Why Only Rear U-Joint Zerk doesn't accept grease?

Any idea why my 1999 4Runner rear U-joint zerk is blocked and does NOT accept grease? I have successfully greased all the other zerks without any problem. My grease gun is new too. I pushed over the ball with a small flat screwdriver. It seems to move. I even applied some heat to the zerk and the U, but still no cigar!

Is it possible that the U-joint is really full and can NOT accept any more grease? Last time, it was greased by the dealer.

Any insight about this problem will be very much appreciated.

 

Take the zerk out and verify that it alone is open and will except grease, if it is then you have an issue somewhere else.

 

Thanks, great idea, sure I will test the zerk by itself.

Also, when greasing the U, where the old grease comes out? Or does any old grease come out at all? For all the other zerks, I could see the old grease was coming out somewhere except for the front U. For the front U-joint, I just gave it 3 pump without seeing anything ooze out any where.

 

Yes, pump till new grease is visible. Is it the slip yoke zerk that is not taking grease?

 

Yes, it is the slip yoke in the rear which does NOT accept the grease. No problem in the front one. But, I still did not see anything coming out of anywhere for front one either.

 

Fitting fail they get full of dirt

 

The slip yoke can vapor lock, sometimes just removing the the zerk and releasing the air will fix it.

 

Vapor lock??? Wow, never thought about this one that is probably what it is since this particular zerk was not very dirt at all when I started to grease the shaft. I will let you know after I get the zerk out and try it.

Thanks very much for the ideas, guys. I will let you know about the results.

 

For the rear zerk, just pump until you see the slip yoke move a little.

 

Hope you guys have had a good weekened.

Well, still no cigar! I got the zerk out and tested it alone. No problem with the zerk, grease comes out of it. I noticed the slip yoke was filled with grease. I pushed a small screwdriver into the hole. Indeed, it was full of grease. So, the screwdriver created an empty path in the slip yoke. However, after taking a 15 minute break before putting back the zerk, I noticed the empty path was filled and grease was again right at the zerk hole. My garage is hot and it was around 100 F, yes, an oven (live in Phx, AZ). So, grease flows easily

I tried to grease the slip joint after putting back the zerk. But, still to grease doesn't go in. I varied the pressure on the zerk with no luck. The only reason comes to my mind is the slip joint is really full and it does not have any room to accept more grease. Am I right in my way of thinking? If so, what happens as the grease gets old?

Any other idea? Is it possible that there is a vapor lock somewhere in the slip yoke because of the extreme heat and even removing the zerk did not get rid of it? May be I have to wait until the weather cools off later in the fall or cool the slip yoke somehow!

Thanks again for all your ideas.

 

As long as you know there is grease in that slip yoke youshould be fine. Since it dosent see high temps like the u joints the grease wont really "get old" or better said get used up...it is kinda strange that it wont accept any new grease though.

As others said already, on the u joints keep pumping till new clean grease starts to ooze out!

 

I think it's more of an air lock, instead of a vapor lock. Shouldn't be any vapors in there. But what happens is the grease traps air in the cavity of the driveline. On the drivelines in land cruisers of the same vintage, if you were to pull the driveline apart at the slip joint, you'll find a felt seal that Toyota uses to keep the grease in the joint and keep the elements out. When this felt seal is new, it isn't airtight (and it shouldnt be airtight either), so when you pump new grease in to the slip joint it will allow the air to escape the joint but keep the grease in. As these felt seals age they harden up and actually create an airtight seal, this isn't good. Then any new grease pumped in, after the felt has hardened, will create excessive hydraulic pressure as the air can't escape and the new grease is being forced in. This hydraulic air lock will then transfer the force/pressure to the pinion bearings in the differentials and the transfer case. This can cause premature bearing and seal failure at both ends, the diff and the transfer case. The zerk not allowing you to add grease may in fact be saving you from this failure happening.
One thing you can do, if you're comfortable with it, and it sounds like you would be, is remove and separate the driveline. Before separating it though, you need to mark it someway that you know it goes back together with the same exact splines lined up as you separated it. They are weighted and balanced and you will get vibrations that you didn't have before. So with the driveline marked and now separated, wipe the old grease off of the outer splines and from the inner splines and wipe new grease on/in both ends as well. Put the driveline back together in the exact way you separated it and reinstall it. Once installed, as you did before, use the little flat screwdriver to press the ball into that zerk fitting to relieve excess pressure, if any, in the slip yoke. After that I'd recommend driving over a curb slowly, to compress the driveline, and then go back and repeat the screwdriver into the zerk again, just to ensure there is in fact no excessive hydraulic pressure trapped in the yoke. Then rest easy, you know you've taken the right steps to not screw up you transfer case and pinion bearings as you made sure your driveline slip yoke splines are lubed up. While rare, number one cause of slip joint failure in the Yotas I've seen is grease not getting to the splines in the slip joint.
This procedure may sound hard or long, but that's only because I've tried to explain it thoroughly. Hope that helps you out.

 

Holy chit, just now saw how long that reply was. My bad, brother, my bad.

 

"Holy chit, ...." , hahahahaha Please don't feel bad about your long reply.

You have solved the puzzle and how to make it right. What you are saying makes total sense about the felt and getting hardened with age. I remember a few years back, when I would grease the slip yoke, the grease would come out of the drive shaft further down. So, this was puzzling to me why even the grease would not go in this time. Now, I know it is a Toyota thing and age for the year of my 1999 4Runner.

I think I know now what I have to do and probably the sooner the better since I like to keep my 4Runner. I don't know if I will do it myself since my garage is so hot these days. I have to think about this one.

Thank you again for your detailed response and setting me straight Also, I like to thank others for pitching in and trying to solve my problem. You guys rock, thanks. Scott

 

Awesome, glad my jumbo made sense. Happy to share. Knowledge is power!