A Story of Indecision and Frivolous Spending

[jjvw]

I like the idea of the shock travels matching the spring travels. So the longer the spring travel the better.

So many of the big RTI and CTI scores are coming from rigs with springs that fall out. If the springs are falling out, there is no down pressure beyond the weight of the tire on the ground. An unweighted tire that skates across the ground isn't doing much, so why build in that travel?

 

[psrivats]

One other thing to add to @Chris' post above is that we also confirmed we have the same type of resonance vibration issue. Mine was much worse in the intensity (higher amplitude in scientific terms) and starts off at a lower speed, but the cyclical, rythmic nature of it was unmistakably the same (very similar time period of repitition, ie the same frequency of oscillation).

I think the intensity of mine being worse is related to the standalone crossmember I had instead of the factory skid, but not sure. Still thinking about it.

@Chris after today's discussion going with Savvy installed by a different shop is the best option unless you are willing to wait a very long time.

 

[Chris]

I like the idea of the shock travels matching the spring travels. So the longer the spring travel the better.

So many of the big RTI and CTI scores are coming from rigs with springs that fall out. If the springs are falling out, there is no down pressure beyond the weight of the tire on the ground. An unweighted tire that skates across the ground isn't doing much, so why build in that travel?

That makes sense, and this is what I took away from Dave. There's no sense in using those Fabtech 4" springs, as they are much too short. In addition, everything you say about the springs falling out, this is exactly what we were discussing.

So then that leads to the next question, what were the little "tricks" you did you get the LJ rear springs to work? I might go that route since I am going to need to order some new springs this weekend.

 

[jjvw]

What made you run the LJ rears as oppose to the non LJ rears? Was that extra inch worth it?

I wanted the length. I was able to make it work because of my heavy tire carrier. Also remember that I reduced the ride height when I relocated both the upper and lower spring seats. Then I went back in and added a 1" spacer. Basically, I opened up the space between the upper and lower seats, then used a spacer to adjust the ride height. If I ever switch to a lighter carrier, I might need to run a thinner spacer.

 

[Chris]

Oh yeah, I forgot to mention that Sri and I drove both our Jeeps back-to-back with each other in the vehicle. His vibration is unreal, unlike anything I'd ever heard. It comes on strong about 40-45mph, and it is a major, major cyclical vibe. It has an up point, and a down point in the vibration, with maybe a second or two in between.

Mine does the exact same thing, but mine doesn't come on until about 60-65mph, but it's literally identical after that. This is no pinion angle vibration, this is a true harmonic vibration and just listening to it you'd think you were inside of a speaker hearing the frequencies bouncing around. If you saw it on an oscilloscope, you'd literally see an up and down pattern.

 

[Chris]

I wanted the length. I was able to make it work because of my heavy tire carrier. Also remember that I reduced the ride height when I relocated both the upper and lower spring seats. Then I went back in and added a 1" spacer. Basically, I opened up the space between the upper and lower seats, then used a spacer to adjust the ride height. If I ever switch to a lighter carrier, I might need to run a thinner spacer.

That makes sense. I purchased these brackets to relocate my rear spring perches: https://genright.com/products/rear-coil-spring-correction-kit.html

I shouldn't need to relocate the rear perch with those, but I'm curious how much ride height I will gain with those (if any at all), as that might be a determining factor in whether or not to put an LJ rear spring on there, or a TJ rear spring.

 

[psrivats]

I'm now pretty sure both mine and yours are not related to pinion angle or wheel balance. It's simply not an option to live with itn given how intense it is.

I remember (and from my notes) that my vibes started at a higher speed with the factory skid on, like 57-60. However this was 6 weeks ago. Changing the skid did do something. They need to run the experiments we've provided them and confirm things systematically.

If no progress happens wrt my Jeep in a week or so, I'm taking it back and having my regular mechanic have a go at this. I'm tired of pushing them honestly.

 

[jjvw]

....

So then that leads to the next question, what were the little "tricks" you did you get the LJ rear springs to work? I might go that route since I am going to need to order some new springs this weekend.

Trick pics are in the outboard thread from a couple days ago. The upper seat is trimmed and pushed as high into the frame arch as possible. The lowers are flattened out to reduce the lift gained by raising the pinion. I lost at least an inch of ride height by doing this. The final ride height is then established through springs and spacers.

A trick with spacers that very few understand, is that if the springs are not near bind at full bump, then a spacer up to the thickness of the remaining spring travel can be used to add ride height and also increase the overall spring travel. Make sense?

 

[jjvw]

Oh yeah, I forgot to mention that Sri and I drove both our Jeeps back-to-back with each other in the vehicle. His vibration is unreal, unlike anything I'd ever heard. It comes on strong about 40-45mph, and it is a major, major cyclical vibe. It has an up point, and a down point in the vibration, with maybe a second or two in between.

Mine does the exact same thing, but mine doesn't come on until about 60-65mph, but it's literally identical after that. This is no pinion angle vibration, this is a true harmonic vibration and just listening to it you'd think you were inside of a speaker hearing the frequencies bouncing around. If you saw it on an oscilloscope, you'd literally see an up and down pattern.

Fascinating

 

[Chris]

I'm now pretty sure both mine and yours are not related to pinion angle or wheel balance. It's simply not an option to live with itn given how intense it is.

I remember (and from my notes) that my vibes started at a higher speed with the factory skid on, like 57-60. So changing the skid did do something. They need to run the systematic experiments we've provided them.

