenuous conditions, the shock would work just fine with NO gas pressure in it at all (just like they did in the good old days). In fact, until or unless the oil starts to foam, there will be no difference in damping performance between a brand new gas-charged shock and one that's identical inside, but they forgot to put in the gas.

 

Here's some good info from KYB that talks about the difference between the twin-tube (low pressure) and monotube (high pressure) designs and how the damping is accomplished:

 

http://www.kyb.com/kyb-tv/the-differences-between-monotube-twin-tube-shocks/

http://www.kyb.com/knowledge-center/shock-tech-for-pros/monotube-vs-twintube/

http://www.kyb.com/kyb-tv/how-shocks-struts-wear/

 

Don't equate "hard to compress because it's got gas in it" with high damping.

Don't equate "slow or won't rise after being compressed" with low damping.

 

Those tests don't tell you anything about the damping, they just tell you how much gas you have left. Yes, if your shock is supposed to be gas charged and all of the gas has leaked out, it's not healthy like a new one, but assuming it's not worn out inside, it will still damp like a new one until you foam the oil. So, I'm certainly not telling you that you weren't due to change your strut inserts, but your old ones might still provide reasonable damping despite not being gas-charged anymore.

 

Please forgive if you knew this stuff already. I worked on cars for many years and didn't... Here's hoping I wasn't the only one. 

[Zedyone_kenobi]

As usual your writing and clear choice of words is never insulting or condescending in any way at all. I thank you for the lengthy response and the clarity you provided

 

Just a note, decided to get help with the glad nuts on the fronts. I could not move them once I removed the front strut from the car. I had no way of holding them while trying to loosen the nut. I took them to a local shop that has some experience with these cars.  

 

Also ordered a spring compressor and more ATI brake fluid from amazon.  It has been two years since I put that in and it was time.  It had absorbed quite a bit of water in that time.  I may have to go back to using DOT 3 as it is less hydroscopic than DOT 4.

Edited April 6, 2015 by Zedyone_kenobi

[Captain Obvious]

Excellent. One last thing before I bow out and let you get back to the real topic at hand. The KYB guys didn't talk much about the expansion chamber and why it's needed at all. My read on this is twofold:

First, as the hydraulic oil heats up during use, it will expand. And if there isn't some provision for compliance somewhere in the system, the pressure could rise above a level suitable for the shaft seal (or worse).

Second, as the shaft is compressed into the tube, the volume of the shaft itself displaces some oil, and that oil has to have someplace to go. If there wasn't a compressible volume in there somewhere, you could never press the shaft down at all since the internals would be "hydro-locked".

So some answers to questions that you didn't ask, but it puzzled me a little at first when I saw the position of the floating piston change a little as they compressed the monotube. Figured maybe the same thing caught your eye. That changing position is due to the volume of the shock shaft as it enters and leaves the oil chamber.

[ericjump]

Outstanding pixtures! It sure helps us "New" guys visualize that you're doing.

Thanks

Ericjump

[Zedyone_kenobi]

I love it when you get everything clean, and you have a couple of hours to get something done and everything goes exactly how you planned it would, due to preparation, skill, organization, and experience.

 

 

 

 

 

 

 

 

 

 

Then you realize in all your awesomeness you built up 4 beautiful struts and left the bump stops off

 

 

GRRRRRRR

[Diseazd]

My gosh Stephen.....you're human too. Must not have had your safety socks on!

Edited April 10, 2015 by Diseazd

[rossiz]

or you put the springs in back-to-front...

now, how many times do i have to publicly admit to that one??

 

no worries - you'll forget all about it after the first sweet corner...