SYE vibes

I've searched, found a million threads but havent seen one that really helps me out. Put a SYE on my 242 (HnT only option) had a machine shop tap it for me. Got a front driveshaft, had a shop do a complete rebuild with spicer u-joints, balanced and everything. Shimmed it so the pinion angle is 1 degree lower than the output of the tcase.
Now the problems-first i think my output bearing on my tcase is bad, its leaking fluid slowly out of the output shaft now. Most likely caused my the vibrations right?
The main problem im having is a vibration at 50 mph+ when i LET OFF the gas. Acceleration is fine, and slower driving is fine.
From what i've searched i need to shim the axle so there is more of a difference in the pinion angle, but wouldn't that put it out of the recommended operating range and possibly give me vibes on acceleration?

Its a 2000 with RE 3.5 full leaf packs that sit at 4.5" 8.25 rear, 242 case and drop brackets that lower the tcase by about 1/8"...

You want the axle yoke pointing as close as possible to the cv at the transfercase. if you are still running parallel with the transfercase you'll get vibes. Also depending how damaged the bearing is on the output shaft of your TC, you could possibly be getting vibes there. From your description of vibs when you let off the throttle you may want to start with the bearings

Well, without knowing what your actual angles are, it does sound like you could rotate the pinion up a tad.

But measuring (and telling) your angles would help.

Robert

If your output bearing is bad, that in itself could be causing the vibes. When there is a load on it, it wouldn't be too loose, but when unloaded it's a different story.
If you have a bad bearing, you need to fix it before undergoing further diagnosis, even if it turns out to be the angles.
The leaking would be in the seal, but a bad bearing is generally the cause of this.

ill get the bearing and seal replaced, then come back with exact angle measurements.

yeah with a CV shaft and SYE you want the pinion parallel with the driveshaft, not the output shaft of the t-case

I agree with those who said replace the bearing first.

Not that it's the same thing, but I used to get vibes (only when coasting) in one of the Civic transmissions I had. I opened up the tranny and all the input shaft bearings rolled out. Replacing the bearings fixed the vibes.

ok its been awhile but i recently got my jeep back from having gears put it in and have some measurements-still getting vibes on decel

angle at hack and tap flange at tcase-87 degrees or 3 degrees...
driveshaft angle 14 degrees
angle at rear diff cover bolts, 79 or 11 degrees

from my thinking that should put me 3 degrees below being parallel, this is with a 4 degree shim. Would moving to a 6 degree shim and taking that to 1 degree solve my decel vibe problem? i would be concerned that bringing it up would cause vibes on acceleration. I checked the output bearings on my tcase and they seem tight, driveshaft seems tight-any help here?

it should - might want to go with a 5 degree though. Depends on how stiff your springs are and how much they wrap under accel/decel.

I have a 4" lift with CV SYE and run a 4 degree shim...flawless operation

And I would ditch the TC drop. I don't think its helping you. I also have a 242 with an 8.25

Philprof said:

And I would ditch the TC drop. I don't think its helping you. I also have a 242 with an 8.25

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you are correct i have the same setup as you-but mine is not working flawlessly. I dont have a tcase drop-i have the RE drop brackets which are 1/8th inch thick and lower the crossmemeber like a tcase drop.

StylerG said:

Shimmed it so the pinion angle is 1 degree lower than the output of the tcase.

Click to expand...

I didn't notice this the first time I read your post - this might be the problem. The angle difference between the driveshaft and the pinion yoke is supposed to be 1 degree, not the difference between the pinion angle and tcase output angle. Maybe I'm just misreading your post? This kind of thing would result in really severe vibes.

yeah i just mistyped that! good catch i had to go back and re-read it myself. I am trying to get the pinion angle 1 degree lower than the driveshaft angle. The strange this was when i took my jeep to the shop it sat exactly at 4.5" and now getting it back it sits at 4" perfectly-which i wouldnt think would cause the variation im seeing now in my angles measuring before and after but have no clue. So now i think ill try a 6 degree shim and see if that brings it up, then if i still have vibes track down a 5 degree shim and go from there.
Since its been gone it got regeared with limited slips front and rear and new bumpers, but the crok rear bumper i got doesnt weigh that much and my lift has been on for more than a few years without settling. Ill try the shims and check back in with you guys

update

the 6 degree shims put my angles within .5 degrees on one another once i got it back on the ground-thought i was gonna have problems and it turns out that its perfectly fine. Picked up a vibe at upper speeds on the highway when i let off the gas still but its nothing i cant live with. Thanks for the suggestions guys.