overflowing diff fluid (1 Viewer)

[semlin]

Okay, I drained off the remaining excess diff fluid in my front diff this weekend . Another 250 ml or so came out so it was a total of 3/4 of a litre overfull. I also installed a diff breather extension on the front axle (thanks to Beowulf for the plans). There was no blockage at all in the old hose or the valve. On a sunnier day this time, the gear oil was slightly transparent and had a hint or tinge of green but no debris.

I didn’t change the diff oil because I couldn’t find SAE 90W anywhere in town. I notice at least one on the board running on the 80/90 that is recommended in the FSM below minus 18 degrees and good up to 10 degrees celsius. It is hotter than that here! 80/90 is readily available in synthetic or dino and is what the Toyota dealer told me they would use. The only other option I can find is SAE 90 marine gear oil (lower end) which is dino and a tad pricey but available and meets the API GL 5 standard.

So, I assume gears are gears and gear oil is gear oil but maybe someone can tell me whether I should use 80/90 or the marine stuff.

Also, I tried to check the transfer case – %$$&*@ grease monkeys have aired it up so tight I can’t get it to turn.

 

[cruiserdan]

80-90 in the diffs, 75-90 in the transfer...................

 

[BTLSHP]

I would appreciate some advise/input. FJZ80 with 234k of mostly (98%) highway miles. The 2% were some pretty rough dirt roads in West Virginia that kick up a ton of dust.

My dad is the owner and currently uses it to drive around a retirement community, but it gets regular outside exercise and the odd long trip by my daughter. She will take over the car in a year or two and bring it to Denver. She is a climber.

His old independent shop convinced him that Birfs were a lifetime thing. Until a comment by he current mechanic he would simply not entertain the idea of servicing them. We are going to address several issues before turning over he car.

2,500 miles ago, the front diff was topped up with what the mechanic said was less than 2 cups of diff fluid. The Birfs got 61 squirts of grease in each side at the same time. Three weeks ago it went on a 700-800 mile highway trip. During an inspection this week the mechanic observed two things:

- The front diff was overfilled by a quart but no signs of grease contamination.
- Each Birf took 21 squirts of grease to get to what he deems 2/3rds full.

There was no sign of grease in the Diff fluid.

My reading here suggests the vent filter/flap is likely caked with WV dirt, same as the EVAP filter on my car. This caused a vacuum to persist in the front diff on the trip drawing grease in from the Birfs causing the overfilled condition. Reasonable?

The car needs to make a second trip to WV to finish filming a video. I can address the vent tube front but no chance I can get the birf's done on short notice.

Will it seriously harm or complicate things if grease does mix with the diff fluid?

Or should I have her use another car on her next trip?

Thanks

 

[Kernal]

Many of us have driven thousands of miles with grease in the gear oil without noticeable harm. IME at a certain point when there's significant contamination the mixture becomes thick like a frothy grease oil milkshake and that can lead to more rumble from the diff as the gears plow through the thickened mixture.

Also many of us have bypassed the factory front axle breather using a length of hose from the pipe on the axle housing going up to the engine compartment then installing a small filter in that end. While you're doing that you can remove the pipe that threads into the axle to clean it out as it's known to get plugged with grease.

You could check the gear oil level and condition before you head out on a trip.

 

[Mark W]

Grease does not migrate from the knuckles into the axle/diff. Gear lube only enters the knuckles from the axle/diff when the axle tune seals are bad.

*IF* you did get grease into the gear lube in the axle/diff, that would not be a major concern unless the amount was extremely extreme.

Gear lube in the knuckles is another story, as it mixes with and dilutes the grease and the resulting soupy slop leaks out past the wiper seals which are not capable of retaining anything but grease.

"My reading here suggests the vent filter/flap is likely caked with WV dirt, same as the EVAP filter on my car. This caused a vacuum to persist in the front diff on the trip drawing grease in from the Birfs causing the overfilled condition. Reasonable?"

Not really. If the axle vent was plugged and there was enough vacuum created as the diff cooled to pull grease past the tube seals, there would also be enough pressure created as the diff heated up to push lube into the knuckles.

It is possible to overfill the diff. Almost expected that most will over fill it at least a little bit. It would not be difficult to purposely overfill it well beyond what normally is done by most folks who fill it until it runs out and plug it quickly. Particularly if you are using a pump and (snug fitting) hoes, not just tipping a quart bottle and squeezing it.

To be perfectly honest, I have to wonder about your mechanic's determination that it was a quart over full. Especially since he quantified the amount of grease he put into the knuckles with the term "squirts", apparently put the same amount in each one and supposedly was precise about it enough to tell you "21 squirts"... not "20 or so". Not "about 2 dozen"... But "21". and I guess "61" the first time around???

And... just how does he know how full of grease the knuckles are if he is adding grease by "squirting" it... into the knuckle plugs I assume? Your steering knuckles and wheel bearings can use up to about a 1 pound container of grease for each side when a full service/rebuild/regrease is done. But not everyone who services them will pack them that full. So, both "61" and "21 squirts" are meaningless since you don't know exactly full the knuckles we packed whenever the last comprehensive service was done.

I would NEVER attempt to quantify the lubrication of the steering knuckles based on how may times I squeezed the handle of a grease gun.

