Reducing NVH (Noise, Vibration, Harshness)

a good set of shocks will make the drive alot smoother. i swapped from pro comp es9000 to bilestein 5125 the difference is pretty noticable

and i 2nd the brown dog motor mounts. very beefy mount, but even with the super flex rubber mount i get alot of vibration while idling. i have tried loose, tight, etc but the vibration wont go away
 
bmpweXJ said:
Can someone explain how the shackle angle affects the ride of the springs?
Click to expand...

When the shackle is not in a position to swing easily the initial shock of hitting a bump or whatever is transmitted directly into the vehicle. Basically the same idea as not running short arms that point into the chassis instead of in parallel.
 
bmpweXJ said:
Root moose:
Can you link to this rubber joint? I've looked around their site but all I found was: http://www.ballisticfabrication.com/Ballistic-Forged-Poly-Bushing-263_p_1646.html This doesn't seem to be what you're describing.
Click to expand...

Hmm, that's what I remember seeing in my mind's eye. Maybe there was a rubber version that has been discontinued? I do remember them going on sale about 6-9 months ago. Maybe they cleared them out? Or maybe I was just fantasizing about such a part...

FWIW, the poly in the long arms is further down the list in requiring attention compared to the rear shackle angle and interior sound deadening - at least on my Jeep.
 
Last edited:
Also, just to add to some of the other points made I did find a difference adding the stiffeners. A lot of the squeaks and rattles went away.

My 4.56 gears are fairly noisy (installed properly - just the nature of the beast). For the way I use the Jeep I'll need to add extra sound deadening over the rear axle and kind of wished I'd installed 4.10s. I'll likely do 4.10s on my MJ. If off-road gearing becomes an issue there's transfer case gears.

Tires make a big difference in vibration but not so much in noise IME. The Truxus MTs I had on the Jeep basically rattled the entire interior apart. POS tires. I'm still chasing the rattles.
 
bmpweXJ said:
How have the WJ arms held up? Does your XJ get flexed often? Do you think the improvement was due to the rubber bushings?
Click to expand...

My off roading is mostly soft sand beach, so not much flexing.
I think the large oval shaped bushing that connects on the frame side is the key here, I read that Jeep designed these bushings to reduce NVH (Noise, Vibration and Harshness) & they seem to work.
 
Milford Cubicle II said:
They're also called flex discs. It's one of these:

113549.jpg
Click to expand...
I would not run one of those on an XJ. They are known to come apart. But my main concern is that they are mainly used on cars with very low drive line angles. If you have an SYE running one with a double cardan joint would be interesting. The joint is meant to flex a bit and has a similar purpose to a DC joint, but on a setup with very low angles.

However, mentioning that did bring up an idea. Some drive shafts have a harmonic damper mounted on them, similar to the harmonic balance on the front of the engine. I have also seen dampers bolted to transfer cases and transmissions as well.

Root Moose said:
On the friction tape thing, I'm not sure what is better to use on the various dash peices:
Click to expand...
That 3M one is similar to what I used. However, I don't know which one is better.
 
Talyn said:
I would not run one of those on an XJ. They are known to come apart. But my main concern is that they are mainly used on cars with very low drive line angles. If you have an SYE running one with a double cardan joint would be interesting. The joint is meant to flex a bit and has a similar purpose to a DC joint, but on a setup with very low angles.

However, mentioning that did bring up an idea. Some drive shafts have a harmonic damper mounted on them, similar to the harmonic balance on the front of the engine. I have also seen dampers bolted to transfer cases and transmissions as well.
Click to expand...

Yea, the flange off of a SYE is pretty much the only way I saw that as being feasible. Durability wise I'm not sure about. Yes, they fail - but so does every other part. However, I've got 103k miles on mine and that's in a 300hp/ft lb car that's not driven very gingerly at all. But then again my car doesn't go through deep snow, mud, water, etc. You just have to do a visual inspection at every oil change. Might not be everyone's cup of tea but I thought it'd be worth pondering.

But the harmonic balancer I've always thought would be a good idea with hardly any drawbacks. I just don't know of/haven't looked for one that will work for us.
 
