Dzimm Posted February 23, 2020 Share Posted February 23, 2020 So I'm swapping in a C8.25 from a Liberty. They come with this weight thing attached to the axle and hangs off the driver's side that I assume is a counterweight. I also assume it's there because of the coil springs in the Liberty but with leaf springs it won't be necessary. My question is, do I need to leave this on or am I fine to leave it off? It's like 15 pounds so I really don't want it on there. Link to comment Share on other sites More sharing options...
jdog Posted February 23, 2020 Share Posted February 23, 2020 It's just a vibration damper, should be fine with out it Stock 1988 swb 4.0 ax15 np 231. Link to comment Share on other sites More sharing options...
AZJeff Posted February 23, 2020 Share Posted February 23, 2020 That is a chassis-specific vibration damper. It's for NVH--noise, vibration, harshness. In other words, it's needed on a Liberty, but not on any other chassis. Take it off, and enjoy it as is. Link to comment Share on other sites More sharing options...
omega_rugal Posted February 24, 2020 Share Posted February 24, 2020 if you attach it to the frame would improve some NVH? or at least can help to no twist the axle under load? Link to comment Share on other sites More sharing options...
Dzimm Posted February 24, 2020 Author Share Posted February 24, 2020 Thanks for the answers, definitely not worried about harshness/vibrations in a race truck. Link to comment Share on other sites More sharing options...
omega_rugal Posted February 24, 2020 Share Posted February 24, 2020 race truck? never mind then Link to comment Share on other sites More sharing options...
AZJeff Posted February 24, 2020 Share Posted February 24, 2020 Keeping that weight on the 8.25 when installed in any vehicle except the KJ may actually INCREASE the NVH in the vehicle. Those weights are VERY specific in mass and mounting location, and are designed to deal with some unique vibration that was found on the KJ during development. (Notice how the weight actually hangs off only one side of the axle housing) i remember my ex-wife has a Ford Fairmont with a 4 cyl. engine it it that had such a NVH weight on the tail shaft housing for the automatic trans. My buddy had a Fairmont as well, but with a V8. The V8 Fairmont did not have that NVH weight. Different driveline, different vibrations. Link to comment Share on other sites More sharing options...
amsuco Posted February 24, 2020 Share Posted February 24, 2020 Keep us updated on this. Several times now I've seen the Liberty axle mentioned as a swap option, but I think you're the first person that I've heard was actually doing it. Did you get disk brakes on yours? Link to comment Share on other sites More sharing options...
Dzimm Posted February 24, 2020 Author Share Posted February 24, 2020 2 hours ago, amsuco said: Keep us updated on this. Several times now I've seen the Liberty axle mentioned as a swap option, but I think you're the first person that I've heard was actually doing it. Did you get disk brakes on yours? Yes, in 03 they went to disks. Mine is off an 03 so it's got the disks on it. It's very difficult to find any info on the internet for the Liberty C8.25, all I can ever find is about the XJ one. So far I've found that it's roughly (eyeballed with tape measure on the tires) 3" wider than the D35/XJ C8.25 but that only equates to 1.5" each side. The diff housing itself is much beefier and it has a speed sensor in the diff. I haven't measured for length difference at the pinion yet. I'd also mention that there is only one extra bracket on each side compared to an XJ axle and I'd say it was actually much easier to cut off the spring pads on this than spring perches on the XJ axle. I've seen many people shy away from this swap due to all the brackets but it's only 3 per side and the welds are small. Took me about 2 hours to unbolt all the extra stuff and cut all the brackets off. I'll do a write-up on the Libby swap when I'm done. Link to comment Share on other sites More sharing options...
omega_rugal Posted February 24, 2020 Share Posted February 24, 2020 16 hours ago, AZJeff said: Keeping that weight on the 8.25 when installed in any vehicle except the KJ may actually INCREASE the NVH in the vehicle. Those weights are VERY specific in mass and mounting location, and are designed to deal with some unique vibration that was found on the KJ during development. (Notice how the weight actually hangs off only one side of the axle housing) i remember my ex-wife has a Ford Fairmont with a 4 cyl. engine it it that had such a NVH weight on the tail shaft housing for the automatic trans. My buddy had a Fairmont as well, but with a V8. The V8 Fairmont did not have that NVH weight. Different driveline, different vibrations. a V8 has less vibrations... Link to comment Share on other sites More sharing options...
