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Discussion Starter · #1 ·
I recently purchased a new to me 2004 Rocky Mountain edition wrangler 4.0 with 5 speed manual transmission with Dana 44 rear end. Previous owner installed 4â€Â� lift with double carden driveshaft. The lift only replaced the lower control arms and it has the stock uppers. I plant to eventually get adjustable arms next year but want to drive it now. The lift also used a 1.5â€Â� TC drop. So yesterday I added 4 washers under the skid plate to help rid the vibes. I replaced the transmission mount as it was shot as well. No more vibration but I have a question. When measuring the pinion angle, if I did it correctly, the pinion shows 11° and the driveshaft is 15°. Is is possible to not have driveline vibes at those angles?
 

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the happy place can be a zone rather than a spot. within a couple degrees should work. but i'm wondering why the washers to drop the TC? this is what the adjustable CA's are for, to control the pinion angle and make a happy drive line for that DC shaft.
 

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It's plain to see from the second photo that your rear pinion angle is too low which is what's causing the vibrations. You cannot drop the tcase with spacers like you did for your aftermarket CV driveshaft, that only works/helps for the OE stock non-CV driveshaft.

At a minimum you need adjustable length upper control arms you can lengthen a tad to raise your rear axle's pinion angle. Also, you cannot just live with the vibrations which will start taking out components like u-joints, seals, or bearings.

Your rear pinion angle MUST look like this...
 

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Discussion Starter · #4 ·
I do not have rear adjustable control arms yet, I plan on getting them in the future. Dropping the skid plate down put the shaft much closer to the same angle as the pinion angle than where it was originally and the vibrations stopped after I did this. I’m just curious why there are no vibrations with the variance in angles. Is it just that I can not feel it but it is still happening? Multiple throttle positions, any gear I don’t feel any vibrations. I definitely felt them before I added the additional drop.
 

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I do not have rear adjustable control arms yet, I plan on getting them in the future. Dropping the skid plate down put the shaft much closer to the same angle as the pinion angle than where it was originally and the vibrations stopped after I did this. I’m just curious why there are no vibrations with the variance in angles. Is it just that I can not feel it but it is still happening? Multiple throttle positions, any gear I don’t feel any vibrations. I definitely felt them before I added the additional drop.
The transfer case drop is not helping in this case. With a CV driveshaft, the pinion angle needs to match or be slightly below (.5°-1°) the angle of the driveshaft. The only way to accomplish this is with adjustable control arms (generally upper). You also don't want to eyeball it. Get an angle finder.

I understand that you plan to get adjustable control arms in the future, but this is not something that can be put off. If one of those u-joints fail, the driveshaft is going to spin like a propeller and damage or destroy everything it contacts, plus you'll need to buy a new driveshaft. As Jerry stated, the vibrations can also damage the rear differential.

Get adjustable control arms or remove the rear driveshaft and drive in 4H until you can.
 

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The transfer case drop is not helping in this case. With a CV driveshaft, the pinion angle needs to match or be slightly below (.5°-1°) the angle of the driveshaft. The only way to accomplish this is with adjustable control arms (generally upper). You also don't want to eyeball it. Get an angle finder.

I understand that you plan to get adjustable control arms in the future, but this is not something that can be put off. If one of those u-joints fail, the driveshaft is going to spin like a propeller and damage or destroy everything it contacts, plus you'll need to buy a new driveshaft. As Jerry stated, the vibrations can also damage the rear differential.

Get adjustable control arms or remove the rear driveshaft and drive in 4H until you can.
X2, well said.
 

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Discussion Starter · #8 ·
Thank you everyone. For the time being I did remove my rear drive shaft and will run in 4 Hi for now. Thank you for the links I will check those out too. Will running in 4 hi hurt anything and am I okay to run this way with the transfer case drop?
 

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i would deduce that the front of the TC tilts up a hair when the rear tilts down..........this of course would not be optimal running the shaft joint into a steeper angle than necessary. but the front shaft is longer and a bit more forgiving. and the slight misalignment might be easier to absorb in the top double joint. adding an MML does similar and prob a fat degree or 2 more than dropping the TC. but i would remove it to correct this issue when you get some adjustable arms.

i don't run my rear DC dead on, i run it 1.5* low of the pinion, under load it'll twist up some and be right there within a .5*, that 1/2 degree ensure all my roller bearings turn always. and my axle is happy with it. but every jeep has it's own personality if you will and may/can be slightly diff.
 

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Thank you everyone. For the time being I did remove my rear drive shaft and will run in 4 Hi for now. Thank you for the links I will check those out too. Will running in 4 hi hurt anything and am I okay to run this way with the transfer case drop?
I would remove the transfer case drop, but it should not be an issue for the front drive shaft.

You should be able to drive without the rear drive shaft for awhile (couple weeks?). I would personally stay off the freeway, but any speed acceptable for 4WD will be fine in FWD. You will quickly realize however why FWD cars use CV joints instead of u-joints.
 

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Discussion Starter · #11 ·
Okay I got my Rokman adjustable arms today and got them installed. I measured the pinion angle and the shaft angle and both are dead on 16.5°. I feel a slight vibration in first gear and slightly into 2nd gear. The angle looks good to me eyeballing and with the angle finder. Here are some pictures. I can’t tell if the vibration is the driveshaft or the tires. What’s the best way to determine if it’s tires or the driveshaft?
 

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Rokmen is a excellent choice.

With the pinion and driveshaft at the same angle, the axle is likely twisting under acceleration and increasing the angle of the pinion. First, try adjusting the pinion slightly below the angle of the drive shaft and see if anything changes. You may have to adjust the control arms a few times before you find the perfect angle.
 

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Okay I got my Rokman adjustable arms today and got them installed. I measured the pinion angle and the shaft angle and both are dead on 16.5°. I feel a slight vibration in first gear and slightly into 2nd gear. The angle looks good to me eyeballing and with the angle finder. Here are some pictures. I can’t tell if the vibration is the driveshaft or the tires. What’s the best way to determine if it’s tires or the driveshaft?
Tires will vibrate at about 2x the rpm of the tires. Driveline is another 4x as fast as that.
 

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Discussion Starter · #14 ·
I adjusted the rear pinion angle down slightly and the vibration is still there. Is a slight vibration at take off okay for for the long term? I doubt it, but I’ve tried multiple angles and I’m still having vibrations.
 

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rotate wheels if you suspect them. and/or inspect the joints in the shaft, maybe something got sloppy runnin odd angles.
 

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Discussion Starter · #16 ·
I just had the tires balanced and rotated, everything including u joints are tight. The tires are rough treads that vibrate at low speeds due to the lugs. I have the stock tires and wheels, and I plan on putting them on and try and see if it is the tires or driveshaft. I’ll keep everyone posted. I checked the manufacture date on the current tires and they are 8 years old. Might be time to upgrade. They are 33x12.50x15 Goodyear MTR’s w/Kevlar on pro comp 7069 wheels. I know nothing about these tires except they took a ton of weight to balance.
 
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