Rear unsettled at high speed

[Bluemustang]

I took a drive this weekend to Richmond to see my brothers family and I noticed something about the car I didn't notice earlier. The rear feels very unsettled at certain times at high speeds. I noticed at speeds around 80 it feels very bouncy in the rear especially if the road was curved or bumpy at all. A lot of bounciness.

I did not have this problem before doing the Steeda LCA bearing and differential bushings inserts. Right now I'm thinking about upgrading my rear shock mounts to the Steeda versions. It's been reported by some that it solves the bounciness.

But I wanted to seek some opinions before I go out and spend more money on it. My other thought is to just start removing all my aftermarket IRS parts. I'm growing tired of the unknown NVH effects every time I add a part that claims no NVH. I need some common sense injected here.

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[wildcatgoal]

Rear shock mounts do work... I was one of the first to notice and spent a lot of time prior to that trying to adjust out bounciness even having adjustable shocks. Got it close, but the shock mounts eliminated the objectionable bounciness entirely (YMMV of course).

As for claims of no NVH. Those claims are generally "no NVH with an otherwise stock car". Regardless, I am also annoyed when that is said by any company. Ford set up the car with rubber all over the place in the IRS after spending MILLIONS on testing. They decided to strike the balance of handing vs. NVH at a certain price point. The second you tighten up or remove bushing compliance, you will get NVH. Adding a spherical bearing will change suspension articulation such that it is not inconceivable that the fact the rear stock shock mount has a bushing (vs. a bearing like Steedas) then becomes an issue. The BMR CB005 will allow NVH through the chassis. The Steeda IRS braces can, too. Either company's differential bushing inserts are, IME, one of, if not THE, primary causes of the added NVH people find objectionable, especially in M/T vehicles who, without any modification, were plagued with a clunky driveline (such as my car). I always try to suggest those be done last (unless the car will be biased towards drag racing).

Let's all face the facts: your car, stock, is the "low NVH baseline". You will not get any quieter short of quieter/softer tires. Adding any new part, even just lowering springs, and you open the door for more NVH. How perceivable that is (if at all) is different by individual driver and, somewhat significantly so, by individual car. I went through this mind warping decision process (which I now call a phase) myself.

If you decide to remove your parts, I do suggest keeping the IRS bushing supports (above and below the IRS at each blue bolt). Ideally, IMHO, you have the Steeda solution, which fills more of the gaps at the rear bushings, but the BMR ones work in the same way. If you have the CB005, remove the arm but not their IRS bushing supports. Leave those, and you will get the more stable IRS feeling and probably no perceivable NVH (or at least very little and only occasionally).

 

[keltymd]

from my testing I have found the BMR BK051 differential inserts made the most NVH (I actually removed them). The CB005 makes a bunch of NVH when compared to the Steeds IRS subframe braces but the steeda subframe braces do not make the rear end feel as solid. I have not tried the Steeda IRS Bushing support kit. The Toe Link bearings I installed do make a little noise transfer from the wheels so if you are sensitive to road noise I would not recommend them.

 

[Bluemustang]

Thank so [MENTION=21494]wildcatgoal[/MENTION] and [MENTION=26181]keltymd[/MENTION] for your input. I am going to take wildcat's suggestion of doing the rear shock mounts from Steeda, and I think I am going to remove the diff inserts also. The constant clicking when the engine loads and unloads is maddening if you're sitting in traffic. Plus I don't think at my level that the diff inserts are giving me that much performance benefit anyhow.

I'm gonna try to stay calm and approach this one step at a time. Go with the rear shock mounts and I HOPE it solves the bounciness right off the bat. Not gonna remove the CB005 just yet as the performance benefit is too much to ignore.

 

[BmacIL]

Thank so [MENTION=21494]wildcatgoal[/MENTION] and [MENTION=26181]keltymd[/MENTION] for your input. I am going to take wildcat's suggestion of doing the rear shock mounts from Steeda, and I think I am going to remove the diff inserts also. The constant clicking when the engine loads and unloads is maddening if you're sitting in traffic. Plus I don't think at my level that the diff inserts are giving me that much performance benefit anyhow.

I'm gonna try to stay calm and approach this one step at a time. Go with the rear shock mounts and I HOPE it solves the bounciness right off the bat. Not gonna remove the CB005 just yet as the performance benefit is too much to ignore.

Pretty sure the mounts will take care of it. [MENTION=26233]Rebellion[/MENTION] just installed his over the weekend and was surprised at how effective they were.

 

[Rebellion]

Pretty sure the mounts will take care of it. [MENTION=26233]Rebellion[/MENTION] just installed his over the weekend and was surprised at how effective they were.

Yeah, they do have a pretty significant effect on smoothness of the ride, a lot less vibration and jumpiness, and less "underdampened" bouncy feel.

Now that I put the shock mounts, I'm certain that the bouncyness doesn't have to do anything with damping or springs. You can still feel the bumps and other surface imperfections, but it recovers as expected and doesn't create oscillations.

Who would have thought that such a simple mod can have this effect? Seems to be the only mod that reduces NVH without any cons. I'm not sure it adds anything to the handling, but for someone who has stiff springs and dampers, I think this mod is worth it just for the comfort alone. Makes me believe I can even go stiffer in springs without really getting the car to be uncomfortable.

[MENTION=19599]Bluemustang[/MENTION], one additional effect for us that have the Steeda LCA...it gets rid of the road feel at low speed that we "gain" from the LCA. The car still clamps down to the road hard and responds scary quick, but without feeling the road imperfections of low amplitude. Feels like the shocks are finally damping them.

 

[Bluemustang]

Yeah, they do have a pretty significant effect on smoothness of the ride, a lot less vibration and jumpiness, and less "underdampened" bouncy feel.

Now that I put the shock mounts, I'm certain that the bouncyness doesn't have to do anything with damping or springs. You can still feel the bumps and other surface imperfections, but it recovers as expected and doesn't create oscillations.

Who would have thought that such a simple mod can have this effect? Seems to be the only mod that reduces NVH without any cons. I'm not sure it adds anything to the handling, but for someone who has stiff springs and dampers, I think this mod is worth it just for the comfort alone. Makes me believe I can even go stiffer in springs without really getting the car to be uncomfortable.

[MENTION=19599]Bluemustang[/MENTION], one additional effect for us that have the Steeda LCA...it gets rid of the road feel at low speed that we "gain" from the LCA. The car still clamps down to the road hard and responds scary quick, but without feeling the road imperfections of low amplitude. Feels like the shocks are finally damping them.

Thanks [MENTION=26233]Rebellion[/MENTION]. This is the sort of feedback I was hoping for, which should make my decision that much easier. I'm hoping I will end up with the same results.:cheers:

 

[qtrracer]

Maybe it's the shock valving rather than the mount? The shock valving should control those oscillations, unless the mounts are moving around. If they aren't it could be the shocks aren't valved for the springs used.

 

[BmacIL]

Maybe it's the shock valving rather than the mount? The shock valving should control those oscillations, unless the mounts are moving around. If they aren't it could be the shocks aren't valved for the springs used.

No, the mount contributes far more than people expected. The stock mount is secured to the shock shaft on a hard rubber bushing. This, combined with the bushing at the bottom of the shock at the control arm, causes the system to bind and not allow free articulation. The dampers can't work effectively to control the oscillations. The billet mounts have spherical bearings with allow for articulation.

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