Axle side yoke end play!!!

[Duke W.]

Well, here we go again. We've been down this path before, and at this point
I think I'm just trying to prove to myself that I'm not crazy.

I'm helping Bill Bradley write an article on Corvette positration axles and want to take another shot at the side yoke end play issue.

I recall from many years ago when I rebuilt the axle on my car that there
was a specified side yoke end play. I found the spec in a borrowed Chassis Overhaul Manual, 1971 vintage as best as I recall.

Bill's '66 Chassis Overhaul Manual has a differential side gear/differential pinion gear backlash spec range (note that this is different than the ring and pinion backlash), but no spec on side yoke end play. Incidently, the two are directly related. The '63 Corvette Shop Manual says nothing about either the differential side gear/pinion gear backlash or side yoke end play, but it illustrates the old Borg-Warner type positraction that was superceded by the Eaton design.

Joe Lucia looked at his available documentation some time ago and couldn't find a side yoke end play spec, but I want to ask everyone with a Chassis Overhaul manual from the sixties to seventies to take another look. I recall that the side yoke spec was in the axle overhaul chapter, particularly in the section on positration, and it was a note in the text, but check the specs section, too. I don't recall that there was a differential side gear/differential pinion gear backlash spec. Is it possible that the backlash spec was replaced by a side yoke end play spec in later years? As I said, the two are directly related, so if one is set within a specified range, the other should fall within a range if all the parts are within production tolerance.

We want to try and put this issue to bed if possible, but need help from the membership to research all years of the Chassis Overhaul Manual in the C2/C3 era.

BTW, this should be a great article for those of you who like to dive deep into technical details, and those of you who what to understand how a differential, in particular a positration differential, works, but never quite figured it out. Positraction axles are probably on of the least understand technologies on cars. Bill took a lot of great photos to go with the text that go a long way in helping to explain how positraction axles work, and how to do a proper overhaul.

Either respond in this thread or send me an e-mail if you find anything.

Duke

[Wayne W.]

Re: Axle side yoke end play!!!

Probably just prooves my feeling that it aint very important anyway. The end play just ends up measuring the distance from the shaft bumping on the center pin to the lock ring bumping on the face of the spider. Who really cares whether it is .005 or .050. It makes no difference in the operation of the unit. The only time I get concerned is when its .5. Then I know that the clip is off.

[Chas Kingston]

[Jim T.]

Re: Axle side yoke end play!!!

Duke I just reviewed my 1971 Chassis Overhaul Manual. Under disassembly it reads to inspect side gear yokes closely for spine wear or yoke cracking. Mentions side gear yoke and/or seal replacement. Very last entry for the Corvette sectin of rear axle differential carrier 5. Insert side gear yokes into side gears and install snap rings. (fig. 30C). Perhaps the information is in a later year Chassis Overhaul Manual.

[Jim T.]

Re: Axle side yoke end play!!!

Reread Duke's post and read through the 71 Chassis Overhaul Manual Positraction Differential Cases and found no mention of the end play for the side gear yokes in this section either. Will check out my 85 and 96 service manuals to see if there is any information on side gear yoke end play.

[Joe C.]

Re: Axle side yoke end play!!!

Duke:

My 1963 Shop Manual has NO ref to either pinion to side gear lash, or side yoke end play........which is also what you found. Also, my 1965 Supplement only shows side gear to spider lash as .001" - .006"..............also what you found.

I replaced my pinion shaft, which was eccentric @ the stub axle interface by about .002". I also replaced 1 stub axle, which showed galling @ the pinion shaft interface. I also installed new retainer clips for the yokes (these were .002" thicker than the old ones. When I rebuilt my diff case, I shimmed for .006", and 005" L and R pinion to side gear lash, respectively. UPON COMPLETION, I measured the stub axle end play..............it was less than .001", both sides. It required 59 ft lbs to cause diff clutch breakaway @ 70* F ,53 @ 40* F.

THIS IS INTERESTING:

My 1985 Shop Manual HAS a stub axle end play spec. It is .0005" - .0085". It also specifies different color coded snap rings to achieve the desired end play.

Joe

[Jim T.]

Re: Axle side yoke end play!!!

Duke concur with what Joe posts about what is in our 85 service manuals. My 96 service manual lists the end play of the inner axle shafts the same except the mm size is listed first re: 0.013 mm (0.0005 in.) minimum to 0.216 mm (0.0085 in.) maximum. The seven snap rings for the model 36 start at 0.050/1.27 in./mm and end with 0.080/2.03 in./mm. The eight model 44 start with 0.075/1.91 in./mm and end with 0.110/2.79 in./mm.

[Joe C.]

PS

It seems that the early posi units, i.e. the BW design used up until '64, were still very new, and probably not well understood. You can see that the specs were more comprehensively written for the second generation (Eaton) unit. By the time the C4 came around, they had long since perfected it, and the Dana 44 and 36 units finally showed a stub axle end play spec.

