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Old 04-03-2014, 08:19 PM   #1
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Rear pinion angle

I Recently put a RC 2.5" progressive spring kit and 1" Daystar BL on my stock '98 Wrangler TJ. It is a 4.0L with a 5-speed MT. After installing the spring lift, I noticed a shudder when releasing the clutch in first gear. I didn't notice a shudder in any other gear unless I accelerated hard. I measured the rear drive line angles and noticed I now have a 4 degree difference in the TC yoke and the rear differential pinion. Unfortunately I do not know what the angles were before, but I do know the difference needs to be less than 1 degree and the axle would have rotated a bit with the spring lift. I have an adjustable lower CA set on the way so I can push the lower CA point on the axle back, which will reduce the pinion angle. I would appreciate any feedback and/or opinions on this approach. However, I assume this is a solid approach on a budget for the occasional off road use. What I am hoping somebody can provide is the distance between the upper and lower CA connection points on the rear axle, and the front if you have those too. I need the distance to calculate the length increase of the lower CA to give the correct pinion rotation without having take them in and out multiple times.

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Old 04-03-2014, 08:27 PM   #2
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The issue with your shudder is most likely a bad transmission mount. If you had drive line vibes, they would get worse with speed.

As far as adjusting ca's, just disconnect both lowers with a bottle jack under the pinion. Lower the bottle jack as needed until your pinion angle matches your transfer case angle, then adjust the ca's to fit.

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Old 04-03-2014, 08:29 PM   #3
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That shudder isn't caused by the pinion angle, it's caused by excessive u-joint angles caused by a driveshaft that has become too steep from a suspension lift.

Trying to adjust the rear pinion angle is not the fix, you simply need to reduce the angles the driveshaft u-joints have to work into... and adjusting the pinion angle is not the way to do that.

You can ether install a transfer case skidplate, install a pair of 1" taller motor mounts, or install a SYE eliminator which will allow a longer rear CV driveshaft to be installed. Any of those three will reduce the angles the u-joints have to work into.

This is how the relationship between your rear pinion angle should look with the t-case output shaft when you have the stock OE rear driveshaft... they need to be parallel as shown here...
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Old 04-03-2014, 08:35 PM   #4
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Your pinion angle is dependent on the type of driveshaft you have; i.e. a CV type or standard U joint on each end. If youre running a CV shaft the angle of the drive shaft and your pinion should be the same. some people choose to go a degree down to compensate for torque under hard throttle. If youre running the standard type then youll have to make sure the angle of the driveshaft to the pinion is the same but opposite of the angle to the driveshaft at the transfer case.

This might sound confusing but if you google "Jeep Wrangler pinion angle adjustment" there are a couple really good sites that go into great detail on this subject.
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Old 04-03-2014, 08:41 PM   #5
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I am performing an 8.8 swap, the Dana 35 has been removed, measured its position relative to the frame on the ground, now jigged the 8.8 in place, the brackets have not been welded yet, the sye has been installed, but have not had the driveshaft cut, how can I determine the pinion angle without a driveshaft?
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Old 04-03-2014, 08:42 PM   #6
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Thanks for the quick responses! I measured 6 deg at the TC, 19 deg on the stock drive shaft, and 10 deg on the rear axle pinion. This is how I determined the 4 deg diff between the U joints at each end of the drive shaft. Is 13 deg angle between TC U joint and drive shaft too much?
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Old 04-03-2014, 08:50 PM   #7
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One more thing. I installed a rear track bar relocation bracket to keep the rear axle centered side to side.
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Old 04-03-2014, 08:52 PM   #8
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U-joints vibrate from working into an excessive angle. I gave you three good ways above to reduce it with dropping the tcase skidplate an inch being the cheapest and easiest.
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Old 04-03-2014, 08:56 PM   #9
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First thing to do IMHO is take it for a short straight drive in 4Hi, and see if you still have the shudder in 1st gear. If it goes away in 4wd, it is almost for sure because of the transmission mount (the torque on the front drive shaft will counteract the torque on the rear one.) If that's the case, change the mount first, that may solve your problems, and you may not have to go further.

If that doesn't solve your issue, try putting two or three washers on each tc skid to frame bolt between the skid and the frame to drop the skid slightly and try driving it that way.
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Old 04-04-2014, 07:06 AM   #10
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Thanks guys. I'll see how the weekend goes...
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Old 04-04-2014, 10:19 AM   #11
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Related question...I had a t-case drop and put an 8.8 w/SYE in. I removed the drop and dialed in the pinion angle. Is there any other adjustment I need to make related to removing the TC drop? It was a 1" drop and I have appox. 3" lift.

Thanks!
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Old 04-04-2014, 03:50 PM   #12
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Quote:
Originally Posted by juan_p__m View Post
I am performing an 8.8 swap, the Dana 35 has been removed, measured its position relative to the frame on the ground, now jigged the 8.8 in place, the brackets have not been welded yet, the sye has been installed, but have not had the driveshaft cut, how can I determine the pinion angle without a driveshaft?
Put a right angle on your 8.8's flange so that it points to your TC yoke. You want the pinion to point one or two degrees down in reference to the TC yoke to avoid potential axle wrap. Go to the Tom Woods site for more info.

Tom Wood's Custom Drive Shafts - Tom Woods Custom Drive Shafts Custom Driveshafts Specialist

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