AZJeff Posted February 24, 2020 Share Posted February 24, 2020 1 hour ago, omega_rugal said: a V8 has less vibrations... Precisely. Who knows what sort of vibration the Liberty had in the rear end. The manufacturers put them on special shake fixtures to analyze the chassis for such types of behavior. Link to comment Share on other sites More sharing options...
omega_rugal Posted February 24, 2020 Share Posted February 24, 2020 14 minutes ago, AZJeff said: Who knows what sort of vibration the Liberty had in the rear end. it had a 90 degree V6, not the smooothest design, also they wanted it to drive as as car as much as they can, a sold axle is not the best way to do that Link to comment Share on other sites More sharing options...
schardein Posted February 24, 2020 Share Posted February 24, 2020 It's funny (odd) how some cars have quirks like this. In the past, I drove a PT Cruiser and if you had the windows part way down there would be a "whumpa-whumpa" wind effect in the cabin, like a helicopter. It was even mentioned in the owner's manual that this was normal and not a defect. In my heavily modded CJ, I have a high frequency buzz at a very specific speed and rpm, right before shifting from 2nd to 3rd, lasts a couple seconds. I always wonder if the next mod will alter or stop it. Link to comment Share on other sites More sharing options...
derf Posted February 25, 2020 Share Posted February 25, 2020 That air hammer effect happens in a lot of cars. My Subaru does it bad. Link to comment Share on other sites More sharing options...
mjeff87 Posted February 25, 2020 Share Posted February 25, 2020 18 hours ago, omega_rugal said: it had a 90 degree V6, not the smoothest design........ You win the understatement of the year award for that one, LOL Every time I'm stopped in traffic with my KJ it feels like the engine is missing spark on random cylinders. It also has the "air hammer" when the rear windows are down but the front ones are up. I've mitigated that some by installing vent shades, but it still does it. Cracking the passenger side window makes it go away. Link to comment Share on other sites More sharing options...
AZJeff Posted February 26, 2020 Share Posted February 26, 2020 23 hours ago, mjeff87 said: Every time I'm stopped in traffic with my KJ it feels like the engine is missing spark on random cylinders. My wife drives a 2004 KJ with the V6. For all of it's life until the past year, the engine vibration in the cab was very minimal. Then, over the past 12 months, the engine seemed to have developed more vibration, and thought it was some sort of misfire type situation. It turned out to be bad motor mounts. After replacing all the mounts, the vehicle is back to being very smooth considering it's a V6. If you feel any significant vibration in your KJ when it's idling, check your motor mounts. I would bet they are collapsed, if they are the original ones. Link to comment Share on other sites More sharing options...
AZJeff Posted February 26, 2020 Share Posted February 26, 2020 On 2/24/2020 at 4:12 PM, omega_rugal said: it had a 90 degree V6, not the smooothest design, also they wanted it to drive as as car as much as they can, a sold axle is not the best way to do that I think you are confusing things here. The weight on the axle is NOT intended to deal with engine vibrations as much as it's designed to deal with some sort of interaction between the rear axle and the chassis (frame). Engine vibrations are usually dealt with by motor mounts and/or placement of mounts on the engine block. A 90 degree V6 that has no counterbalance shafts or split connecting rod journals has a weird type of vibration. If you were to be able to view a running V6 from the front of the crankshaft pulley, the engine will have a rocking couple that tries to make the crankshaft rotate about an elliptical path, with the narrow side of the eclipse being vertical. This is why, when modern V6's get very big in displacement, they tend to add in counterbalance shafts, because not reasonable amount of motor mount compliance can hide that second order harmonic elliptical vibration. This in the mechanical engineering explanation for V6 engine vibration. If you already knew all of this, I apologize, but it's worth noting that, for those of us who cruise around using a 4.0 engine, we are spoiled by it's inherent smoothness, and thus tend to forget how shaky a V6 can really be. Link to comment Share on other sites More sharing options...
mjeff87 Posted February 26, 2020 Share Posted February 26, 2020 The 3.7 (and 4.7 big brother) does have a counterbalance shaft, of sorts....that's why the timing chain system is such a nightmare to work on. Trust me, I know this well....lol. It's not that the engine is shaking around in mine, although I will check the motor mounts as they most likely are original, it just feels/sounds like it "skips" firing a cylinder every couple seconds at idle. Kinda hard to explain unless you are actually driving it. It sounds completely normal from outside the cab, and does run fine, but just feels choppy when sitting inside in the driver seat. My little 2.0 in the Focus is much smoother, and the 4-banger boxer engine in the wife's Subaru is damn near silent. So much so that I have to look at the tach to make sure it's still running at idle. No complaints from me on the KJ though, it's an almost 20 year old vehicle (only 140K miles on it though), running 20 year old Chrysler technology For what it is, I'm quite happy with it. Link to comment Share on other sites More sharing options...
Pete M Posted February 26, 2020 Share Posted February 26, 2020 1 hour ago, AZJeff said: If you feel any significant vibration in your KJ when it's idling... does not apply to me I have to look for new vibrations. Link to comment Share on other sites More sharing options...
strictlyxjs Posted February 29, 2020 Share Posted February 29, 2020 On 2/25/2020 at 9:26 AM, derf said: That air hammer effect happens in a lot of cars. My Subaru does it bad. Wow I'm glad it wasnt me that noticed this My moms van did that back in the 90s and i rember as a kid it really bothered me. Link to comment Share on other sites More sharing options...
Pete M Posted February 29, 2020 Share Posted February 29, 2020 our pt cruiser is so bad at it that I instinctively hit 2 switches at the same time. as long as 2 are cracked, all is well. Link to comment Share on other sites More sharing options...
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