GR86 Reducing Front End Noise

callahan

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As mentioned on the Sound Generator thread, I seem to have a solution for the noisy front end.

I do a reasonable amount of mileage and unfortunately a lot of that is on our motorways and dual carriageways that can be a bit noisy.

There is always going to be tyre noise with cars like ours, but I felt that the noise I could hear didn't sound like it was coming from the tyres, but sounded almost like a bearing at the front of the car. This had been driving me potty for a while, until a conversation with fellow man-of-great-taste (and Grey GR86 owner) @Banksy . He had taken his car to the guys at https://www.cambridgeautosound.com/ to have the speakers upgraded and some sound deadening added.

While he was testing the car he heard the same noise that I could and he came to the conclusion (after removing them and driving it) that the front strut braces were causing it - they're hollow so end up taking vibration from the strut towers and transmitting it to the front bulkhead and it seemed to be around the 200hz region.

I work with audio stuff (expensive Home Cinema speakers primarily) so any random noises annoy me way more than they should, and 200hz is in the vocal range so is more likely to dominate over other noises, so I had to do something about it.

I had a couple of these feet lying round, they're designed to isolate subwoofers from the floor so I thought they'd be a good option:

IMG20240404133244.webp


I cut them in half lengthways as they were too thick to fit, then put a notch in opposite sides to fit around the mounting bolts and fit them between each end of the strut braces and the body / bulkhead, like this:

IMG20240404173433.webp

IMG20240404173442.webp


It took longer to cut the foam in half than it did to fit it, so it's a very easy change. I drove to Leeds and York last week and didn't notice the drone any more, so I'd say it worked and I can now start to obsess about something else instead :D

This is the stuff I used, but I had convenient round bits: https://vibratec.se/product/regufoam-vibration-510-plus/

Hope this is of use to someone.
 
As mentioned on the Sound Generator thread, I seem to have a solution for the noisy front end.

I do a reasonable amount of mileage and unfortunately a lot of that is on our motorways and dual carriageways that can be a bit noisy.

There is always going to be tyre noise with cars like ours, but I felt that the noise I could hear didn't sound like it was coming from the tyres, but sounded almost like a bearing at the front of the car. This had been driving me potty for a while, until a conversation with fellow man-of-great-taste (and Grey GR86 owner) @Banksy . He had taken his car to the guys at https://www.cambridgeautosound.com/ to have the speakers upgraded and some sound deadening added.

While he was testing the car he heard the same noise that I could and he came to the conclusion (after removing them and driving it) that the front strut braces were causing it - they're hollow so end up taking vibration from the strut towers and transmitting it to the front bulkhead and it seemed to be around the 200hz region.

I work with audio stuff (expensive Home Cinema speakers primarily) so any random noises annoy me way more than they should, and 200hz is in the vocal range so is more likely to dominate over other noises, so I had to do something about it.

I had a couple of these feet lying round, they're designed to isolate subwoofers from the floor so I thought they'd be a good option:

View attachment 26623

I cut them in half lengthways as they were too thick to fit, then put a notch in opposite sides to fit around the mounting bolts and fit them between each end of the strut braces and the body / bulkhead, like this:

View attachment 26624
View attachment 26625

It took longer to cut the foam in half than it did to fit it, so it's a very easy change. I drove to Leeds and York last week and didn't notice the drone any more, so I'd say it worked and I can now start to obsess about something else instead :D

This is the stuff I used, but I had convenient round bits: https://vibratec.se/product/regufoam-vibration-510-plus/

Hope this is of use to someone.
Do you think that wrapping them in something like silent coat or dynamat would help?
 
Do you think that wrapping them in something like silent coat or dynamat would help?
That's what Cambridge Autosound did with Banksy's car, as well as a bitumen-like material where I put mine (possibly silent coat with the foil removed).

I was looking at it from a sound isolation and vibration reduction standpoint, so if the feet I used can isolate one of these beasts I thought it would probably work on my car: https://procella.audio/product/v21-2/
 
Got to admit I have reservations with this, my concern with the foam method is that the bracing is no longer rigid and therefore you are prone to flex. Need to be careful that the bolts won't loosen either as the material is not solid, the threads aren't fully engaged on the strut tower.
 
