Please help... bad diff?

[euroZ06]

Hi,

I recently purschased a 3rd member (489 3.55 posi) from a member on this board.

I installed it, and went for a test drive today, and noticed really bad noise.
When you are on gas/on power, there is no noise that i can hear, everything seems to sound good. As soon as i let go of gas, this really bad noise comes on. Back on gas, and no noise. I got it up to speed a bit and threw it in neutral, noise is there.

Im in a pretty bad situation with this, i paid top dollar for this part, and it took me a long time to install it... i live in NYC and its really hard to find any shop that knows much about these cars.... ugh... i made a vid, maybe someone has an idea of what could be wrong? I spoke to the seller, he said to add some extra lsd additive... but it sounds pretty bad for an additive to solve it.

https://youtu.be/ksv9oVA8-K0

[euroZ06]

I have added lsd additive, and test drove again. Noise is still there, but noticed that if i go in reverse, it isnt there.

[BLK 68 R/T]

Did you adjust the axle endplay when you put the axles back in?

[euroZ06]

Did you adjust the axle endplay when you put the axles back in?

It seemed to be within the same spec as when i took it apart. Just a small play.

Could that be really causing this noise?? I thought the end play is more of a long term problem.

[BLK 68 R/T]

Can you define small amount of play. We talking like 1/8 inch or ?. It should only be about .010 if I remember right. Have you jacked the rear up and listened to it while it is in drive?

[euroZ06]

Can you define small amount of play. We talking like 1/8 inch or ?. It should only be about .010 if I remember right. Have you jacked the rear up and listened to it while it is in drive?

The video i posted is from it being jacked up.

Very little play, like barely any.

[BLK 68 R/T]

Are the thrust spacers installed in the center section? They fall out relatively easy.


Other than pulling the pumpkin back out and verifying backlash, gear pattern, etc. not sure what else there is if everything else checks out okay.

[justcruisin]

Those thrusts are out of a 742, the OP has a 489, the thrust wont fall out of a 489 sure grip. Has the thrust been removed for green bearings?

I think you need to locate where the noise is coming from, did it feel good on the bench. Can you hear where on the diff the noise is coming from.

[John_Kunkel]

As soon as i let go of gas, this really bad noise comes on. Back on gas, and no noise. I got it up to speed a bit and threw it in neutral, noise is there.

Classic R&P noise. Bad gears.

[BLK 68 R/T]

Those thrusts are out of a 742, the OP has a 489, the thrust wont fall out of a 489 sure grip. Has the thrust been removed for green bearings?

I think you need to locate where the noise is coming from, did it feel good on the bench. Can you hear where on the diff the noise is coming from.

Didn't know that. 

[Challenger340]

Gas ON no noise, and gas OFF noise/howling..... sounds like "rear" Pinion Bearing to me ?

The Pinion gets sucked into mesh with the Crown under acceleration which loads the front Pinion Bearing, and conversely, gets thrown OUT of mesh from the Crown under decel loading the rear Pinion Bearing.
Remove the driveshaft and see if you can move the Pinion even the slightest amount forward or backward ? which will indicate loss of crush on the Pinion crush sleeve and Bingo... there's your noise.

[euroZ06]

Gas ON no noise, and gas OFF noise/howling..... sounds like "rear" Pinion Bearing to me ?

The Pinion gets sucked into mesh with the Crown under acceleration which loads the front Pinion Bearing, and conversely, gets thrown OUT of mesh from the Crown under decel loading the rear Pinion Bearing.
Remove the driveshaft and see if you can move the Pinion even the slightest amount forward or backward ? which will indicate loss of crush on the Pinion crush sleeve and Bingo... there's your noise.

It does seem like the noise comes from pinion area. Thank you for the explanation.

Now another qusstion: im going to be taking it to a shop this week, but they dont specialize in mopars or classics (very good shop though with great mechanics). Any advise on this can be fixed, what parts would i need, and how many hours would the job take? Is this something a good mechanic can fix? Im in brooklyn ny, and dont know of anyone who knows mopars.

[euroZ06]

Gas ON no noise, and gas OFF noise/howling..... sounds like "rear" Pinion Bearing to me ?

The Pinion gets sucked into mesh with the Crown under acceleration which loads the front Pinion Bearing, and conversely, gets thrown OUT of mesh from the Crown under decel loading the rear Pinion Bearing.
Remove the driveshaft and see if you can move the Pinion even the slightest amount forward or backward ? which will indicate loss of crush on the Pinion crush sleeve and Bingo... there's your noise.

