Rearend savvy people, video of my 8.75 gears...update!

[AKcharger]

Hi fellas, still kicking around getting this chunk fixed for summer. If you recall from another post, last time I had the 3.91s in the car before and it sounded AWFUL! I pulled 'em out after 5 miles. Anyway, I put my 3.91 gears and another extra 3.23 chunk side by side. You can hear the 3.91s as they spin, but the 3.23s are quiet. Weird thing is if you hold the pinion and move the ring gear, the play on the ring is about the same between them but the 3.91s make noise all the time...and they both have the same amount of lube on them.

History on the 3.91s is fuzzy, but I THINK someone rebuilt them then sold it to a guy I know who never installed them who int-turn sold them to me. Now, one big red flag was when I got it home and inspectred it carefully, I noticed part of that spacer button wedged in the ring gear   Looks like it must have fallen out at one time and "took a ride" Anyway, no teeth are chipped or damaged and the wear pattern looks OK to me. I even had a guy (who claimed he did rearends all the time) come check it out and put some micrometers and such on it and said it good. So I installed it and found out...not so much.  

So from this video what do ya' think, easy fix, serious damage or is it a boat anchor? (for a very small boat)



Thanks

AK

[AKcharger]

Oh, if it matters both are 489 units with the 3.91 being a clutch type SG and the 3.23 a cone SG

[Tilar]

Could be a bearing, pinion preload which could mean a crush tube that was used over again or it was torqued down too tight. Also pinion depth but I'm not sure if depth is adjustable on these or not. I'd pull the bearing caps and take a look at the bearings and races. If there is a mark on the bearings or races that you can see it can cause a noise, If you can feel a mark it WILL make a noise.

If you are not familliar with differentials, the caps must match. If someone had this apart and put the caps on the wrong side there is a really big chance that the bearings are in a bind.

If I had this on my bench and were going to check it out, I'd pull the bearing caps and the ring gear assy out and see how the pinion feels when you turn it. Both differentials should feel the same when you turn them.

[mauve66]

either bearings or teeth whine, you can use some white lithium grease on the teeth then rotate it around and check the engagement, should be centered top to bottom and side to side per the manual, has pics in there also

[elacruze]

Pinion bearings.

Pull the carrier out, spin the pinion by itself. I don't see any way that can be noise from the gears themselves.

[firefighter3931]

Bill, the 489 cases use a collapsable crush sleeve to set the pinion pre-load. If the same crush sleeve was re-used and the torque values not matched identically the pre-load will be off and noise wil result. That appears to be the case here. Ratech makes a solid spacer kit that comes with shims to custom tailor the pinion pre-load and this is a worthwhile upgrade. The crush sleeve is a common failure point with the 489 centersections because under extreme conditions (or improper R&R) the sleeve can collpase and proper interface between the pinion gear & ring gear will be compromised resulting in excessive noise and eventually failure.

It could also be a bad bearing as mentioned above.

If it were mine i'd send it to DrDiff for an inspection and overhaul. Cass does a lot of 8.75 & Dana rebuilds and has all the tools to do the job right. His pricing is very fair and you will get a top shelf piece in return that will give you years of service without worry 



Ron

[68chargerboy]

the reason that they move like they do when you were wiggling them is because the backlash is wayyy out of spec.  did you just rebuild it? the pinion has nuthing to do with backlash.  also you said both ring gears seem to move the saem but .003" out of spec could casue this and no way noticeable by feel/eye.  where are you located? ive redone a tone of axels so if ur in my area i can check it out for ya.  as for people saying its the sidebearing caps, you would feel a crazy amount of total turning pre-load when turning the yoke, and in the vid it didnt seem all that hard to turn.

zach

[68chargerboy]

ps i just saw that u said the wear pattern is good, backlash cannot be seen when doing a contact pattern 
im guessin its backlash

Zach

[John_Kunkel]

I would but a load on the ring gear (bear down on it with the palm of your hand) as you're turning the 489 to see if the noise changes.

[AKcharger]

Thanks for the feedback guys:

- John, I pressed down on the ring gear as you described while turning, MUCH quieter but still more noise that the 3.23 set-up
- 68chargerboy, Thanks for the insight and offer to help...but Alaska is a bit far. TO tell you the truth though it might be worth a plane ticket to fly one of you guys up vs. pay for a shop to do the work 
- Ron, copy all on that crush sleve, since this was supposedly rebuilt not too long ago I bet the guy did it wrong. Shipping to/from Dr. Diff woud kill me so will have to be a local fix

[John_Kunkel]

On the 489 you will occasionally see well-used Sure-Grips that actually have wear marks where the pinion teeth have made contact because the pinion was set too shallow in the case, this might be one of those cases. Put some marking compound on the backside of the pinion and spin it to see if it's making contact with the SG unit.

[AKcharger]

Guys
Here's where I'm at:

- I coated the S/G unit in a thin layer of white lithum grease like Ron suggested and spun it a few times, no contact.
- I pulled out the ring unit and checked the pinion...didn't wiggle around or anything BUT it doesn't turn freely. It's not as bad as when the ring is installed but you can feel it binding as it spins
- All the bearings/races looked good on the ring/SG side as well as no obvious damage to ring pinion so sounds like it's that preload thing you guys were talking about

So 2 questions:
1) does that binding pinion sound like the smoking gun?
2) If it is, Am I still looking at $700 to get it fixed???

[elacruze]

The way I see it, you now have a $700 budget to buy tools and learn the skills yourself!
You don't need very much besides patience, if you already have a decent set of hand tools. The one thing most people don't have is a GOOD Inch-pound torque wrench; you may be able to borrow one instead of buying, if you don't plan to use it very often.

Here's great reading;

http://www.differentials.com/install.html (I didn't link to the disassembly/inspection, be sure to mark your caps etc.)

