Incorrect Rear Wheel Bearing

[okayfine]

Byron, approximately what amountish of grease do you use to fill the cavity?

[HudsonMC]

Hi Hudson,

Sorry to hear you are in this predicament – what a PITA.

However, I can give you some advice while you have this apart. The bearings you buy will (likely) be sealed bearings – as in they have seals on both sides. You’ll notice the bearings you removes have no seals on the inner faces (which obviously face each other) in the area which has the sleeve. From the factory, this area was packed with wheel bearing grease.
I have done a number of wheel bearing exchanges over the years – but never twice on the same car. I have always emulated this factory procedure of not having the seals in place in the spacer area, and have always packed this area as the factory did.

Having said this, others have commented on this site over the years that they have left the seals in place and there for saw no need to pack this area with grease and have had no issues.

What I question is the longevity of the grease in a factory sealed bearing. There isn’t much in there. My thought have always been – well the first bearings lasted 45 years, why not emulate that installation as I’ll never be replacing them again in my lifetime!

Just FYI – hope it all works out for you, keep us posted.

Byron

I think we're in agreement here. The more grease, the better, as far as I'm concerned. In a location like this, this stuff is there to trap dirt and grime as much as it's there to lubricate. I wasn't aware, however, they were selling completely sealed bearings. The bearings I received are only sealed on one side, like the one in the picture above. Good to know, however. Thanks for all the help guys! Just a few more days to wait, not a big deal

[zKars]

Just can't resist carrying on the issue of how much grease and where to put it. That and I'm back to work today and not surprizingly, don't feel ONE DANG BIT like working, so you get to listen to my rambling.


Think about these few points for a minute and perhaps some clarity will result.

1. What parts rotate with respect to each other that touch and hence require a lubricate?

2. Does the grease that's in the bearing cavity move around during use? Put another way for you techni-phobes, what is the grease transport mechanism in that cavity?

3. Does the grease have any other purpose other than to lubricate those moving surfaces?

The only point of reference we have is something many of us have observed. When you take apart an untouched in 40 year bearing housing, you find grease throughout.


1. This one is easy. Only the bearing balls in their races move directly against each other.

2. Trickier. Very hard to test and see when in operation. Perhaps a single observation will shed light. If the grease moves or flows around due to heat induced viscosity reduction, centripital force or gravity, would the grease not eventually end up in the bottom of the bearing housing, defeating its purpose? You would be left with only what ever thin film "sticks" to the bearing balls and races. To rely on central rotating axle/spacer to "fling" grease back out to the bearings can't work, the flinging force is not in and out longitudinaly, toward the bearings, only radially to the housing walls.

3. The grease's primary purpose is of course to provide the lubricating film between the balls and the race. Trapping impurities is good too. Cooling? Nope. Would have to fill the cavity completely to have effect on carrying bearing heat to the housing. And besides, the bearings have no reason to run hot enough to need cooling if they are lubed properly. They are metal and are pressed in the housing, any heat they make leaves via the metal to metal contact at much faster rate than through the grease....

So, in my humble estimation, it seems that grease need only be in the immediate area of the balls and races. AND the grease has to have properties that ensure it stays around of its own free will, not relying on any transport mechanism. And if you read Wikipedia, http://en.wikipedia.org/wiki/Grease_(lubricant) you will discover this is exactly what greases are formulated to do. Stay put.

This does not in any way explain why Nissan put grease in the rest of the cavity. Or why we religiously pack the front bearing cap cover thing with grease to ensure the bearings never run dry. Seems like a waste of grease to me.

The only failure mode of the grease is contamination and then age breakdown. Keep your seals in shape and change that bearing grease every 40 years.

[datzenmike]

I doubt they get very hot. What's the melting point of that grease anyway... 350F or so? If the bearing gets that hot, (it must be close to dry) heat will melt the extra grease and it will flow in and lube the bearing and this should be self limiting. This is probably why a bearing can fail and get growly and run this way for a long time before changing it.

BTW once grease melts, also known as it's dropping point, it should be replaced as it doesn't gel properly after.

[HudsonMC]

2. Trickier. Very hard to test and see when in operation. Perhaps a single observation will shed light. If the grease moves or flows around due to heat induced viscosity reduction, centripital force or gravity, would the grease not eventually end up in the bottom of the bearing housing, defeating its purpose? You would be left with only what ever thin film "sticks" to the bearing balls and races. To rely on central rotating axle/spacer to "fling" grease back out to the bearings can't work, the flinging force is not in and out longitudinaly, toward the bearings, only radially to the housing walls.

The bearing is constantly spinning, and the extreme pressures at the interfaces between the balls and the race will carry grease up the race, as the viscosity of the grease here is much higher than when it's in the can (non-Newtonian fluid ) I'd venture you get pretty good transport...within the bearing at least. Even if the movement of the grease out of and into the bearing is small, it's better than nothing, which is what you get from a sealed bearing.

If any of the grease oxidizes or if the base oil volatizes, you've got that "sink" to spread the damage out or make up for the lost volume. Wheel bearing leakage is definitely an issue as well, there are ASTM tests for bearing lubricants for this parameter (D1263 and D4290). The effects of water in the relatively small volume of grease in a sealed bearing is also something I might think about...

I know it seems like overkill, but in this case, grease is cheap, and I'd rather be safe(r) than sorry. I'm sure the sealed bearing works great. Really, it's just different strokes for different folks, but I'm not sure any of us understand the movement of the grease inside the axle housing well enough to say one way or another, which is really what this all hinges on. Maybe we pick this back up in 10 years. Either bearing is sure to last at least that long, right?

[bertvorgon]

I put new rear bearings in my car over 37 years ago...27 years of hard racing, both solo, some track days, literally, sanctioned street races, those on 9.5" wide race tires, driving to and from the events, plus our years of some very serious Cannonball/Scenic tours and 500 miles days...still going strong..packed a ton of grease in the middle and called it done.

It's amazing really!

[Byron510]

Julian, to answer your question directly, I full that cavity absolutely full. As Hudson points out, grease is cheap, and my labour to do this job is not.

Jim, as always you share great insight with us, and I do admit you put very good points on the table. However, given the life that the bearing have already given me - I pack that space liberally just for good measure. However the measure I am mostly after is heat transfer. I am aware the grease does not flow....ever. If it got hot enough in a bearing space for grease to flow, my machining and metallurgy experience tells me it's already too late for the bearing anyways. The amount of heat at the ball and race surface would be so high that spalling would likely have occurred. At that point its all down hill as failure is imminent.

So, I pack liberally. If nothing else, I know that rust won't form in the space. The same goes for the front hubs

Byron

[510rob]

point of clarification - cartridge bearings are available with SHIELDS not 'seals'.

[Byron510]

Thank Rob - you are correct.

Julian - to better answer your question - the cavity is not 100% stuffed full of grease. Actually you'd be hard pressed to achieve this. But 90% give some room for expansion and to not blow the "shield out" should the whole works warm up some what. Then I'd say your good to go.


Byron

[zKars]

I love these discussions. Always such great insight from the variety of experience here. It is true that there are very few if any downsides to having too much grease in there. Just wanted to get everyone's grey matter generating some heat!

I can't believe I missed the RUST prevention use of the grease. You'd think this would be something we wouldn't miss! Makes me want to get the grease gun out and fill every cavity of the entire car!