Milford Cubicle II said:
Yea, the flange off of a SYE is pretty much the only way I saw that as being feasible.
Click to expand...
Yeah it wouldn't work too well with the stock yoke. And I don't think it would work very well with a SYE.
Durability wise I'm not sure about. Yes, they fail - but so does every other part. However, I've got 103k miles on mine and that's in a 300hp/ft lb car that's not driven very gingerly at all. But then again my car doesn't go through deep snow, mud, water, etc.
Click to expand...
We also have one in one of our cars. Its about the same numbers as yours. But its a car so drive line angles aren't bad. Its also an IRS vehicle, so the drive line doesn't cycle. And it has a pillow block/center support bearing.
But the harmonic balancer I've always thought would be a good idea with hardly any drawbacks. I just don't know of/haven't looked for one that will work for us.
Click to expand...
From what I read most are (or should be) be tuned to a certain harmonic to eliminate. But I am not sure how crucial that is. I want to say the WJ has one bolted to the transfer case as well as another 4x4 I worked on recently. Might be the Toyota sitting at work. I'll have to check.
 
I think that instead of retrofitting a guibo on the rear shaft you'd be better served by retrofitting CV axles into the front drive like used on ZJs and WJs.
 
If you like replacing grease boots, sure. The U-joint axles contribute little noise to running. Especially since you shouldn't be using 4x4 on the road unless you have a NV242 or loss of traction. If you feel you u-joints in 2wd or even in 4x4 full time your joints are bad, with maybe the exception at full lock.
 
Root Moose said:
I think that instead of retrofitting a guibo on the rear shaft you'd be better served by retrofitting CV axles into the front drive like used on ZJs and WJs.
Click to expand...

Why would one want to do this? Assuming you keep your stuff in good shape, what's wrong with the u-joint? You are talking about what to use as front axle shafts, right?
 
bmpweXJ said:
Why would one want to do this? Assuming you keep your stuff in good shape, what's wrong with the u-joint? You are talking about what to use as front axle shafts, right?
Click to expand...

CVs transmit less NVH. If they didn't none of the manufacturers would bother with them.
 
Last edited:
Milford Cubicle II said:
Possibly the horrible bind and weakness at full lock?
Click to expand...

0.000000000000001% of my XJs 110k road miles have been at full lock.
0.1% of my 2k offroad miles has been at lull lock.

Not worth the trade offs in my opinion.
 
The best NVH improvements I've had to date were going to a high quality shock w/ improved mounts. I had been running JK shocks with BPEs nutted on to some welded-in studs (in the rear) and the noises were pretty bad. I assumed it was in the nature of the beast.
Until I put Bilstein B6es back there, got rid of the BPEs & bolted it all up. LOTS of noises just went away, lots of others just got quieter.

My point is that a good NVH starting place is to upgrade / repair anything that is even "marginal" and keep your rig tight, replacing bushings as needed. After all of that... sound deadener, bigger bushings, fix your shackle angle (if applicable) and look at alternate tires if you are running anything that could live under an F-250.
 
yossarian19 said:
The best NVH improvements I've had to date were going to a high quality shock w/ improved mounts. I had been running JK shocks with BPEs nutted on to some welded-in studs (in the rear) and the noises were pretty bad. I assumed it was in the nature of the beast.
Until I put Bilstein B6es back there, got rid of the BPEs & bolted it all up. LOTS of noises just went away, lots of others just got quieter.

My point is that a good NVH starting place is to upgrade / repair anything that is even "marginal" and keep your rig tight, replacing bushings as needed. After all of that... sound deadener, bigger bushings, fix your shackle angle (if applicable) and look at alternate tires if you are running anything that could live under an F-250.
Click to expand...

Because Bilstein supplies shocks to OE manufacturers the bushings and materials used are specifically made to keep NVH to a minimum and last for many years as opposed to generic aftermarket shocks with cheap (and hard) urethane bushings.

I have done a number of upgrades for the new 5160/5165 series Bilstein shocks where the lower rod end is swapped for the heim end from the 7100 series but the upper factory bushing is maintained. This allows increased articulation with less bind while not introducing the increased NVH of a dual heim shock. The combination works well for weekend wheeling while still passing the "wife" test on road.
 
You must log in or register to reply here.

Similar threads

A
Vibration after rebuilds
Replies
17
Views
1K
asymptonic
A
C
Seeking Tuning Advice for Gen 1 SVT Raptor Shocks on a Jeep XJ
Replies
1
Views
182
Evan03
E
G
2000 xj Where to start
2
Replies
28
Views
2K
Jeepedo129
Jeepedo129
1
Feeler for sale of my XJ crawler.
Replies
0
Views
465
1-tonxj
1
R
Which steering box brace? Bearing or not?
Replies
7
Views
3K
75SV1
7
Back
Top