How Much Grease in Steering Knuckle (1 Viewer)

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Rookie2 said:
I figure that after they were overfilled, there was no room for the grease to breathe. So now you go driving. Through your test, we already know that the inside of the birf is somewhat of a mixing bowl. Once the grease heats up, it's going to expand some. Combine that with flapper on the diff vent, and it's just a bad formula. I think these things created enough preassure/vacuum to push grease past and compromise the axle seal.

So anyways, about a month or so after I filled the knuckles, it looked like a cow had taken a shat on my axle balls.

:beer:
Rookie2
Click to expand...

I don't think there is any way for grease to "expand" that much that it would exert serious pressure on anything in there unless the grease was seriously compacted in in the first place... When solids or liquids expand due to high temp thermal effects, we are talking about %s of volume, not huge amounts. It's not like liquid water and ice....
 
e9999 said:
I don't think there is any way for grease to "expand" that much that it would exert serious pressure on anything in there unless the grease was seriously compacted in in the first place... When solids or liquids expand due to high temp thermal effects, we are talking about %s of volume, not huge amounts. It's not like liquid water and ice....
Click to expand...

First off, I don't think it takes serious pressure to push grease past the axle seal. Have you seen the axial seal and felt how the axle shaft runs through it?

Many folks thought I was smoking crack when I explained why I felt that grease circulated inside of the birf too. How about this: You fill your birf up, minus the small percent of thermal expansion as you say, and we'll see if my experience was just coincidence.
 
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Rookie2,

I agree overfilling can get grease past the seals, it's just that I and others can't see any damage to the seals occurring from thermal expansion. It would just weep past the seals onto the outer balls faster for a short period of time. That's it.

So, I wonder if you felt the grease coming out indicated a failure, when in reality it was just the seal doing its job. It's supposed to continuously weep grease. Some incorrectly feel they have a problem when there's grease on the ball, but I'm here to tell you (and others) that you have a problem if you DON'T have grease coming out the seals onto the balls.

I really think whatever failed early (sounds like the axle seal, actually) was due to an install problem. On the axle seal, it's very easy to tear up the axle seal on inserting the shaft.

DougM
 
IdahoDoug said:
I really think whatever failed early (sounds like the axle seal, actually) was due to an install problem. On the axle seal, it's very easy to tear up the axle seal on inserting the shaft.

DougM
Click to expand...

Doug,

Please don't take this as getting smart with you, but we're either having a communication problem here or you are not correctly reading my post. What I'm talking about and have been saying in all the posts above is an "axle seal" failure (and by failure I mean the allowances of diff fluid and knuckle grease to mix). I'm not talking about felt seals here. And I completely understand that a small amount of grease is "supposed" to weep by the felt seals. In about a months time, BOTH of my balls went from a thin film to completely covered in what could best be decribed as diarrhea. Have you ever had a serious case of mud-butt? This wasn't a thin film... I'm talking mud-butt!

The thermal expansion, I agree is small. But as I mentioned above, this was only one of three factors that I felt were contributors. I'm not sure why you and Eric are hung up on the thermal expansion thing.

:beer:
Rookie2
 
Rookie2 said:
Doug,

Please don't take this as getting smart with you, but we're either having a communication problem here or you are not correctly reading my post. What I'm talking about and have been saying in all the posts above is an "axle seal" failure (and by failure I mean the allowances of diff fluid and knuckle grease to mix). I'm not talking about felt seals here. And I completely understand that a small amount of grease is "supposed" to weep by the felt seals. In about a months time, BOTH of my balls went from a thin film to completely covered in what could best be decribed as diarrhea. Have you ever had a serious case of mud-butt? This wasn't a thin film... I'm talking mud-butt!

The thermal expansion, I agree is small. But as I mentioned above, this was only one of three factors that I felt were contributors. I'm not sure why you and Eric are hung up on the thermal expansion thing.

:beer:
Rookie2
Click to expand...


