Vibration when I let off the gas.

[hotrod22]

I have a 95 XJ 4.0 5-speed w/NP231, 6" lift(custom-short arm w/heim joint upper/lower), 8.8" rear w/4.10 Trac-Loc, a non-disconnect front D30 w/4.10 Detroit Soft-Locker. When I let off the gas it sounds like my transfer case is a pager on vibrate! It is not really noticeable at lower speeds (20-30) but at highway speeds it is really noticeable. My friend (who is waaay more knowledgeable on 4WDs than me) said this is normal for a locked non-disconnect front axle to give feedback to the transfer case because the gears are not exactly the same, something about the front 4.10s being slightly more than 4.10 but you can't sell it as a "4.10 1/2" so it is labeled as a 4.10, therefore it gives "feedback" to the transfer case. Does this sound right to you guys? Also... can I get some different ends for my control arms that have some cushion in them? Those heim joints (all metal) ride like chit!

 

[bshaw]

what's the angle on your rear d-shaft look like? do you have any degree shims installed? do you have sye yet, and new d-shaft? I had the same problem with only 3.5" of lift at one time until I installed my Tom Woods sye and cv d-shaft. I'm betting your rear d-shaft angle is messed up........

 

[JeepFreak21]

I'm assuming you have an SYE? If not, get one. If so, check the bolts from the driveshaft to the transfer case.
Billy

 

[xjj33p3r]

You might have a bad u-joint. Check out to see if it's wearing properly.

 

[Rocketman]

Check to make sure your exhaust isn't hitting anywhere before you start spending money!

 

[Gridikal]

Had exact same problem. It turned out to be rear driveline angle related.

 

[nhrocker]

I get the same thing in my rig (95, 4.0, AW4, 231, D30 front, 8.25 rear, stock gears, open front/rear, 3" front, about 5" rear, 3/4" tcase drop, 4* shims) I had some driveline vibes under braking from the rear output shaft yoke until I put in the shims and the tcase drop.

Now that's all gone, but I still get the vibes when I let off the gas. It sounds like it's coming from the front of my tcase, but I'm not sure. I thought my linkage was off, but it looked ok to me, so I'm trying to track down the same thing as you now...

 

[hotrod22]

I got a 2nd opinion on the rear driveshaft angle and it is supposed to be right. No, I do not have a SYE(I was told I didn't need it). No, I do not have a transfer case drop(I was told I didn't need it). Exhaust is not hitting anything. How can I(myself) check the driveshaft angle? What should it be? Also... are there any male/heim joint type control arm ends that have poly(cushion) in them?

 

[JeepFreak21]

No, I do not have a SYE(I was told I didn't need it).

Your vibrations say otherwise.
Billy

 

[HoodRichXJ]

Something else to consider when checking over your drive line system for this kind of vibration is your transfer case (NP231). I friend of mine is in the process of removing his, out of his TJ, to have it rebuilt. The chain needs to be replaced. At first we thought it might be the Lockrite in his D44 rear, but upon checking the gears and oil in the differential nothing was found so we moved up the driveline to the T-case and found it to be the problem. I'm not telling you this is your problem but its best to start and one end and check everything throughly, and sometimes if your lucky you'll find other problems too! -steve

 

[bshaw]

Your vibrations say otherwise.
Billy

x2
Get the SYE and a new CV d-shaft. If you still have vibs after that, look into getting some angle shims to correct the angle of the d-shaft. Or vise versa.......

 

[jacktowncrawler]

I got a 2nd opinion on the rear driveshaft angle and it is supposed to be right. No, I do not have a SYE(I was told I didn't need it). No, I do not have a transfer case drop(I was told I didn't need it).

Same thing happens on my 99 with a t-case drop and 3.5" lift. Who ever told you you didn't need the SYE, was wrong. Get the SYE and the CV shaft and feel good.

 

[2xtreme]

If you have not figured it out by now, there are LOTS of things it COULD be. Best bet before you spend lots of money on all sorts of things that MIGHT fix it is to figure out where it is coming from. Try removing the front drive line, any change, When did this start? after the lift? after the gears? after the lockers installed? etc.

Narrow down the options for us.

Usually this symptom (vibrations when let off the gas) is due to u-joints going bad. But this assumes that it is a new symtom and have not made changes to the drivetrain recently before the issue occured.

Michael

 

[TheFortuneAteMySon]

Pull the front driveshaft and go for a spin.
Trust me on this one.

 

[hotrod22]

The lift, gears, 8.8" rear and front locker were installed at the same time. I was thinking of removing the front driveshaft, drive it and if it still does it, then the prob is in the rear driveshaft angle, and if it does not, then the feedback has to be coming from the front axle. Just reminding, it is a non-disconnect D30 w/Detroit Softlocker, so the front is always turning, unlike an open diff. That is what makes sense about what my friend said. Either way, I'm gonna pull the front shaft and let you know the outcome.

 

[TheFortuneAteMySon]

Just reminding, it is a non-disconnect D30 w/Detroit Softlocker, so the front is always turning, unlike an open diff.

You are incorrect.
Open/locked has no effect on the driveshaft turning.
If you have a non-disco axle, the shaft is turning, no matter if you have an OX, ARB, LockRight, or whatever.
The Warn hub conversion is the only thing that will eliminate this on the HP30.
Even with the disconnect axle, the drivers axleshaft is still 'driving' the driveshaft.
HTH.

 

[ECKSJAY]

You are incorrect.
Open/locked has no effect on the driveshaft turning.
If you have a non-disco axle, the shaft is turning, no matter if you have an OX, ARB, LockRight, or whatever.
The Warn hub conversion is the only thing that will eliminate this on the HP30.
Even with the disconnect axle, the drivers axleshaft is still 'driving' the driveshaft.
HTH.

Half speed for open diff, full speed for a locker like a Lock Right. Another benefit to running the manually actuated lockers is that they don't lock on their own and turn the front shaft at full speed. So technically there *is* an effect on the driveshaft turning...just not what he was talking about

 

[hotrod22]

Well... without the front driveshaft, there is less noise in general because of less moving parts obviously, but... the noise I was wondering about is still there. So... my friend is full of poop, and I do need a SYE? And a cv drive shaft? Is there a preferred brand?

 

[DDawg16]

I was just about to chime in and say that the first and second opinions sure needed a lot more experience....6" lift with stock ds? Without a CV ds and SYE, you WILL have vibrations. Mute issue now....you know better.

I have the RE Hack and tap kit. No problems or leaks after 4 years. However, I am a littel disapointed in my 6 States Dist CV driveshaft. The CV joint wore out after less than 20K miles. I have heard that Tom Woods makes the best driveshafts (he used to work at 6 States). You should also check with a local driveshaft shop. They will most likely be able to buid you a custom one for about the same price as anyone else. In reality, there is nothing really custom about them except length.

 

[ECKSJAY]

In reality, there is nothing really custom about them except length.

...and shaft diameter, and wall thickness, and spline shaft diameter, and spline length, and boot, and type of u-joints...