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Ideal Pinion Angle for SYE?

DaveD912

DaveD912

NAXJA Forum User
Location
NJ
Yes, I've searched and yes it's been covered many times before, but the info is conflicting. Should the pinion be parallel to the driveshaft or a couple degrees below? The reason I ask: I have a '99 with a 3" lift and an SYE. Before the SYE, I had bad 35-40mph vibes. Now I've got a mild vibe/drone at 55+. I've had imbalanced tires before and this is different. My pinion is perfectly parallel with the DS (both 10*) using a 4* shim. Is trying a 2.5* shim a good idea or should I look elsewhere?
 
Pointing 1.0-1.5* (errrr... "slightly" if you are using a calibrated eye-ball) below the x-fer case yoke will allow you to account for axle wrap under acceleration...

...so... the ds-pinion angle should make a slight "V" (opening up)...a 2.5* shim will probable do you well.
 
Are you sure it's not the front? I've had alot more trouble with my front shaft than my rear. After I lifted my XJ and put in the SYE I would get vibes from my front shaft at about 55mph. I angled the pinion up slightly (at the sacrifice of some steering characteristics) but got the vibes to go away. With such a small lift and an SYE, I'm sure you'll find a way to get those vibes down. What shafts are you running?
 
baldwinwb said:
Are you sure it's not the front? I've had alot more trouble with my front shaft than my rear. After I lifted my XJ and put in the SYE I would get vibes from my front shaft at about 55mph. I angled the pinion up slightly (at the sacrifice of some steering characteristics) but got the vibes to go away. With such a small lift and an SYE, I'm sure you'll find a way to get those vibes down. What shafts are you running?
Click to expand...

I haven't pulled the front yet, so far I haven't found anyone that's had a problem in the front with just a 2" spacer. I guess it's not too hard to pull the front shaft and find out for sure though. The rear is an AA SYE with a Woods shaft.
 
What type of SYE is it? If you have a hack n tap, then you may want to make sure the output shaft was ground flat. I had vibes around 50 mph until I went back and ground the shaft so the mounting face was flush. Now I have no vibes at all even at 75+ mph.
 
monkeyevil said:
2 deg below directly pointing at the tcase output at ride height.
Click to expand...

Any advice on how to measure that angle? Or don't I need to be that precise? A 2* shim would put me 2* below the DS angle, so I might end up with no shim.
 
Assuming the same length as my springs 51.25" and a 3" lift, you need about a 2.68 degree shim. 51.25/(1/tan(3))
So yeah, a 2.5 should do it.
 
Before you start changing things, does the vibration occur when you are on the gas? How about when coasting? Vibes under acceleration that go away when you take your foot off the gas should be an indication that the pinion is too high. Just wanted to confirm that's what was happening...
 
EricsXJ said:
Before you start changing things, does the vibration occur when you are on the gas? How about when coasting? Vibes under acceleration that go away when you take your foot off the gas should be an indication that the pinion is too high. Just wanted to confirm that's what was happening...
Click to expand...
Exactly! Vibes occurring when deaccelerating are also an indication of an incorrect pinion angle.

Tom Wood (http://www.4xshaft.com read his tech section) generally recommends shimming so that the pinion is 1º below the angle when pointed directly at the transfer case output. However, this advice is followed with every vehicle being a bit different, so YMMV.

Most likely this is a result of your pinion angle. I would start with a 3º shim first and see if that improves it.
 
The vibe is still there when I let off the gas, but it's much less. Thanks for all the help, I can't wait to have a smooth/quiet ride again. It'll be a few days before the shim gets here, but I'll post up the result when it's done.
 
I just eyed mine years ago on my own junk.... but if you get a piece of string and an angle finder you could get a pretty accurate measurement.

Just tie the string between the two yokes (try to keep it in the center as much as possible. 2 deg below that angle should be your pinion angle.

This isn't super scientific, but being as accurate as you can will get your shaft as smooth as possible. I was at about ~7.5" in my YJ with no vibes at 80 with just the calibrated eyeball :)
 
I agree that you can often get a pretty good angle by eyeballing it, but it can also be decieving, especially at first. On my current setup I used "eyeball calibration" and with a 2* degree shim my angle looked very good... at least thats what I thought. I then took some better measurements with an angle finder only to realize that my pinion was actually 7* lower than the driveshaft. (Technically, the angle between the driveshaft vs pinion was 173* (180* being a straight angle...)) So I put back in my 6* shims bringing the pinion only 3* lower and its very good since then. (I did that about 2 years ago). My only point with this is that by eyeballing it, I got it wrong. It pays to take good measurements rather than guessing. :thumbup:
 
Angle finders can be bought at your local hardware store for fairly cheap and, as Eric said, they're much more accurate than "eyeballing" it.
 
Just wanted to follow up. I pulled my 4* shims and replaced them with 2* shims. The vibe (audible, I don't actually feel it) doesn't start now until I'm over 65mph. That's fine with me. With a lift and off road tires, I don't need to be going that fast :)
 
I am still confused as to where to measure for the pinion angle. I have an angle finder.

Sticking it on my driveshaft shows me 17 degrees. Putting it on various places on the axle (which appear to be linear with the pinion) shows about 10 degrees. I have heard you can measure it on the diff cover, does this give you a true measure?

Help!

Oh, and if 10 is right, do I really need 7 degree shims?!? (well, 6 accounting for axle wrap on accel.) I have like 2 inch shackles, and only 5 inches of lift, I thought shackles would point the pinion up a degree or two.
 
I used one of these angle finders for mine http://www.sears.com/sr/javasr/product.do?cat=Hand+Tools%2C+General+Purpose&pid=00940760000&vertical=TOOL&subcat=Precision+Tools&BV_UseBVCookie=Yes
and simply measured the angle between the driveshaft and pinion.

If you are using an angle finder like the one CanMan linked to, you would find the angle of the drivehshaft, find the angle of the pinion, and calculate the difference between the two.

Edit: It sounds like you may have measured correctly in which case a 6* shim would work leaving the pinion 1* lower than driveshaft, or a 4* shim leaving a 3* difference.
 
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