Your query is a very interesting one, but the question might be, WHEN, exactly, did the end play spec first appear? Did it start with the Dana rear, or some time before?

Here is some more food for thought. I did not find any spider to side gear clearance (lash) spec for my 1985, only the aforementioned end play spec.

Because the total stub axle end play is a function of:
1. Spider to side gear clearance.
2. Snap ring thickness.
3. Wear/galling on the thrust end of the stub axle.
4. Wear/galling on the contact surface of the spider (pinion) shaft.

It stands to reason that, IF the side gear lash is set correctly, AND, the stub axles and pinion shaft show no wear, THEN the end play will fall within acceptable bounds. The only condition that will cause excessive wear to the stub shaft thrust surface(s), and/or the pinion shaft contact surface is gross mismatch between diameters of the rear tires OR prolonged periods of driving under clutch breakaway conditions (i.e. Gymkhana racing).

So, the specification issue becomes a matter of semantics. In later years, the yoke end play number becomes determinant. In earlier times (post 1963), lash becomes the determinant. And 1963 and before, CLUTCH BREAKAWAY was the determinant. Indeed, if the BW clutch unit slipped before the required 70/40 ft-lbs range, then this indicated a problem with clutch paks, preload springs, lash, pinion shaft wear, or stub axle end wear. I would think that many folks in the BW period who tore down their diff, and found no galling/wear on the stub axle ends and pinion shaft, and serviceable discs and preload springs, would reassemble their diffs and call it good. There would be some, however, who would TEST for the clutch breakaway threshhold, and if it failed, then the only option would be to decrease the spider to side gear clearance (this is empirical deduction at its best). There were probably lots of folks who assembled their "posi" diffs, and actually had open rears. BOTTOM LINE: if the breakaway torque is not up to snuff, then you do not have a limited slip diff.

Joe

[Duke W.]

Re: Axle side yoke end play!!!

Does the '85 Shop manual specify BOTH differential side gear/pinion gear backlash, AND yoke end play?

The way the C2 diffs are engineered, it appears that the gear backlash is set to spec and the yoke end play is "net build" based on all the various dimensions that come into play, though yoke end play is apparently not specified.

It sounds to me that the C4 diffs allow both to be tuned into a specified range - case shims for the backlash and different clip thicknesses for the yoke end play. Is this how C4 diffs are set up?

Duke

[Joe C.]

Re: Axle side yoke end play!!!

Duke:

The '85 Shop Manual only specifies the stub axle end play (and this is assuming that the stub axle thrust surfaces, and the pinion shaft interface has not been worn/galled by severe duty).
Again, upon visual inspection of the C2 Eaton unit , if all components (clutches, stub axles, pinion shaft, stub retainer clips)show no wear, then if the spider/side gear clearance is set to spec, then all else will be within tolerances. Bottom line will be the clutch breakaway torque.

[Duke W.]

I found something!

Chevrolet Power Manual, Fifth Edition, page 6-12:

"The yoke end play must be reduced to less than .005" using hardened steel shims, which must be fabricated".

I assume this means that shims must be fabricated and placed on the yoke between the side gear and retaining ring. If the side gear/pinion gear backlash is within the .001"-.006" spec and all other components are within OE machining tolerance, the yoke end play will likely be no more that about .010", which should be adequate for normal street use.

The Power Manual recommendations are additional prep and tolerances recommended specifically for racing.

This same verbiage is in the fourth edition, but my copy of the Second Edition says: "The yoke end play must be reduced to less than .005" using shims provided in the yoke kit (???). No yoke kit with shims part number is referenced. Maybe that's why the verbiage changed in later editions.

Duke

[Craig S.]

Re: I found something!

Duke - while not a spec, Charlie Smith in the BG classes state he prefers the stub end play in the 0.001-0.005 range after rebuild. He also feels over 0.030 is the point where internal wear on the clutch packs or axles is at the point where the rear should be rebuild. I know there are other opinions out there.....Craig

[Duke W.]

Re: I found something!

One to five thou sure sounds okay to me. What I don't have is data
to correlate differential side gear/pinion gear backlash to yoke end play,
but I THINK that if the backlash is within the one to six thou spec the yoke end play will be somewhere under ten thou (assuming that all critical dimensions are within blueprint spec) and the tighter the backlash the tighter
the yoke end play.

For a street rebuild I would prefer gear backlash near minimum, but be sure
to give it an easy breakin. For racing, backlash in the mid to upper range would probably be preferable if it's going to be run hard from day one.

Duke

[Roger Legge]

Re: I found something!

Chevrolet Power Manual, Second Edition has it worded exactly the same way.

Roger

[Steve D.]

Re: Axle side yoke end play!!!

Joe

When you measured breakaway torque, did you have the clutch plates lubricated or dry?

This is a very timely thread for me, as I am reassembling my unit. (63 convertible, 67 Eaton unit)

Steve