How Much Play (lash) at Pinion Hub is Too Much?

rand49er · #1 (**permalink**) 08-19-09, 04:15 PM

Have this ongoing sound/noise while driving (duh!) that I've been trying to get my arms around for a while now. Gave Nutz a ride the other day at the Dream Cruise, and he suggested that it could be the pinion bearing is shot.

Well, a few minutes ago, I got under the car to yank and pull on the pinion hub, and it's as solid as can be ... no noticeable clunk or side-to-side movement. BUT, when I turn the pinion hub by hand, I'd say there's a good 1/4" (6 mm) play or lash as measured at the circumference of the pinion hub before the axles start to turn. AND, it gives a good "clunk" when I do that!

Is that amount of play "normal?" Is that too miuch? This isn't the sort of measurement that guyz would normally have done very often let alone have it on their lips during everyday conversation, so I don't expect a huge response. Anybody observed this before? Thanks!

Kmajecki · #2 (**permalink**) 08-19-09, 05:35 PM

Where is the pinion hub? Sorry, i really dont know. Are you talking about where the driveshaft enters the rear diff?

**The Tony Show** · #3 (**permalink**) 08-19-09, 05:48 PM

Cue Darkman with a .pdf scan from the shop manual. Damn, he's handy!

DILLIGAF · #4 (**permalink**) 08-19-09, 06:07 PM

Normal in the getrag.I freaked the first time my car was on a lift and turned the rear tires both directions.

**The Tony Show** · #5 (**permalink**) 08-19-09, 06:18 PM

I think Rand is talking bout how far the driveshaft will turn before it "engages" the diff and turns the axles. The rears turning both directions is just a sign of a limited slip diff- even my old Miata does that.

darkman · #6 (**permalink**) 08-19-09, 06:23 PM

Quote:

Originally Posted by DILLIGAF

Normal in the getrag.I freaked the first time my car was on a lift and turned the rear tires both directions.

Bingo! The true ring-pinion gear back lash is only 0.008 to 0.013 inch, but what you feel at the pinion hub is the play of the limited slip clutch packs which is much more, and as DILLIGAF reports is "normal in the getrag."

nmaier2201 · #7 (**permalink**) 08-19-09, 07:22 PM

Randy I also have that exact same amount of play... so you asked the same question I had in the back of my head.... and now I have an answer! Score another one for Darkman! Thanks for the Q and the A

rand49er · #8 (**permalink**) 08-19-09, 08:24 PM

No-o-o-o-o-o! I don't want this to be normal!!! I want it fixed!

Please tell me that if I replace _______ (<-- fill in the blank), it'll be better!

ewill3rd · #9 (**permalink**) 08-20-09, 07:56 AM

What you are feeling is "backlash" and it needs to be there.
Sorry.... and what you are feeling is not the "actual" backlash but probably accompanied by some other play that is also normal.

atdeneve · #10 (**permalink**) 08-20-09, 09:00 AM

Bit off topic, but since we're in the general area, anyone happen to know the accel/decel percent lock-up of the limited slip.

Never saw it documented anywhere and I wanz to know...

rand49er · #11 (**permalink**) 08-20-09, 09:21 AM

Quote:

Originally Posted by ewill3rd

What you are feeling is "backlash" and it needs to be there.
Sorry.... and what you are feeling is not the "actual" backlash but probably accompanied by some other play that is also normal.

I was hoping you'd chime in, Bill. Thanks.

Quote:

Originally Posted by atdeneve

Bit off topic, but since we're in the general area, anyone happen to know the accel/decel percent lock-up of the limited slip.

Never saw it documented anywhere and I wanz to know...

j/k I've got my answer ... I'm good. Well, maybe not good ... maybe more like okay. Well, maybe not okay more like no worse off than before.

Slithering_Joe · #12 (**permalink**) 08-23-09, 01:00 PM

Quote:

Originally Posted by darkman

... but what you feel at the pinion hub is the play of the limited slip clutch packs which is much more...

What do you mean by "play?" For each side, a clutch pack/disc is right up against a side gear which is directly attached to the axle shaft. There's no "play" in this area. Unless, the Getrags have a lot of "slop" between the clutch disc/plate grabs the teeth of the side gear. Just curious.

darkman · #13 (**permalink**) 08-23-09, 02:27 PM

Quote:

Originally Posted by Slithering_Joe

What do you mean by "play?" For each side, a clutch pack/disc is right up against a side gear which is directly attached to the axle shaft. There's no "play" in this area. Unless, the Getrags have a lot of "slop" between the clutch disc/plate grabs the teeth of the side gear. Just curious.

The play in question is the total degrees one must turn the pinion gear before the axle, which is driven by the ring gear commences rotation. Thus, the play is inclusive of all rotational clearances. Additionally, every one degree of rotational play of the ring gear components translates into almost four degrees (3.73 to be exact) of play measured at the pinion gear because of the gear ratios. The primary component after the ring-to-pinion gear clearance is the clutch packs. I have not examined these particular clutch packs, but based on my experience with multi-plate wet clutches in motorcycles of similar design I think most of the rotational play would be found between the teeth of the seperator plates and the hub in which they reside.

Slithering_Joe · #14 (**permalink**) 08-23-09, 06:37 PM

Sitting on jack stands with the tires in the air, the clutch pack should not contribute any 'play' since there is no load on the tires. The tension on the clutch pack even if they are crapped out should hinder any additional rotation.

darkman · #15 (**permalink**) 08-23-09, 08:43 PM

Quote:

Originally Posted by Slithering_Joe

Sitting on jack stands with the tires in the air, the clutch pack should not contribute any 'play' since there is no load on the tires. The tension on the clutch pack even if they are crapped out should hinder any additional rotation.

The play being discussed exists whether the tires are on or off the ground. Specifically, if you grab the driveshaft or pinion yoke and turn it you feel 1-2 inches of rotation before you meet resistance. If the wheels are off the ground you can, with enough force get them to turn by continuing pas t this point of resistance. If the wheels are on the gournd you cannot, by hand, make them turn for obvious reasons.

In looking at the internal components there are only a few places that look to be candidates to explain the play. Since the ring gear is bolted to the transfer case there is no play there. From the transfer case the power is transmitted to the separator plates in the clutch set through teeth riding in groves in the transfer case. Since that arrangement must have some clearance to operate at different temperatures there is some clearance which would add to the play. The power goes from those separator plates to clutch plates via friction surface. Since this is under tension it does not seem to add to the total play. The power then goes from the clutch discs to the axle side gear through splines, which again must have some clearance. Finally, the axle side gear transfers power to the axles through another set of splines, again which involve some clearance and therefore contribute some play. It is based on this series of power transfers that the play must occur. My explanation was simply to use the label "clutch pack" to encompass all of this set of components.

If you have an better explanation, by all means educate me. I have no stake in any particular explanation.