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Extra quart of oil in the Rear HP D44

J

jammerjamesharmon

NAXJA Forum User
Location
austin
After a pinion bearing went out, after a 100k miles, I decided to give her some more oil. The high pinion D44 can't oil the pinion bearing as well as a normal D44, and mine is even a little tilted up toward the transfer case, which cannot help either. I know I don't have an oiling problem, because it went 100k, this just makes me feel better. I just added another fill hole higher up, this allows for an extra quart of oil.

DiffCover01.jpg


james
www.geocities.com/jammerjamesharmon
 
BrettM said:
i forget the exact explanation, but I've heard that overfilling can actually prevent the pinion bearing from getting the oil it needs...

I would consider 100k miles excellent and leave it as is, but let us know how this one goes.
Click to expand...


I sure would like to hear that explanation...........
 
BrettM said:
fiiiiine.... search in progress, i think it had something to do with foaming
Click to expand...
Yeah, from what I recall the explanation was that the oil ends up being beaten into the foam which being a mixture of plenty air and little oil stops doing it's job.
 
What would cause such foaming? I can't think of any reason that a higher oil level would cause a problem that doesn't exist with a quart less oil. Woudn't oil slung off the gear teeth cut through the foam and reach the pinion bearings anyway? Or if the level is high enough wouldn't the pinion bearings be submerged, protected from any potential foaming? No experience, just thinking aloud.
 
Lucas said:
What would cause such foaming? I can't think of any reason that a higher oil level would cause a problem that doesn't exist with a quart less oil. Woudn't oil slung off the gear teeth cut through the foam and reach the pinion bearings anyway? Or if the level is high enough wouldn't the pinion bearings be submerged, protected from any potential foaming? No experience, just thinking aloud.
Click to expand...

I think the highfalutin name of this 'foaming' condition is called cavitation. whats BAD is that this foam has a crapload of air in the bubbles (like most ordinary foams have.) and -I think- that entrapped air displaces or inhibits what might normally be a steady flow of slung oil. (A 44 being an axle that gets it's pinion bearing lube from oil slung upon it by a slinger not oil slung off the gear teeth...)
 
A d44 low pinion cover is the same as a HP cover. This makes your oil level low on an HP, because your cover is upside down. Check it out if you don't believe me.
 
woody said:
I think the highfalutin name of this 'foaming' condition is called cavitation. whats BAD is that this foam has a crapload of air in the bubbles (like most ordinary foams have.) and -I think- that entrapped air displaces or inhibits what might normally be a steady flow of slung oil. (A 44 being an axle that gets it's pinion bearing lube from oil slung upon it by a slinger not oil slung off the gear teeth...)
Click to expand...

I know the pinion is fed by a slinger, but since the ring gear is throwing oil towards the pinion anyway (at least in the rear) I thought that a lot of oil would reach the pinion that way. Plus, I have seen more than one pinion intalled without the slinger and shims to make up for the lost depth. What actually causes the foaming/cavitation. If a ring gear chopping out of then into a pool of oil doesn't do it in a normal diff, I don't see how a pinion gear could whip the oil into foam in an overfilled one.
 
Gotta Way in.
LP/HP doesn't matter. Overfilling the differental will cause foaming. Fill'er up, drive it 20 miles, heat it up good, go home, drop the cover. It WILL be 20% foam.
100,000 Miles is good for any bearing, especially a rotated pinion.
MHO
 
When at speed, the normal oil capacity is being circulated and the amount sitting in the bottom is actually quite small. Overfilling will cause foaming. The gear picks up oil of the bottm of the hsg. and throws it either forward into the pinion reservoir(rr. axle) or back toward the pinion where the slinger and/or pinion gear pick it up and throw it up to the top of the hsg. where it then runs down the hsg. into the pinion area. Normally, HP axles do have a higher fill level. But the poor oiling in rr. applications is more due to the oil flow than the level. Frt. apps usually have a little wing sticking out of the oil passage(oriented frt. to back) that picks up the oil slung off the pinion. The wing helps collect the oil which then can run down hill toward the pinion brgs.
 
Lucas said:
I know the pinion is fed by a slinger, but since the ring gear is throwing oil towards the pinion anyway (at least in the rear) I thought that a lot of oil would reach the pinion that way. Plus, I have seen more than one pinion intalled without the slinger and shims to make up for the lost depth. What actually causes the foaming/cavitation. If a ring gear chopping out of then into a pool of oil doesn't do it in a normal diff, I don't see how a pinion gear could whip the oil into foam in an overfilled one.
Click to expand...

I think it's because a few things that may be working together:

The pinion is spinning 3.x-5.x faster than the ring gear & center section is, and they have different shapes. Besides the #1 job of putting torque to the axles, the contour of gears create secondary forces.

The ring/diff is producing a secondary force like a paddlewheel going through the oil (raising the oil level or pinion tilt angle = probably little effect on inner & axle bearing oiling, since they're always running in it...)

But the pinion bearings are fed oil up passages into the 'snout' using the slinger (or not) and I'll take a wild stab that the pinion -at it's higher speed and with it's "corkscrew" shape, acts like a boat propeller pulling RPMs partway up out of the water. In too deep oil it's creating a pocket of foamy oil that can starve the bearings?

I :dunno: I'm here to learn too. Hmmm, I have a few axles we could cook... and access to a pair of temp monitor/recorders. Send clear covers, gear oil, and video equipment to 28327.
 
After some search time I have found that you guys are right about the HP vs LP covers. I retract my flawed statement.

I don't remember where I got that info, but it has been round filed.
 
So what's worse? using a stock cover on a highly angled HP housing and potentially starving the pinion, or overfilling and foaming up the diff?
Or on the grand scale of things are they about the same?
 
That looks like a LP cover in the pic.

If this is a HP in the rear a 100K is an excellent life. HP in the front is kind of crappy unless you run it with the hubs locked all the time.
 
Lucas said:
So what's worse? using a stock cover on a highly angled HP housing and potentially starving the pinion, or overfilling and foaming up the diff?
Or on the grand scale of things are they about the same?
Click to expand...

Ummm neither. Use the HP cover and don't fill till it flows out, but add the right amount and then a little bit more to account for the angle change.
 
Use synthetic and add the extra quart. we had the same problem (looseing pinion bearings) in a 9' Ford in the dragster - probably because the acceleration moves the oil to the back of the case, uncovering the pinion bearing. i beleive synthetic is more resistant to foaming - and I know it has better "cling" providing lubricant even when uncovered.
 
Kejtar said:
Ummm neither. Use the HP cover and don't fill till it flows out, but add the right amount and then a little bit more to account for the angle change.
Click to expand...

This is what I do. Works quite well.
 
High Pinion rear?????? Didn't think there was any such animal.
 
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