Hi Rook:
You are the one who brought up the thermal expansion issue in post 19 I believe. You mentioned the breathers too but not obvious to me what that has to do with an overfilled knuckle causing seal failure. I was merely asking what it is that you thought could possibly cause the seal to fail because of a filled knuckle. (Note that I mentioned that I would leave some space. It would not be easy/possible to *really* fill it up all the way, in any case, I think.)
 
e9999 said:
Hi Rook:
You are the one who brought up the thermal expansion issue in post 19 I believe.
Click to expand...

Yes. You're correct about that. But this wasn't the entire basis of the reason I felt the axle seals had failed (or maybe more correctly.., allowed cross contamination). I think it could have been a combination of any or all of three things: 1) the pressure exerted from churning inside the knuckle (kind of like a blender) 2) some thermal expansion when the grease heats up and 3) having a flapper on the diff breather. The first two wouldn't be an issue (IMO) if I hadn't overfilled the knuckle.

e9999 said:
You mentioned the breathers too but not obvious to me what that has to do with an overfilled knuckle causing seal failure.
Click to expand...

The main reason that folks are doing the breather flapper mod is due to the suggestion that the presence of the flapper allows a vacuum to develop inside the axle, pulling grease from the knuckle, past the axle seal and mixing with the diff fluid.

Sorry to beat this to death, but it's just my opinion overfilling the knuckle caused my axle seal to be compromised. I'm not going to do that no more.

:beer:
Rookie2
 
well, let's just say that we should count our blessings that we can spend our time discussing these little things while some of our non-cruiser friends commiserate about losing a trans every 50K....! :)
 
Rookie2 said:
Sorry to beat this to death, but it's just my opinion overfilling the knuckle caused my axle seal to be compromised. I'm not going to do that no more.Rookie2
Click to expand...

Here is what I think, based on what I have seen owning six of these:

1. If you overfill the steering knuckle cavity, the remaining AIR can expand when it gets hot and push moly past an otherwise properly working inner axle seal. This will continue until the pressure equalizes.

2. The rubber seal and felt wiper are designed to work together to keep grease off the back of the ball, period. The seal keeps grease in, the wiper keeps dust out. There should not be enough grease remaining after turning to even collect dust, though I recognize that some do. Anything more than that is abnormal IMO. Grease getting past the rear seal is a factor of saturation over time more than thermal expansion.

3. A stuck flapper can create a vacuum inside the axle housing that will eventually cause grease to be sucked past the inner axle seal and into the diff. I have heard air rush in on mine several times when opening the fill plug.

4. Under normal operation, the axle will eventually wear on the axle seal enough that it will leak moly into the diff lube.

4. Moly in the diff lube means that at least one of these are happening or have happened.

That's my opinion and I am sticking to it.
 
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So what fitting is used to squirt the molly into the knuckle? Is the hole big enough to put a normal grease fitting all the way inside?
 
Hop under your wagon and have a look , If you are not sure what you are looking at I suggest you get an en expert to rebuild your front end while you watch and learn.
 
tech_dog said:
So what fitting is used to squirt the molly into the knuckle? Is the hole big enough to put a normal grease fitting all the way inside?
Click to expand...

I use a rubber flex hose on my grease gun, and the tip just fits in the knuckle hole, very tight.
 
I'm a fan of more grease in the knuckle. IMHO the more grease you get in there the less water can get in there when playing hardcore. I don't pack it full to the brim, I leave an air space. I think it's the air expanding as opposed to the grease expanding, therefore less air = less pressure build up.
I've seen many failures caused by water contamination, lack of grease, seal failure, incorrect grease and oil contamination. Never seen a failure directly caused by over filling of grease.
Pack as much in as is easy to get in, leave a small airspace and extend your breathers. Make sure the breathers actually breathe clearly.
Just my 2c, it works for me, has done for last 15 years working as a 4wd mechanic.
:cheers:
 
Rookie, Maybe I'm missing something but you stated that you had a pile of grease on the axle ball housing. That would lead me to believe you had bad felt and rubber seals not an inner axle grease seal. In the service manual it states that you should "top off" the housing each service interval. To me this means fill er up. I do every time I check the level. I use a straightened coat hainger and push it all the way to the bottom of the nuckle.
 
