Excessive play in axleshafts (at the spline - sidegear junction) ?

Hello to all Mopar folks!
On my 69' Road Runner, equipped with an aftermarket or refurbished 742 8.3/4 Sure Grip, I have some play in the axelshafts. See on videos below. I wonder if it is normal, or if this could explain the strange noises I hear in the rear drive train under specific conditions (details below).





I confirm the axles can be rotated back and forth while the pinion (and crown) do not move. There is zero play in the longitudinal direction, or any other direction when shaking the axles.
According to the mechanic who worked on the car, it might be caused by worn out splines. Phenomenon is seen on both sides but seems more accentuated on passenger side.
The axleshafts seem original, beside this potential worn out splines they look ok, bearings are clean and must have been changed some time ago. (There are 30 splines on the internal side of the axles).

The rear diff was also inspected, but not torn apart, it looked fine, teeth on the crown are ok. Fluid was super clean when drained (Motul 300 Ls + redline friction modifier). The gear tooth contact pattern was tested, it was nominal (although there might be a little more than recommended backlash between pinion and crown, we chose not to modify this at this stage).

Apart from this play, or because of it, I have bad clunking noises coming from the rear drive train every time :
- I turn left on a tight corner (so with moderate speed, for example at a red light or at an intersection) + I give some acceleration (if I take the same tight turn without accelerating, just being in drive with some initial speed, no noise at all)
- I go backwards with my steering wheel turned to the right, the more I turn the steering wheel the more the phenomenon occurrs. Car is like moving but with small hesitations.

Lastly, I add that we had checked the driveshaft connection on the transmission side. The splines of the trans axle bite enough in the yoke.

Thank you for any good comments on this.

New axleshafts can be bought but these are pricey items!
Marc

I would say normal. Hopefully someone else will chime in.

Those axle splines should be a close fit in the side gears. Second video of diff on bench.
Something is wrong in that differential or you have a mis-match of components.

It has green bearings.. I wonder if someone forgot to remove the thrust buttons

Could be the thrust button left in and the carrier has been chewed out.
I would definitely pull that diff completely apart.
All the parts should fit "closely" together - axle spines in to side gear splines - side gears in to carrier.
I think the problem will be fairly obvious once you start to check stuff.

RemCharger said:

It has green bearings.. I wonder if someone forgot to remove the thrust buttons

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When I installed green bearings 20+ years ago in my 8 3/4 with 489 case and Detroit Locker with the large thrust button, I left it in because I didn't know any better. Years later when I swapped gears, the 2 halves were in the bottom of the diff housing. No damage was done.

in you initial post you state when you turn to the right you get small hesitations when turning , that sounds like you have clutch chatter ,, add more friction modifier and go out and drive your car to heat up the oil then find somewhere to safely do a series of tight right and left turns ( donuts ) at slow speed this will distribute the gear oil over the clutch plates and should solve that problem .. if it doesn't you will have to do a fluid change go with 75w140 Royal Purple and a bottle of Ford friction modifier if you have it available to you ,, the free play turning the axle shafts is normal .

steve340 said:

Those axle splines should be a close fit in the side gears. Second video of diff on bench.
Something is wrong in that differential or you have a mis-match of components.

Click to expand...

Hi Steve, you mean, wrong by the level of play of the axle ?

OKDart said:

When I installed green bearings 20+ years ago in my 8 3/4 with 489 case and Detroit Locker with the large thrust button, I left it in because I didn't know any better. Years later when I swapped gears, the 2 halves were in the bottom of the diff housing. No damage was done.

Click to expand...

Hum, we did not hear any part moving in the diff once removed, when we moved it from one place to another in the shop, or under the car. Yet, now that you mention it, I am bit worried about this thing!

john-9 said:

in you initial post you state when you turn to the right you get small hesitations when turning , that sounds like you have clutch chatter ,, add more friction modifier and go out and drive your car to heat up the oil then find somewhere to safely do a series of tight right and left turns ( donuts ) at slow speed this will distribute the gear oil over the clutch plates and should solve that problem .. if it doesn't you will have to do a fluid change go with 75w140 Royal Purple and a bottle of Ford friction modifier if you have it available to you ,, the free play turning the axle shafts is normal .

