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  #1  
Old July 27th, 2004, 21:50
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BillR BillR is offline
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front driveshaft vibration...

I searched the posts on this, and didn't find a definitive answer...
Since installing the 4:88s, I have a vibration coming from the front driveshaft. It starts at about 45 mph and gets worse as speed increases. With the front driveshaft out, it's really smooth. I replaced the front driveshaft to see if that was the issue, and it does the same thing with a brand new driveshaft. (the old one only has 59K miles on it!)
I'm thinking the driveshaft turning faster due to the 4:88s is magnifying whatever the problem is. Is this correct?
It tracks fairly straight, and the pinion angle in front doesn't look bad at all. (I haven't measured it) The alignment is recent, only a month or so ago. The transfer case was rebuilt 4K miles ago with new seals and bearings. The ONE bearing that was not replaced was the rear of the front output that's pressed into the back half of the case.
Is a manual hub kit the only fix for this problem?
Thanks!
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  #2  
Old July 28th, 2004, 00:28
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Rawbrown Rawbrown is offline
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Re: front driveshaft vibration...

you have a lift... pinion should point parrallel with the driveshaft. try adjusting it. also try rotating the yoke on the joint 180.
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  #3  
Old July 28th, 2004, 00:37
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Re: front driveshaft vibration...

if it only happens when the driveshaft is there, but it isn't a bad driveshaft or u-joint, it would seem the problem is with your angles. amplified like you said by the higher driveshaft speed with the 4.88s.

cutting and turning knuckles isn't as hard as some would lead you to believe, so get the pinion pointed perfectly and if your caster isn't what you want, turn the knuckles.
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  #4  
Old July 28th, 2004, 07:42
XJJPR XJJPR is offline
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Re: front driveshaft vibration...

A hub kit is the only bolt on fix for your situation.

Turning knuckles is for the experienced welders/fabricators.

Remove front shaft and replace for wheeling works also.

hinkley
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  #5  
Old July 28th, 2004, 07:51
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BillR BillR is offline
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Re: front driveshaft vibration...

That's what I was afraid of...
Additional info:
caster is 4.5 degrees, 6-7 degrees is "spec"
I AM using a HP front axle; I couldn't imagine what the vibes would be like with a LP axle.
I COULD adjust the UCAs some more and get the angle closer, but I had an issue with the coils showing a "bow" with the arms adjusted out more.
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  #6  
Old July 28th, 2004, 08:10
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Re: front driveshaft vibration...

The FSM says the caster angle should take precedence over the pinion angle. Safe handling being more important than bearing/ujoint life.

Drive shaft R&R or hub kit are the only quick fixes.
I suffer the same issue. Mine shows up around mid to high 50's though. So when I drive it, I just dont push it.

I bought a trailer to get it to events.

Derik
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  #7  
Old July 28th, 2004, 08:49
Talyn Talyn is offline
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Re: front driveshaft vibration...

Quote:
Originally Posted by DaffyXJ
The FSM says the caster angle should take precedence over the pinion angle. Safe handling being more important than bearing/ujoint life.


Derik
What FSM? Mine says the pinion angle has priority over caster.

"Changing the caster angle will also change the front propeller shaft angle. The propeller shaft angle has priority over caster."

-Chris
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  #8  
Old July 28th, 2004, 09:00
Nay Nay is offline
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Re: front driveshaft vibration...

Quote:
Originally Posted by BillR
That's what I was afraid of...
Additional info:
caster is 4.5 degrees, 6-7 degrees is "spec"
I AM using a HP front axle; I couldn't imagine what the vibes would be like with a LP axle.
I COULD adjust the UCAs some more and get the angle closer, but I had an issue with the coils showing a "bow" with the arms adjusted out more.
Don't worry about specs. Don't worry about bowing coils. That is life with a D30 and a properly aligned pinion angle on 6" of lift, unless of course you rotate the knuckles. To bring the pinion up, the coil seats rotate forward.

Here's the deal: every inch of lift will cost you about one degree of caster if you keep the pinion perfectly aligned, i.e., a zero u-joint angle. So on a 6" lift you'd have about 1 degree of caster. A CV shaft can handle about 3" of angle max at the pinion without vibes, and 2 degrees or under is likely to work the best in concert with your gear ratio (you may not be able to run with more than a degree).