Great thread. Full birfs = happy birfs. Wet film on spheres where felt seals wipe = happy birfs. Dripping from same area = unhappy inner axle seal letting thin gear oil into birf and it then drips out felt seal designed to hold thick grease, not thin oil. IMHO it is impossible to do any damage whatsoever by overfilling the birfs. Thermal expansion, if it became an issue (somehow filled it to within a few percent of full - leaving air volume of about an acorn), would simply force grease past the felt seal faster and possibly some past a weak inner axle seal.

Elevated front axle vents w/ flapper removed = happy front diff for longer time as it will dramatically reduce grease/oil mixing via inner axle seal.

DougM
 
I'm with Doug-I love threads like this. All of us have an opinion and none of us have data. I'm in the (nearly) full cavity camp as well. Someone once posted this: Where grease is, water is not. Amen.

Mine get opened and regreased at less than 60k intervals, but even so, I squirt grease in the filler plug several times per year. Before squirting in the grease, I use a zip tie as a dip-stick and check the grease level and condition with that. If it looks anything less than pristine, I do a full clean and repack, but normally I squirt in 40 pumps per side with my grease gun. There is no way to over pressurize the cavity. It's open to the air.

Here is a bit of data you can interpret as you wish...I used to use Valvoline Moly grease in the knuckles of my FJ60 and it's black. I added about 50 pumps of Amsoil Moly grease which is purple before Surf and Turf 2004. I did a knuckle rebuild after Surf and Turf 2004. The purple grease had definitely mixed into the birfield cup. This was an unexpected but happy finding. I personally think Toyota's engineers knew what they were talking about when they made the reccomendation for regular lubrication through the fill plug.

So my take on this is that adding grease through the plug can help. It is not as good as a real birf repack, but it is better than nothing. It also lubes the knuckle seal as well. Remember to replace the inner seals at reasonable intervals, or if there is any hint the seal has gone bad-like grease/oil mix on the dipstick test, or goopy knuckles in the axle ball area. Do those things and your front axle will have a long and trouble free life.
 
Filling the cavity does not pack the joint directly BUT what it does do is keeps the grease in the joint because it has no where to escape to if the knuckle cavity is full. If the cavity is low the jont has a place to spin the grease out to.
 
If overfilling the knuckle results in grease moving into the diff there is a detrimental result, and that is that grease mixed in the diff gear oil can result in excessive foaming of the gear oil. Foaming gear oil does not lubricate as well. This is another reason to extend diff breathers and remove the rubber flapper that can cause grease to be pushed past the axle seals.
 
at 219 thousand miles, I have never done a repack of the swivel pin (birfield or call it what you like) or its parts, but now and then, I remember to pump it full of about 15 to 20 pumps of grease from a regular old grease gun, its like mayonnaise on a ham sandwich, add enough for easy chewing and whatever else squeezes out, it will just fall to the ground.
 
well, I guess I'm also one of those who doesn't think that filling the knuckle would hurt anything much. Can't see what deleterious effect that would have... Worse might be that a bit of grease goes into the diff oil... I can live with that. So, next time, I'm just filling them up. Tired of trying to guess how much to put in. Btw, FWIW, I found that I can't trust a visual inspection into the little fill hole. Seems like there is much more than there really is as seen when you measure with a stick.
 
Roller bearings should be packed 1/4 to 1/3 full, more than that can cause overheating and failure of the seals. Roller bearings have a lot of fast-moving parts that can really agitate the grease and heat things up. Birfs are relatively motionless at high speeds, just rotating without much relative movement between parts. They do most of their internal moving at fairly low speeds, not much agitation or heat generated. They seem to be built to lose slight amounts of grease to the felt wiper to keep the ball clean, kind of like your eyelids on your eyeball. I don't think any pressure can build up with the felt seal, so I'm sure it's the vacuum in the axle that sucks in grease, never pressure within the birf. I vote pack 'em full.
 
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