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Changing rear coils on Blue GT

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Mike Austin
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Drives: Polo Blue GT
Location: Bristol

Changing rear coils on Blue GT

Post by Mike Austin » Wed May 16, 2018 5:47 pm

My Blue GT has only 7,300 miles on the clock (still 2 years to go on warranty), but I have traced an intrusive ongoing cabin noise to the coils at the rear. By 'plucking' the coils with my fingers, I can match the frequency to the noise in the cabin. I note that the coils do not sit on any form of dampening pad. I am happy with the ride and handling, so I should not need to change the overall spring rate. Are there after-market options to change to, for example, variable pitch coils that might reduce the noise? Or to insert some dampening pads? Or even to use composite springs of some sort?

Ricmondo
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Re: Changing rear coils on Blue GT

Post by Ricmondo » Wed May 16, 2018 8:40 pm

That sort of noise eventually drives you mad, once you hear it you can’t get away from it.

I had the same problem some years ago with a Triumph. I had some ‘coil spring helpers’ lying around the garage. They were essentially small shaped blocks of springy rubber that you inserted between the extended coils, once returned to normal height they were trapped by the coils. They altered the harmonic frequency and cured the problem.

I used the same trick on a troublesome Tatra’s front end slotting anti roll bar bushes over the springs as I couldn’t track down any helpers.

One rubber per spring was enough. I don’t know if they still sell helpers but a session with a hacknsaw and some block rubber should do the trick.

I’d suggest you have a look at a selection of exhaust hangers, you might find one that requires minimal butchering to start a new life as a helper.

I hope you find a solution, ear plugs are not the most comfortable thing to wear.

veteran
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Drives: TSI 90 Match Edition 1.2
Location: London, UK

Re: Changing rear coils on Blue GT

Post by veteran » Thu May 17, 2018 9:42 am

Ricmondo,

I notice that both Mike and you run Blue GT's, though in your case you don't specify which year model you have. Do you not hear that noise (it's more of a low-frequency background drone) yourself? Depending on road surface, I certainly do with my Polo Match 1.2.

Conceivably, a better solution would be to include a rubber, or some other durable compliant bush, between the base of the coil (remember, we're talking essentially here of just the rear suspension) and its seat on the trailing arm. It would appear that, on the SEL, Match and GT, VW has omitted such a bush from that interface, as one is certainly shown in parts diagrams of the rear suspension. As a result, not only does the bottom end of the coil constantly grind against the seat when the car's in motion but also tyrenoise energy more easily finds its way on to the coil.

Mike Austin
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Re: Changing rear coils on Blue GT

Post by Mike Austin » Thu May 17, 2018 12:31 pm

Ricmondo wrote:
Wed May 16, 2018 8:40 pm
I had the same problem some years ago with a Triumph. I had some ‘coil spring helpers’ lying around the garage. They were essentially small shaped blocks of springy rubber that you inserted between the extended coils, once returned to normal height they were trapped by the coils. They altered the harmonic frequency and cured the problem.
Thanks Ricmondo. I have seen coil spring assistors of various sizes for sale. These are mainly to stiffen the springs to allow, for example, for caravans. These may be too hard but softer rubber might just do the trick.
I have been chatting with 'veteran' by PM. His idea of some compliant interface at the spring end would be best. However, your idea is quick and tunable without interfering with the suspension fittings.
I would have thought other Blue GT drivers would have experienced a similar problem and that there would be after market fixes, such as custom made rubber inserts.

veteran
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Drives: TSI 90 Match Edition 1.2
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Re: Changing rear coils on Blue GT

Post by veteran » Thu May 17, 2018 1:23 pm

Mike,

It might well be that many, if not most, 6R/6C Polo owners regard this background drone as being normal, or perhaps simply tolerable. After all, people's perception of noise varies from person to person. What one person with acute hearing and a lifetime of experience with different cars may regard as 'unacceptably annoying' may, for someone else with more-average hearing and less experience be either unnoticeable or 'perfectly acceptable'.

Getting back to the question of the add-on assistors, what view might the local VW workshop or the MOT tester take of such things being fitted to the springs? I suspect that, to avoid arguments, you'd be faced with having to remove them every time you took the car to the VW agent for any work to be done, and certainly annually when the MOT came around.

