Driveline Vibrations

Bruce20

Bruce20

TJ Enthusiast
Joined
Jun 2, 2018
Messages
313
Location
Pennsylvania
My Jeep has a 2.5” lift and 33s and there is a slight vibration only when I’m in 3rd gear at 1700rpms and accelerating. I also have a sound that feels like something hitting my feet with a knocking sound when I just release the clutch the whole way in first. Once I get over 1600rpm, it goes away. Do I need a t-case drop? What is the knocking?


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With a 2.5" lift you definitely need a transfer case drop, no question about it.

Either that or a SYE and DV driveshaft combo.

This is where your vibrations are coming from, I'd almost guarantee it.
 
Even if they are very minor? I can barely feel them and they only occur once in awhile. Could my tires be off balance? What about the knocking noise?


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A mml (motor mount lift) has a large chance of solving your vibration problem. As far as the knock goes check the torque on your control arms. Balancing the tires never hurts. Also, if you didn't already do an alignment.
 
Alex01 said:
A mml (motor mount lift) has a large chance of solving your vibration problem. As far as the knock goes check the torque on your control arms. Balancing the tires never hurts. Also, if you didn't already do an alignment.
Click to expand...

Does a MML require something with the fan shroud. Do I need to do anything to the tranny or linkage. This is off topic, but my Jeep won’t go into 4wd. What can I do other than getting a cable system.


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Thanks for the link. I don’t want to do a body lift because I like the height I’m at. I’m going to check the oil in the case. I’m afraid to pull hard because I don’t want to break the lever.


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Bruce20 said:
Thanks for the link. I don’t want to do a body lift because I like the height I’m at. I’m going to check the oil in the case. I’m afraid to pull hard because I don’t want to break the lever.
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Click to expand...
After a lift you always need an alignment. It’s easy to do since you’re just adjusting the toe in to 1/16”.

Your vibration is coming from the lift. You have one of three options; 1) TCase drop about 1/2”, 2) 1”MML. You will have to move the fan shroud up 1”, which requires slotting the four holes in the shroud and trimming where the radiator hose rests above the fan shroud. 3) SYE and DC driveshaft. I personally vote for the MML.

@Tigerman, the MML raises the engine, the hinge point is the transmission mount, this tilting the TCase output down, correcting the driveline angle sufficiently up to ~3”. It also gives you more clearance at the oil pan.

@Bruce20, as to the 4WD. First thing is to check the stock TCase shifter for binding. It may need adjustment.

Can’t help with the knock. Happy trails.
 
I’ve started to have what I thought was clutch chatter upon engagement. But it ocurred to me that I first started to notice this after a 3/4 inch transfer case lift and additional 1 inch suspension lift (to a total of 2 inches). This is a Rubicon so there is no slip yoke but I don’t have a double cardan drive shaft. Could it be that what I thought was clutch chatter is just driveline vibration? It seems to be smooth after full engagement and I am rolling at a few mph. When stopped I can set the parkng brake and slowly engage the clutch without vibration. This would seem to indicate it is not a clutch problem. What do ou think?
 
TurboTJ said:
I’ve started to have what I thought was clutch chatter upon engagement. But it ocurred to me that I first started to notice this after a 3/4 inch transfer case lift and additional 1 inch suspension lift (to a total of 2 inches). This is a Rubicon so there is no slip yoke but I don’t have a double cardan drive shaft. Could it be that what I thought was clutch chatter is just driveline vibration? It seems to be smooth after full engagement and I am rolling at a few mph. When stopped I can set the parkng brake and slowly engage the clutch without vibration. This would seem to indicate it is not a clutch problem. What do ou think?
Click to expand...
Are you running stock control arms? My guess is that if you where having any issues it would be in the rear. But, typically 2 inches of lift doesn't cause and issues but every jeep is different.
 
Alex01 said:
Are you running stock control arms? My guess is that if you where having any issues it would be in the rear. But, typically 2 inches of lift doesn't cause and issues but every jeep is different.
Click to expand...

The control arms are Currie. Springs are OME HD. The clutch was replaced about 6 months ago and was smooth at first. It may just be a coincidence that this is happening now and is unrelated to the transfer case lift and slight suspension lift increase (I went from LD to HD springs) but I am suspicious. It is not bad but I miss that buttery smooth engagement I used to have. I am thinking about dropping the transfer case again to see if it goes away. If it is the clutch I am pissed because I went the full nine yards with new everything including the flywheel.
 
While your down there make sure your u joints look good.

I just noticed your from WC. There's a good chance I've seen your jeep before. I work in Alamo and live in Martinez.

 
TurboTJ said:
The control arms are Currie. Springs are OME HD. The clutch was replaced about 6 months ago and was smooth at first. It may just be a coincidence that this is happening now and is unrelated to the transfer case lift and slight suspension lift increase (I went from LD to HD springs) but I am suspicious. It is not bad but I miss that buttery smooth engagement I used to have. I am thinking about dropping the transfer case again to see if it goes away. If it is the clutch I am pissed because I went the full nine yards with new everything including the flywheel.
Click to expand...

Edit: I removed the Barnes skidplate and put the shovel back on. That lowered the transfer case 3/4 inch to the stock height. I think that took care of the problem. I am surprised that 3/4 inch would make a difference. The next question is, if I do a 1 inch MML would that allow me to put the Barnes skidplate back on? Or is a double Cardan the only solution?
 
I would bet a mml would solve your issue.
 
It's worth a try. At least then your oil pan will be one inch higher from harms way. Sounds like you got the same Barnes skid I got.
 
I just measured my drive line angles and I think I may have found the problem. The transfer case flange is 6 degrees down and the diff flange is 8 degrees up. As I understand it, the diff should be 1 degree less than the transfer case or 5 degrees in this case meaning there is about a 3 degree error. With the Barnes skid plate raising the transfer case 3/4 inch that will further decrease the angle on that end to 5.2 degrees which would require the diff to be at 4.2 degrees. That is 3.8 degrees off from where it is now. Sounds like I should adjust things, don't you think?
 
I have single adjustable Currie control arms. How do I adjust them? I am guessing I need to take both springs out so when I remove a pair of control arms the axle won’t be forced out of position by the spring loading, even with the axle all the way down down with the shocks and sway bar disconnected.
 
I reinstalled the Barnes skid plate and put in a Tom Woods DC driveshaft. I have not been able to get the pinion angle perfect (it is about 1 degree too low) because of track bar to fuel tank interference. Still, the clutch engagement problem seems to have largely gone away. I get some slight vibration (thrumming sound actually) at about 50 to 55 mph but I think that is just from the tires. With my hand on the gear shift there is no vibration to be felt.

It appears to me that the only way to get the pinion angle absolutely correct is to use larger bump stop extensions. My lower control arms are minimum length and lengthening the upper arms allows the track bar to hit the gas tank. The track bar is an adjustable JKS and I am using the angled bracket. I was told that this combination should not result in interference but it does on my TJ.
 
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