Dampers, bushes and top mounts

Discussion on Advanced and Defensive Driving.

Postby Garrison » Wed Aug 19, 2015 12:24 am


Strictly speaking not AD but car related.

My 996T's front top mounts and rear control arms bushes (coffin arm) are a little tired. Should I go for 1) OE or 2) adjustable top mount and poly-bushes in the control arms?

Also, one of my rear dampers is misting slightly. They are Bilstein B4. Dave, should I go for 1) OE or 2) try to find some adjustable Koni or upgrade to Bilstein B6? I don't want to drop the ride height.

Cheers
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Postby true blue » Wed Aug 19, 2015 1:08 am


My experience of poly-bushes is that they change the ride from OE setup, and not for the better.

Sadly I gather that they're also much harder wearing, so I'm stuck with them on my Jag for the foreseeable future!
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Postby Kimosabe » Wed Aug 19, 2015 7:18 am


I looked into poly bushes for my MX5 recently and everyone who fits them to MX5s said that they stiffen the ride and most often make the whole thing fairly uncomfortable. Fine for track use but I'm never driving my car on a track, so it's pointless. Every MX5 specialist, apart from one, along with my mechanic, told me to go OEM.

Hope this helps. Maybe it's different for your car but I suspect not.
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Postby akirk » Wed Aug 19, 2015 7:52 am


my z3 - gone oem, it is amazing the transformation from tired oem to fresh oem!
also when it comes to poly bushes I think you need to understand why and be selective...
on the z3, it is known that there are some bushes where it can make sense and others where the extra stiffness just seems to add vibration...

A classic rangerover I put onto poly bushes though was transformed - it had so much looseness that a little bit extra stiffness helped!

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Postby trashbat » Wed Aug 19, 2015 9:07 am


I have polybushes (Powerflex), front and rear, on my Alfa.

I couldn't tell you whether they improve the ride per se, as I can't compare fresh OEM with fresh poly. They improve the ride over tired and worn OEM, I can tell you that. Firmer in a responsive and compliant kind of way is about the best I can describe it.

The only problem is they get noisy after a while. I just had them regreased (the fronts are two years old, the rears new) with a different grease and it's currently silent.

On this car, OEM suspension parts are frequent consumables so this also helps reduce the ongoing costs.
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Postby Kimosabe » Wed Aug 19, 2015 9:40 am


StressedDave wrote:
Kimosabe wrote:I looked into poly bushes for my MX5 recently and everyone who fits them to MX5s said that they stiffen the ride and most often make the whole thing fairly uncomfortable. Fine for track use but I'm never driving my car on a track, so it's pointless. Every MX5 specialist, apart from one, along with my mechanic, told me to go OEM.

Hope this helps. Maybe it's different for your car but I suspect not.

It's worth noting, on your particular car, that the assembly process in Hiroshima, leaves the bushes in a torqued up state limiting wheel travel and adding a preloaded spring that's stiffer than designed into the handling. It's worth getting someone to loosen off all the suspension bolts, relieve the pressure and tighten them up again.


I had forgotten about twisted bush syndrome.... on mx5s....Thanks for reminding me. Once I've had the Konis fitted, that's a definite job to have done while its up in the air.

Thanks again Dave. :wink:
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Postby Mr Cholmondeley-Warner » Wed Aug 19, 2015 11:10 am


Indeed - a nice man did this for me on the Boxster the other day because he suspected I'd done them up with the wheels dangling. I hadn't, but I'd probably not been able to jack the hub up as much as the weight of the car would have depressed the chassis. He altered the ride height by 1mm by do doing.
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Postby TripleS » Wed Aug 19, 2015 12:26 pm


mefoster wrote:
Kimosabe wrote:I had forgotten about twisted bush syndrome.... on mx5s....Thanks for reminding me. Once I've had the Konis fitted, that's a definite job to have done while its up in the air.


Just for the avoidance of any confusion: the bolts need to be tightened when the car is on the ground/ramp and the suspension is "settled"/in normal running position. Tightening the bolts with the car in the air/on a lift and the suspension on full droop is what causes the problem.


That all makes sense, but we fail to remove the 'twist' or pre-load in the bushes, does it also shorten their life, in addition to being detrimental to the behaviour of the car? I would imagine it does, to some extent.
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Postby TripleS » Wed Aug 19, 2015 12:29 pm


Mr Cholmondeley-Warner wrote:Indeed - a nice man did this for me on the Boxster the other day because he suspected I'd done them up with the wheels dangling. I hadn't, but I'd probably not been able to jack the hub up as much as the weight of the car would have depressed the chassis. He altered the ride height by 1mm by do doing.


