Acceptable ring/pinion play

[DIRTBIKEUSA]

I was under the cruiser today pulling the front drive shaft for a U-joint replacement and noticed that the front pinion/ring lash seemed excessive. Like maybe 15 deg of play in rotation, enough to hear the gears rattle a bit and bang together.

Time for a differential rebuild?

I have the parts lined up just wanted to hear some opinions. I did just change the gear oil and it was very bad, glittery but no chunks.

 

[baldilocks]

How much glitter? Pics? Does the pinion seal leak? Have you heard concerning whining, grinding, or other noise from the front diff?

 

[DIRTBIKEUSA]

I don’t have pictures of the drained fluid but it was THICK dark and glittery for sure.

I have not heard and unusual noises. Everything seemed ok until I seen the fluid and then checked the drive shaft today.

 

[baldilocks]

Thick and dark indicates moly grease has migrated from the knuckles into the gear oil; no concern there. Milky looking gear oil bad juju… Differentials wear and oil that’s been in use for years will display the evidence of that wear.

Based on what you have posted so far, I’d say fill it with the correct oil and run it. The axle oil seals probably need to be replaced.

 

[DIRTBIKEUSA]

Thick and dark indicates moly grease has migrated from the knuckles into the gear oil; no concern there. Milky looking gear oil bad juju… Differentials wear and oil that’s been in use for years will display the evidence of that wear.

Based on what you have posted so far, I’d say fill it with the correct oil and run it. The axle oil seals probably need to be replaced.

Good point on the Molly grease.

My concern is the amount of lash I think I have. The pinion rotation feels good.. it’s the lash between the pinion and the ring gear I’m concerned about.

For a lack of better terms, Do they typically feel “sloppy” or tight?

 

[JoeCova]

Too much human error in your diagnostics for us to tell.

If you had that much backlash your R&P would barely engage and probably have all kinds fo noises. When I checked my factory gears before I regeared they were 0.008 and doesnt change unless you destroy something or someone did a sloppy job when they were in there.

Can always pull it and check the backlash

 

[baldilocks]

There needs to be a certain amount of lash or space. Your estimated 15 degrees might be a little on the fat side but given your answers to my original questions, and it were my truck, and I didn’t have $1,000 falling out of my pocket, I’d run it.

What you could do for peace of mind is pull the third member and do a bench inspection. For further confirmation you can take it to a shop for inspection and go from there.

 

[BILT4ME]

Good point on the Molly grease.

My concern is the amount of lash I think I have. The pinion rotation feels good.. it’s the lash between the pinion and the ring gear I’m concerned about.

For a lack of better terms, Do they typically feel “sloppy” or tight?

If you are talking about moving it by hand from full left to full right being 15°, then it's probably in the ball park. That includes all axle spline, birfield tolerances, drive flange tolerances, and all other sloppiness in there.

When there is no oil in it, you turn the DS ever so slightly until you feel it touch the ring gear left and right. That is less than a few degrees.

My truck has 357K on it and I have noticed the splines on my axle shafts are worn about halfway through so I get a serious clunk when I let off the throttle and get back on it.

 

[thegadgetguy]

FWIW, I was also concerned about the amount of radial play I was noticing on my front pinion the last time I rebuilt my front axle. I was already planning on replacing the pinion seal, so I went ahead and pulled the front 3rd member. When I had it on the bench, I realized that basically all the play I was feeling was in the axle splines/birfs - there was so little play in the actual pinion/ring gear interface I couldn't feel it by hand or see it visually at all. Unless something has gone very wrong in your front 3rd, this spline/birf play is most likely dominating what you are feeling by hand, and is normal.

 

[Broski]

If you are talking about moving it by hand from full left to full right being 15°, then it's probably in the ball park. That includes all axle spline, birfield tolerances, drive flange tolerances, and all other sloppiness in there.

When there is no oil in it, you turn the DS ever so slightly until you feel it touch the ring gear left and right. That is less than a few degrees.

This ^^^
I was concerned when I snapped both front RCV and was doing a full tear down to inspect everything. So I took the third to the shop that does my gear setup and what he told me is the same as @BILT4ME just stated. I put it back in all is fine

 

[DIRTBIKEUSA]

I’m glad I asked. Seems like there are a bit more moving parts that would feel like bad carrier bearings or worn pinion/ring.

Typically when I have pulled a third member (heavy duty) it is because the pinion bearing had play and the ring was clashing. I do remember front diff clearances are looser in SFA applications. Just wondering what you all have run into.