There's really very little to screw up, it just takes patience and measurement. I'd install new pinion bearings and seal, at least though.

[AKcharger]

Thanks e-cruise. I've never done a rear end but it galls me to think it would cost $700 to pull a pinion, install it with shims, mic check it and pull it apart and repeat till its right. I sure am tempted to just get the tooling. Only problem is I'll likely never do the job again and I'll have the stuff laying around.

So think just reshimming it would do the job?

[elacruze]

Thanks e-cruise. I've never done a rear end but it galls me to think it would cost $700 to pull a pinion, install it with shims, mic check it and pull it apart and repeat till its right. I sure am tempted to just get the tooling. Only problem is I'll likely never do the job again and I'll have the stuff laying around.

So think just reshimming it would do the job?

ok wait a minnit, up thread you said the pinion doesn't turn easily...it has some preload so it will have some resistance. Is the noise still present at all, or did it go away with the carrier removal?

I went back and reviewed the video again, I'm pretty confident it's pinion bearings. Impact the pinion nut off, and have a look. The races should be smooth with no pits, dents, or discoloration. The bearing cages must be straight and loose, too.

[AKcharger]

It still make noise but not as bad. Biggest thing to me was it's not "Smooth" when the pinion is turned. I can understand a little pre-load but it turns with "rough spots" The carrier bearing looked almost new, I suspect the same for the pinion but unfortunatly tearing that down is beyond my tool capacity right now

[Challenger340]

Some thoughts;
You've definately got a problem there ? yeah right, nothing ya don't already know ?

Bottom line here is Pinion "Depth" upon installation, is Critical to a good Gear setup, and the MOST important Factor !
For definition of "depth", what I mean here is the Pinions installed position, relative to the Carrier Case Front to Rear, which is determined in Thoudsandths of an Inch, from the Centreline of the Carrier Main Caps to the Visible Top Flat Part of the Pinion Gear.

NO two Carriers are the same from the Factory, and NO two sets of Gears are either.
NOTHING has more influence upon good Gear Setup, than Pinion Depth. Without it, it NEVER happens, unless you just plain "Get Lucky".

First thing you have to do, is dis-assemble that Carrier & Pinion, and Inspect all Bearings/Races FIRST.
If OK,
Then before you re-assemble, look for a "Pinion Dimension" stamped on the Head of the Pinion.
The dimension is "particular" to THAT Pinion only, from when it was produced and measured at the factory.
That is the dimension you must satisfy, from the C/Line of the mains, to the HEAD of the Pinion, by use of Installed Shims, behind the Pressed On Rear Pinion Brg.
This is usually done by use of a Pinion Depth Gauge, to actually "measure" in Thousandths, a "mocked up" setup for adjustment.
Then, the procedure can begin, whereas the Brg can be pressed off, shims added or removed, pressed back on, and "re-try" again until successful/proper dimension from the head of the Pinion is satisfied.
No easy task for someone who may only ever do this once ?
Thats why shops who do this Regularily, have Pinion Depth Gauges, and various "Honed out" Brgs that don't need pressed ON or OFF to make the process speedier ?
Once Proper Pinion Depth is achieved, a Final Pinion/Crush Sleeve assembly can be performed @ Torque, and the correct Rotational Torque Force measured with the Inch Pound measurement.
After that, Backlash on the Ring Gear can be set easily, by adjusting the "side to side" Carrier Cap Preload.

Questions;
Is there a "stamped" Dimension visible on the Pinion Head ?
or,
Just the "Chalk" Marks ?

[AKcharger]

Thanks 340...hmmm that makes me less inclined to try it myself, I thought I'l just be dealing with the pinion depth  Anyway, only numbers I could find is those painted numbers in the above picture.  Sounds like it will need to go to the shop, all I need now is some $$$

[Cooter]

I gotta "741" 3.91 Sure Grip  if you can't get this one going.....Lemme know...This one IS quiet..

[firefighter3931]

Thanks e-cruise. I've never done a rear end but it galls me to think it would cost $700 to pull a pinion, install it with shims, mic check it and pull it apart and repeat till its right. 

Bill, who quoted you $700 to setup that centersection ? That's way over the top, inmo. Maybe if you supplied a bare housing with no parts i could see that but all you need is a spacer kit for the pinion ($30) and possibly a bearing kit ($120) and a few hours labor by a shop that knows what they're doing. Even a rebuild kit for the cluch suregrip is only $100 and it might be worthwhile having that done while it's all apart....or at least inspected closely to see if it's in descent shape. 

Bob's explanation is on the money, lots of expertise and precision involved to properly set one of these up. That's why I leave it up to a drivetrain specialist that has all the tools and knows all the tricks. 



Ron

[AKcharger]

Well I did say a "rebuild" so perhaps that's adding in some time. I really thought I'd get a big savings bringing the chunk in but I guess not. One shop I go to all the time, kind of a general repair place has a guy that does rear ends and he said about $700 in labour. Then I went to a gear and transmission place and they said "about $1000 including parts" so that's about the same. Perhaps if I told them I just need the pinion reinstalled?

[AKcharger]

Gent

Just some follow-up. The problem was with the pinion. Seems the rebuild guy only replaced one of the pinion bearngs and screwed up the installation. I had the whole thing rebearinged and the SG rebuilt, will pick up tomorrow....$714 

[elacruze]

We demand burnout video. 

[AKcharger]

 

[firefighter3931]

Gent

Just some follow-up. The problem was with the pinion. Seems the rebuild guy only replaced one of the pinion bearngs and screwed up the installation. I had the whole thing rebearinged and the SG rebuilt, will pick up tomorrow....$714 

It had to be a pinion issue based on the noise it was making....glad it's fixed Bill 


Ron