The dif looked fine, there was no wear on the gears (that i could see), everything was rotating with no isseus. Ill try to disconnect the driveshaft and see if there is any play.

[Challenger340]

If it is suspected as the 8 3/4 Pumpkin....
Part of the further differential carrier diagnostics, beyond removing the driveshaft and first checking if the Pinion has any play IN or OUT..... if it then comes to the point of removing the carrier for inspection ? would be to do what's called a "backlash" Check(about .008")..... and then a gear contact "pattern" check, to visually see just WHERE the Pinion teeth are engaging and applying load on the Crown gear teeth on both drive and coast sides.
Problem being,
if the gearset was setup incorrectly, and has been run for any length of time in that condition, excessive wear and accurate pattern checks are difficult, let be if this was a "new" gearset setup that way(incorrectly) that did not break-in properly, all bets are off for "reset" and future quiet operation.
You may get lucky, and I'm not trying to forebode disaster, just say'in.... setting up Diffy's can be troublesome at the best of times, and without at the very least a Pinion Depth Gauge with Carrier Bearing mounts specifically for a Mopar 8 3/4 Case it can be "by guess by golly" on used gears ?

If a Pinion "move" is indicated from a pattern check(ie: displacement evident in the pattern between drive & coast sides), complete dis-assembly of the unit will have to occur to facilitate, and either a new "crush" sleeve obtained for reset ? or, if these guys are really slick they can machine a solid sleeve spacer to size on a lathe, but only AFTER trial and error to find the correct Pinion Bearing shim thickness to apply.
Either way....
I always used to just Hone out the I.D. on an old rear Pinion Bearing so it would slip ON & OFF the pinion easily.... that way I could just assemble/dis-assemble easy without having to press the Bearing ON & OFF each time trying different Pinion shims until a good contact pattern check was obtained, then... and only then after which I could final assemble with the new Bearing and crush the new sleeve.

I would highly suggest you find a Shop that has the following specialized Tools, and familiarity with setting up Diffy's
* Pinion Depth gauge
* Honed out 8 3/4" Mopar Rear Pinion Bearing
* Yoke Wrench to hold the Yoke while crushing the sleeve to correct Pinion Bearing preload. (and a Torch to anneal the sleeve a bit beforehand)
* Hydraulic Press and Bearing separator.

All else fails ?
Call up Cas at Dr. Diff and just order a new 8 3/4 pumpkin.... might be cheaper in the long run ?

[euroZ06]

Oh my. Im not sure if my local mechanics shop has the special tools for this.

I found a shop in NJ that offered to rebuild it, they know these cases. $385 to take it all apart and $185 for the bearing kit

[Charger-Bodie]

I am the person he purchased this from. I feel bad that he's having trouble ,but I don't know how much I can do from so far away 200. Of the 800. Purchase was shipping. It looked and felt smooth by hand. How am I to be sure that it was installed properly. How am I to be sure it was full of oil?

How much warrentee is there expected on a 50 year old part?

[Challenger340]

I am the person he purchased this from. I feel bad that he's having trouble ,but I don't know how much I can do from so far away 200. Of the 800. Purchase was shipping. It looked and felt smooth by hand. How am I to be sure that it was installed properly. How am I to be sure it was full of oil?

How much warrentee is there expected on a 50 year old part?

Used parts are purchased "where as as is".

Unless you had some useful personal service continuity with the part, ie: drove it, used it, or had taken it apart/inspected/certified it..... and were offering that personal continuity and verbal testimony to that parts condition within and attached to the Sale as an "expectation" ..... and in lieu of NO actual written or verbal warranty ?
Then IMO,
this is no more than unfortunate circumstance devoid of any malicious intent.

There is also sufficient information available on the internet, and even some I have outlined in my earlier post, that some simple checks could, and should have probably been performed, before any potential Sale or Installation by either party as just good mechanical practise. (backlash check, gear contact pattern check, etc)

I am wondering here....
did anyone at any point in time undo the Pinion Nut ? you know the big NUT that holds the Yoke on ? Say for the purpose of changing the Pinion SEAL?

