How to Install Universal Joints in Axles Properly - Using OEM U-Joints

[inline6]

 I have started replacing the u-joints the 240Z I am restoring.  I think the u-joints I removed are original to car.  Can anyone confirm?  

 

What tells me they are factory?  Well, there is a fair amount of evidence from looking at the history of the car, the receipts, and the amount of crusted dirt that was on the u-joints.  Basically, the car appears to have about 120k miles on it - a notable amount of crust that I had to remove from the u-joint spider, and the snap rings I removed look just like the ones that came with the NOS u-joints (different from all the aftermarket u-joint snap rings I have ever seen).  Anyway, on to some selected text from the factory shop manual and some questions. 

When looking at the RA chapter from the workshop manual (Rear Axle & Rear Suspension)...  First, a little bit of levity - per the manual, did you know that "The drive shaft should be disassembled only when lubricating the ball spline" and further "The lubrication is required every 50,0000 km (30,000 miles)"?  Bet you didn't, and you'd better get on that. 😛

Setting that aside, oddly, when addressing replacing the universal joints from the axles, the factory workshop manual refers the reader to the "instructions described in the paragraph covering the propeller shaft if faulty condition is detected".  So, I turned to that section of the manual.  

Unfortunately, the propeller shaft (drive shaft) is a bit different than the axles.  So, I am left with some ambiguity and therefore, some questions.  

Let's start with "Before disassembling the journal, verify the component alignment and relationship so that the yoke direction and snap ring thickness are not changed (when the yoke direction and/or snap ring thickness is changed, the tube and journal center alignment is deviated and the propeller shaft is unbalanced) because the journal is balanced as an assembly.  It is desired not to disassemble the propeller shaft so that the alignment is not unbalanced."

So, translation?  Don't take it apart if it can be avoided.  Of course, I have already taken the u joints out and found them to be in need of replacement.  I have only disassembled one axle - just the u-joints removed so far.  And before I did so, I marked everything so as to keep all parts in their factory assembled orientation.  Axle yokes, axle, u joints, u joint snap rings... all laid out per their assembled orientation.  

Now, a few words about the new oem u-joints.  These are new old stock.  Note that the D and "dot" seem to be indicating where the u-joint is drilled and tapped for a grease fitting (the package includes a screw plug):

    

These original equipment u-joints come with an assortment of snap rings: 

    

 

Note the colors painted on the edges.  There appear to be 6 sets of two.  The factory workshop manual only provides info for 4 colors, and those are for the driveshaft u-joints, which are different than the axle u-joint snap rings.  Those for the driveshaft are measurably thicker, varying from 2.00 to 2.06 mm (.0787 to .0811 inches).  I measured the snap rings that came with the axle u-joints.  Generally speaking, they range from .059" to .066".  So....

One of my more important questions is, what snap rings should I use?  Turning again to what is written in the workshop manual: 

"Reassembly" 
"The component parts are reassembled in reverse sequence of disassembly.  When reassembling, select and use a proper snap ring out of the following types (four types) so that the journal moves under the following conditions:

1.  Bending resistance of the journal unit is less than 1- kg-cm (9 in-lb).
2. When a yoke in one side is set stationary and a load of 10 kg (22 lbs) is applied to the other yoke alternately, the relative displacement of the yoke toward the axial direction is less than 0.02 mm (0.0008 in)."

The four types, by the way, appear to be the four colors for the driveshaft u-joint.  For the axle u-joint, it looks like we have 6 types (colors).  My measurements of the supplied 6, again ranging from .059" to .066" roughly corresponded to two of each of the following: .059", .060", .061", .063", .065", and .066".

Separately, the snap rings I removed from the old u-joint are mostly, to my measurement, .062".  Interesting.  

Looking again at number 2 above, I think what I am supposed to do is use two snap rings of the same size at opposing journal locations.  For example, I could install the old ones - .062" at each of the four journal locations, or perhaps two .062" opposite each other, along with two .061" opposite each other.  Next, I should attempt to use a pressure of 22 lbs against the "other yoke" and check for axial movement (which would occur if the spider of the u-joint were to sink further into the u-joint cap.  Success in determining the correct snap ring is achieved when "the relative displacement of the yoke toward the axial direction is less than 0.02 mm (0.0008 in). 

Right? Thoughts?  

I've been looking through all of this this evening trying to figure it out.  I wonder... how many people install new u-joints and don't get the movement in the axial direction sufficiently tight?  If axial movement is "too much", it could cause wild vibration.  

