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theksmith

laying under the jeep at 80MPH...

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...ok not really - just using a GoPro to take video of the driveshafts to try and figure out my highspeed vibes. here's the front and then the rear driveshafts, going around 70 to 80 MPH.

 

 

it looks to me like the front shaft is still not quite straight, but hard to tell. compare to the rear though in the second part of the video and tell me what you guys think...

 

the backstory

 

a long time ago, after swapping in JK axles and getting new custom driveshafts at the same time (and i think the 242HD went in at the same time too, but i can't remember anymore) i had a horrible high speed vibration. too many things changed at once to know for sure where the problem was.

 

i had the new drive shafts re-balanced at a different shop, and they re-welded one due to the runout being so bad. that helped some, and then i even had them re-balance a second time.

 

over time the vibes got better - at first i thought it was just me getting used to them, but others riding in the Jeep think so too... so no idea what could cause that improvement. motor and trans mounts have been changed multiple times so angles didn't change due to sagging.

 

currently the vibes are livable but annoying. at over 70mph i can no longer tell what type of car is behind me using the mirrors! the vibes get worse up to 80, then level out and don't really get much worse after that. the vibes do sort of "pulse", i.e. you can feel them slowly get slightly worse/better in a cycle about once or twice per second.

 

removing the front shaft pretty much fixes the problem. there are still some very minor vibes then, but they are always there at any speed and i think they are from uneven mud terrain wear.

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Did you try swapping the front and rear tires with the front shaft removed?

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I would try off-set u-joints on the diff end on the front drive-shaft. It's just a wild guess, but it might work.

 

G :cool:

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Looks like there may still be some excessive run-out in the front shaft. From the video, it appeared that the splined portion of the shaft may be slightly bent. If removing the front shaft mostly cures it, I'd start there. Does yours have different yokes from mine? I'd be willing to let you use my front shaft for testing.

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Looks like there may still be some excessive run-out in the front shaft. From the video, it appeared that the splined portion of the shaft may be slightly bent. If removing the front shaft mostly cures it, I'd start there. Does you have different yokes from mine? I'd be willing to let you use my front shaft for testing.

 

ok good to have second pair of eyes confirm what i was seeing - i agree it looks like maybe the spline portion of the shaft isn't welded straight to the long tube, or maybe the long tube part is not even welded to the t-case end straight.

 

when i first took both of the new shafts to TAD Driveline (Phoenix Rack & Axle made them originally), they said they re-welded one of them and re-balanced both, but not sure which one they re-welded.

 

it's got flanges at both ends, but thanks for the offer to loan me yours. and unfortunately the front is also a little too short to swap into the rear to test it. i'm considering just going ahead and getting a new shaft made with longer travel so that it can work in front or be a backup for the rear if that broke. currently trying to figure out which local shop to trust, not sure if TAD has parts for long travel, guess i'll call them first.

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The noise in the second part sounds just like my shop-vac.

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I would try off-set u-joints on the diff end on the front drive-shaft. It's just a wild guess, but it might work.

 

G :cool:

 

This is pretty much guaranteed to make vibes worse- they even tell you this when you buy the joints.

 

Removing the front shaft removes the worst part of the problem- so, as we say in the South: "There's yer problem!"

 

Of course you're going to have SOME vibes- but between removing the shaft making the lion's share of the issue go away, and you seeing the runout isn't correct, it's pretty obvious what the issue is.

 

I'm curious how you mounted the camera. An underbody cam would be super helpful in diagnosing some wierd suspension sounds I'm chasing. I don't want to risk an expensive camera falling off at 70MPH though.

 

Something else you might want to try to get rid of the last of the vibes is Centramatic balancers. These things are the cat's pajamas, I run them on everything I possibly can. I haven't used a wheel weight on a daily driver in about 12 years.

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...

 

I'm curious how you mounted the camera. An underbody cam would be super helpful in diagnosing some wierd suspension sounds I'm chasing. I don't want to risk an expensive camera falling off at 70MPH though.

 

Something else you might want to try to get rid of the last of the vibes is Centramatic balancers. These things are the cat's pajamas, I run them on everything I possibly can. I haven't used a wheel weight on a daily driver in about 12 years.

 

 

i have an old ultrapod that i zip-tied to the control arm, combined with the tripod mount/adapter for the gopro. i was a little sketched that the tripod screw part might vibrate and loosen up, but it held for that short trip. if i was going further i would have used some loctite on it.

 

i just bought the gopro jaws clamp mount and it's actually pretty strong, i wouldn't have any issue using it under the rig: http://offroadpassport.com/forum/showpost.php?p=39429&postcount=996

 

 

i used ceramic balance beads that go *inside* the tire on one vehicle and had mixed results, decided they were more of a PITA than worth - but i realize those a little different than the disc type. i figure i need my tires rotated every other oil change at least anyway, might as well just have a place do that and re-balance them each time.

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slow progress...

