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Unread 08-28-2010, 09:36 PM   #1
Unlimited04
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Pulsing Vibration after Regear

Had the 4.88s installed, now I've got a pulsing vibration on the highway. I've put maybe 50 miles on the gears so far.

The vibe behaves like a sine wave, with an amplitude peak of roughly 1 per second. It pulsates almost like a heart beat while on the throttle. Upon removing throttle input vibe remains constant. Becomes noticable above 60mph and gets gradually more intense with speed. Only went to 70mph, but vibe was slightly more intense.

If you've ever seen the movie "Contact", the pulsing signal is exactly what this vibe feels like.

Any ideas? This common during break in?

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Unread 08-28-2010, 09:42 PM   #2
Jay12
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some people have to have their driveshaft rebalanced after a regear from the increased speed of it turning. that may be a place to start
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Unread 08-28-2010, 10:53 PM   #3
seabass2020
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I have the exact same problem. I removed the front DS and the problem goes away. I haven't had it rebalanced yet.
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Unread 08-28-2010, 10:58 PM   #4
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yep, driveshaft balance is much more critical with high gears, especially when your running smaller then recommended tires.
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Unread 08-28-2010, 11:15 PM   #5
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i'm actually having a hard time finding someone who balances driveshafts. The main driveshaft place in town only checks for out of round, and said they would rebuild the CV joint.
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Unread 08-29-2010, 06:50 AM   #6
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Try taking out the front driveshaft. I might have spare that is right length you can try and see if that takes care of the problem. Bring it back over and we can try it. Or if you want me feel the vibe. I will go for a ride with you. Guess I got lucky when I put 4.56s in the TJ I didn't get any vibes from the DS running 33s. Or when I put 5.13s in the Ranger and shorted the rear DS myself no balance no vibes at 85 mph with 35s.
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Unread 08-29-2010, 07:12 AM   #7
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Originally Posted by seabass2020 View Post
i'm actually having a hard time finding someone who balances driveshafts. The main driveshaft place in town only checks for out of round, and said they would rebuild the CV joint.
It's a lost art, rebalancing drive shafts that is. Find a performance shop, the guys who build dragsters and they'll be able to point you to some one.

I had the same thing happen in a Corvette, went from a 2.78 gear to a 3.75 and got the same noise at highway speeds. Had to send it to Houston, 100 miles away. The two local shops I used for years were both closed.
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Unread 08-29-2010, 08:56 AM   #8
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Quote:
Originally Posted by Unlimited04 View Post
Had the 4.88s installed, now I've got a pulsing vibration on the highway. I've put maybe 50 miles on the gears so far.

The vibe behaves like a sine wave, with an amplitude peak of roughly 1 per second. It pulsates almost like a heart beat while on the throttle. Upon removing throttle input vibe remains constant. Becomes noticable above 60mph and gets gradually more intense with speed. Only went to 70mph, but vibe was slightly more intense.

If you've ever seen the movie "Contact", the pulsing signal is exactly what this vibe feels like.

Any ideas? This common during break in?
Driveshaft and pinion angle. Point the pinion directly at the driveshaft, screw the 1 down BS. Get your driveshaft rebalanced perfectly.

Also, does the harmonic seem like it cycles from front to rear through the vehicle and then start over?
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Unread 08-29-2010, 09:15 AM   #9
Jay12
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i also have a vibe after swapping my 8.8 with 4.56s in. front axle still has 3.07 because i havent got the hp30 in yet. the vibes are from about 30mph-37mph and my pinion is about dead on. could this be my front driveshaft as well?
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Unread 08-29-2010, 04:17 PM   #10
seabass2020
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I'm wondering if this could be the CV joint needs rebuilt as well??
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Unread 08-29-2010, 04:58 PM   #11
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Originally Posted by mrblaine View Post
Also, does the harmonic seem like it cycles from front to rear through the vehicle and then start over?
Just wondering what would cause that?
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Unread 08-29-2010, 06:20 PM   #12
Stang5lgt
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Just wondering what would cause that?
The frequency of the vibration. I had a DS that would do it. It would pulse just like he stated.
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Unread 08-29-2010, 06:47 PM   #13
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Quote:
Originally Posted by mrblaine View Post
Driveshaft and pinion angle. Point the pinion directly at the driveshaft, screw the 1 down BS. Get your driveshaft rebalanced perfectly.

Also, does the harmonic seem like it cycles from front to rear through the vehicle and then start over?
pinion angle is awesome. i'm at 6.5 deg caster with the HP D30 and 2.5" of lift, the driveshaft is almost straight...rear is dialed in dead on, no 1 deg down BS. the rear shaft is actually -sean-'s old DS...so its been run with 4.88s before, i would expect it to be balanced well...

i unhooked the front shaft and tied it to the engine skid. drove up to 65mph or so. it was definitely better, but not "holy crap" better.

the harmonic does cycle, but not sure about front to rear...the whole vehicle vibes. enough to vibe the rearview mirror like a good set of car stereo subwoofers in a low rider. the cycle is about 1 sec between peaks, it gradually increases and decreases, just like a sine wave.

i think i'll going to pull the front shaft and take it to a driveline shop and have them look at it.
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Unread 08-29-2010, 08:03 PM   #14
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I had the same thing happen to me. After having the shaft checked and screwing with the pinion angle, I finally figured out that the nut on my rear TC yoke was not quite torqued and caused a little play in the yoke. I never noticed it until I was running 4.88s and 33s

I just tied up my front shaft because I still had a very slight vibe. It seems to be better so I'm going to have it checked for balance. I did rip the boot off in the rocks, so that could have done it.
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Unread 08-30-2010, 11:56 AM   #15
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It ain't the front shaft. totally removed it and drove 50+ miles, vibe is still present. rear pinion seal is leaking like crazy too.

ideas? rear shaft balance? pinion bearing preload?
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