About 2 weeks ago I noticed a rumbling under the truck. Seemed to start after getting stuck in a particularly deep, wet hole that I couldn't climb out of.

The rumbling (sort of sounds like nobby tires) sound can be heard when accelerating but as soon as the foot comes off the gas the noise goes away. Touch gas there it is......

I've been working on tracking the noise down and have narrowed it down to the rear pinion bearing. Have been searching the site but can only find info on replacing pinion seal. The FSM does not explain the process very.

What needs to happen? Does the whole diff need to come apart to replace the bearing?

Any insights would be greatly appreciated. <img src="/forums/images/graemlins/cheers.gif" alt="" />

~ Jon

If I'm understanding your descriptions correctly, yes the whole diff gets disassembled. The pinion bearing is pressed off/on and then all the clearances get re set. Aka it's a rebuild of the diff. Plus if any respectable driveline shop was to take on a bad pinion bearing, they would require all bearings to be changed as no tolerance specs exist for mixed/matched new and used parts. Again, aka full rebuild, if you are really sure it's the pinion bearing.

Get a used one ...

And your u joints are good?When you put it in gear does it clunk at all, or with foot on the brake, in gear and tap the gas does it klunk ?Are the u joints serviceable? If so pump em full of grease and see if the noise changes at all. If not Id probably replace them first since you'll probably want to do that if you rebuild the rear-end anyway. Or could you have bent the drive-shaft in the deep hole or knocked a weight off and now its out of balance? Good luck. MM

I'd agree that your problem is far more likely to be your rear u-joint than the pinion bearing. Disconnect the driveshaft and feel for any roughness or resistance when moving the u-joints through their range of motion. Any slop or anything other than nice smooth movement means it's time for new u-joints.

Have not noticed a klunking but yet just the rumble. I'm suspicious of the pinion because the one in the rig has more play than my spare.

Did disconnected the driveshaft, the u-joints feel solid. I have a good spare laying around will swap and take for a test drive this afternoon. That's away easier fix!!

If noise does not change will swap rear ends and look at rebuilding later.

Will keep you posted.

Thanks,
~ Jon

lock the rear wheels with the ebrake and see if there's ANY slop in the rear ujoint needle bearings in the cross. Wiggle the pinion shft up/down/sideways and see if there's play in the bearing.

Total gear backlash at the pinion flange should be under 1/4", i.e., you can turn the dust cover over the bearing that much.

Setting pinion height is the most critical and difficult task on a diff. I would not try it without the special mitsu tools or a fully equipped driveline shop. And I've never seen one go bad on a lubed diff in a Monty/Raider.

Well swapped the driveshaft and replaced the fluid in the transfer case without luck.

Eventually just jacked up the back of the truck and put my wife in it.

With her revving the engine, I listened to the transfer case. There was a little noise but not what I was hearing when driving. Then I walked around to the back of the truck and the rear diff was popping and pinging.

Not positive what is going on in the rear diff but it is the issue. Swapped out the diff last night and today with my spare, have a little clean up tomorrow to wrap up the process.

When I have a chance will crack open the old rear diff to see what the issue is.

Thanks for all the help guys <img src="/forums/images/graemlins/cheers.gif" alt="" />

~ Jon

I'm curious what you find, as I've rarely heard of montero diffs dying.

Me too. I am petrified of something happening to mine, being as SR axles aren't to common <img src="/forums/images/graemlins/rolleyes.gif" alt="" /> in the local junkyards. I check the fluid everytime I go and play in the mud and/or water.