Arrows on the factory U-joint castings - what do they mean?

[inline6]

As I was glass bead blasting the axles from the car I am restoring, I noticed something I have never seen before, an arrow on the casting of the factory (I think) u-joint:

  

I note in the direction it is pointing, it seems to me that the area of the casting between the journals is flatter than the other, similar areas.  Is the arrow indicating that a grease fitting should be installed on that "corner"?

Also, can you drill and install grease fittings on installed u-joints?    

[dutchzcarguy]

8 hours ago, inline6 said:

Is the arrow indicating that a grease fitting should be installed on that "corner"?

When i saw your first picture i thought there is the inlet for the grease.. but pic 2 told me it's not!  Maybe on the older ones there is the little screw were one can install the greasenipple to grease the thing.. and is yours a newer one that's greased for life and has no inlet for grease any longer.. the arrow is still in the casting but has no use..  just my 2 cents.. could be wrong..

I can see 3 of the 4 corners that could have the little ( brass?) screw were you can install the nipple but i guess on the 4th spot is also no little screw?

8 hours ago, inline6 said:

can you drill and install grease fittings on installed u-joints? 

If they have no little screw those u-joints are greased for (a shorter?) life..  I don't think you can drill holes in u-joints..

ALSO..  aren't you worried that there gets dust from the sand or coal in your u-joints?

Or do you take them apart after blasting and pack them with new grease?  I WOULD!  It's a tedious job but saves you later on a lot of headaches!

(If possible and in budget i would renew these important parts i think u-joints are!  still good ones with known low miles i would reuse with new grease.) 

Edited March 16, 2023 by dutchzcarguy

[dutchzcarguy]

Those arrows can have something to do with the in-out speed of a u-joint.. i bet the other u-joint in the same axle has the arrow 180 degrees turned!

A output of a u-joint has a sinus wave like outputspeed and the next u-joint needs to be in a 180 degrees setting to undo this and not double this problem???  I have no idea.. does that make any sense?  haha.. 😮

More here:  Universal joint - Wikipedia

Edited March 16, 2023 by dutchzcarguy

[inline6]

As far as I know, the u-joint is symmetrical.  So, I don't think its installation in the axle has to be "clocked" a certain way.  But, I don't know for sure.  I don't recall seeing grease fittings on any of the factory u-joints on my Datsuns over the years.  However, I believe all of the aftermarket ones I have bought in the past did have them.  

So, the arrow is still a mystery.  

Regarding getting sand/coal dust under the seals, I don't think it can happen.  The seals on the original u-joints are made out of plastic and fit tightly, with no gap for the particles to wedge into.  I may still take them apart however, as installation of grease fittings seems worthwhile.  I mean, while I have them off the car and stripped of paint, it is only a small (relative) amount of work to disassemble them and put fresh grease.  I may drill and tap the u-joints for grease fittings as well.
 

Edited March 17, 2023 by inline6

[Zed Head]

35 minutes ago, inline6 said:

I don't recall seeing grease fittings on any of the factory u-joints on my Datsuns over the years.

All of the 280Z and 280ZX halfshafts I had had grease fitting holes, and I collected a bunch.  They had the small sealing screws installed in most cases.  Maybe Nissan was working their way up to it and the 240Z's didn't get them.  Or, maybe it was part of the "budget" sports car program.  Left off to save a few cents.

Maybe somebody out there has a 280Z or ZX half shaft that they can examine for an arrow.  I don't have them anymore.

[dutchzcarguy]

8 hours ago, inline6 said:

I may drill and tap the u-joints for grease fittings as well.

I doubt that is possible.. as there are also internal grease "lines" neccessary.. When/if you take them apart.. don't use any force as it will give you a lot of stress.. if it go's wrong with those tedioes needle bearings, take some time off as it's really a pain sometimes..

As your u-joints are not new and you will have sand in them i would for sure clean em out and install them with new grease. (Those seals are never so good to withstand the pressure of the sand.. and the (sand/coal) dust will ruin your needlebearings.)

About the arrow, is there another arrow on the other u-joint at the other end of the drive axle? and is it pointing in the same direction?

[inline6]

I located a couple of NOS driveshaft u-joints in my "boxes of stuff" tonight.  I was curious if they were drilled for grease fittings.  I found out that they are.  Interestingly, if you look at the corners and markings, you see they are similar to the ones on my shafts.  However, instead of an arrow, there is a D on the corner that has a flatter surface than the other corners:

    

Additionally, the brand is Koyo for the two I have in boxes, and not grease fitting was included, but instead a plug was.

    

 

I still suspect that I could drill and then tap the existing u joints for a grease fitting.  I will need to decide how to proceed before I prime and paint the axles.  They were painted after assembly at the factory (paint over rubber boots and bands as well), and I am thinking about replicating that. 

I am leaning toward taking the u-joints out and apart and cleaning them and repacking them with grease.  I may attempt to drill and tap and install grease fittings into them. 

[inline6]

I removed the u-joints from one of my axles tonight.  I can't see any beads that got past the seals, but I will be cleaning them regardless. 

On 3/16/2023 at 8:25 AM, dutchzcarguy said:

Those arrows can have something to do with the in-out speed of a u-joint.. i bet the other u-joint in the same axle has the arrow 180 degrees turned!

Took a look at that with the axle I worked on tonight and the arrows are at 90 degrees - not 180.  I'd like to know if these are replacements or original.  I have since a two different brands that are original so far: "Torrington" and Koyo".  No idea if these N T N are also OEM.  

 

[Captain Obvious]

22 hours ago, inline6 said:

I still suspect that I could drill and then tap the existing u joints for a grease fitting.

I suspect the U-joint spider is heat treated and would be difficult to drill and tap. Depends on how hard they made it. I know the tips where the bearings contact have to be quite hard. The body doesn't need to be that hard. but unless they selectively hardened the tips (inductive heating), the whole body would be hard.

I'd hit it with a file first to see how hard it is. If the file just skates, it's a tough job to drill and tap that.

[inline6]

On 3/28/2023 at 10:26 PM, Captain Obvious said:

I suspect the U-joint spider is heat treated and would be difficult to drill and tap. Depends on how hard they made it. I know the tips where the bearings contact have to be quite hard. The body doesn't need to be that hard. but unless they selectively hardened the tips (inductive heating), the whole body would be hard.

I'd hit it with a file first to see how hard it is. If the file just skates, it's a tough job to drill and tap that.

Well, I won't be attempting to drill them because I found a small amount of pitting on the surface of the journals when I took the u-joints out to inspect them.  Time to replace them.

Inner u-joint... and outer u-joint for one axle:

  

 

 

[Captain Obvious]

Yeah, that's done for. I'm no bearing expert, but I believe that's known as "spalling".

However, at this point, if it were me, I'd take the opportunity to check the body hardness and see if it was ever a possibility to drill and tap.

I gots to know.