Lastly, I wonder if the grease fitting location on the u-joint matters in any way?  So far, I have one new u-joint installed.  Should I install the second one on the axle as pictured - with its grease fitting location 180 degrees opposite, in this orientation?

Edited April 5, 2023 by inline6

[Patcon]

I believe you ciphering is correct...

I would think 180 out makes the most sense. If the old spider has similar dimensions to the new I would be inclined to use the old snap rings, maybe...

[inline6]

I find it curious that the snap rings supplied with the new u-joint are in thicknesses which are paired in twos and thicker and thinner than what I took out.  Possibly they were trying to supply a broader range on purpose.  Consider, why not provide 3 groups of 4 of the same size, for example? 

I am going to take some measurements of the distance between the yoke ears or whatever you call them.  Perhaps the distances vary a bit and will give me guidance on what thickness snap rings need to be used.  It will be interesting to see variances.

Edited April 5, 2023 by inline6

[Patcon]

I thought pairs was odd too.

[inline6]

I am surprised at how many hours it took to replace the u-joints.  What took the most time was measuring everything and trying different snap rings until I got the right factory free play of about one thousandth (factory spec = .0008").  However... I realized something much later in the day, and I'm going to have to go through snap ring sizing part again.  Let me explain why:

Generally speaking, the distance between the yoke ears on both the center axle assemblies and between the yoke ears on the outer axle flanges measures around 2.200 to 2.205 from inside surface to inside surface.  To measure the u-joints where it matters, I installed opposing needle bearing caps, and put the u-joint in a vise, squeezing it lightly until the caps bottomed out on the u-joint spider.  I used paint sticks to protect the caps from the vise jaws.  While in the vise, I took vernier calipers and measured from innermost edge of snap ring groove to the same innermost edge of the opposing cap.  That measurement was about 2.080. The difference, divided by two, is theoretically the snap ring size you need on each snap ring groove - or close, anyway.  So, by the measurements I was seeing, (2.205 minus 2.080) divided by 2 equals .0625.  

I didn't realize the info in the paragraph above until I was working on the second axle.  Additionally, while working on the second axle, I began to suspect that the u-joints may have been replaced before.  The first thing that tipped me off to this was that on the second axle, I was more diligent with measuring each of the snap rings as I removed them.  And I kept track of their respective locations.  For the second axle, here is what I found when I took them out:

Inboard u-joint:
"Top of axle (arbitrary, but I marked it as such)": snap ring - .060"  --- opposite journal - "bottom of axle": .062", and "left" journal: .062" and opposite "right" journal: .065"

Outboard u-joint:
"Top of axle": snap ring - .060"  --- opposite journal - "bottom of axle": .062", and "left" journal: .065" and opposite "right" journal: .062"

Thinking about the snap rings... I just don't see how it could be right to use different thicknesses on paired journals.  Maybe I am wrong, but certainly from an ideal standpoint, the outer flanges should be machined such that the 4 bolt holes which secure the axle to either the differential or axle - these would be oriented such that the center of the flange would align with the center of the u-joint.  If the machining process on the outer flanges achieves this, when you install the u-joint and you use a snap ring of a thickness of .065" on one journal, and .062" on opposing side, then that u-joint is going to be .003" off center.  And for every revolution of the axle, it is going to be .006" out-of-round.  Seems bad... like it shouldn't be like that.  Wouldn't that cause vibration?

The second thing that indicated the u-joints had been replaced was some dings on the inside surfaces of the yoke ears.  I am pretty certain I did not cause those.  I lightly dressed them with a file so the snap rings were sure to fit properly.  

First pic: dressed some marks on the inside surface with a file.  Second pic, no dressing was needed:  Third pic: measuring u-joint free play:

    

So, tomorrow, I'll be going over the axles one more time, looking for the right snap rings.  The good news is that the total thickness of each pair of snap rings should be right, as I measured everything and got the free play right.  However, for each opposing pair, I'll need to measure the thickness of each snap ring, and "split the difference".  So, for example, the .062" and .065" combo will need to be swapped out for two .063" or two .064" snap rings - whichever gets me closest to the .0008" free play.   