It might be that a different damper (shock-absorber) and/or a compliant bush inserted at the bottom of the spring (between the seat and the spring) would 'de-tune' the setup sufficiently to eliminate the noise. But the everyday 6R/6C Polo owner isn't going to risk experimenting to that degree on their own (even though it might be worth doing), so the only hope, as I see it, is that a specialist Audi/VW firm picks up on this issue and themselves find a combination of coil and damper that works in this regard.

I think we need to get away from the notion that VW is always the last word on suspension for a given model. Past personal experience with a Mk3 Golf proved that to be patently not the case. We need to bear in mind that the suspension on these Polos has been very much 'built down to a price', and that therefore, with the right approach, some significant improvements in ride, handling, and susceptibility to road noise could be made, even though it'd cost more.

Ricmondo
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Re: Changing rear coils on Blue GT

Post by Ricmondo » Thu May 17, 2018 7:51 pm

My local garage, not Inchcape Twickenham but a local independent say that add ons would not affect MoT testing. The main intention is to modify the harmonic frequency of the spring so soft rubber should work.

If you don’t change the acoustic characteristics insulating the spring from the body and suspension should work but it’s not a five minute job.

My BGT is a Nov 2014 model, I haven’t experienced any noise from the rear suspension with or without my hearing aid....that physical factor could of course be very significant!

gobsteruk
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Re: Changing rear coils on Blue GT

Post by gobsteruk » Thu May 17, 2018 9:21 pm

I have the bgt, and don't notice any noise from the road. 2017 with 8k on the clock. You could always turn the radio up haha

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Mike Austin
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Re: Changing rear coils on Blue GT

Post by Mike Austin » Thu May 17, 2018 11:58 pm

gobsteruk wrote:
Thu May 17, 2018 9:21 pm
I have the bgt, and don't notice any noise from the road. 2017 with 8k on the clock.
What tyres do you have? The coils may resonate with some tyres but not others.

gobsteruk
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Re: Changing rear coils on Blue GT

Post by gobsteruk » Fri May 18, 2018 3:07 pm

Bridgestones, I may not notice any noise as I drive a work van most of the time. But I'm sure the wife would of moaned about it if it was noisy.

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Mike Austin
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Re: Changing rear coils on Blue GT

Post by Mike Austin » Sat May 19, 2018 3:35 pm

I have tried inserting a rubber block into the coils but, surprisingly, to no effect whatsoever. I took a rubber sanding block:
Image
I fashioned two small blocks with v-notches and put a hole in:
Image
The size was enough to wedge very tightly in the coils. They were held in by two cables ties:
Image
Image
So, I am stumped again. I would have thought there would be some effect, with the possibility of a bit of 'tuning'. After fitting the blocks, 'plucking' the coils did sound noticeable quieter. Unfortunately, this made no difference in the cabin.

veteran
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Re: Changing rear coils on Blue GT

Post by veteran » Sat May 19, 2018 4:14 pm

What do you see if you remove the rear wheelarch liners? Does that then give access to some broad expanses of panelling that might be being vibrated by tyrenoise that's travelling up from below? If so, it might be worth adding some bitumenised pads to them, before then replacing the liners.

Incidentally, although you praised the quietness of your former vehicle, the Skoda Fabia, you never said which tyres were used on it. Care to inform us?

Mike Austin
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Location: Bristol

Re: Changing rear coils on Blue GT

Post by Mike Austin » Sat May 19, 2018 4:55 pm

I am a bit loathe to jack up and take the wheel, and liners, off at this stage. I prefer to experiment with the least intrusive tweaks first. I was able to insert the rubber blocks while the car was parked as normal in the garage.
On my Mk1 Skoda Fabia 2.0i (I actually had two identical ones, trading in one after two years for another), I never had a noise problem with any of the tyres. They were 195/50 R15. The last Fabia was delivered with Dunlop SP2020E, then I changed to Firestone TZ300 alpha. I don't recall what was on the first Fabia, possibly Goodyear NCT.
It may be an idea to find another Blue GT owner nearby with a view to asking them to compare cabin noise. I live in Bristol. Any offers?

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