driveline vibe diagnosis

4Doors · Jan 16, 2008

Hey guys, my bro-in-law has a 99, 4.0, AW4, 31" all terrains, 3.5" Rusty's lift with 3 degree shim and t-case drop. He has new u-joints on the driveshaft. He has a vibration at around 65 mph. Someone on another forum told him to disconnect the driveshaft and run it at 65 mph in 4-high to see if his vibes were coming from the front driveshaft. I told him the idea scared me but I figured I'd check with you guys first. Any thoughts? Thanks for your time.

urdaddy · Jan 16, 2008

I had a 05 jeep wrangler that would shake so bad that i thought that the front axel was goin to fall out. They never could figure it out at the dealer but they changed pretty much my whole front end and then they said that it was something with the tires but needless to say i got rid of that junk.

4Doors · Jan 16, 2008

I should add that it's not a severe vibration, and he said it started as soon as he lifted it. That makes me think driveshaft angle, but we're almost afraid to try for a larger shim. Could a 6 degree shim hurt anything?

Funny, I lifted my 91 the same height and never had the slightest problem, but I've also heard that the older ones had a shorter tail shaft and could handle lift a little better. Don't know just how true that is though.

ingrain · Jan 16, 2008

i have that same setup and i get slight vibrations between 52 and 57 mph(yes its that exact) nothing before or after that and i have had it going 80 at one point. if it isnt bad i would just leave it alone, i figured i would either make it worse or make it vibrate at another speed if i messed with it. its been going for over a year with zero problems.

330LICIOUS · Jan 16, 2008

if he doesn't have an SYE and CV driveshaft, then he shouldn't need to shim. just the t-case drop is enough. take out the shims and try.

and to see if it's coming from the front driveshaft or not, just take the front driveshaft off, period, and drive it in normal 2wd. if the vibes disappear at this point (while running only with the rear driveshaft), then it's easy to conclude that it was indeed coming from the front.

impetus-93xj · Jan 16, 2008

x 2 the shims or the t drop alone should be enough. together the angle would to much

4Doors · Jan 16, 2008

330LICIOUS said:
and to see if it's coming from the front driveshaft or not, just take the front driveshaft off, period, and drive it in normal 2wd. if the vibes disappear at this point (while running only with the rear driveshaft), then it's easy to conclude that it was indeed coming from the front.

Now why didn't I think of that! I'll tell him the things you guys said about shims and t-case drop. I think he's talked to Rusty's several times and they would have been the ones to recommend the drop+shims. Is there either one that he should keep over the other? Because of course it would be easier to take out the t-case drop and leave the shims, but is there a reason he should keep the drop and remove the shims instead? Thanks for all the help.

89xj · Jan 16, 2008

first see why he has vibs, is it the front shaft or rear shaft?

if the shims are aluminun, take the shims out, if they are steel, i would take out the transfercase drop.

driveline vibe diagnosis

4Doors

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urdaddy

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4Doors

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ingrain

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330LICIOUS

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impetus-93xj

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4Doors

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89xj

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