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Humming noise after SYE

S

steventure

NAXJA Forum User
Location
Indiana
My 97 has about a 2 1/2” lift closer to 3” in the rear. Combination HD leafs from general spring and jks boomerang shackle. Anyways I was getting some vibes so I had a shop install a SYE and new driveshaft. After picking it up I noticed a pretty pronounced hum when accelerating. Different from the vibes I felt before. Took it back, they pulled the Tcase and checked everything, built a new driveshaft. Noise still there. Pulled the front driveshaft and now the noise is gone. So is this related to pinion angle in the rear most likely? Is there a specific type of driveshaft that should be used? Do I need to shim the rear?
If someone can please educate me on these things. This shop has had my Jeep for almost a month now and I’m not sure I have much faith in them anymore.
 
From the IRO instructions, you need 1" movement of the driveshaft in the front and 2-3" for the rear. So, take off the front connection and see if it will move back 1" from the yoke.
 
I was just giving the source of the information I used. It should apply to your situation. Still, the problem may be elsewhere. The driveshaft needs to be able to expand and contract or slip in and out.
 
If you switched to a CV style driveshaft (assuming you did with the SYE), your pinion angles are AFU. With a single U-joint per side driveshaft, the angle needs to be equal on both sides. With CV style driveshafts, you need to have the pinion in line with the rear section of the driveshaft.

cv-vs-non-cv-angles-jpg_7af638a26ddf36518028ab8e45332c36bea51867-jpg.2554663
 
Yes. CV driveshaft. When I asked them about the rear pinion angle they said “it’s ok” I just got it back this morning and I can tell it’s not ok. I threw a bunch of weight in the back to lower it a bit and the vibes softened a bunch. I ordered some 2 and 4 degree shims so I guess I’m gonna try those. Would that be the best way to proceed?
 
steventure said:
Yes. CV driveshaft. When I asked them about the rear pinion angle they said “it’s ok” I just got it back this morning and I can tell it’s not ok. I threw a bunch of weight in the back to lower it a bit and the vibes softened a bunch. I ordered some 2 and 4 degree shims so I guess I’m gonna try those. Would that be the best way to proceed?
Click to expand...

Your already doing what is needed but measuring before-hand "can" save steps.
 
You never did say whether it's a H-n-T or a full HD kit?
 
You can measure the pinion angle off the 2 manufacturing boss's on the back of the diff housing, you can measure the TC output off the engine valve cover.
 
Well I tried some shims, started with 2 then 4. Didn’t seem to make much of a difference. Found my angle reader so I’ll actually measure today and see where we’re at. But I kind of feel like it’s coming from the rear differential. It’s constant through all speeds, and goes away as soon as you take your foot off the gas. I’m gonna pop open the diff cover and have a look. Other than metal shavings, what else should I check for?
 
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