Rear bearing noise? How long I got?

[amccanoe]

Hi all.

Have an 84 Eagle with a 3.08 rear end. Something like 130k miles. Spend most of its life in Fairbanks Alaska.

I have a "grinding" sound coming from the rear. Its not particularly loud but it is there. And it sounds just like I'd expect failing/worn out bearings to sound. I am working on figuring out if that is actually the case.

So...any WAG as to how long I've got before major failure? Would I get any warning....like sound getting louder and louder? Would that progression be slow or fast or ?

And lets say my maximum drives before the car sits for a long period of time are about 10 miles in length. Most of those drives being 35mph ish stop and go traffic. And the occasional 10 mile jaunt....only a handful of lights...45 to 55 mph ish. NO long trips or high speed trips.

Thanks!

[TheBirdman]

Id say id depends on if its a wheel bearing or a carrier or pinion bearing. Judging from the incredibly poor outer axle design on these amc 35 axles, its likely the wheelbearing. One thing you can do to check is take it out on the open road with no other cars around, get it up to a speed where you can hear the noise pretty well, then turn left and right sharply enough to throw the weight of the car around. If the noise changes when you do that, its likely a wheel bearing, as you just put either more or less weight on the bearing thats going out. If the noise doesnt change, it still could be a wheel bearing, but it could be a carrier or pinion bearing. Might also be worth popping the brake drums off to see if anything came loose in the brakes and is causing the grinding noise.

Like I said, its probably a wheel bearing, as the seals on these axles are inboard of the wheel bearings, so they dont get any lubrication from the gear oil, just from the grease they were packed with when they were installed. Its not a very complicated job to replace them, but depending on how rusty the axle is, it might take a monumental amount of torque on a puller to pop the hubs free. If it is wheel bearings, you can get a few short trips out of it, but I wouldnt take it on the highway, worst case if the bearing grenades you could lose the wheel going down the road.

PS, if you do end up replacing the wheel bearings, you can drill a hole through the axle shaft where the bearing sits and add a grease zerk so that you can add grease to the new bearings every few years.

[AMC of Houston]

And let's not forget the famous Eagle fractured right axle!!   Your's may already be fractured, but has not totally let go yet (still has some internal contact with the splines).

[amccanoe]

Thanks for the input folks!

I like the idea of adding the grease fitting!. Yeah....bearings that are running on grease packed in there 40 years ago...not the best thing in the world!

Another question. My manual calls for 85W-90 for the diff and I think 85W-140 or? 90W-140 if you are towing.

First...I went to 2 auto places and Walmart. Neither had 85W-90...they only had 80W-90. Is it safe to use the 80W-90? I live in northwest Florida. We get a handful of cold snaps per winter where it will drop a bit below freezing and be in the 40s during the day. And we get measurable amounts of snow about every 20 years...so that's the extent of concerns regarding "cold" weather.

Secondly is there any downside to using the heavier oil? Given that our problem around here is ungodly heat and the fact that eventually I intend to use this car for driving long distances on country roads and the interstate I am thinking the heavier differential oil would be a good thing.

Thanks again for the input!

PS. There is a lunar eclipse early Tuesday morning. Last one till 2025. If anyone needs any pointers for viewing or figuring out the timing of what happens when...let me know I'll be glad to help!

[TheBirdman]

yeah, with florida heat Id probably lean towards the 140

[amccanoe]

Is there any downside to using the -140 rather than the -90?

Perhaps a bit more friction/drag from the higher viscosity?

Oh....another basic question. Was looking at a local donor Eagle for sale locally. Trying to figure out the rear diff ratio. Jacked up one side. Notes not handy at the moment. Guy spun the wheel while I watched the axle underneath. We were getting about 1.2 turns of the wheel per one turn of the axle. So double that? (only one rear wheel spinning free)....and you get 2.4.....so its probably got a 2.35 rear end diff?

[TheBirdman]

Most likely its a 2.35, based on the fact that most eagles were 2.35. You should count yourself lucky to have a 3.08 one. If you wanted to know for sure, you can clean the gunk off of the rear axle on the passenger side of the diff cover. There will be a letter code. I dont remember off the top of my head what letters mean what ratios, but you can find it from some google searching.


PS, otherwise, there is also a steel tag attached to one of the diff cover bolts on the front axle that will say the ratio, but sometimes it gets lost or falls off over the years.