basic front diff (pinion bearing) question

[bitofaclue]

I'm getting some noise from the front diff on the 97 Grand Cherokee (ZJ) that I've just done the motor swap and electrical repairs in.  It's been suggested that it's a bad pinion bearing.  I've never worked on one of these things before; been reading the manuals but don't yet have a clear picture of how it's built.

Where is the bearing - on the inside or outside?  That is, do I just have to pull the CV cup and the bearing seal from behind to get at the bearing, or do the guts have to come out so I can pull the pinion out the front to get at the bearing?  And if the shaft is scored, has anyone used a repair bearing (sleeve and bearing) kit?

Judging from the assortment of RTV colors I found when I pulled off the cover, it's been off a few times before.  Does that suggest I'll be replacing the collapsible spacer as well?

Thanks much.

Jonathan

[BlackYJ]

Did you check the oil level before you took the cover off?  It could have been just low on oil

[bitofaclue]

Yeah, it was right up to the plug.

[Bnine]

Check for pinion play. Any up down, or in out is a sign the bearings are worn.

Is the pinion seal leaking? Another potential sign of worn bearings.

[bitofaclue]

No leakage I can see, and the level's never dropped on me, so I don't think that's a problem.

What's the best way to check for play?  Is it enough to try to jiggle the CV cup?  Should I unbolt the CV from it first?

[Bnine]

just grab the pinion yoke and test for movement. You can leave the driveshaft.

[vantagetes]

To elaborate on what Bill is saying just lay on your back underneath and grab the drive shaft close to the front u-joint. If you can push it up then pull it down and see movement  your pinion bearing is hooped. It will be obvious.

[bitofaclue]

(Months later...)

So with all that was going on earlier in the summer (motor swap and much related and unrelated debugging) I didn't do anything with the front diff (this is my '97 Grand Cherokee) before we hit the highway.  Middle of Saskatchewan:  Blew the front driveshaft CV.  Pulled the shaft out and continued to Ontario in 2WD.  Got a new shaft at a wrecker in Niagara, bolted it in, and made the drive back to Montana.  All well so far.  Then suddenly, after we settled into the campground on Flathead Lake, the bad thing started.

After I hit about 80 km/hr and tried to accelerate, I'd get a really violent THUNK every few seconds - one that really jarred the vehicle.  Once over 80, the harder I stepped on the gas the higher the frequency of the bad thing.  Certainly felt like it was from the front end of the drivetrain, so I pulled the new driveshaft out and we came back to Calgary without further incident.

So now I think the front diff is packing it in on me.  I haven't gotten underneath to inspect yet, but is this how a failing diff behaves?  Has the pinion bearing finally given out and and is now causing misalignment of the pinion and a jamming of teeth?  Or does it sound like something else?

[binare]

Months previously you experienced a failing diff, months later your experiencing a failed diff. World works in mysterious ways

[bitofaclue]

Yeah, okay.  But I'm looking for a little more understanding here.  I've never had a diff fail on me, so I'm looking to learn about it.  If all I was getting earlier in the summer was a little bearing whine and now there's something more serious happening, can you explain the failure mechanism, please?

[JackstandJohnny]

drive it until it spits out a part number. 

or pull it apart and find whats broken.  maybe its an axleshaft CV, maybe your diffs full of ring gear teeth now.

maybe your used driveshaft crapped the bed.

my guess is whatever was whining stopped; now somethings done broke. go find it.

[Knox]

Months previously you experienced a failing diff, months later your experiencing a failed diff. World works in mysterious ways

pft spoiler alert