Greasing your driveshaft may cause extreme pressures

[Bambusiero]

WARNING
If you grease the splines of your driveshafts according to the Factory Service Manual, it MAY create an extreme amount of pressure on your transfer case and axle pinion shaft by acting as a hydraulic ram piston.

The FSM says to pump in grease with a grease gun until it begins to ooze out. For the U-joints it's not a problem. It oozes out very readily.

However, for the splines, at least some vehicles seem to have grease seals that are too good. When you pump in grease with a grease gun, it can't get past the seal and just jacks up the drive shaft so the splines can't slide and get shorter when you go over a bump. Some seals seems to be looser and let some grease squirt by and don't have this issue.

One guy reported actual breakage of the transfer case.

Here's a thread on this some time ago for more background:
https://forum.ih8mud.com/80-series-tech/20022-updated-warning-greasing-rear-drive-shaft.html

When I finally got around to greasing my truck, I found that I had this problem. I could actually see the axle being moved by about 1/8 inch as I pumped the grease gun. The suspension bushings were being compressed. So, I removed the drive shaft to check into it.

Photo 1) The drive shaft between 2 blocks clamped to a 2x4. Pumping the grease gun flexed the 2x4 pretty easily.
(No, I didn't miter saw the drive shaft )

Photo 2) After a number of flexes, the blocks slid in spite of the clamping friction. They started out even with the pencil line.

Photo 3) This shows grease oozing out of some pressure relief grooves I filed in the seal. It was jacked against the blocks again, just to see what would happen. Obviously, the filing was done while the 2 pieces were taken apart, not as shown. With a the thin edge of a needle file, I took about a dozen strokes on the inside surface of the seal at several places. I don't know what the right answer is here, but I made a groove at every 2nd spline.

 

[jonheld]

This is old information, but good to bring it up again for those that don't know. Only 2 or 3 pumps from a grease gun should be plenty for the slip yolks. If you feel that the yolk is hydro-locking, simply remove the grease fitting for the yolk and compress the shaft. This will squeeze any excess grease out.

In actuality it is a testament to Toyota quality. The splines are tight and have plenty of engagement.

 

[e9999]

what material is that seal and what was its condition?


(and you did index everything so you can put it back as was, right?)

 

[Rookie2]

Yep, old news but good to bring up. You don't pump grease into the driveshaft zerks until it oozes, just the u-joints. The common accepted method discussed here is pump a few squirts in, but if you see the driveline shafts starting to push apart when pumping, stop.


Rookie2

 

[blzrfn]

How often should we lube the driveshaft?

 

[Cruiserdrew]

How often should we lube the driveshaft?

Every oil change or after any deep water.

 

[medtro]

Is that moly grease?

 

[gray]

Moly for the slip yolks, non-moly for the U-joints. Ditto; remove the zerk if too much grease. Very important (old) bit of info for those who do not know; never grease the slip yolks when the wheels are off the ground; you will for sure damage something if you fill them completely when extended and then drop the vehicle back on it's wheels.

 

[blzrfn]

Thanks Drew.

 

[medtro]

Moly for the slip yolks, non-moly for the U-joints.

No mention of moly in my FSM.

 

[gray]

No mention of moly in my FSM.

Some previous years mention Moly for the slip yolks; but it is also common sense if you think about it. What is the purpose of "Moly"

Wikipedia:
"Molybdenum disulfide (MoS2) is used as a lubricant---. It forms strong films on metallic surfaces, and is highly resistant to both extreme temperatures and high pressure."

Moly is a solid lubricant and does not wash off as easily as the rest of the grease, so something is left behind if you forget to lube the shaft or water washes everything else away. Should avoid it's use however in U-joints as it can build-up inside the tight spaces around the pin/roller bearings apparently causing them to stick.

Back to the OP's idea of putting grooves in the seal; not sure if I would do that; if grease can get out more easily, water and grit can get in, more easily.

My solution would be to tap a hole into the large plug that is pressed into the end of the shaft and screw in a one-way pop-off/pressure valve that would allow any excess grease to squirt out, but not allow water or grit in.

 

[Bambusiero]

Yes, It's EP moly grease you see in the photo.

Agreed that the FSM calls for MP (multi-purpose) grease, but as gray says, EP moly grease just makes perfect sense for the spline application. I just can't see how it could the wrong choice here.

Now, as for the U-joints, I also chose to use EP moly grease there for the following reasons:

1) U-joints bearings don't really spin at high speed, they oscillate back and forth over a limited angle.
That makes it seem like an application that's about half way in between EP and MP.