Click to expand...

I'll do the donut turns again yes. Motul 300LS I put in has these specs : 75W90.
Since I added the friction modifier some months ago (because I had these chattering noises), I did not see any improvement. But I admit I did not do the donut turns back then (I would have expected the additive to be correctly distributed over the clutch plates since) Let's give it another try.
I am pretty much convinced this has to do with the friction between the plates that send small jolts when in action, which then makes any loose piece play and resonate where it can

I installed a set of the non-adjustable "Green" bearings when I restored my Satellite based on a friend's recommendation. The rest of the rear was, and still is, original - 742 case, 3.23 sure-grip. The rear end "clunked" when turning afterwards. The bearings started making noise at highway speeds after about 15 yrs and 15-20k miles so I went back to the factory setup - adjustable, tapered roller bearings - and all the rear end noise went away.

That's an old green bearing, no snap ring for a stop. Think that the thrust buttons should have been removed for those. The snap ring green bearings do not require them to be removed. Have three cars with snap ring type, buttons are still in.

Yes in the second video of the differential on the bench something does not look right.
Seems to me that "looseness/play" is not right.

Bird 426 said:

That's an old green bearing, no snap ring for a stop. Think that the thrust buttons should have been removed for those. The snap ring green bearings do not require them to be removed. Have three cars with snap ring type, buttons are still in.

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From the technical diagrams I've seen, removing the thrust button would let the axle penetrate more deeply in the differential, is that right ? For what benefit ?
When we put the axle back in place, the axle could be pushed in until the plate shown on pic with the arrow reaches the axle housing. So, from that perspective, no "depth issue"

Well, the new greens have a stop snap ring on the bearing race, it sets the depth of how far the axle should go in.

'69 BDX said:

From the technical diagrams I've seen, removing the thrust button would let the axle penetrate more deeply in the differential, is that right ? For what benefit ?

Click to expand...

Sort of right. Factory, the 2 axles butt up against the thrust buttons , and then one side is adjusted to the correct amount of play( clearance). So if you just jam in 2 non adjustable axles... how will you know if they are under pressure or not. You won't. Might get lucky, might not. If there is side pressure on the green bearing, that's what kills them . That style of ball bearing wants zero force on either side.

'69 BDX said:

When we put the axle back in place, the axle could be pushed in until the plate shown on pic with the arrow reaches the axle housing. So, from that perspective, no "depth issue"

Click to expand...

You don't know if the axles are butting together when you do the final torquing.

'69 BDX said:

View attachment 1872734

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RemCharger said:

Sort of right. Factory, the 2 axles butt up against the thrust buttons , and then one side is adjusted to the correct amount of play( clearance). So if you just jam in 2 non adjustable axles... how will you know if they are under pressure or not. You won't. Might get lucky, might not. If there is side pressure on the green bearing, that's what kills them . That style of ball bearing wants zero force on either side.

You don't know if the axles are butting together when you do the final torquing.

Click to expand...

Very interesting, thanks a lot.
It encourages me to have the whole rear end reviewed by some specialist.

Been slowly driving in circle tonight, once proper oil temperature reached. In both directions and also in reverse gear. No chatter or funny noises whatsoever during those donuts, nor hesitations, a very smooth ride. When pressing more the gas pedal, just as smooth. Upon harder press, wheels would just start to drift.
But later on, back in normal driving conditions, noise would be heared again on very specific move (turning at an intersection)..
I'll probably try a thicker oil upon next fluid change...and try to get in touch with other mechanics in the meantime.
Thanks to everyone for your contributions

I was always told to do figure 8s and I have for over 50 years. Kim