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Really interesting and it makes sense that those struts would channel noise straight to the bulkhead. But I too would be a bit wary of what you've done there. I would at least keep checking regularly to make sure those bolts aren't coming loose as that foam might allow a bit of play in the mounting.

I like the idea of wrapping the struts in Dynamat, that might help damp some of the vibration at least. Or perhaps just opting for an aftermarket strut brace which connects only the two towers and doesn't touch the bulkhead?
 
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Or perhaps just opting for an aftermarket strut brace which connects only the two towers and doesn't touch the bulkhead?
I think this is a good option. Remove the stock braces and fit a conventional strut brace. There will still be some change in rigidity but it would be better than having nothing, I imagine a convention type brace isn't used for pedestrian crash protection reasons, there is space for the bonnet to crumple.
 
Yes, all good points, an aftermarket strut brace would be the better long-term fix.

I do keep checking the fixings and the foam is extremely dense so there isn't any noticeable movement. The nuts are nylon (or similar) so they weren't super-tight in the first place.
 
Really interesting reading. I think I will have to rein myself in with spending on my car. So much to buy, so little money!
 
Got to admit I have reservations with this, my concern with the foam method is that the bracing is no longer rigid and therefore you are prone to flex. Need to be careful that the bolts won't loosen either as the material is not solid, the threads aren't fully engaged on the strut tower.
I agree, the flex in the joint will cause the nuts to either come loose or introduce bending forces in the threaded pins.
One solution would be to have a rather high shore rubber piece wedged under the brace, and using large washers under the nuts with a double rubber washer there too. If you tighten that, there will be more flex under the nut then under the brace, keeping pretention on the nut so it won't move. Also the friction will be so high, there brace will be able to tranfer forces but now damped by the rubber.
 
Sorry, +1 on not a fan of this solution either. If there's enough give in it to damp vibration then there's enough give in it to not do what it was intended to do. Whether that will be actually noticeable in normal driving is another matter. How tight they stay in the long term would be more a concern.

I wouldn't have said the bolts where not tight to begin with, more that it is surprising to most how little torque is needed to correctly torque up smaller nuts
 
I wonder if those GR performance dampers eliminate the noise? I think they are a direct replacement for those struts and have a damper built it which is meant to improve NVH, presumably not being just a solid bar. they would transmit less noise. Think a couple of people on this forum have them fitted, but can't remember who. Would be good to hear what they think.
 
The tubes / braces do seem to be causing the noise, so a (safe) solution to reduce the vibration can definitely improve nvh and makes the car much better for longer journeys, imho of course.

I'll keep an eye on my solution and report back on it's long term safety, but take on board all of the thoughts on here.
 
I don't think it would be unsafe its just more an inconvenience if they come undone. A chap in the US removed his completely and it made the world of difference in terms of noise, he said it also made the ride a bit more supple which is nice for daily driving.
 
This is all rather interesting particularly if putting something in there eliminates a decent amount of drone I'd be well up for it.

Surely there some sort of semi rigid compound like rubber or polybush that would be good?
 
This is all rather interesting particularly if putting something in there eliminates a decent amount of drone I'd be well up for it.

Surely there some sort of semi rigid compound like rubber or polybush that would be good?
It's a balance, the whole parts function is to provide additional stiffness (not strenght, or? ), putting a polybush with several mm of movement in, one might just as well delete the stay altogether...
 
I don't think it's a problem for every car, suggesting the resonance is generated in a narrow set of circumstances. If you change the material or deadening the braces themselves it might be enough to change the resonance to a frequency where it's not going to bother anyone. All speculation of course.
 
Might be better to drill small holes in the braces and inject with expanding foam spray ?
 
Might be better to drill small holes in the braces and inject with expanding foam spray ?
If the firewall is "the drum", filling the metal drumsticks with foam won't make a big difference....
 
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