A bit of a dissertation ....
Not quite.
- When you grease the slip yoke you should pump grease until new grease comes out of the seal. (Per FSM)
- It will usually be proceeded by some water emulsified dirty grease getting pushed out and then followed by the fresh new grease.
- This needs to be done every three thousand miles! or more often in severe conditions. Severe is stop and go and towing, not just outback travel.
- The manual recommends daily if you do any water crossings.
- This is because the grease in the slip is consumed and contaminated as the slip joint does it's thing (slip). Grease is deposited in the area of travel and then is lost to exposure on extension . Dirt/water on the shaft is pushed into the grease and seal on compression.
- Grease also seeps. The lubricating oil separates from the thickeners and flows out of the shaft to evaporate. So it must be renewed often.
This is what you want to see ...
Front drive shaft showing new Moly grease (shiny purple) pushing out old Amsoil 2000 series grease (red). If the old grease was contaminated or emulsified with water this flushing action would be more important.
Clean new grease spilling past the grease seal on the rear yoke. This is what you are after.
Here is the problem and area of controversy.
- Lots of trucks are not greased nearly enough because quick change places and shops hardly bother to grease now that so many cars lack lube points and oil change intervals are often 7500 miles. (Plus, it's dirty under there)
- When not lubed often enough the seal gets dried and caked with dirt to the point that it no longer allows a flow of grease.
- When new grease is pumped into the yoke it extends the shaft slightly rather than pushing old grease out.
- Some have been concerned that filling the yoke with uncompressable grease will prevent the slip yoke from compressing properly transmitting shock to the drivetrain.
- They therefore recommend only shooting in a pump or two of grease.
My thoughts -
- Too much grease is not the problem. A malfunctioning seal is the problem. Fix the problem.
- If the seal isn't working because its been under lubed in the past then purposefully under lubing it into the future is not the right answer.
- Without a flow, grease is not getting to the contact parts that need lubrication.
- A poorly lubricated slip yoke is also likely to transmit forces in excess of the design. (Thunk!)
- If no old grease is coming out and at each lube you place two pumps in it. Then you are just going slower to the dreaded Hydro-locking situation. (There may be some benefit as the lubricating oil separates from it's thickeners and migrates where it's needed.)
- Get a grease gun ($10), a flex hose for the gun ($5) and some grease ($2-5) and do it yourself. Otherwise you'll never know if it was done right.
What to do -
- First try to pump until old grease flows out of the seal area (where the slip happens).
- If you get a little extension don't sweat it. Keep pumping.
- If you can no longer get grease into the zirk and no old grease has left the seal then your's is blocked and needs to be unblocked.
- If you know it's blocked then fix it.
Ideas to free a blocked seal.-
- Pump some NGLI #1,0, or 00 weight grease into the shaft and let it sit. (these are basically the same grease only with fewer thickeners and could loosen the crud at the seal as the lubricating oil migrates). After establishing flow lube with a NGLI #2.
- Heat the shaft gently with a hair dryer ect.. to improve flow. (not trying to cook the oil, just heat it to a flow.)
- Clean the shaft of rust and dirt. Emory cloth ect...
- Jack the truck up to full extension, pump full with grease and lower slowly to put a lot of pressure on the clogged seal.
- Clean with a little solvent.
- Remove the driveshaft, take apart and clean. Reassemble and grease.
Other notes - Watch for grease compatibility. Just about any grease will do for this application but some don't work well together. Lithium thickened greases may not work well with some marine greases.
I use a Amsoil Synthetic EP Lithium NGLI #2 with 3% moly (it's purple). Mobile 1 #2 should work well although those who have studied such things say that it trends thick for a #2.
If you hear or feel some "thunk", grease it again.