....jack the hub up/depress the chassis? I don't understand that. :?
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Postby Mr Cholmondeley-Warner » Wed Aug 19, 2015 12:49 pm


TripleS wrote:
Mr Cholmondeley-Warner wrote:Indeed - a nice man did this for me on the Boxster the other day because he suspected I'd done them up with the wheels dangling. I hadn't, but I'd probably not been able to jack the hub up as much as the weight of the car would have depressed the chassis. He altered the ride height by 1mm by do doing.


....jack the hub up/depress the chassis? I don't understand that. :?


Car on axle stands. Insert new suspension arm and longitudinal facing bolt at inboard end. Arm is meant to be secured with the car in its running position as Mark posted. There is an arrow on the arm which should line up with a similar one on the chassis member. You can either lower the car so that the weight compresses the spring and lines the arrows up - in which case you can't get underneath to do the bolt up, or you can jack up the hub, with the car still on stands, to attempt to achieve the same thing. In practice what happens is that the car starts lifting off the axle stand before the running position is achieved, but I got nearly there. Hope that explains?
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Postby TripleS » Wed Aug 19, 2015 5:02 pm


StressedDave wrote:
TripleS wrote:....if we fail to remove the 'twist' or pre-load in the bushes, does it also shorten their life, in addition to being detrimental to the behaviour of the car? I would imagine it does, to some extent.

Probably not - they're designed in rotational shear, so having a preload on them does very little to change their life compared to the grief they get from a car driving up a road.


OK, you should know better than I do.

I just thought that if they are already suffering a bit of torsion with the car standing at its normal ride height, when they get to more extreme suspension movements, they'd be going beyond the amount of shear that they would normally be expected to bear, if you see what I mean.

Ah well, methinks I think too much at times. :roll:
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Postby TripleS » Wed Aug 19, 2015 5:04 pm


Mr Cholmondeley-Warner wrote:
TripleS wrote:
Mr Cholmondeley-Warner wrote:Indeed - a nice man did this for me on the Boxster the other day because he suspected I'd done them up with the wheels dangling. I hadn't, but I'd probably not been able to jack the hub up as much as the weight of the car would have depressed the chassis. He altered the ride height by 1mm by do doing.


....jack the hub up/depress the chassis? I don't understand that. :?


Car on axle stands. Insert new suspension arm and longitudinal facing bolt at inboard end. Arm is meant to be secured with the car in its running position as Mark posted. There is an arrow on the arm which should line up with a similar one on the chassis member. You can either lower the car so that the weight compresses the spring and lines the arrows up - in which case you can't get underneath to do the bolt up, or you can jack up the hub, with the car still on stands, to attempt to achieve the same thing. In practice what happens is that the car starts lifting off the axle stand before the running position is achieved, but I got nearly there. Hope that explains?


Yes, thanks.
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Postby Mr Cholmondeley-Warner » Wed Aug 19, 2015 5:11 pm


and in case it helps to illustrate:

Image

The bolt is visible more or less at the exact centre of the picture, at the inboard end of the track control arm (the shorter of the new shiny arms), and you can even see the arrows cast into the arm and the chassis member.
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Postby Garrison » Wed Aug 19, 2015 11:42 pm


StressedDave wrote:1 - OE, unless the car is going to spend all it's time on track and you're such a good driver that bush compliance is limiting your lap speed.
2 - Dampers should mist slightly... otherwise OE. Handling problems are, in the main, caused by a loose nut behind the wheel. I find that trying to bend the car to your will is an exercise in unfruitfulness.

But, in any case, it's a 996 turbo. Do you really believe that the suspension is holding the driving experience back?

edited for bad speeling and punctuashion

Thanks Dave, OE for top mount and track control arm bushes. I'm just thinking more from longevity point of view, that the top mount and bushes will be longer lasting than OE for the same cost.

A question - why should dampers mist slightly? It is just that I cannot find misting in the other 3 dampers, which lead me to think it is a leaking damper.

Not that my car is holding me back. It is just that I find John's C4 is sweeter handling but obviously a C4 has narrower track, smaller diameter wheel and narrower tyres, plus more linear throttle response, better exhaust noise, etc. etc. ...
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Postby IcedKiwi » Thu Aug 20, 2015 7:30 am


StressedDave wrote:lots of very interesting stuff.....non-aspirated

Very interesting discussion, but sorry it's Naturally Aspirated (this is the internet after all :twisted: ) please continue
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