Technical Koni FSD rear shock rattle.. Shock!
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Technical Koni FSD rear shock rattle.. Shock!
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Spoke to a chap today about getting some made up. He mainly produces parts for motorcycles, but in his opinion the bolt should definitely fit the bush with only a clearance of a few thou, and anything else is just ridiculous.
He's offered to make them at the end of the second week in January when he's running something similar. Not got a price yet, so I don't know how it will compare with Staffordmike's quote, but I don't think it's going to be horrendous.
He came across as a bit "old school" which I like, so I'm going talk to him again in January and get some made up. Either way bolts that fit properly have got to be better.
Staffordmike - do you want to wait until January to see what price I can get them for?
He's offered to make them at the end of the second week in January when he's running something similar. Not got a price yet, so I don't know how it will compare with Staffordmike's quote, but I don't think it's going to be horrendous.
He came across as a bit "old school" which I like, so I'm going talk to him again in January and get some made up. Either way bolts that fit properly have got to be better.
Staffordmike - do you want to wait until January to see what price I can get them for?
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The Twins
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Not really noticed and difference.
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The Twins
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Yes but I don't have a vernier guage : /
Well the rattle is back with a vengance with the 14 steelies and winter tyres.
From what I can recall when the new rear shocks were fitted the changes made were minimal. I will check.
I have my old koni rear shocks sat in the garage if any help.
From what I can recall when the new rear shocks were fitted the changes made were minimal. I will check.
I have my old koni rear shocks sat in the garage if any help.
I've got a digital gauge, pm me and we can meet up sometime and measure your shock bushes.
I don't venture on here very often, but I believe Fiat knew of this issue from the off as the OEM Abarth dampers have a flexible bush by simply having holes in the rubber on the top mount bush of the damper. All the aftermarket dampers I've seen have a solid bush as is the norm on dampers, as to get them to work correctly you really want them mounted as solidly as is possible without transmitting noise.
I believe that by having a solid bush through time the bush will move against the undersized bolt inside the U shaped mounting point as has been suggested. You can tighten the bolt up massively to try to curtail this, as we have done, but a correct size bolt would be a better solution.
Why the Bilstein dampers don't knock, one can only guess, but the bush ID may be a tighter tolerance on the bolt than the Koni or AVO dampers that I know knock as to manufacture a flexible bush would take a lot more R&D to get it to work correctly with the damper.
I believe that by having a solid bush through time the bush will move against the undersized bolt inside the U shaped mounting point as has been suggested. You can tighten the bolt up massively to try to curtail this, as we have done, but a correct size bolt would be a better solution.
Why the Bilstein dampers don't knock, one can only guess, but the bush ID may be a tighter tolerance on the bolt than the Koni or AVO dampers that I know knock as to manufacture a flexible bush would take a lot more R&D to get it to work correctly with the damper.
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If the bolt was moving in the metal eye (hole/sleeve through the bush) it would surely wear the facing surfaces of the bush eye/sleeve rendering the bolt loose. If this was the problem it would mean constantly tightening the bolt as it would wear the faces of the bush over and over. The bolt on my shock remains very tight. This us why I'm not convinced it's the bolts.
More likley it's hydraulic knock. This occurs if there us the slightest void not filled by the damping fluid. The same thing happens in mountain bike forks and also have had this happen in the rear shock if mtb. Fox (who also make shocks for motocross bikes and also special off road vehicles confirmed that this type if knock is typical in 1. Shock with 'platform' damping (like the FSD's) and when oil chamber has any sort of void/under filled. Also only one of my rear shocks rattles btw.
More likley it's hydraulic knock. This occurs if there us the slightest void not filled by the damping fluid. The same thing happens in mountain bike forks and also have had this happen in the rear shock if mtb. Fox (who also make shocks for motocross bikes and also special off road vehicles confirmed that this type if knock is typical in 1. Shock with 'platform' damping (like the FSD's) and when oil chamber has any sort of void/under filled. Also only one of my rear shocks rattles btw.
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Still got to be worth a try though, if the bolts can be had without too much outlay, otherwise we won't know one way or the other.
It's not just Koni that knock, AVO do as well and we have tightened them up to over the prescribed torque, 70NM rings a bell which isn't that much, and stopped the knocking. This is not guess work, it's through first hand experience.
As stated the standard damper has a flexible rubber bush, this is not standard practice on a damper as it should be mounted as solidily as possible. On race car applications it has no rubber bush at all, but solid rose joints to increase accuracy and efficiency of the damping, but on a road car too much NVH would be transmitted and is therefore not practical. The Trofeo Race cars had this which I did some work on during the single season they ran in the UK.
I don't believe a manufacturer like Koni who produce thousands of dampers would get something like valving or gas pressurisation in the oil chamber wrong, but wouldn't rule it out off hand.
I don't believe mountain bike forks are gas pressurised, though I have no experience of them but the 2011 BMW motorbike forks on a friends expensive bike that I rebuilt with an anti dive pack, was just a spring inside a tube with oil, a car damper is way more complex than this, but then a car damper has to work much harder as it fights the forces of a much heavier vehicle.
FSD damper is gas pressurised, this process stops cavitation of the oil which aerates when worked hard and temperature rises. I only mention as some folk think a gas damper means no oil, it doesn't it just means it's sealed with an inert gas like Krypton used to control the cavitation process.
As stated the standard damper has a flexible rubber bush, this is not standard practice on a damper as it should be mounted as solidily as possible. On race car applications it has no rubber bush at all, but solid rose joints to increase accuracy and efficiency of the damping, but on a road car too much NVH would be transmitted and is therefore not practical. The Trofeo Race cars had this which I did some work on during the single season they ran in the UK.
I don't believe a manufacturer like Koni who produce thousands of dampers would get something like valving or gas pressurisation in the oil chamber wrong, but wouldn't rule it out off hand.
I don't believe mountain bike forks are gas pressurised, though I have no experience of them but the 2011 BMW motorbike forks on a friends expensive bike that I rebuilt with an anti dive pack, was just a spring inside a tube with oil, a car damper is way more complex than this, but then a car damper has to work much harder as it fights the forces of a much heavier vehicle.
FSD damper is gas pressurised, this process stops cavitation of the oil which aerates when worked hard and temperature rises. I only mention as some folk think a gas damper means no oil, it doesn't it just means it's sealed with an inert gas like Krypton used to control the cavitation process.
I have standard rear shocks lying around as they are left after having Esseesse Koni kit fitted lately. Upper shock bush has 11 mm diameter, lower shock bush has 12,5 mm diameter. Original upper shocks bolts have 9 mm shaft diameter, lower shocks bolts have 11 mm shaft diameter.
FYI - my Konis from Esseesse Koni kit have the latest OE number 5744631 which replaces 5743691. Date when it was replaced: 16.10.2012.
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I meant of course shank diameter... Sorry!
My car has had its rear shocks replaced under warranty today....but I had my dashcam in the car and it stays on for 15 mins after the ignition is turned off.
I could see the roadtest and listen to the mechanic saying that it's probably my winter tyres or the child seat in the back and not the shocks. I will edit it down and upload it later.
I could see the roadtest and listen to the mechanic saying that it's probably my winter tyres or the child seat in the back and not the shocks. I will edit it down and upload it later.
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Boodajuda
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Please take a pic if the label on the shock if poss. Would be good to know the new part no info.
Boodajuda
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If you can get these with the correct shank diameter and washers, I'd be interested in 4 top and 4 bottom bolts.
I have some coupe bump stops and powerflex rear beam bushes waiting in the wings!
For info on new part number check my post above.
