IRO SYE vibes!!!

[Darky]

First remove the reasr shaft and drive it in front wheel drive to ensure that the problem is actually coming from the rear end.

 

[IslanderOffRoad]

I've had that thump you're talking about before... how are your motor/trans mounts?

Your trans mount could be shot or loose after removing the tc drop.

 

[keep0njeepin0n]

did find out the source of my thumping under the floor board...the exhast hanger bushing on the side of the transmission mount had an elongated hole from the t-case drop...so I fixed that and I also too pics of the angles so I'll post those tonight

I've had that thump you're talking about before... how are your motor/trans mounts?

Your trans mount could be shot or loose after removing the tc drop.

Already found and fixed........................

 

[JJacobs]

Let me see if I can summarize this thread..

You have vibes.
The members of tell you how the Jeep should be set up and how to troubleshoot.
You ignore the setup instructions and ask for step by step, 'what do I do now?'
When given a recommendation you ignore it and say it doesn't make sense, although it actually does.

Gee, wonder why I'm not gonna weigh in on the technical aspect of this one..

 

[keep0njeepin0n]

Ok so I took Everyones advice and isolated the problem and removed the front DS....just as I thought, the vibes are coming from the rear...now that we got that out
of the way....what next? I'm thinking about removing the shims but then I read in tom woods driveshaft site that the pinion should point straight at the ds when using a double cardan type shaft...then again it didn't mention anything about an sye.....

 

[Andy in Pa.]

OK, so you had vibes... you put an SYE on and a new rear shaft and removed the t-case drop. Now you still have vibes, only slightly worse. I suspect the vibes are from the front, only because NOTHING CHANGED when you did the SYE/rear shaft.

This is how you diagnose driveline vibes...

Step 1. Remove FRONT shaft.... test drive it (in 2wd)

If you still have vibes...

Step 2. Re-Install front shaft, remove rear shaft.... test drive it (in 4wd-high)

Please report back with your results...

 

[keep0njeepin0n]

Ok I did that with the exception of taking the rear shaft off but with the front ds off and sitting in the garage the jeep has the exact same vibes...doesn't that pretty much say it's in the rear...especially since
most
of the vibes are during acceleration only???

 

[Andy in Pa.]

Ok I did that with the exception of taking the rear shaft off but with the front ds off and sitting in the garage the jeep has the exact same vibes...doesn't that pretty much say it's in the rear...especially since
most
of the vibes are during acceleration only???

Then do Step 2...

Report back...

 

[dinorl007]

have u checked the u joints? i would assume they were new, but check for binding in them, if they are tight or hard to move sometimes u can tap the yoke with a hammer to center them and free them up had the same prob as u r having and traced it back to a tight ujoint not seated properly hth

 

[91XJRubicXD]

and I had to cut the yoke down too

Just wondering, wouldn't that create a balance issue in itself ?

 

[keep0njeepin0n]

Ok so I removed the rear ds and vibes went away just like I thought...so should I remove the shims? What about on Tom woods' site where it says the pinion should be pointed straight at the ds when using a double cardan shaft? Or does it not factor in an sye??

 

[98stocker]

So, either the shaft is bad(slip joint, u joint, or cv joint loose or shaft out of balance)

or the angle is wrong. Since we cannot look at the angle gauge with you, measure it carefully again. I would turn the pinion yoke vertical (with the driveshaft off) so that you can measure off the yoke. Might not hurt to clean up the yoke to be sure you are getting an accurate number. Then reinstall the driveshaft and measure the angle on the driveshaft. If you have stock, soft springs I would go for around 2 degrees lower on the pinion than on the shaft. If you have stiffer aftermarket springs, 1 degree might be better. If your numbers need changing, then remove those shims and install the correct ones.

Once you are sure your angle is correct, recheck for vibes. If still present, switch shafts or replace worn parts if you can identify which ones are bad.

If there is an obviously bad part of the shaft, fixing that would of course be your first step...


And finally, you really need to do more research. This has all been covered a bazillion times. You don't have anything special going on with your jeep.

 

[Crasher]

Try this. Put the rear axle on jack stands. Block the front wheel. Have someone get in and run the engine in in drive ( 2WD ONLY ) Run it up to the vibration speed. Look at the driveshaft. I was able to see a slight movement in the shaft when the vibration was felt. I then went underneath with a sharp rod that I could bring up against the shaft and marked the spot that was moving. Do this with engine idling and in drive. Shut it down and do it again to confirm the spot that is wobbling. I found this after the new shaft had been balanced 3 times by reputable driveline shops. I took my findings back to one of them and he spent 5 hours confirming what I had found and replaced the tube and slipspline. Total cost was $78.

 

[Andy in Pa.]

Ok so I removed the rear ds and vibes went away just like I thought...so should I remove the shims? What about on Tom woods' site where it says the pinion should be pointed straight at the ds when using a double cardan shaft? Or does it not factor in an sye??

Yes, take the shims out. If the vibes are still there, it sounds like the d-shaft needs balanced. One way to be sure is to put your front driveshaft in the rear (as long as its the right length) and see if the vibes went away. If no vibes, then the new rear shaft is not balanced properly.

 

[keep0njeepin0n]

Shims out and vibes are gone!!

 

[keep0njeepin0n]

Ok, update!!!! All vibes are gone at WOT and low speeds, now I get slight constant vibes at 60+ with steady throttle applied. If I let off the gas, it goes away. So, I'm thinking, maybe installing a 1 degree shim?? I don't know if the vibes increase or go away above 65, as I have not been able to safely achieve that speed without getting in trouble!

 

[winkosmosis]

Edit: oops... misreadhttp://www.stu-offroad.com/axle/pinion/pinion-1.htm

 

[kastein]

You're correct winkosmosis... though more specifically it's supposed to be 1-2 degrees below being parallel with the driveshaft. That only goes for leaf spring suspensions, for coil based suspensions the pinion angle should be the same as the driveshaft angle at ride height (no spring wrap to compensate for) though that's probably inherently obvious to anyone building a linked suspension.

 

[winkosmosis]

This guy says some people like to angle it a degree so that under load it aligns http://www.stu-offroad.com/axle/pinion/pinion-1.htm

 

[winkosmosis]

You're correct winkosmosis... though more specifically it's supposed to be 1-2 degrees below being parallel with the driveshaft. That only goes for leaf spring suspensions, for coil based suspensions the pinion angle should be the same as the driveshaft angle at ride height (no spring wrap to compensate for) though that's probably inherently obvious to anyone building a linked suspension.

I misread and thought he said the pinion should be the same angle as the tcase:anon: