Does control arm bushing composition affect ride quality or NVH?

[k-huevo]

The word from Synergy today is the 01 TJ bushing will no longer be produced.

I recently installed Synergy's non-adjustable lower control arms in the front. I expected handling quality would be different, and it is. Much had to do with the poor condition of the former OE bushings, some has to do with a little more caster, and, the front axle is now squared. The bushings seem to deliver high frequency road surface feedback, but nothing jarring or harsh.

 

[Fargo]

The word from Synergy today is the 01 TJ bushing will no longer be produced.

I recently installed Synergy's non-adjustable lower control arms in the front. I expected handling quality would be different, and it is. Much had to do with the poor condition of the former OE bushings, some has to do with a little more caster, and, the front axle is now squared. The bushings seem to deliver high frequency road surface feedback, but nothing jarring or harsh.

Well that really sucks if they are not going to make them any more.

Thanks for the feedback. I am really considering doing this myself this winter. Can you provide more detail about what you meant by high frequency feedback. Is it something that would cause NVH annoyances. Does the steering feel any tighter?

 

[k-huevo]

High frequency as in road surface with large aggregate. I would classify it as V, and it's tolerable to me.

Yes, steering is tighter. When I first drove this Jeep I thought it needed a new steering box. I know now the sloppiness was the result of tolerance stacking; looseness at every steering linkage, track bar, and worn bushing.

 

[Fargo]

High frequency as in road surface with large aggregate. I would classify it as V, and it's tolerable to me.

Yes, steering is tighter. When I first drove this Jeep I thought it needed a new steering box. I know now the sloppiness was the result of tolerance stacking; looseness at every steering linkage, track bar, and worn bushing.

Thats what I thought you meant. I ask as I am trying to decide between Synergy or the Savvy with Johnny Joints. So I'm trying to figure out which will offer the best ride and handling trade off vs NVH. I've also considered JKS or something with Clevite.

I think I have the same sloppiness from bushings. I've already installed a new trackbar and Currie steering.

 

[jjvw]

... I ask as I am trying to decide between Synergy or the Savvy with Johnny Joints. So I'm trying to figure out which will offer the best ride and handling trade off vs NVH. I've also considered JKS or something with Clevite.

...

I forget. Is this the thread where we learned that Johnny Joints are squishy?

 

[Fargo]

I forget. Is this the thread where we learned that Johnny Joints are squishy?

Yeah, its funny, I was planning on going Synergy because I thought the JJ was too stiff. Now it seems the JJ might actually be a softer material and have less NVH than the Synergy. So I'm still dealing with all this confusion on which way to go. I also see pros and cons to each of the arms themselves apart from the material. But for now, I'm just trying to get a better handle on the materials used and the NVH of each.

 

[k-huevo]

...I've already installed a new trackbar and Currie steering.

Same here.


Plus front shocks with plenty of low speed damping. Cornering performance had already been vastly improved, and death wobble eliminated. The new arms still made an appreciable difference. My guess is if my tires had better compliance, I probably wouldn't feel feedback the same.

I do plan to replace the poly bushings on the front track bar with rubber, and replace the rear track bar rubber bushings with something else. After that I'll address the front upper control arms, because I want more of a good thing.

 

[Fargo]

If I go with the Synergy arms I will also go with the Synergy trackbar. I wonder if they have a bushing that you could use in your current track bar. I just have a Moog on at the moment. It was slightly longer than my factory so I am pretty well centered with it until I get taller springs. But I might also see if Synergy has a bushing that will work in the OEM/Moog trackbar. I think that would be an interesting experiment to compare the clevite trackbar to the DDB trackbar.

 

[Fargo]

Tell me something. If you had to guess how much stiffer the DDB bushing is compared to your factory clevite bushings what would you guess. Maybe 20%, 30%, 40%, 50% or even more?

(I'll get to my reasons in the next post.)

 

[k-huevo]

Sorry, I can't quantify comparative stiffness.

The vibration I experienced after the new install was relatively innocuous, and short lived. I suggest not thinking too much into it.

 

[Fargo]

Sorry for the late reply. The reason I asked was because when I spoke to a tech at Synergy some time back, I asked about how stiff the DDB bushing was. He made a quick comment that the hard durometer was 95 and the soft durometer was 85. I had no idea what he was talking about with these numbers so I just left it at that.

Later I found this web page about car bushings with the image I posted below. https://powerflexusa.com/howtochoose.aspx

That page talks about different durometers and something called the Shore scale for durometer ratings. They talk about their proprietary bushings and mention that a 70a is 25% stiffer than stock, a 80A being 30% stiffer than stock, and a 95A that is 80% stiffer than stock. Assuming the stock bushing they refer to is Clevite or something similar to our control arms I thought that might give us some indication of how stiff the DDB bushing is.

