Deceleration whirring noise and fix

Sonny · Mar 8, 2020

Last month I replaced my 8.25 rear with a 8.75, 489, 3:55 gear with sure grip. Went for a 2 hour trip and now it’s whirring while decelerating from 50 mph down then gets quiet from 20 mph to 0. I’ve read it could be pinion bearing and or its preload.

can someone provide a link to how to check and/or adjust the preload? I’ve read I’ll need a torque wrench with the needle to set it. Does the nut on the u joint flange also set the preload or is there another nut under the flange?
Thanks

khryslerkid · Mar 8, 2020

Under the yoke/flange there's a crush sleeve that sets the two bearings preload. That's the resistance on those bearings.

The backlash is the distance between the pinion gear and the ring gear. Too much backlash might be causing your wining on decelerating. You can jack up the rear and with the tires off the floor see how much the one wheel moves to engage the drive shaft. If it's a lot and you hear a clunking, there might be too much backlash.

Grab the driveshaft close to the pinion and see if there is any up and down play. You don't want any. Then see how much it takes to turn the yoke back and forth before the wheels engage.

Here's a video I made showing how much play this rear had. After removing the center section from the housing, I checked the backlash with a dial indicator on the ring gear and it was .012 which is the utmost limit for a used set of gears. This rear had a harmonic sound at 50 mph.

69L48Z27 · Mar 8, 2020

Look for some videos on 8.75s. Couple out there.

Pinion load is set with shims under the bearing against the pinion sleeve. The torque wrench is used to check the load when turning the pinion nut. The 8.75 does not use a crush sleeve. At least my 742 case didn’t.

Bottom line is you’re in for a full tear down.

khryslerkid · Mar 8, 2020

69L48Z27 said:
Look for some videos on 8.75s. Couple out there.

Pinion load is set with shims under the bearing against the pinion head. The torque wrench is used to check the load when turning the pinion nut. The 8.75 does not use a crush sleeve. At least my 742 case didn’t.

Bottom line is you’re in for a full tear down.

The 489 uses a crush sleeve for bearing preload. Good news, they make a crush sleeve eliminator for the 489 that works like a 742 pinion with shims to set the bearing preload. The 489 has the shim behind the large pinion bearing to set the pinion depth like the 742.

Cranky · Mar 8, 2020

69L48Z27 said:
Look for some videos on 8.75s. Couple out there.

Pinion load is set with shims under the bearing against the pinion sleeve. The torque wrench is used to check the load when turning the pinion nut. The 8.75 does not use a crush sleeve. At least my 742 case didn’t.

Bottom line is you’re in for a full tear down.

The 489 does use that piece of crap crush sleeve.....

khryslerkid · Mar 8, 2020

Cranky said:
The 489 does use that piece of crap crush sleeve.....

$30 smackaroos!
https://www.doctordiff.com/8-3-4-489-case-crush-sleeve-eliminator.html

Cranky · Mar 8, 2020

khryslerkid said:
$30 smackaroos!
https://www.doctordiff.com/8-3-4-489-case-crush-sleeve-eliminator.html

They've gone up since the last time I bought one. Bought one many years ago when it was a new thing unless you made your own and the one shipped to me was too long and had to machine it shorter to be able to adjust the preload with shims. Contacted the company that it came from and they said they would send another but just told them how it was machined to work and just wanted them to know about it being too long. The next one that was ordered was real close to being on the money and that told me they listened.

Sonny · Mar 8, 2020

khryslerkid said:
Under the yoke/flange there's a crush sleeve that sets the two bearings preload. That's the resistance on those bearings.

The backlash is the distance between the pinion gear and the ring gear. Too much backlash might be causing your wining on decelerating. You can jack up the rear and with the tires off the floor see how much the one wheel moves to engage the drive shaft. If it's a lot and you hear a clunking, there might be too much backlash.

Grab the driveshaft close to the pinion and see if there is any up and down play. You don't want any. Then see how much it takes to turn the yoke back and forth before the wheels engage.

Here's a video I made showing how much play this rear had. After removing the center section from the housing, I checked the backlash with a dial indicator on the ring gear and it was .012 which is the utmost limit for a used set of gears. This rear had a harmonic sound at 50 mph.

Thanks. Mine moves up and down about a 1/32” and has rotating movement as much as or a little more than your video. What are my options? I bought this unit with sure grip for $700 as is. Is this something a novice like me can fix?
Sonny

Cranky · Mar 8, 2020

Sonny said:
Thanks. Mine moves up and down about a 1/32” and has rotating movement as much as or a little more than your video. What are my options? I bought this unit with sure grip for $700 as is. Is this something a novice like me can fix?
Sonny

Working on this stuff is not really a novice thing but.....that's how I 'learnt' doing rear ends. You have the positive of the internet but there wasn't much on the net 35 years ago. The plus for me was these things were cheap in the pick and pull yards back then.....

Sonny · Mar 8, 2020

Cranky said:
Working on this stuff is not really a novice thing but.....that's how I 'learnt' doing rear ends. You have the positive of the internet but there wasn't much on the net 35 years ago. The plus for me was these things were cheap in the pick and pull yards back then.....

Ok. Do I have to take the case back off or fix it from the u joint side?

dadsbee · Mar 8, 2020

Sad part.. it all has to come apart Sonny, axles out and the works.

Sonny · Mar 8, 2020

dadsbee said:
Sad part.. it all has to come apart Sonny, axles out and the works.

Alright. That’s not that bad. I’ll need to read up on the internal part.

khryslerkid · Mar 8, 2020

Sonny said:
Alright. That’s not that bad. I’ll need to read up on the internal part.

Read until you're sick of reading about 8 3/4 rears. A couple of videos I've seen weren't exactly the way I would do one. Cutting torches, air chisels, impact tools. It's not what's in my tool box for doing one. I did see a video on rebuilding a rear set for a 1963 Chevy which was very close to setting up a Mopar rear.

There's a couple of good threads on here and over on A bodies by members taking you through their rebuilds.

Demonic · Mar 8, 2020

If you like books and reading....

https://www.cartechbooks.com/jeep-d...ebuild-the-8-1-4-8-3-4-dana-44-60-amc-20.html

vance.dykes · Mar 9, 2020

hear watch this and go to my mopar and down load the repair manual for more info

Darter6 · Mar 9, 2020

And not to be a Debbie Downer but, Gears will take a "set" after a few miles of use. Being a used set it might be possible to still have the whining noise still after your re-do.

Sonny · Mar 9, 2020

So here’s my novice questions:
1. Would changing only the front bearing buy me any time?
2. If I only change the pinion bearings and sleeve and leave the chunk together, that should be much simpler, yes? I realize I still need to recheck clearances and contact area.

Demonic · Mar 9, 2020

1 No.

2 Impossible. The carrier and ring gear must be removed to change the pinion bearings.

Sonny · Mar 9, 2020

Demonic said:
1 No.

2 Impossible. The carrier and ring gear must be removed to change the pinion bearings.

Thanks. I know the carrier and ring gear has to come out, I just meant remove it and get it out of the way, replace the pinion bearings and sleeve, and reinstall ring gear without messing with it.

khryslerkid · Mar 9, 2020

I sort of did the same as you did, bought a used unit and installed it thinking it was ok. Found out it had a harmonic sound resonating up through the drive line. Sounded almost like an exhaust system drone. Removed the center section this winter and disassembled everything to find it was really worn out. I'm totally rebuilding it with new bearings and new ring and pinion. I'll have around $600 in parts.

Deceleration whirring noise and fix

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