Overfilled rear driveshaft with grease: now what?

[Beej]

Hey folks,

I thought I'd knock out a little PM yesterday and in doing so I overfilled the rear drive shaft.

I did the U-joints, no problem but what I had read told me to keep pumping u-joints until grease comes out of the seals and pump grease in the shaft until it "moves".

Well, it didn't move and I kept pumping until grease squirted out of the dust seal (or slip yoke?).

I know this is bad and I know I need to pull the shaft. I can look at the FSM for instructions on removing but FSM doesn't seem to say anything about proper greasing and MudSearch isn't turning up any instructions I hadn't read before I screwed this up.

Any pitfalls removing the driveshaft per FSM instructions and once I do, how do I properly lube the driveshaft?

Is it worth doing the front also or better to just do 3 pumps in there and count myself lucky I didn't eff that one up too?

Thanks in advance for any replies!

-- Beej

 

[greentruck]

BTDT, it can lead to a serious vibration.

Usually, you don't need to remove it. The zerk you put the grease in can be unscrewed. This will release the pressure. Then put the zerk back in and test drive. If you have vibrations, take the zerk off again, unfasten the shaft at one end and press the free end against the other end and that should get enough grease out to solve it.

When greasing the slip joint, I pump until the very first sign of movement occurs in the slip joint. But if you grease regularly, 3 to 5 pumps of the grease gun should be adequate.

 

[FloridaCruiser813]

Green truck got it. Just unscrew the zerk

 

[l1coeea9]

What you just described is my SOP for the past 20 years with my 91. Apparently my truck doesn't know I'm not supposed to do this and it just coughs up the excess.
I'm still waiting for something bad to happen. (Although now I do tend to go a little easier with the grease gun.)

 

[Rivman1243]

What's supposed to happen if you "over fill" the slip yoke

 

[elhombre]

What WILL happen is the grease will not allow the driveshaft to compress. When you hit a bump in the road, the rear axle moves upward due to the bump. The axle travels in an arc. When the axle is fully compressed, it is closer to the transfer case. When the axle drops in a hole, it is further away from transfer case. Too much grease means all the energy from the bump pushes against the transfer case via a driveshaft that won't shorten in length. The bearings in the transfer case are designed to handle rotating forces, not compression forces from the rear axle being shoved into it. You actually shove the transfer case forward, which shoves the transmission case forward, all the way up to the engine block receiving some of this compression force. Slip joints take care of all of this, IF it can slip back and forth.

Also, the u-joint needs free movement to fly around at great speed. Too much grease in the drive shaft will constantly try pushing it out of it's circular pattern.

 

[Rivman1243]

doesn't it purge out the end like a normal driveshaft

 

[elhombre]

NORMAL drive shafts have a seal that keeps all the road crap out, and all the grease in. Once you see grease slinging all over the muffler and gas tank, the seal is compromised and "no bueno".

More importantly, compare it to an old school bicycle tire pump. An over filled slip joint is like filling a bike pump with water while the handle is up. How much time and energy will it take for a person to push the handle all the way down, and force the water out of the little pump hose? You will get all the water out of the pump eventually, but it will require time. Relate the small bike pump hose hole to the space the grease is trying to get out from around the slip joint splines. Those splines are suppose to be very close and tight to each other, meaning it is a very small exit hole. Axles travel up and down at least a few times a second when hauling ass down a dirt road.

Hope that analogy works for you.

 

[greentruck]

Good run down by elhombre.

Overfilling the slip joint turns the driveshaft into a hydraulic pump, ready to hammer away front and back (the pinion seal in the third member is also in for abuse) as it attempts to follow the constantly changed geometry of hooking up the tranny(2WD)/transfer case(4WD) output to the axle input.

I learned this the hard way, the first time I serviced my still-new-ish FJ55 (see avatar.) I was younger, skinnier, and even had more hair then, but I was still learning. Saw the shiny area of the slip joint as something that needed to be covered when done right (WRONG!) so I pumped that puppy full. Drove to work that night and discussed my new bad vibration despite having just serviced the truck around the breakroom table. I think it was my buddy Steve F. who called it right. I was quite relieved to find Steve was on the money when I back that zerk out and the grease spewed from it.