 

so i decided to go ahead and get a new shaft. primary goal is of course to get one that is straight and well balanced to hopefully kill the vibes. i also discovered my existing 2.5" diameter shaft was rubbing the edge of the transmission oil pan a bit, so a secondary goal is to get one with a smaller 2" tube. a third "nice to have" is to get one with enough travel that it could work as a spare for the rear (ScottL tells me driving cross-state in 4-HI with just a front shaft in makes for crazy highway handling and is slow going)!

 

 

new flange?

 

i wanted to try a shorter flange on the front t-case output before getting a new shaft. this would have given me a front DS closer in length to the rear, and also helped the overall operating angle of the front shaft. here is the shorter flange i tried: http://www.polyperformance.com/J-E-Reel-32-Spline-Flange-For-Atlas-Stak-Rubicon-NV241-NV241J-Rock-Trac

 

unfortunately it interfered with the shifter arm, so i put the one i had back on: http://www.polyperformance.com/J-E-Reel-Jeep-JK-CV-Flange.

 

my front shaft at ride-height is 33" long, and the rear is 37.25" long. to get a new front shaft that can work as an emergency rear spare means i need a "super" long travel design.

 

 

everything's complicated

 

the shafts i have now are both 1330 CVs with 1310 pinion end joints. sounds strange, but it turns out there was good reason...

 

the t-case end's flange-yokes are currently standard 1350 style (4.25" bolt circle with 2" female pilot). however, i can't run 1350 joints because the H-yoke part of the CV would likely be too big to clear the transfer case shift linkage bracket (i already had to trim the bracket some because the 1330 H-yoke was rubbing it). fortunately there is still a 1330 CV flange with the standard 1350 configuration (http://www.drive-lines.com/parts1.php?pn=N2-2-1369).

 

the lower end of my shafts are using flanges that mate to a standard JK pinion flange. this is only available in a 1310 joint... so i have one joint weaker than the other 2 which also messes with my OCD. to get a stronger joint i'd have to change the front pinion flange, but then i want the front and rear to be the same so i'd have to do that in the back as well and change that driveshaft too. also there is no such thing as a 1310 CV flange that bolts to that standard 1350 t-case flange style, so i can't just run all 1310 joints either.

 

... and so that is how i ended up with bastard-jointed shafts.

 

 

just take my money

 

after reading some online reviews, the net didn't turn up any local companies with stellar reputations that could handle a really long travel shaft, so i emailed 4 of the popular online places - tom woods, je reel, coast driveline & gear, and carolina driveline.

 

- je reel, took 2 emails and nearly a week to get back to me, had a high quote. to be fair, when i first looked into this issue a couple years ago, he took time to talk to me on the phone for a quite a while.

 

- tom woods immediately asked about angles and wanted to help me figure out the issue instead of just selling me a shaft. he said he couldn't do a shaft with enough travel to work as a rear emergency use shaft though (which is weird as his site indicates he can do really long travel stuff). he took a long time to respond to the first and subsequent emails as well.

 

- coast driveline & gear also took nearly a week and a second email before they responded at all. they did ask about angles, but then never followed up with an actual quote.

 

- so this brings me to carolina driveline. they responded within a couple hours to the first email and we've emailed back and forth many times trying to get everything figured out. they respond to every email quickly (though since they are east coast, their quittin' time is early for us and sometimes it's the next day before they get back to you). their initial quote was super cheap, but then went up once we figured out that they couldn't make it all 1310. i think we have everything figured out now, including the super long travel option, and i'm just waiting for confirmation on the price for the final configuration.

 

 

notes

 

i decided to go with .120 wall tube. i think i have .180 now as Joe had mentioned they were "heavy duty thick shafts". the .120 is of course slightly lighter so if there are still some vibrations then it has less mass actually whipping around and therefore should translate to less noticeable force from those vibes.

 

currently my front shaft sits at 10*, the front pinion is pointing up at 7*, and the t-case is unfortunately pointing up also (the wrong direction) at 3*. this means the effective operating angle of my front joint is 3* which is fine (10 - 7 = 3). however the rear joints are each operating at 6.5*. this isn't ideal but the consensus from multiple shops was that those numbers alone shouldn't be causing major vibes. fyi - since my t-case is pointing away from the shaft, you add the angles instead of subtracting, then divide by 2 because of the 2 cv joints: (10 + 3) / 2 = 6.5. also worth mentioning is that getting the angles with my phone and a free clinometer app (https://play.google.com/store/apps/details?id=com.plaincode.clinometer) was much easier than my first attempt with a standard angle meter (http://www.homedepot.com/p/Johnson-Pitch-and-Angle-Locator-750/100193539).

 

so ultimately if the new smaller, lighter, straighter shaft doesn't solve my problems then i'll have to figure out some way to fix the t-case angle. raising the transmission mount would help the t-case angle, but would hurt the overall DS angle. so really, lowering the engine would be ideal - not sure if that is even feasible from a clearance perspective (not to mention the custom fab work on the mounts). so fingers are crossed that i can get the new shaft ordered today and that it is the silver bullet!

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