How Often do Diff Bearings fail?

[RWBeringer4x4]

Hey all,

I'm getting ready to order parts to do a complete knuckle overhaul/FJ60 knuckle swap on my 1975 FJ40. The truck also has a leak from the differential seal, so I was planning on replacing the diff seal, cover seal, and Pinion seal at the same time.

In speaking with Bryce over at Cruiser Outfitters last week, he suggested looking at a diff overhaul kit, including carrier bearings, etc. since the axle will be out of the truck anyway. So my question is this:

How often do these bearings fail? How often should differentials be overhauled, in general? Currently, there's no grinding or whining from the differentials that I am aware of, and they seem to function properly. There's just the one slow leak I'm hoping to patch up while the axle is out. In order to patch it, I'll need to pull the diff - so I can see Bryce's logic! That said, I'm a total rookie when it comes to things like this, and differentials are pretty intimidating. If there is a good chance I can get away with leaving the differentials intact, I will most likely do that.

Thoughts? Opinions? Thanks!

Rick

 

[Chamba]

I would not worry a bit about the front unless it's making noise. Your rig is from Cali originally, so as long as it's got lockout hubs I'd be amazed if you've got more than a few thousand miles cumulative on that diff.

 

[RWBeringer4x4]

I would not worry a bit about the front unless it's making noise. Your rig is from Cali originally, so as long as it's got lockout hubs I'd be amazed if you've got more than a few thousand miles cumulative on that diff.

Very possibly true - but I worry about lack of use, as much as I worry about overuse/abuse. If the gears in that diff haven't spun too often, in the last several decades, I worry that the parts that were "out of the oil" will be in rough shape. I've only had it in 4WD for about 3 minutes after I replaced the T-case to ensure the case shifted properly. No noises noted then, but I guess this is a case of "I won't know until I'm in there..."

 

[reddingcruiser]

I would not worry a bit about the front unless it's making noise. Your rig is from Cali originally, so as long as it's got lockout hubs I'd be amazed if you've got more than a few thousand miles cumulative on that diff.

Yeah, what he said. If you're trying to stop leaks just replace the gaskets and seals. If you take it out you can check the general condition, see what's stuck to the drain plug magnet, see what's in the bottom of the housing. If nothing or just fine particles, then check the backlash, reset if necessary and put it back in.

 

[John Smith]

Rick, Grab the driveshaft and pull it side to side and up and down at the pinion. If it doesn't move, the pinion bearing is probably fine. If you have slop, the bearing is done, and that is why your pinion seal is leaking. Under normal use and maintenance, pinion bearings can last a very long time. My 84 Suburban, which spent most of its life towing, just had a rear pinion bearing go bad at 187K miles.

 

[RWBeringer4x4]

Rick, Grab the driveshaft and pull it side to side and up and down at the pinion. If it doesn't move, the pinion bearing is probably fine. If you have slop, the bearing is done, and that is why your pinion seal is leaking. Under normal use and maintenance, pinion bearings can last a very long time. My 84 Suburban, which spent most of its life towing, just had a rear pinion bearing go bad at 187K miles.

Thanks John,

It's not leaking from the Pinion, it's actually leaking from where the differential bolts to the housing...which I believe is a paper seal. There's no play in the front pinion. A little bit in the rear...but it's also not leaking

 

[reddingcruiser]

Rick,
Good point, be sure to go back with a replacement paper gasket, not the cork one used for the rear diff cover.

 

[RWBeringer4x4]

In order to check backlash, I'll need a dial indicator, correct? Any recommendations on a brand? This is one of those tools I'll probably use twice, so I imagine "cheap, but effective" is the name of the game here...

 

[reddingcruiser]

I bought mine off craigslist, it's a nice used Starrett, but I bought the magnetic base from Harbor Frieght and it works great. I think the HF dial indicator is fine for what you are doing for $14.

 

[shelfboy1]

i drove my 70 soa for 35 years about 79 or so i put 78 axles in it and plowed with it plus other stupid s*** until a year or so ago with no bearing failure ever.the frame broke in half but the bearings never failed .keeping the pinion nut tight is a key to not having problems i did mine every year or so .

 

[RWBeringer4x4]

Sounds to me like I'll be safe just resealing the differential, checking lash, and making sure the pinion nut is on tight!

Shelfboy - do you mean you tighten it every year? Or do you physically replace it every year? Isn't it torqued and staked? I'd imagine it probably isn't going anywhere...

Has anyone used the Marlin pinion seal, or does everyone go OEM?

 

[Fast Eddy]

If you're going to remove and reseal the diff, you can take a look and see just how brand new it is inside. Unless it was run without oil, I'm guessing it's like new inside.

 

[shelfboy1]

they are staked but the bearings wear a bit and the nuts loosen up ,i checked them because we have state inspection every year and im under thier anyhow .over the years i have had quite a few loose ones on mine and others .i dont mean falling apart loose usually 2 turns or less even staked my electric impact will remove them with the stake intact .my 69fst that i drove back from cali in the late 70,s still has its original pinion bearings, gear lube level is also important that small amount of being loose has also been the cause of some vibrations but thats just my experiance not gospel.good luck

 

[RWBeringer4x4]

Awesome, thank you guys for the responses -

Are there any opinions on the Marlin Pinion Seals vs. OEM seals?

 

[climber8483]

When I was buying my rebuild kits a couple of months ago a very qualified Mud mechanic told me it was highly recommended.

HTH,
B

 

[RWBeringer4x4]

When I was buying my rebuild kits a couple of months ago a very qualified Mud mechanic told me it was highly recommended.

HTH,
B

Hey climber - by "it" do you mean the marlin seal, or the OEM seal?

 

[Tools R Us]

If you're going to remove and reseal the diff, you can take a look and see just how brand new it is inside. Unless it was run without oil, I'm guessing it's like new inside.

Yep, most all of the fronts that we have had apart are very nice, often they haven't been run much. When we get the chance, stitch front and rear diffs, stock type seals work fine.

 

[RWBeringer4x4]

Yep, most all of the fronts that we have had apart are very nice, often they haven't been run much. When we get the chance, stitch front and rear diffs, stock type seals work fine.

What is involved in switching the front and rear diffs? Is it basically just a straight "unplug from front, plug into rear," or is it more complicated?

Alternatively, if I wind up with a spare diff from the FJ62 axle (front diff) will that work in the rear of the 40? I believe they are both 4.11's

 

[Chamba]

What is involved in switching the front and rear diffs? Is it basically just a straight "unplug from front, plug into rear," or is it more complicated?

Alternatively, if I wind up with a spare diff from the FJ62 axle (front diff) will that work in the rear of the 40? I believe they are both 4.11's

Yes and yes, depending on your spline count. If your '75 has original front axle than your spline count will be different from the fj62 I believe. Eddy? Living in the Past?

However, easy peasy to swap front to rear; hard part is removing the front and you're doing that anyway.

 

[RWBeringer4x4]

Yes and yes, depending on your spline count. If your '75 has original front axle than your spline count will be different from the fj62 I believe. Eddy? Living in the Past?

However, easy peasy to swap front to rear; hard part is removing the front and you're doing that anyway.

It currently has the stock front axle - but it is going to 60 outers with the knuckle swap. Did the inner axles have a different spline count as well?

Just found out today that the front end doesn't have a diff cover...so I'm not sure how to disconnect the axles from the dif - further research necessary!