 

[Patcon]

I hate to say it but maybe the mismatched rings are an intentional balancing technique. Which would be impossible to replicate without a drivline balancer. If you find it's necessary we have a very good and regionally know driveline specialist here in Spartanburg

[inline6]

6 minutes ago, Patcon said:

I hate to say it but maybe the mismatched rings are an intentional balancing technique. Which would be impossible to replicate without a drivline balancer. If you find it's necessary we have a very good and regionally know driveline specialist here in Spartanburg

That thought occurred to me, but it seems too cumbersome from a production efficiency standpoint to me.  I could go through and swap out rings to get them as close to the same size as possible, and then send the axles (and driveshaft) to a driveshaft balancing place like you mention to check balance / re-balance.  I believe I worked with The Driveshaft Shop on a group buy of short axles for a Z31 CV conversion on my highly modified 240Z many years ago.  They are in NC.  Who are you referring to in SC?

[Patcon]

Carolina Driveline Inc

Howard st, spartanburg

They do it all. Common through Nascar...

I agree, it does seem cumbersome but I can't come up with another teason for the asymmetry you've seen.

[Zed Head]

Looks like one of those conflicting instructions areas.  They say "don't change anything" but if you do change them so that certain conditions are met.  Kind of like wheel bearing instructions - rotational torque or axial play?  You have a dilemma.

[Racer X]

Regarding the orientation of the grease fitting plugs: Did the original trunnions have them? If so, what was their relationship?

Also, after greasing the joints, removing the zerk and installing the plugs would be a good idea. The joints are pretty small on these shafts, and a grease zerk might interfere with the joint as it rotates.

Regarding the various thickness keepers. You are correct that they are for setting the clearance, between the inside of the caps, and the ends of the trunnions. If there isn’t any clearance, the parts will rub and get hot, causing failure of the bearing (a u joint is a complex bearing). If the clearance is too great, the end play will result in vibrations, and premature failure. 

If you are concerned about the balance after replacing the u joints, take the assemblies to a drive shaft shop and have them balanced.

Oh, and get some brass soft jaws for your vise. Way better than wood sticks.

 

[inline6]

1 hour ago, Zed Head said:

Looks like one of those conflicting instructions areas.  They say "don't change anything" but if you do change them so that certain conditions are met.  Kind of like wheel bearing instructions - rotational torque or axial play?  You have a dilemma.

I think someone was here before me, so too late not to change anything.   
 

24 minutes ago, Racer X said:

Regarding the orientation of the grease fitting plugs: Did the original trunnions have them? If so, what was their relationship?

Also, after greasing the joints, removing the zerk and installing the plugs would be a good idea. The joints are pretty small on these shafts, and a grease zerk might interfere with the joint as it rotates.

Regarding the various thickness keepers. You are correct that they are for setting the clearance, between the inside of the caps, and the ends of the trunnions. If there isn’t any clearance, the parts will rub and get hot, causing failure of the bearing (a u joint is a complex bearing). If the clearance is too great, the end play will result in vibrations, and premature failure. 

If you are concerned about the balance after replacing the u joints, take the assemblies to a drive shaft shop and have them balanced.

Oh, and get some brass soft jaws for your vise. Way better than wood sticks.

 

I examined only one of the axles with regard to the arrows I mentioned at the beginning of this thread.  The arrows pointed to a "flatter" of the four corners of the trunnion, but they were not drilled and tapped for grease fittings.  The relationship was 90 degrees one to the other, not 180, or in alignment.  Thanks for the tip about brass jaws. 

 

I was able to get the snap rings matched up for each opposing journal pair.  .062" was the most common size snap ring I needed to use.  If I recall correctly, the new snap rings which came in the package with each of the new u-joints were of the following sizes: .060", .061", .062" and .064", .065", .066"  There were 12 supplied with each u-joint - two each of those sizes.  Oddly, .063" seemed not to be present.  I carefully lapped two .064" snap rings to get the .063" I needed.

With the axle in the vise and using the dial gauge, I was able to confirm  about .001" of free play axially for each direction on the trunnion.  The u-joints feel a bit "heavy" in their movement.  However, I am certain after very careful checking that the free play is what it should be.  I could see the needle on the dial gauge move easily and then stop, as I applied pressure to move the u-joints up and down in their installed state.

I may very well send the axles off for balancing.  Since I am installing a 240SX transmission, I may need to get a driveshaft made also.  If I can use my driveshaft as is, which may be possible, I will likely send it off for balancing with the axles.   

Numbers indicate the snap ring used in thousandths at each location with opposite journals using same sizes, of course.

  

 

[Mark Maras]

Nothing wrong with having the axles balanced but because they turn approximately 3 1/2 times slower than the drive shaft I've never experienced or heard of a balance problem with them. Driveshaft balance problems are very common however.