Using those numbers I came to the conclusion that the numbers Synergy gave me must be the Shore A durometer numbers. So I estimated that the softer durometer might be about 35% to 50% stiffer than stock. But that is just an estimate and probably doesn't mean much in the end since both durometers work together and the thickness of each one plays a role. Not to mention there are at least 2 other Shore ratings. Althought Shore A seems most likely. A search for Shore ratings will provide some interesting info and lots of charts showing were things fall at in the hardness scale.

Another interesting chart here: https://mechanicalrubber.com/elasto...ploads/2013/08/Durometer-Conversion-Table.pdf

A short article here, that equates bushings to cartilage in the human body. But I think his math is too simple. I don't think you can simply divide the hardness scale of 70 by 1.25 to get the factory stiffness of 56 as he says. The same math doesn't work out for the rest of the stiffness estimates. Although it does provide a reasonable range of 53-62 for factory bushings. Which is close to a rubber tire. So maybe not too far off.
https://blog.edgeautosport.com/breaking-down-bushing-stiffness

Anyway, I'm not sure if this really helps predict the handling difference of a DDB vs a JJ or Clevite. But it certainly is interesting if your into the details of these things.

 

[fuse]

I have some personal butt dyno results to report that may or may not be useful.

I just finished installing new Moog control arms to replace the old stock control arms, because the old Clevites were in sorry shape. This is what 13 years and 130k road miles does to stock bushings:

I replaced the control arms in sets, rear upper, rear lower, front lower, then front upper, because I was only wrenching for a couple hours after work. So I got to drive the Jeep in between changing each set, and I could see if changing one set made any difference.

Butt dyno said that new front LCAs made a huge difference. New rear LCAs were also a noticeable improvement, but not as much as the fronts. Couldn't really tell that new UCAs made any difference at all.

Looking at the old rubber, the LCA bushings are in much worse shape than the UCA bushings. From that and the butt dyno results, I'd guess that the LCA bushings take much more abuse and have a much greater impact on NVH than the UCA bushings.

 

[k-huevo]

I replaced a poly bushing on the front trackbar with a Moog rubber bushing. Moog's k7252 trackbar bushing is used on Dodge Ram 4WD trucks, and it takes a big kahuna 14mm bolt. Currie's poly trackbar bushing is very hard, the rubber bushing not so much. Ride quality noticeably improved after installation.

So far I haven't located a substitute for the stock rear trackbar bushings.

 

[Chris]

I replaced a poly bushing on the front trackbar with a Moog rubber bushing. Moog's k7252 trackbar bushing is used on Dodge Ram 4WD trucks, and it takes a big kahuna 14mm bolt. Currie's poly trackbar bushing is very hard, the rubber bushing not so much. Ride quality noticeably improved after installation.

So far I haven't located a substitute for the stock rear trackbar bushings.

Dave uses those same bushings on his track bars as well. He likes them better than the Currie ones.

 

[bobthetj03]

I replaced a poly bushing on the front trackbar with a Moog rubber bushing. Moog's k7252 trackbar bushing is used on Dodge Ram 4WD trucks, and it takes a big kahuna 14mm bolt. Currie's poly trackbar bushing is very hard, the rubber bushing not so much. Ride quality noticeably improved after installation.

So far I haven't located a substitute for the stock rear trackbar bushings.

There are a few TB makers that offer adjustable TB's with rubber bushings. Rough Country is one that comes to mind because I have one on my rig.

 

[k-huevo]

Currie also has a Clevite rubber bushing model CE-9120TJS, which uses stock or 10mm bolt. I had that model, but the axle bracket holes were badly ovalized, so I installed model CE-9120TJJ. It uses a 1/2 inch bolt. The downside of that model's poly bushing is a flange on each side, which eliminated misalignment capability.

In my case one of the advantages to stepping up to a larger size bolt hole was a chance to make the bracket holes concentric. It bugged me a lot that I couldn't fix the misshaped bolt holes entirely by drilling out to a 1/2 inch. A higher grade, larger diameter bolt, also allows higher torque to be applied. David Kishpaugh, and Chris' proclivity for sharing details, saved my day.

 

[astjp2]

I wonder if anyone has any real data on NHV using vibration sensors between rubber, ddb and johnny joints? I think that there must be some point of diminishing return in ride quality and flexibility. Tim

 

[k-huevo]

New bushing installs:
Left and right machined JJs on the front axle and Synergy UCAs.


Synergy rear UCAs


Not shown are new Moog rear LCAs.

The main difference I feel from all OE, is suspension freedom of movement. I don't feel like I'm being pitched from one side to the other over rough pavement. Replacing the LCAs highlighted how much the left & right UCAs were working against each other. New LCA's also squared both axles at ride height.

This Jeep's suspension was probably misaligned more than usual. Both front and rear wheel bias was 1.25" to the right before I began work on it.

 

[bobthetj03]

What are the front lowers?

 

[k-huevo]

...I recently installed Synergy's non-adjustable lower control arms in the front...

Post #281