Dragging and vibration after driving 60 MPH or higher for an hour or more

[FhPt]

I have a 94 JGC and I'm having an issue that feels like driving over a bunch of cattle gaurds that have been spaced out on the highway (rough then smooth then rough then smooth, etc,.). Feels likes something is pulling on the Jeep during rough part. Can't really tell if vibration is from the front or back. It only happens after driving 60 MPH or higher for an hour or more. Letting off the gas makes it worse and constant. Problem still exists when putting Jeep into neutral and coasting (engine will also rev fine while coasting in neutral). Once the problem starts, it continues even at slower speeds. Pulling over and letting it cool for 15 to 45 minutes allows you to drive another 30 to 60 minutes. History: Transfer case had been rebuilt in 2001 (120K miles on Jeep). CV half shafts and drivers side hub bearings replaced in spring of 2003 (140K miles on Jeep). First noticed problem starting in Fall of 2003. Most of the time didn't have to drive far, so didn't do any work on it. In summer of 2004, problem continuing, changed fluid in transfer case. Changed fluid and filter in transmission. Didn't see any metal shavings. Levels were fine in differentials, but I don't remember if I changed the fluids out. Several months later (Thanksgiving 2004), with 167K on Jeep now, was on a 4 hr trip. Had to pull over after an hour, but after letting it cool on a cold night, for an hour, had same problem after only 5-10 minutes of driving. Problem then rapidly got worse. Pulled over, smelled burnt oil, had smoke coming off of rear differential. Replaced entire rear end (differential, axles, hubs) with a used one that had 68K miles. Problem remained, but was a lot better. However, it is becoming just as bad again after only putting on 500 - 800 miles after replacing the rear end. Replaced fluids in rear and front differentials with synthetic, adding the additive to the rear for the TracLok. No help. Was going to check to make sure the coolent lines to the transmission weren't blocked next. Then was thinking about the front bearings or front differential. Any ideas on a root cause here? The Jeep is still in great shape other than a brake problem I'm having after the rear end was replaced. That is in a different post.

[fredjacksonsan]

Have you ever checked your universal joints?

[FhPt]

A mechanich at the Jeep dealership checked out the U-joints. He said they were okay. Those probably wouldn't be that expensive to change out though, just to see.

[JDPascal]

What transfer case do you have --- what is the 4wd lever label have for positions??

JD

[FhPt]

It is the 249 transfer case.
The shift lever has 4 wheel all time, Nuetral, and 4 Lo.

[JDPascal]

Could the the viscous coupler.


Check your tires. should all be the same make, same model, same size, same tread depth and same inflation pressure.

When the jeep is cooled off and not doing the vibrations, do figure 8's in a parking lot somewhere and see if that gets it to the problem stage like highway driving does.

Try using synthetic ATF in your transfer case. That will usually make the TC run cooler and reduce problems a bit.

JD

[FhPt]

Cool. Thanks. I'll try the tight figure 8's this weekend and report back.

[FhPt]

Tires are all the same type and size. Inflation pressures were all good (33 PSI cold). Did the tight figure 8s. Get what I thought was the ABS kicking on. Get the humming noise, then when you put your foot on the brake you feel the pulsation. I think this is an ABS issue and not the viscous coupler, but maybe I didn't do enough figure 8s. I did 4-5 figure 8s. I'm not sure what the noise/feel is if the viscous coupler is bad. What happens when you have a bad viscous coupler.

Noticed my vent tube is broken off the side of the transfer case. Does anyone know if those are just press fit in? I'd like to replace it. Probably happened when the transfer case was rebuilt.

My exaust pipe after the muffler is crushed in a little, makeing more a half circle, at the bend just before running out the back. This must have happened when we got clipped on the back passenger side about 3 or 4 years ago. If there were any restriction issues, they wouldn't take an hour of driving to present themsleves though, right?