If no progress happens wrt my Jeep in a week or so, I'm taking it back and having my regular mechanic have a go at this. I'm tired of pushing them honestly.

Can wheel balance even create a cyclical vibration like that? One that literally has an up-and-down to it? But even if so, how would that be possible that both of us just happened to end up with wheel balance issues right after a re-gear? I don't buy it.

 

[Chris]

Trick pics are in the outboard thread from a couple days ago. The upper seat is trimmed and pushed as high into the frame arch as possible. The lowers are flattened out to reduce the lift gained by raising the pinion. I lost at least an inch of ride height by doing this. The final ride height is then established through springs and spacers.

A trick with spacers that very few understand, is that if the springs are not near bind at full bump, then a spacer up to the thickness of the remaining spring travel can be used to add ride height and also increase the overall spring travel. Make sense?

Makes perfect sense. I see what you mean about pushing the upper spring perches as high into the frame as possible. I'll ask that the new shop do this with those GenRight perches. I could see how doing that and changing the angle of the lower spring perch would definitely cause you to lose some ride height, but the spacer makes perfect sense.

I have to imagine these guys know this... but I'm going to come armed with the knowledge just so they know what I'm after.

 

[jjvw]

That makes sense. I purchased these brackets to relocate my rear spring perches: https://genright.com/products/rear-coil-spring-correction-kit.html

I shouldn't need to relocate the rear perch with those, but I'm curious how much ride height I will gain with those (if any at all), as that might be a determining factor in whether or not to put an LJ rear spring on there, or a TJ rear spring.

I reused the factory pieces. They are easy enough to cut out intact. But even those GR mounts can be trimmed and fitted higher into the arch. Since the pad is bolted on, spacing them down is pretty easy too.

 

[Chris]

I reused the factory pieces. They are easy enough to cut out intact. But even those GR mounts can be trimmed and fitted higher into the arch. Since the pad is bolted on, spacing them down is pretty easy too.

Yes, I see that pad is able to be positioned up to an inch forward or backwards. But it just dawned on me, I'll also need to relocate the bottom perch as well, since I'll need the upper and lower bump stops to line up perfectly.

The crazy part is I get all of this. I could literally do it myself if I knew how to weld and had a lift. I'd just hate to do this on my back, in the garage, on jack stands, with no welding skills, haha.

EDIT: I could have just reused the stock mounts. But the GenRight ones were 15% off, which made them cheap enough that I didn't think twice.

 

[psrivats]

Can wheel balance even create a cyclical vibration like that? One that literally has an up-and-down to it? But even if so, how would that be possible that both of us just happened to end up with wheel balance issues right after a re-gear? I don't buy it.

Wheel balance cannot, but bad pinion angle can feel similar. They have to be really, really, really bad for that to happen. I don't think they would suddenly get bad, likewise with the wheels.

What we felt and saw and experienced is a resonant vibration (which is by default rythmic, cyclical, harmonic, it all means the same). The entire structure was resonating at it's resonant frequency which is why both Jeeps felt so similar. We were sitting inside a box with a speaker right next to it and the speaker was playing a subwoofer level low note.

 

[jjvw]

...

I have to imagine these guys know this... but I'm going to come armed with the knowledge just so they know what I'm after.

If they truly do, then it's a good shop. The only person I've ever seen discuss this type of nuanced juggling act is ftgiles over on JF.

 

[Chris]

Wheel balance cannot, but bad pinion angle can feel similar. They have to be really, really, really bad for that to happen. I don't think they would suddenly get bad, likewise with the wheels.

What we felt and saw and experienced is a resonant vibration (which is by default rythmic, cyclical, harmonic, it all means the same). The entire structure was resonating at it's resonant frequency which is why both Jeeps felt so similar.

And in regards to the pinion angle, why wouldn't it be present before the gear install, but be there after the gear install? That doesn't make any sense either.

You should have felt mine at 100 mph on the way home. I literally felt like I was standing on the Tacoma Narrows Bridge. It was vibrating so loud with that rhythmic vibration that it felt like the TJ was going to fall apart!

 

[Chris]

If they truly do, then it's a good shop. The only person I've ever seen discuss this type of nuanced juggling act is ftgiles over on JF.

I think the issue is that a lot of these guys don't hang out online. For instance these guys are local and seem to do some nice stuff: https://www.facebook.com/HammsOffroad/

However, this guy doesn't spend time on forums or anything like that, yet after talking with him about my mid-arm, he clearly knows what he's talking about.

 

[jjvw]

...

The crazy part is I get all of this. I could literally do it myself if I knew how to weld and had a lift. I'd just hate to do this on my back, in the garage, on jack stands, with no welding skills, haha.
....

I bought my very first welder and taught myself how to use it during the mid arm install. Then I figured out the outboard. That started two years ago and nothing has fallen off.

 

[psrivats]

And in regards to the pinion angle, why wouldn't it be present before the gear install, but be there after the gear install? That doesn't make any sense either.

You should have felt mine at 100 mph on the way home. I literally felt like I was standing on the Tacoma Narrows Bridge. It was vibrating so loud with that rhythmic vibration that it felt like the TJ was going to fall apart!

I'm scared to drive my Jeep past 70 to be honest. Amazed you went to 100! I would never be able to do it :risas3:

 

[psrivats]

I bought my very first welder and taught myself how to use it during the mid arm install. Then I figured out the outboard. That started two years ago and nothing has fallen off.

Man that takes commitment. Amazing @jjvw !