Drivetrain Vibrations

[Dakota]

I installed a 2.5" lift on my jeep last weekend and now I have driveline vibrations. Id rather not lower my transfer case, so will a 1" motor mount lift work? I've heard mixed opinions on it

 

[PStov98TJ]

Theoretically, it will lessen the angle between t-case output and driveshaft. So yes, it is a viable solution.

 

[Chris]

I agree that the MML should lessen the angle between the t-case output and driveshaft and therefore potentially solve the vibration issue. I can't say with certainty, but it should.

Still, if you are experiencing drivetrain vibrations you really ought to put a transfer case drop on there temporarily until you do the right thing and get a SYE.

 

[Luke]

Be careful with the MML because your fan might get into your fan shroud


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[John Carmony]

You need to check the angle from the transfer case yoke and the diff yoke. It needs to be paralell Don't get confused, it does not have to be a straight line, but the angles have to match.

 

[Jerry Bransford]

That first drawing is misleading, it will never look like that on a TJ. With a stock TJ rear driveshaft, the correct angles will actually look more like the second drawing.

And if you don't want to drop the tcase skid plate, yes a 1" motor mount lift will work.

The correct angles when you have the stock rear driveshaft will look like this...

 

[Luke]

Chris if you add an MML wouldn't it angle the output down and look like the 3rd drawing?


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[Chris]

Chris if you add an MML wouldn't it angle the output down and look like the 3rd drawing?


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If you added a MML without a body lift, then yes, it would I believe. But if you added a body lift and a MML then it would even things out.

Someone correct me if I am wrong, but in my head that makes sense.

 

[Luke]

Wouldn't you need to raise the tc the same amount as the MML?


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[Jerry Bransford]

Adding the MML tilts the engine and thus the transfer case output shaft to a slightly steeper angle. That better matches the steeper angle of the rear driveshaft caused by the suspension lift. That eliminates the excessive angle between the driveshaft and output shaft the u-joint would have to work in, eliminating the vibrations caused by the u-joint.

 

[Luke]

Yeah so it would look like the third diagram


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[Chris]

Yeah so it would look like the third diagram


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Not necessarily. If you had a big enough lift that your rear pinion angle was pointing upwards more (due to lack of adjustable control arms) then it would look almost like the third photo in that diagram but the rear pinion angle would be pointed slightly up more essentially causing things to be more parallel, thus reducing potential vibrations.

I'm pretty sure at least...

 

[Luke]

Oh okay I see


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[Jerry Bransford]

Yeah so it would look like the third diagram

No, not even close. The only one of those four illustrations that is like what we'd see on a Jeep with the factory driveshaft is the 2nd one. The others are not good examples of anything we'd likely ever see on a Wrangler. Drivetrain geometry can be fairly complex but it's not hard to get your head around if you read up on it a little.

An EXCELLENT source of information on drivetrain geometry is at from Tom Wood at http://www.4xshaft.com/. Click on "Tech Info" at the top of the page, then click on "Geometry 101" where you'll find the golden keys to understanding all of this.

 

[John Carmony]

@Jerry Bransford the photos are for reference.

@Dakota That is why you need to physically check the angles. Raising the engine, leaving the transfer case the same, would make the transfer case yoke point down. If you lifted your jeep 2.5 inches I am assuming it is lifted the same rear and front and therefore the angles should remain the same. The only thing you have done is increased the vertical distance. If you lifted 2.5 in front and 2in in read, the angles could be slightly off