Adding grease by squirting it into the knuckle plug with a grease gun can't hurt anything. But it really does not give you any idea how much grease is in the knuckle, and more importantly it does not let you know the condition of the grease in the knuckle... and more importantly in my mind, it totally ignores the amount/condition of the grease in the wheel bearings.
Soupy grease that is contaminated with gear oil will migrate between the steering knuckle and the wheel bearings. Normal unadulterated grease will not do so to any significant amount however.


Anyway, to answer the specific question you asked, a bit of grease in the diff fluid will not harm anything.

I would be more concerned with the grease in the knuckle and the wheel hub/bearings

If the "21 squirts" of grease has actually brought your level in the knuckles to "2/3rds full" (as in the voids around the birfield are full of grease 2/3rds of the way up the interior inner and outer knuckle), then yes, that is absolutely sufficient. So long as it is grease and not gearlube/grease soup. But that really is a theoretical level since the grease will be moved churned and shifted constantly and never simply fills the bottom of the knuckle.

Appropriate grease in the wheel bearings is MUCH more important to verify before a long road trip. I burned up a brand new set of wheel beings in the Yukon... maybe northern BC... a few years back after an assistant helping with pretrip maintenance got it wrong. Dealing with that while sitting alongside the highway sucked in so many different ways.


Mark...

 

[BTLSHP]

Many of us have driven thousands of miles with grease in the gear oil without noticeable harm. IME at a certain point when there's significant contamination the mixture becomes thick like a frothy grease oil milkshake and that can lead to more rumble from the diff as the gears plow through the thickened mixture.

Also many of us have bypassed the factory front axle breather using a length of hose from the pipe on the axle housing going up to the engine compartment then installing a small filter in that end. While you're doing that you can remove the pipe that threads into the axle to clean it out as it's known to get plugged with grease.

You could check the gear oil level and condition before you head out on a trip.

Thanks, we will keep on top of it until I can find a place (shortly) to do the Birfs. Worst case is Iron Pig or LCH are within an hour's drive.

 

[BTLSHP]

Grease does not migrate from the knuckles into the axle/diff. Gear lube only enters the knuckles from the axle/diff when the axle tune seals are bad.

*IF* you did get grease into the gear lube in the axle/diff, that would not be a major concern unless the amount was extremely extreme.

Gear lube in the knuckles is another story, as it mixes with and dilutes the grease and the resulting soupy slop leaks out past the wiper seals which are not capable of retaining anything but grease.

"My reading here suggests the vent filter/flap is likely caked with WV dirt, same as the EVAP filter on my car. This caused a vacuum to persist in the front diff on the trip drawing grease in from the Birfs causing the overfilled condition. Reasonable?"

Not really. If the axle vent was plugged and there was enough vacuum created as the diff cooled to pull grease past the tube seals, there would also be enough pressure created as the diff heated up to push lube into the knuckles.

It is possible to overfill the diff. Almost expected that most will over fill it at least a little bit. It would not be difficult to purposely overfill it well beyond what normally is done by most folks who fill it until it runs out and plug it quickly. Particularly if you are using a pump and (snug fitting) hoes, not just tipping a quart bottle and squeezing it.

To be perfectly honest, I have to wonder about your mechanic's determination that it was a quart over full. Especially since he quantified the amount of grease he put into the knuckles with the term "squirts", apparently put the same amount in each one and supposedly was precise about it enough to tell you "21 squirts"... not "20 or so". Not "about 2 dozen"... But "21". and I guess "61" the first time around???

And... just how does he know how full of grease the knuckles are if he is adding grease by "squirting" it... into the knuckle plugs I assume? Your steering knuckles and wheel bearings can use up to about a 1 pound container of grease for each side when a full service/rebuild/regrease is done. But not everyone who services them will pack them that full. So, both "61" and "21 squirts" are meaningless since you don't know exactly full the knuckles we packed whenever the last comprehensive service was done.

I would NEVER attempt to quantify the lubrication of the steering knuckles based on how may times I squeezed the handle of a grease gun.

Adding grease by squirting it into the knuckle plug with a grease gun can't hurt anything. But it really does not give you any idea how much grease is in the knuckle, and more importantly it does not let you know the condition of the grease in the knuckle... and more importantly in my mind, it totally ignores the amount/condition of the grease in the wheel bearings.
Soupy grease that is contaminated with gear oil will migrate between the steering knuckle and the wheel bearings. Normal unadulterated grease will not do so to any significant amount however.


Anyway, to answer the specific question you asked, a bit of grease in the diff fluid will not harm anything.

I would be more concerned with the grease in the knuckle and the wheel hub/bearings

If the "21 squirts" of grease has actually brought your level in the knuckles to "2/3rds full" (as in the voids around the birfield are full of grease 2/3rds of the way up the interior inner and outer knuckle), then yes, that is absolutely sufficient. So long as it is grease and not gearlube/grease soup. But that really is a theoretical level since the grease will be moved churned and shifted constantly and never simply fills the bottom of the knuckle.

Appropriate grease in the wheel bearings is MUCH more important to verify before a long road trip. I burned up a brand new set of wheel beings in the Yukon... maybe northern BC... a few years back after an assistant helping with pretrip maintenance got it wrong. Dealing with that while sitting alongside the highway sucked in so many different ways.


Mark...

Thanks, the front bearings have been correctly serviced every 30k miles. For some reason, the rears have not been as frequent - 50k miles ago but no apparent issues or noticeable heat. For the last several years we have check the birfs by dipping in with a zip tie to gauge the level.

Tough to get appointments at OTRAMM, but we are not too far from Land Cruiser Heaven or Iron Pig and we will see if they can build them.