A buddy of mine (1995 YJ, D60 rear, NP231 w/SYE Kit) has been having problems with a vibration for a VERY long time. It only vibrates under "load", and we have gone through EVERYTHING.

We took the rear end out, checked the pinion bearings, new motor mounts, new tranny mount, blah blah blah.

I went over last night to take a look, and with the rear driveshaft off, the tranny in gear, and it in 2wd, if you look closely at the oil seal around the rear output shaft, it would appear that it's "oblong". :) Meaning that you see that it would appear that the shaft is bent?

Now, has anyone else looked at the shaft without the driveshaft and seen if there's turns "true"?

Could it be bent? What the hell would bend it (other than the fact that it was bent from the factory)?

Any other ideas on this vibration?

Thanks
Out

Originally posted by IndyCJ
It only vibrates under "load", and we have gone through EVERYTHING.


I went over last night to take a look, and with the rear driveshaft off, the tranny in gear, and it in 2wd, if you look closely at the oil seal around the rear output shaft, it would appear that it's "oblong". :) Meaning that you see that it would appear that the shaft is bent?


The pinion is raising up under power and causing the vibration. I would bet the Jeep is SOA with no axle wrap bar?

If the output shaft was bent you should feel a vibration all the time.

Sounds like the pinion angle is changing too much under load. If the angles at the u joints is too great under load, that could cause problems with failed seals, bearings, etc.

Under load, the pinion is going to rise up a few degrees due to spring wrap. It could be moving far enough to cause the d-line angles to be too much.

If you really think the t-case shaft is bent, set up a dial indicator on the yoke (on the seal surface would be best) and rotate the shaft by hand. This will give you a runout reading.

It would not be impossible to bend a 231 output shaft. I bent one by jumping my YJ. The driveshaft slipyoke bottomed out and tweaked the shaft and broke the rear bearing housing.
I am not quite as young and stupid now:rolleyes:

i have a buddy that has bent 2 rear output shafts on his 00 TJ we replaced it the first time with mine after i did the SYE and the next time he went out he bent it again... we put in a SYE and no troubles since