Getting a strange bump on the road

[chesehd]

So this past weekend I've been rolling with the wifey and kids, picking up some pallets in the back of the 'stro. We're almost home, rolling along at about 55 on a back road when if feels like we hit a dip in the road. Neat thing about it was that there was no dip in the road.

I slowed down and tried to listen for a new grind, whine or shriek but I wasn't making any new noises and neither was the van. Picked the speed back up to 55 and the mystery bump returned.

I babied it the last 5 miles home and all was well, so far.

Tonight, I got the van on the ramps and crawled underneath. The U-joints are looking ok...nothing worn in an uneven fashion, no play in the shaft. I turned my head to look at the pumpkin as I was down there and saw that the bottom 1.5-2" of the diff looked disturbingly wet. No rain in days around here and the rest of the van was dry.

I popped the plug out and stuck my pinky down there...no oil. So now I'm feeling a bit queasy.

I won't be able to pull the cover off the diff this weekend but when I do...what should I be looking for? The last time I experienced this mysterious bump in the rear-end (no jokes here, please) the spider gear decided to grenade on me. Scared the you-know-what right out of me while rolling in town. I'm praying that the box isn't ruined but fear the worst.

Ok...rant over. What should I be looking for? I've replaced an upper intake manifold gasket, axle bearing gasket and other miscellaneous odds and ends but not really ever dug into the pumpkin before. I'm capable...just not experienced.

Thanks in advance,

[MountainManJoe]

A missing gear tooth?

When you feel the dip, does the van actually move vertically, or does it stumble/buck? Could it could be misfiring?

[LiftedAWDAstro]

Until you pull the cover and check for chunks, not much you can do. If you find chunks, see where they came from. If it's the spiders, you can replace them pretty easily. If it's the ring or pinion, you got a little more work ahead.

Since your van is AWD, check the front diff too for fluid level.

[astroturf]

A great writeup with pix, can be found here.

http://www.astrosafari.com/viewtopic.ph ... a9cc781391

Hope it helps, Jim

[chesehd]

Ok, so I pulled the cover off the pumpkin this evening.

I'm guessing that it was only about 1/2 full of oil, but not exactly sure.

I didn't see any metal fragments in the bottom. Sorry, no pics but my phone is my camera and the fancy screen doesn't like that oil on there.

I caught the oil and checked, no fragments in there either. There wasn't even any significant chunks of anything on the magnet, either.

So now I can't see anything directly wrong but I have a gut feeling that is where the problem lies. Am I going to have to put the rear on stands and pull the diff out? It's on a set of ramps now.

Ken

[LiftedAWDAstro]

Jack it up so the wheels are off the ground. Make sure you place jack stands underneath. Now you want to place the trans in N and spin the driveshaft over. You want to see all the spider gears and the full rotation of the pinion and ring gear. If you don't see any missing pieces, your problem lies elsewhere. Replace the pinion seal, torque the pinion nut down to the preload it has before removing and then put the cover on with RTV and fill it up with oil. Before you reinstall the driveshaft, remove it completely and check the u-joints for play, noise and roughness.

[1Gary]

I want to add to Dean post you want to be sure you can get the filler plug out before you take it apart.With the rust factor,they can be a real issue.

If you choose,it doesn't hurt to put back on a rear cover with a rear cover filler plug.