 

[Squash]

X2
Spray some brake clean, Pb, or WD40 into zerk fiiting with extension tube, this can loosen the crud.
Drive around for a while and then try greasing again, otherwise R&R

 

[Rivman1243]

I'm a diesel mechanic so I know what's going on. Just seams odd to not be able to purge the grease out. At work Unless our driveshafts are sealed for life they have a purge hole to remove the old and dirty grease. Just because a part says its sealed doesn't mean that dirt and water or mag chloride used to melt ice on the highways.

 

[sea bass]

I drilled out the center of my zerk fittings so it will automatically release the pressure when you take the gun off

 

[LS1FJ40]

Just don't drop your rear drive shaft on your face and knock out a front tooth because you overfilled the slip yoke and can't get it to compress enough. It hurts. And costs a couple grand to have an implant put it.

FYI.

 

[inkpot]

I'm a diesel mechanic so I know what's going on. Just seams odd to not be able to purge the grease out. At work Unless our driveshafts are sealed for life they have a purge hole to remove the old and dirty grease. Just because a part says its sealed doesn't mean that dirt and water or mag chloride used to melt ice on the highways.

The 80 series driveshafts do NOT have a relief/purge hole in the yoke like most, so surplus grease will either breach the dust seal at the big end or force the shaft length to get longer and longer. This, it becomes a hydraulic ram.

 

[4runnerd]

Umm... So I can personally contribute a cautionary tale as to the consequences of over filling- I've done this for years to get bad grease and water out of the slip joint and spiders. Over fill, then take off the zerk, disconnect the shaft at one end and and smoosh out the extra through the zerk hole. It's lazy, but I've never had a problem, and it works.... Until it doesn't, that is.

Was doing the baseline on a 96 cruiser the other night and wanted to force out the old grease... Worked well on the spiders and the front slip joint. Was working as usual on the rear slip joint, then.... POW! .... Grease pours out into the middle of the u-joint. Blew the seal- first time that's happened. Pretty sure that there was some very bad crud in there that prevented the old grease from continuing to come out through the slip joint. Probably still not a bad idea when I want to get water out on a truck I own and know, but I'm gonna alter my baselining procedure for sure.

Now what, indeed...

For the OP, I would unscrew the zerk and the part of the shaft that is the male portion of the slip joint. Push it all the way in, grease comes out of the zerk. Pull it back out, bolt it back down (use proper torque settings...), and then screw back on the zerk.

As for my shaft, I'm gonna have to take it off and have a look. Anybody have any easy fix if it's the seal? Weld it, or just get a new shaft?

 

[Kernal]

4runnerd: do you mean you blew out that pressed in steel blank about the size of a silver dollar on the slip yolk?

 

[Beej]

4runnerd: do you mean you blew out that pressed in steel blank about the size of a silver dollar on the slip yolk?

Right which seal are we talking about?

 

[Malahki]

Yup overfilling makes your drive shaft a hydraulic locked ram. Made the mistake of over greasing before hitting the trail one day. Collapsed the pinion crush sleave in the rear 3rd and had to replace ring and pinion gears

 

[Beej]

I left out the zerk and drove the truck down the highway 100 miles; it'll drive back 100 before the zerk goes back in; hoping if I just pull the zerk periodically it will not build pressure. I was going to pull the male side of the shaft and press out grease but the nuts were frozen. Add that to the PM list.

 

[bloc]

For the OP, I would unscrew the zerk and the part of the shaft that is the male portion of the slip joint. Push it all the way in, grease comes out of the zerk. Pull it back out, bolt it back down (use proper torque settings...), and then screw back on the zerk.

This /\

I left out the zerk and drove the truck down the highway 100 miles; it'll drive back 100 before the zerk goes back in; hoping if I just pull the zerk periodically it will not build pressure. I was going to pull the male side of the shaft and press out grease but the nuts were frozen. Add that to the PM list.

How much grease came out (and is slung all over the bottom of the truck?) You may be fine..