2) To me, grease guns are a total pain in the ass, and crawling out from underneath the truck and getting the OTHER one out and working to take care of a zirk that's 2 inches away is nuts.

It's arguable, I know, but that means it's not totally convincing one way or the other, so I'm going this route. If it turns out to be really the wrong choice, I'll find out soon enough, I suppose.

 

[Bambusiero]

Having pulled the thing apart now to look inside, my opinion is that 2 or 3 squirts will do nothing for it. The zirk fitting is all the way at the end (bottom) of the shaft which has about an inch of widened out, non-splined area (sort of a cup or end cavity). Your 2 or 3 squirts are just going to sit down there at the end where nothing moves, undisturbed and undistributed. If any of it does ever get into the end section of the splines, it certainly won't move the 6 inches or so up the splines to the seal end, and the seal end is where you really need to renew and flush things out, right?

On the other hand, the old grease doesn't evaporate or go away at all, so every time you add a few squirts, it's gradually filling up. It may eventually end up hydrolocking, just as if you did it all at once.

Then, the FSM does NOT tell people to add a few squirts, it says very plainly:

HINT: After installation, pump MP grease into each fitting with a grease gun until the grease begins to flow around the oil seal.

I'm convinced now that it is a bad procedure.

So, really the only reason I bothered to write this up is to demonstrate that the hydrolock effect is real (and strong), and you can "adjust" the seal to achieve some pressure releaving leakage. Then you can pump it in until it oozes, replacing some old grease, and still not have the hydrolock problem. Otherwise, as you say, it's old news.

BTW, the seal is a flat band about 1/8 inch wide of a bristly fibrous material, contained pretty tightly by the crimped steel shell. Maybe the fact the steel shell fits so tightly is what causes such an overly good seal.

gray's idea about a one-way pop-off/pressure valve sounds good, but too elaborate for us "practical" home mechanics

 

[e9999]

I would also try and clean up the seal a bit if it's fibrous. Some solvent just squirted from the outside at first, maybe. May remove dried up grease and loosen things up a bit.

 

[Tools R Us]

Having pulled the thing apart now to look inside, my opinion is that 2 or 3 squirts will do nothing for it. The zirk fitting is all the way at the end (bottom) of the shaft which has about an inch of widened out, non-splined area (sort of a cup or end cavity). Your 2 or 3 squirts are just going to sit down there at the end where nothing moves, undisturbed and undistributed. If any of it does ever get into the end section of the splines, it certainly won't move the 6 inches or so up the splines to the seal end, and the seal end is where you really need to renew and flush things out, right?

On the other hand, the old grease doesn't evaporate or go away at all, so every time you add a few squirts, it's gradually filling up. It may eventually end up hydrolocking, just as if you did it all at once.

In my experience a few squirts with each oil change works well. Some force, my guess is centrifugal, moves the grease out to the outside, it makes a nice ring of lube at the point where the two splines come together. As the suspension moves, the splines move, migrating the grease into them. Overtime it works it's way through and makes a ring of grease outside of the dust "seal".

Probably the "best" method is to pull the splines apart and "paint" them with grease each time. But that's a lot of work and the "few pumps at each oil change" method works well and is much easier.

 

[Chrishdj80]

I simply squirt untill I see some slight movement in the tranny case.
Usually only a couple of squirts.
Use something as a marker and when the tranny moves stop.
The tranny should nicely come back to its original position.
If it "hydro-lock"s you've got a problem.

Well made splines are a though nut to crack.
I've seen splines on agricultural machinery running in a mix of dirt and grease and they simply keep on running.
When the seals stop sealing, you just need to keep squirting on a more regular basis.
Although I'd recommend a new seal before your Toy is totally greased down below.

 

[Bambusiero]

In my experience a few squirts with each oil change works well. Some force, my guess is centrifugal, moves the grease out to the outside, it makes a nice ring of lube at the point where the two splines come together. As the suspension moves, the splines move, migrating the grease into them. Overtime it works it's way through and makes a ring of grease outside of the dust "seal".

Agreed Kevin. If a few squirts does work OK, it must be as you describe. It seems like a weak treatment, but maybe it's just not a big deal anyway. Much ado about nothing?

Bottom line, your choice:
You can be a squirt.
You can be all pumped up.

 

[landtank]

on a lifted truck this isn't really a big deal because as the suspension compresses the shaft extends. So it's not like if you come down hard and compress the entire axle you'll damage something.

And if you have a DC shaft made form a Tacoma shaft there is a hole at the end to prevent hydro locking.

I always pump grease in until I see the shaft start to expand and stop there. Normal driving then draws it down the splines.