That is the Nut that holds not just the Yoke in place, but it is also responsible for the actual Pinion Bearing(s) preload maintained by the crush sleeve. If for some reason that Nut was undone, the Pinion Seal replaced, and then the Pinion Nut was not re-installed/re-Torqued sufficiently.... that could cause the lack of correct Gear mesh and noise ?

[Charger-Bodie]

The pinion nut should not have needed off. The you're was the small yoke , same as his.

[euroZ06]

I have done dif instal on a charger before (twice), its a fairly straight forward job.
I am not a mechanic, but am an enthusiast. You can check my previous posts (from few years ago) when i was helped with the process by members of this board and you will see that my instal was successful with no issues.

@charger-bodie, at this moment i did not bring up your name here, because i know you sell used parts for these cars and i was trying to solve this issue in private.

My take on it is: yes, used parts are sold as is, but due dilligence should have been done to further inspect the prt, that you sold and told me its in good conition. But like challenger340 stated, it is unfortunate circumstance with no ill intent. I am sure you were selling this part with good faith that its in working order, just as i was purchasing it with good faith in a forum member knowledgeable on the subject. Unfortunately, the part has an issue that requires professional mechanic to fix.
Today i spoke to 3 shops that can do the job, ranging from almost $600 to $900.

The cheaper shop charges $385 to take it apart and $175 for the bearings/seals. I also need to pay $36 in tolls each way (adds to $72), i already used 1 gasket, 2 bottles of gear oil and lsd additive (per your advice), so thats another $30 or so. Ill need another $30 worth of fluids to put it together. Thats not accounting for my time spent taking the car apart, and putting it together, and the downtime on it. In my last message i think i have made a fair offer that ill eat up the cost of almost half of this, and you refund the $385. I think broken diffs go for about $250, and on my part i paid $800 ($700 for the part and $100 for shipping).

I am tryig to reasonably solve this issue.

[Charger-Bodie]

I'm not a big seller of parts. I'm sorry this happened ,but if I had all the money bad that I've gambled on with parts for these cars I would be rich. We are dealing with 50 year old parts .

[John_Kunkel]

My take on it is: yes, used parts are sold as is, but due dilligence should have been done to further inspect the prt, that you sold and told me its in good condition

And therein lies the problem.

I have more than a little experience with rear ends and it's near impossible to tell the condition of a third member by looking. I've seen R&P's that look perfect and will sing like a Banshee. I've seen brand new gears that have been setup with a perfect contact pattern whine. (I'm driving one right now) From my own anecdotal experience it seems that the 489 is the most likely to have gear noise, the factory had fits with them.

To the OP I would suggest that you cut your losses; any attempt to quiet the third member with anything less than a total rebuild with all new parts (bearings/gears) with a guarantee is throwing good money after bad.

[c00nhunterjoe]

A full bearing/ seal kit for an 8.75 is 80 bucks, ring and pinions can be bought new for 185. A crush sleeve eliminator can be had for 30 bucks..... you are being ripped off in your repair, not your origonal purchase. Asking the seller of a used part to pay for an overpriced repair of a used part is not going to get you anywhere. Furthermore, a complete new 3rd member can be bought for 1300, so a 900 quote is also overpriced.

[birdsandbees]

In the 70's we'd have just shoved a banana into the filler hole..   

[c00nhunterjoe]

http://www.doctordiff.com/drivetrain/mopar-8-3-4/

Very reputable. Do some price shopping. Im a dana 60 fan. Do the math on what you have spent already, added to what you are about to spend, then price a dana.

[euroZ06]

A full bearing/ seal kit for an 8.75 is 80 bucks, ring and pinions can be bought new for 185. A crush sleeve eliminator can be had for 30 bucks..... you are being ripped off in your repair, not your origonal purchase. Asking the seller of a used part to pay for an overpriced repair of a used part is not going to get you anywhere. Furthermore, a complete new 3rd member can be bought for 1300, so a 900 quote is also overpriced.

That all sounds great, but these are the options i have, sending this piece is about $100 each way. Im already in this at $850, the $570 price to rebuild seems like the only logical option. I asked the shop if i could buy the kit from diff doctor, and they said if i bring my own prts there will be no warranty on work.


Again, i was sold this diff for $700 plus $100 shipping, and was told its in good condition. Beeing that it came out to be a be diff, i respectfully contacted the seller and told him about it. The price of a diff that needs to be rebuilt is $250(from what i gather and what ive seen). I didnt ask him to pay for full repair, just the labor cost on the shop that will be doing the rebuild ($385).