Confirming Rear Driveshaft Vibration

[RobM]

Hoping I can get some level of confirmation I'm on the right track with my post lift vibration. I think I've read just about everything, but something's are a little changing for me.

I put on:
2" EMU Suspension Lift
EMU Transfer Case Drop Kit
33" tires - Baja MTZP3 Radials

Vibration right after install. It's starts at about 40mph, and gets stronger thru 50, and then pretty much goes away by 55.

I've aligned the front end and had the tires rebalanced at a shop I confirmed can deal with the larger tires.

Vibration still there.

SO, .... I just removed the front drive shaft and the vibration is worse!!!! I now notice it around 30mph and it's still there at 65.

Makes me think it must be the rear Driveshaft. I'm guessing with the front installed it might have acted like a damper???

Am I on the right path? Replacing rear U-Joints next?

Thanks,
Bob

 

[pagrey]

Is removing the rear shaft an option? The front and rear can act together to cause problems. I'd check u-joints but wouldn't necessarily replace them unless they are bad. I think replacing u-joints wont fix out of balance unless there is obvious play. Are your motor mounts okay? If you are getting a lot of front/rear coupling they might be adding to the trouble. Wont solve your issue but might help isolate it a little better. And to confirm, you have done a simple rotation of both front tires to the rear with no change?

 

[thekidwithquestions]

Hoping I can get some level of confirmation I'm on the right track with my post lift vibration. I think I've read just about everything, but something's are a little changing for me.

I put on:
2" EMU Suspension Lift
EMU Transfer Case Drop Kit
33" tires - Baja MTZP3 Radials

Vibration right after install. It's starts at about 40mph, and gets stronger thru 50, and then pretty much goes away by 55.

I've aligned the front end and had the tires rebalanced at a shop I confirmed can deal with the larger tires.

Vibration still there.

SO, .... I just removed the front drive shaft and the vibration is worse!!!! I now notice it around 30mph and it's still there at 65.

Makes me think it must be the rear Driveshaft. I'm guessing with the front installed it might have acted like a damper???

Am I on the right path? Replacing rear U-Joints next?

Thanks,
Bob

you probable should get a SYE kit (slip yoke eliminator)

 

[Modoc Guy]

Put the front DS back in and pull out the rear DS. Put it in 4HI and take it for a drive.

Don’t exceed 55mph, the max speed while in 4HI.

See if your vibration is still there. If not, then start with working on the rear.

You have to get the rear diff pinion shaft parallel to the DS. That’s what the T-case drop is trying to do. If it’s not close enough you’ll need some adjustable control arms to get that accomplished. Or maybe a MML.

And you might have vibes at both DS’s. If so, you can try lengthening the front lower CS’s with the stock adjustment. But if that’s not enough, you’d be a candidate for adjustable CA’s in the front too.

But first, isolate the issue. Then decide what steps to take.

 

[pagrey]

Don’t exceed 55mph, the max speed while in 4HI.

Oops, I thought that was more like a guideline and not a rule.

 

[Modoc Guy]

Oops, I thought that was more like a guideline and not a rule.

It’s a limitation of the t-case. That chain in there can only go so fast.

 

[pagrey]

It’s a limitation of the t-case. That chain in there can only go so fast.

Is the chain spinning when you are going 90?

 

[Modoc Guy]

Is the chain spinning when you are going 90?

If you’re in 4HI it is.

In 2HI, no.

 

[pagrey]

It is a shift speed and not a top speed. Somebody needs to rebuild a 231.

 

[pagrey]

I made a mistake about how the power steering works the other day, shit happens, Jeep on.

 

[RobM]

Is removing the rear shaft an option? The front and rear can act together to cause problems. I'd check u-joints but wouldn't necessarily replace them unless they are bad. I think replacing u-joints wont fix out of balance unless there is obvious play. Are your motor mounts okay? If you are getting a lot of front/rear coupling they might be adding to the trouble. Wont solve your issue but might help isolate it a little better. And to confirm, you have done a simple rotation of both front tires to the rear with no change?

Thanks. Good thought. I was thinking they may interact together. I'll check mounts this week. And yes, I've now rotated tires twice.

 

[RobM]

you probable should get a SYE kit (slip yoke eliminator)

It sure sounds that way. But I've read a couple of posts that said you shouldn't really need one with only a 2 inch lift and I've lowered the transfer case. So the driveshafts essential think they are on a 1 inch lift. It's that enough?

 

[RobM]

Put the front DS back in and pull out the rear DS. Put it in 4HI and take it for a drive.

Don’t exceed 55mph, the max speed while in 4HI.

See if your vibration is still there. If not, then start with working on the rear.

You have to get the rear diff pinion shaft parallel to the DS. That’s what the T-case drop is trying to do. If it’s not close enough you’ll need some adjustable control arms to get that accomplished. Or maybe a MML.

And you might have vibes at both DS’s. If so, you can try lengthening the front lower CS’s with the stock adjustment. But if that’s not enough, you’d be a candidate for adjustable CA’s in the front too.

But first, isolate the issue. Then decide what steps to take.

Thanks. I'd like to do that, but can I really do that without a SYE? Won't oil come out where the Rear Ds was?

 

[Trevlaw]

If you’re in 4HI it is.

In 2HI, no.

Everything in a 231 is always spinning all the time, the only difference is there's more of a load in 4wd

 

[Modoc Guy]

Thanks. I'd like to do that, but can I really do that without a SYE? Won't oil come out where the Rear Ds was?

Oh yeah, can’t do that with a stock DS. My bad.

 

[pagrey]

It sure sounds that way. But I've read a couple of posts that said you shouldn't really need one with only a 2 inch lift and I've lowered the transfer case. So the driveshafts essential think they are on a 1 inch lift. It's that enough?

I think @fuse had vibes at that lift height or less, every Jeep is different. If you've pinned it down to the driveshaft then that's what it is. It wouldn't be the first time. All I've suggested is to make sure that's really what it is.

 

[Jeffseven777]

Did you by chance rest or jack up your guts using the output shaft on the transfer case? cause if you did and its stop np231 then you may have bent it. The best way to test this is take off your rear drive shaft. in 2wd put it in gear and have someone tap the gas you will physically see it vibrating.

 

[Jeffseven777]

Everything in a 231 is always spinning all the time, the only difference is there's more of a load in 4wd

yes and no. if you disconnect the drive shaft in the front in two wheel the yoke on the TC will not spin. when connected if the front wheels spin that makes the yoke spin and the chain spin. chain connects to a gear that isnt engaged unless you put in 4 low or hi
and when you put the TC is neutral the TC output shaft is completely separated from the output of the gearbox.

hi low gear

shift fork slides over the gears to select hi or low.

So everything is moving when all parts are connected but not moving when in certain positions which items removed.

 

[Trevlaw]

yes and no. if you disconnect the drive shaft in the front in two wheel the yoke on the TC will not spin. when connected if the front wheels spin that makes the yoke spin and the chain spin. chain connects to a gear that isnt engaged unless you put in 4 low or hi
and when you put the TC is neutral the TC output shaft is completely separated from the output of the gearbox.
View attachment 263703
hi low gear
View attachment 263704
shift fork slides over the gears to select hi or low.
View attachment 263705


So everything is moving when all parts are connected but not moving when in certain positions which items removed.

So what does any of that have to do with not going above 55mph in 4hi.

 

[Jeffseven777]

So what does any of that have to do with not going above 55mph in 4hi.

Nothing. I didnt reply to that. just the everything is moving post. Ive never gone probably over 30 in 4hi