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NVH Issues


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So I finally upgraded my rear suspension from a basically mild setup (slotted crossmember, control arm poly bushings and comp springs) to a Datsport fully adjustable crossmember, whiteline bushings in the control arms, crossmember mounts and mustache bar plus Ground Control coilovers with 250lbs springs. Also a R180 STI diff was installed.  Hah! Big changes that have made the handling much better BUT a significant increase in NVH. Can hear some gear whine now. To the point where I am considering what to do to lessen it. So would love some suggestions to go about this. My initial thoughts are:

1. Do some sound deadening and suppression in the interior since right now it's just carpet on metal. 

2. Swap out some of the bushings back to stock ones? Maybe crossmember and mustache bar?

3. Would changing the rear coilovers down to 225lbs make that big of a difference or any?

4. Would the CV axle conversion improve some of the vibration?

5. Just suck it up and get used to it!


Any feedback?

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A few kilos of sound deadener covering the whole interior will do wonders for the reduction of NVH levels.


Something that should be done anyway.


But as said, rubber bushes transmit far less NVH compared to Poly.


Also if the diff is bad, it'll make noise, so check that out first.

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Poly is not needed except possibly on a 'race car'. Hood pins, rear spoiler, slotted and cross drilled rotors, catch cans, strut brace (the list is endless) of real 'race car' stuff that finds it's way onto the street but doesn't really improve anything over stock. Often they bring undesirable side effects with them... things that are not a concern when racing. 

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I bought poly bushings for everything on the car I took apart way back.




Was planing to do it up back then roll cage and all but for the street. Back then there was no track in New Orleans. Not sure which way I will go now that there is a track in Avondale, LA. I don't really have plans to build it just for track now but since the net and great sites like this I would use rubber for certain parts if used on the street. Like Mike said. Back before when the net was new and had no info all over I thought poly was the way to go even on the street but after reading all the issues people have had with poly on the street sense I have been on this site I would'nt use it for a street car only for a race car setup. That doesn't still temp me from wanting to use it cause I do have it and just run the car on that track to see how fun it would be.

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There are many parts that move relative to each other, such as a control arm. Rubber grips both surfaces but will stretch internally and allow the parts to move. Polly tends to be too stiff and will not twist. It holds one part or the other or neither and will rub the other or chafe. Rubbing will cause squeaking and wear holes oval. One place polly should NEVER be used is on the tension rods. It's lack of compliance forces the tension rod to flex and fracture. In a racing environment suspension parts are inspected and replaced regularly so there is no problem, and squeaks and vibration really do not matter. I suppose you could oil or grease the squeaks but this does not address annoying vibration transfer. Lets be serious here, it would take a race car driver to really notice any handling 'improvement' using polly over stock rubber that is in good shape. 


I have heard that lately polly firmness has been reduced to eliminate the above problems. I don't know for sure and how do you tell? If so AND it is the same as rubber it may be the only source for replacement

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One place polly should NEVER be used is on the tension rods. It's lack of compliance forces the tension rod to flex and fracture.


In a racing environment suspension parts are inspected and replaced regularly so there is no problem,


Most race cars don't fiddle with poly in joints that actually move as part of suspension function, but rather hiem joints.


One would hope, but I've seen way too many build it, and forget it........

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I don't know why the poly is a debate when you can't get new rubber bushings for the mustache bar or the cross-member mounts. Just getting it for the control arms is very challenging! If the choice is to leave old rotten 45-year old rubber in OR change them out for poly, I'll take poly any day. Was hoping for new NVH but I guess that goes with the territory. 


Definitely doing sound deadening this winter for sure. 

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There is some poly bushes now that people drill holes in to allow a bit of twist movement so they aren't too stiff

I believe I have seen this, They are in a circle around a center hole and the outside edge. The ones I have are from way back and are solid. I wonder if they can be modded or will it ruin them.

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