So measure your angles. Start with the best case at three degrees. See if it vibrates. If so, go down to 2.5 degrees. Road test. Repeat until you have a vibe free driveline. And then see if you have enough caster for highway use, i.e., it still tracks straight and doesn't wobble.

FWIW, I never could get my front driveshaft to stop vibrating due to angles on a 6" lift. Caster was always too low (it zig zagged on the highway) by the time the front driveline was smooth. This is a major reason I went to a front 44. But now with long arms (radius arms), it is great with lower caster at around 3 degrees. I don't know why, but my rig wouldn't drive straight with the caster I run now when I had short arms.

I'd get a set of 5 on 4.5 hubs. They make a good fuse and are easy enough to replace on the trail. Plus hubs keep the noise WAY down on the highway and you'll take the load off those expensive throw-away D30 wheel bearings.

Nay
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  #9  
Old July 28th, 2004, 21:36
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Re: front driveshaft vibration...

Thanks for all the help.
I'm going to play with the adjustable UCAs this weekend and see if I can get the pinion angle closer without losing the highway "feel".
More results to follow...
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  #10  
Old July 28th, 2004, 21:45
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Re: front driveshaft vibration...

You know, given my experience, I wouldn't rule out the drive shaft. Have a good driveshaft shop check out the balance. Or possibly swap with a buddy for a day.

As long as the pinion is nice and tight with no slop, and the same is true for the tcase, I would seriously question the shaft. LOL
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  #11  
Old July 28th, 2004, 21:48
Lincoln Lincoln is offline
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Re: front driveshaft vibration...

I'm must not be as sensitive. I ran with about 3 degrees caster for years and was very happy. I had the disconnect housing and no locker but I would run 75-80 in 4wd without any noticable vibes.

In fact I think it was Nay's good idea to use offset ball joints to get caster back.

Went back to stock ball joints and had much better luck. I couldn't tell a difference between 3 degrees and 4.5 degrees caster while driving. I would set the pinion 1-3 degress low then drive it. If it feels ok it must be good. Crap I never worried about angles until everyone said they were having problems.
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  #12  
Old July 28th, 2004, 23:09
RCP Phx RCP Phx is online now
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Re: front driveshaft vibration...

Quote:
Originally Posted by BillR
That's what I was afraid of...
Additional info:
caster is 4.5 degrees, 6-7 degrees is "spec"
I AM using a HP front axle; I couldn't imagine what the vibes would be like with a LP axle.
I COULD adjust the UCAs some more and get the angle closer, but I had an issue with the coils showing a "bow" with the arms adjusted out more.
I had the same problem till I went with the long arms!Still running the LP D30 with no vibes or castor problems!
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  #13  
Old July 29th, 2004, 08:47
Nay Nay is offline
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Re: front driveshaft vibration...

Quote:
Originally Posted by Lincoln
I'm must not be as sensitive. I ran with about 3 degrees caster for years and was very happy. I had the disconnect housing and no locker but I would run 75-80 in 4wd without any noticable vibes.

In fact I think it was Nay's good idea to use offset ball joints to get caster back.

Went back to stock ball joints and had much better luck. I couldn't tell a difference between 3 degrees and 4.5 degrees caster while driving. I would set the pinion 1-3 degress low then drive it. If it feels ok it must be good. Crap I never worried about angles until everyone said they were having problems.
Some rigs are fine with the lower caster. I know a local guy who specializes in aligned lifted 4x4's, and he prefers much lower caster on taller lifts. I run about 2 degrees caster now with radius arms, and it is excellent. I couldn't run under 4 degrees with short arms. Seems that caster does not operate independently of the suspension linkage?

Nay
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  #14  
Old July 31st, 2004, 16:17
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BillR BillR is offline
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Re: front driveshaft vibration...

OK, I got my front driveshaft re-balanced. (It was WAY off!)The vibes are much less now and don't start until around 65mph. Even at 70mph, it's not bad at all. Instead of being a constant drone, now it's a pulsing harmonic sound about 3 seconds apart. This is at 70 mph. I haven't messed with the UCAs yet, and I'm trying to decide if I even need to now.
It's not quite as smooth as my wife's ZJ, but it probably never will be.
Ideas??? Leave it alone?
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  #15  
Old July 31st, 2004, 16:46
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kewlkatdady kewlkatdady is offline
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Re: front driveshaft vibration...

if your okay with it.....leave it alone.
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